HK1235740B - Heat transfer device for producing a soldered connection of electrical components - Google Patents

Description

Heat transfer device for manufacturing solder joints of electronic components

Technical Field

The invention relates to a heat transfer device according to the preamble of claim 1 , which can be used for producing welded joints, for example for a welding machine.

In order to achieve the best soldering effect, when soldering large areas, first, the molten solder and the solder combination or components to be joined should be heated in a controlled manner to above the melting point of the solder, and then the molten solder and the solder combination or components to be soldered should be cooled in a controlled manner to below the solidification point to join the solder combinations together in a cavity-free manner.

Background Art

The terms "component" and "solder compound" generally relate to a substrate, substrate carrier, base plate, workpiece carrier, assembly carrier, etc. made of metal, ceramic, plastic, other materials or any combination of materials, and to a component to be fastened to a component such as a power semiconductor chip, (semiconductor) assembly, etc.

In this article, large-area weld joints refer to, for example, weld joints formed by welding a power semiconductor chip such as an IGBT, MOSFET or diode to a metallized ceramic substrate, or weld joints formed by welding a metallized ceramic substrate to a metal base plate of a power semiconductor module.

Preferably, a welding machine with a heat transfer device designed as a cooling device can include an evacuable chamber, a holder arranged in the evacuable chamber, and a heat sink arranged in the evacuable chamber, wherein the cooling device is used to cool the still liquid solder of at least one large-area solder joint to be produced. This allows the welding process to be carried out under vacuum or in a defined process gas atmosphere in order to exclude contamination or oxidation processes.

A metal plate can be placed in the holder as a test object, with which the operating mode of the cooling device can be tested and checked. The metal plate has a lower main surface, an upper main surface vertically spaced apart from the lower main surface, and an initial temperature of at least 200°C. A number N or more of adjacent rectangular surface sections, each having an area of at least 30 mm x 30 mm or each having an area of at least 50 mm x 50 mm, can be fastened to the upper main surface.

The workpiece carrier or the metal plate can now be cooled in the chamber with the aid of the heat sink. A predominantly nitrogen atmosphere at a pressure of approximately 1013.25 hPa in the chamber can be used as a guide for the cooling effect achieved on the metal plate. However, the cooling operation can also be carried out completely or partially at any desired pressure, such as a negative pressure, for example, which can be in the range of, for example, 1 hPa to 1030.25 hPa absolute, and/or partially at an overpressure, i.e., an absolute pressure greater than 1013.25 hPa. Independently of this, the cooling can be carried out in any desired atmosphere, such as air or in an atmosphere of a protective gas that protects the solder compound from oxidation, such as a nitrogen (N ₂ ) atmosphere, a carbon dioxide (CO ₂ ) atmosphere, a hydrogen (H ₂ ) atmosphere, a helium (He) atmosphere, or in an atmosphere of a mixed gas (N ₂ H ₂ ).

The metal plate is cooled by means of a heat sink in such a way that the temperature of the upper main surface of any rectangular surface portion does not reach a local maximum at a distance from the edge of the surface portion and remains so until any surface portion no longer has a minimum cooling temperature greater than 200°C or greater than 150°C. If the solder has sufficiently solidified at, for example, 200°C or 150°C, a completed, joined solder connection is formed between the solder components. In the actual manufacturing process, one of the solder components can be positioned and precisely fitted into the holder as the lowest solder component, and one or more additional solder components can be placed on top of this one, with solder also being placed between each of the solder components to be joined. The solder can be, for example, a preformed solder sheet ("solder preform") or a solder paste applied to a joining surface that will be joined to another solder component on one or both of the solder components to be joined.

In addition to positioning one of the solder combinations as the lowest solder combination and fitting it precisely within the holder, one of the solder combinations can also be placed on a carrier plate that is inserted into the holder with a precise fit. One or more other solder combinations, along with a solder sheet or applied solder paste, are then placed on the lowest solder combination in the same manner as described above. In this variation, multiple groups of two or more solder combinations can be formed, each placed adjacent to one another in the same manner on a common carrier plate. Once the soldering process is complete, the carrier plate is no longer part of the solder assembly.

The cooling device can, for example, be part of a welding machine, by means of which the soldered product can be cooled in an evacuable chamber of the cooling device, after the soldered product has been heated to a temperature above the melting point of the solder by a heating device in the evacuable chamber or in a separate heating chamber, as described above, so that the solder is melted. When a separate heating chamber and a conveying device are used, a lock can be provided between the heating chamber and the evacuable chamber of the cooling device, and the conveying device is used to convey the soldered product, which has been heated to a temperature above the melting point of the solder used, from the heating chamber to the evacuable chamber of the cooling device. However, a preheating chamber, a soldering chamber, and a cooling chamber can be provided, each of which can be separated from the other chambers by an airtight lock or mechanically, and the parts to be welded can be carried through the preheating chamber, the soldering chamber, and the cooling chamber by a conveying device.

For example, a universal heat transfer device designed as a cooling device according to DE 10 2011 081 606 A1 is known from the prior art. The heat transfer device is constructed to provide a defined heat distribution on the parts to be welded by means of cold air. In order to generate the required temperature gradient on the copper plate, a configuration of cold air nozzles or a cold air screen with multiple openings is provided for this purpose. Alternatively, a radiator can also be provided, which can include an uneven heat conductor, or cooling elements that are arranged adjacent to each other and can move independently of each other in the vertical direction (including nesting each other). The cooling principle is based on gas convection and requires moving parts for circulating the gas, wherein cooling under vacuum cannot be provided. Controllable, partial and comprehensive cooling is also not possible by changing the distance. The copper plate arranged between the cooling nozzle/cooling element and the parts to be welded affects the homogenization of the temperature distribution, making it impossible to provide a defined temperature gradient.

In practice, components or parts arranged on a curved or folded base plate are often welded. The base plate can also warp when heated or cooled, so the welding process usually has to be carried out on a curved base plate. The base plate serves as an assembly carrier for assemblies, for example, semiconductor components for high-power devices, for example, converters such as rectifiers or inverters in motor or generator equipment. An example of such a device is the converter in a wind turbine. Wind turbines of this type are also increasingly installed at sea ("nearshore"), which places high demands on the reliability of all components, since service and repairs incur higher service costs compared to generators installed on land. Due to the amount of power to be transmitted, the welded joints are subject to special stresses, so the requirements for weld quality are very high. The key is to avoid welding faults such as cavities, cracks, etc., in order to avoid expensive repairs and wind turbine downtime due to faulty converters.

In this type of power equipment, the baseplate also functions as a heat sink, dissipating excess heat from the components and cooling them. Finally, it can also serve as a common ground connection, providing a reference potential for the component carrier. To this end, the baseplate is made of a thermally conductive material, typically metal.

In the field of power engineering, particularly in three-phase systems, it is possible to solder three, six, or multiples of three components onto a base plate. These components or assembly groups consist of one or more substrate carriers, such as ceramic or plastic, with a solderable molten metal on the backside. These components or assembly groups are electrically and thermally connected to the base plate over their entire area or at points via soldered connections. This creates a problem: during the soldering process, which can involve high temperature gradients, the base plate and the assembly substrate experience different expansions, resulting in mechanical warping of the entire component, similar to a bimetallic strip. Thermally generated bending deviations of the base plate exceeding 0.3 mm relative to a horizontal reference plane can be achieved. A relatively high cooling rate is crucial, particularly for process engineering, to maintain a sufficiently high temperature differential within the solder deposit. This allows the still-liquid solder to flow into already solidified areas. At low cooling rates, the temperature of the entire product becomes uniform, preventing this effect from being exploited. Cooling rates exceeding 2 K/s are desirable, also to achieve high component throughput in the welding machine.

To counteract the thermally induced warping when creating welded joints between dissimilar materials, the base plate is preformed in some manner, often pre-bent, so that after welding and solidification of the welded joint, the component as a whole has a flat alignment. This creates a problem: components and assemblies are welded to the curved base plate or component carrier and must be heated or cooled in a controlled manner. The heating process is particularly important here because when the dissimilar materials cool, high mechanical stresses are generated that adversely affect the quality of the welded connection.

The purpose of the present invention is to provide a heat transfer device that achieves the following functions:

- Uniform heating of the bent part or base plate over the entire area;

- influencing the solidification process in a controlled manner by locally limited cooling and holding, so that cracks do not occur in the solder; and

- Allows switching to large-area cooling after the solder solidifies, shortening processing time.

It is an object of the present invention to provide a heat transfer device for the controlled heating and/or controlled cooling of liquid solder for large-area solder connections to be produced.

This object is achieved by a heat transfer device having the features of claim 1 .

Embodiments and developments of the invention are the subject matter of the dependent claims.

Summary of the Invention

According to the present invention, a heat transfer device for thermally coupling components to be welded is provided. The heat transfer device includes a heat source and/or heat sink in a welding machine. The heat transfer device comprises at least one base plate designed to be in thermal contact with at least the heat source and/or heat sink. The base plate comprises at least two contact units, in particular a plurality of contact units, each of which has a respective contact surface capable of thermally contacting the component. The contact units are designed such that the relative distance between the contact surface and the surface of the base plate facing the component is variable.

The present invention is based on the concept of specifically establishing thermal contact with a heat source or heat sink, or a substrate connected thereto, via at least two contact units, and in particular multiple contact units, so that only specific, corresponding regions of the thermally contacted component are heated or cooled. This selective cooling/heating effect, based on contact cooling/heating, can provide a cooling/heating effect with high precision and a large temperature gradient. Consequently, thermal contact with the component occurs not with the entire substrate, but only with the subregions containing the contact units, with heating and/or cooling of the component occurring in the region of the contact surfaces of the contact units. The variable relative distance between the contact regions below the substrate's surface facing the component enables reliable contact with non-planar components, such as the aforementioned curved base plate, allowing the distance between the contact regions to be adapted to the contours of the contacted component. This creates multiple points of contact, which is particularly advantageous when welding under vacuum, as convection currents, which can bridge gaps between the substrate and component during welding at ambient pressure, are eliminated. Mechanical implementation is relatively simple, and the cooling/heating effect can be achieved in a vacuum and without convection.

Here, the relative distance between the contact area and the surface of the substrate facing the component is preferably variable against a spring force and/or a positioning force exerted by the corresponding contact unit. This can be achieved, for example, by the contact unit including a spring element or being made of an elastic material, as will be explained in further detail below. However, in principle, the functionality of the heat transfer device is sufficient if the substrate includes a substantially protruding contact surface that enables contact even without a relative change in distance from the component.

The contact surface of the contact unit can be flat or curved. In the case of a curved contact surface, the relative distances relate to the point on the contact surface with the greatest distance from the substrate. The heat transfer device according to the present invention can, in principle, be used regardless of direction, allowing thermal contact between the lower surface, the upper surface, or even both the lower and upper surfaces of a component. This means that in this application, references to directions such as "upper" or "lower" are not restrictive but refer to the corresponding exemplary embodiments and figures.

According to a preferred embodiment of the present invention, the distance between the substrate and the component is variable, wherein the contact unit is designed such that the relative distance between the contact surface and the surface of the substrate facing the component can be varied in response to changes in the distance between the substrate and the component, particularly in response to changes in the contact pressure applied to the substrate against the component. This relative change in the distance between the contact surface and the substrate is achieved through the elasticity of the contact unit. This allows the relative distance of each contact unit to be varied independently of the other contact units. This ensures reliable thermal contact for components that do not have a flat profile or that deform during the soldering process due to heat treatment.

The contact unit is preferably retained in a retractable manner in a recess provided in the substrate, wherein in particular the contact unit can be reset into a retracted position in which the contact surface of the contact unit is flush with the surface of the substrate facing the component. The resettability of the contact unit can in particular be achieved by comprising a spring element or by being made of an elastic material. Furthermore, the contact unit can be reset by means of a suitable adjustment device, for example a mechanical, pneumatic, electromagnetic, or hydraulic adjustment device. The ability to reset the contact unit into the retracted position allows for thermal contact of the component or the carrier plate over a large area, i.e., it is also possible to heat or cool areas of the component outside the retracted position that are not in contact with the contact surface, on which the component is mounted and in thermal contact. Thus, in the retracted position, the relative distance between the contact surface and the surface of the substrate facing the component is zero.

According to another preferred embodiment, the contact unit is formed from an elastic, thermally conductive material, in particular a metal paste, an epoxy resin containing metal particles (e.g., silver particles), and/or an electrically conductive elastic material, which is applied to the side of the substrate facing the component to be soldered. The contact unit is formed from a so-called pad, which can have any desired shape and/or size, and the shape and/or size can also vary from one contact unit to another. This type of contact unit can be manufactured economically and, in particular, allows individual adaptation to different components to be soldered at minimal manufacturing costs.

According to another preferred embodiment, the corresponding contact unit includes a contact pin having a contact surface and being adjustable relative to the substrate. The contact pin itself can be rigid and preferably consists of a material with good thermal conductivity (e.g., aluminum or copper). The cross-section of the contact pin can be circular or polygonal, in particular square. Furthermore, the contact pin can be coated with gold or silver.

In this context, it has been found to be advantageous if a resilient, thermally conductive material, in particular an epoxy resin containing metal particles and/or an electrically conductive resilient material, is applied to the end face of the contact pin. This ensures that the entire end face of the contact pin, or at least a substantial portion of the end face, can come into thermal contact with the component, even if, due to design and/or manufacturing circumstances, the contact pin and component are angled relative to one another, such that, without the application of the thermally conductive material, only a small partial contact area between the contact pin and the component would be possible. In this case, the thermally conductive material forms the contact surface.

Preferably, the contact pins are spring-mounted, wherein they can be mounted, for example, on a substrate or can be mounted via the substrate to a heat source and/or heat sink with which they can be thermally contacted.

In this regard, it has been found that if the corresponding contact pin has a heat-conducting sleeve that is closed on one side, with the closed end face of the sleeve facing the component to be welded, and a spring, particularly a coil spring, is housed in the sleeve, the spring, at least when uncompressed, partially protruding from the open end face of the sleeve and in thermal contact with the sleeve. In particular, a heat-conducting stud is held within the spring at its free end protruding from the sleeve, the stud being thermally connected to the spring. Preferably, the end face of the stud is flush with the end face of the free end of the spring or the end face of the stud protrudes from the spring. Preferably, the sleeve has a cylindrical cross-section. The closed end face can engage a contact surface. At its end face, the stud can be connected or fastened to the heat source and/or heat sink. The stud improves the transfer of heat to the spring and, at the same time, can serve as an end stop for the sleeve, thereby limiting the movement of the spring.

As an alternative to the above-described embodiment, the corresponding contact pin can have a heat-conducting column, the end face of which faces the component to be welded. At the lower end, axially opposite the end face of the column, a spring (particularly a coil spring) can be retained on a spring leaf of the column. On the side of the spring leaf facing away from the column, the spring can be placed on a contact plate, preferably together with the other contact pins. The column can have a radial protrusion at the base of the spring leaf, which, when the spring is uncompressed, rests on a radial contraction of a recess in the base plate. Thus, a contact pin of a contact unit is proposed, comprising a column of heat-conducting solid material. The column has a contact surface facing the component to be welded and capable of thermal contact, and, at the axially opposite end, a spring leaf, which serves as a base for a contact spring for elastically contacting the underside of the component. The spring is supported on a contact plate, on which the multiple contact pins of the contact unit can be arranged. Thus, a contact unit having multiple contact pins can be pre-assembled on the contact plate and then inserted into the recess in the base plate. The contact plate can be thermally coupled to a heating plate or cooling plate arranged below the base plate, so that, for example, the base plate temperature can be selectively varied from the contact element temperature. A radial protrusion at the transition from the spring leaf to the post limits the contact movement of the contact pin in the direction of the component at the radial constriction of the recess in the base plate, and the distance from the end face of the spring leaf of the post to the contact plate limits the contact pin's entry distance.

In this way, different embodiments of the contact unit are proposed, which have a compact structure, exhibit very good thermal conductivity and at the same time allow a desired variation of the relative distance between the contact surface and the surface of the substrate facing the component.

Preferably, the thermal capacity of the contact element (in particular, each contact pin) is configured such that, relative to the contact area between the contact element and the component, the amount of heat required for the temperature difference between the soldering temperature and the solidus temperature of the bulk solder can be absorbed quickly, preferably instantaneously. Thermal capacity is the ratio of thermal energy available to the generated temperature rise, and is configured to suit the selected materials, i.e., the specific thermal capacity and mass, of the contact element or contact pin. For example, at a soldering temperature of 250°C and a solidus temperature of 221°C for the bulk solder, the corresponding temperature difference can be eliminated as quickly as possible from the component solder upon contact between the contact element and the component, and the solder solidifies. In this embodiment, the thermal contact between the contact element and the substrate contributes less to cooling or heating than the heat storage capacity of the contact element itself, which is ultimately reflected in the weight and material selected for the contact element. Typically, the contact pins can be composed of solid copper or another material with good electrical conductivity. Preferably, the contact element can include a phase change material (PCM) that stabilizes the contact temperature and allows for instantaneous cooling or heating upon contact. This allows for large temperature gradients to be achieved, and for optimal adjustment of the solidification properties of the solder from the inner to the outer regions of the solder deposit during cooling, or of the melting properties from the outer to the inner regions of the solder deposit. The thermally conductive connections between the contact elements in the base plate play a role in reestablishing the initial temperature of the contact elements, in particular when changing from one component to the next.

According to a preferred embodiment of the present invention, the contact pins can be adjusted mechanically, pneumatically, hydraulically, or electromagnetically. Thus, instead of the previously described passive adjustment of the contact pins or contact unit using elastic materials or spring elements, the contact pins can also be actively controlled by means of actuators. In this case, the respective contact pins can be adjusted individually, or a plurality of contact pins can be elastically or rigidly arranged on a contact unit carrier that can be adjusted relative to the substrate.

According to another embodiment of the present invention, the contact pins are arranged as at least one group of contact pins, each group comprising a plurality of contact pins. In the uncompressed state, the relative distance between the contact surfaces of the contact pins in each group and the substrate decreases from the inside out relative to the position of the contact pins in the group. The uncompressed state refers to a state in which no compressive force acts between the contact pins and the component and/or a carrier plate in thermal contact with the component, or no pressure from a pneumatic, hydraulic, or electromagnetic actuator acts on the contact pins. This embodiment ensures that the effective contact area of the contact pin group can be varied depending on the distance between the component or carrier plate and the substrate. When the substrate approaches the component or carrier plate, initially only one contact pin or a small number of contact pins contacts the component or carrier plate. As the distance between the component or carrier plate and the substrate decreases, the outermost contact pins in the group gradually come into thermal contact with the component or carrier plate. Different distances in the uncompressed state can be achieved, for example, by using contact pins of different lengths, i.e., sleeves and/or coil springs of different lengths. The contour of the contact pin set can be matched to the components to be welded; for example, the edges of the contact pin set can be rounded or polygonal.

Preferably, the side of the base plate facing the component to be welded is curved, and in particular, the base plate has a shape that complements the component to be welded or the carrier plate that supports it. This ensures that the contact units can make contact with the component or carrier plate as simultaneously as possible, without requiring the contact units to have different lengths. If the contact units can be placed in a retracted position that allows them to be lowered, the curvature of the base plate allows the base plate to make contact with the component to be welded or the carrier plate over the entire area as much as possible.

It has been found that it is advantageous if the heat transfer device further comprises a heat source and/or a heat sink, wherein the substrate is in thermally conductive contact with the heat source and/or heat sink. For example, the substrate can selectively contact the heat source or heat sink, or can form a structural unit comprising the heat source or heat sink. Furthermore, the heat source and heat sink can be combined into a single device. For example, the respective functions of heat source and heat sink can be achieved by selectively allowing a coolant or heating agent to flow through the device, or by activating a heating device.

Preferably, a heat-resistant fluid, such as liquid metal (particularly liquid solder), thermal oil containing silicone oil, or a highly thermally conductive elastomer, can be used as the heating or cooling agent. Phase-change materials can also be used in the substrate or contact unit. For example, the connection between the contact unit and the substrate can be established by a preformed sheet that melts at the solidus temperature and thus represents a phase-change material. In this way, the thermal resistance between the contact unit and the heat source/heat sink can be optimized.

In a subsidiary aspect, the present invention relates to a welding machine having at least one heat transfer device and a component holder, the heat transfer device comprising a heat source and/or a heat sink, wherein a base plate is in thermal contact with the heat source and/or the heat sink, and at least one component to be welded can be fixed in the component holder, wherein the component holder and the base plate are repositionable relative to one another in such a manner that the contact surface of the contact unit can be selectively brought into thermal contact with the component to be welded, and the relative distance between the contact surface and the surface of the base plate facing the component can be varied. In particular, the welding machine can include multiple heat transfer devices, for example, wherein one heat transfer device is designed as a heating device and is in contact with the heat source, and another heat transfer device is designed as a cooling device and is in contact with the heat sink. The component holder, in which the component is fixed, can be selectively brought into thermal contact with these heat transfer devices, wherein the heat transfer device and/or the component holder are designed to be suitably repositionable.

In principle, components can be welded directly. Typically, the components are surrounded by a component carrier, which serves as a component rack for transport and handling, thus eliminating the need for a separate carrier component. The components can be secured in the component rack by means of a pressing device or clamping device. However, it has been found to be advantageous if the component holder comprises a carrier plate, which serves as a support for the component to be welded, and a pressing device, which is designed to press at least the component to be welded against the carrier plate, in particular by means of a spring load, wherein the carrier plate has at least one channel through which a contact element extends in order to establish thermal contact between a contact surface of the contact element and the component to be welded. The component holder makes it possible to secure at least one component to be welded in a simple manner, wherein the component located on the carrier plate can be, for example, a base plate, a substrate carrier, or the like. Pressing the component located on the carrier plate can be performed directly, i.e., by direct contact of the pressing device with the component, or indirectly, for example, using other components that are connected to the carrier plate and in contact with the pressing device.

The use of a carrier plate simplifies adapting the component holder to the dimensions of the component to be welded. It also simplifies adapting the base plate to the component to be welded. In other words, if the component serving as the base plate is curved to compensate for thermal warping on the side facing the base plate, for example, a carrier plate can be used with a complementary curve on the side facing the component, while the other side facing the base plate is flat. This allows the use of a universally suitable base plate. Only the shape of the carrier plate must be adapted to the component to be supported.

According to a preferred embodiment of the welding machine, the component holder and the base plate can also be reset relative to each other, wherein the component holder and/or the heat transfer device are designed in such a way that when the component holder and the base plate are brought close to each other, the contact unit exerts a force on the component to be welded so that the component to be welded is ejected from the support plate.

In some cases, it may be necessary to control or actuate the pressing device in such a way that the pressure of the component to be welded against the carrier plate is reduced or removed. Therefore, it is conceivable to apply the pressure of the pressing device in an adjustable manner, for example, electromagnetically, electrically, or by other means. Typically, the pressure of the pressing device exceeds the spring force or contact pressure of the contact unit to prevent the component from being accidentally ejected from the carrier plate. For example, the heat transfer device according to the above embodiment can be designed such that the contact unit is positioned so as to be repositionable within the recesses and can be lowered into a retracted position within these recesses, so that at least a large portion of the surface of the base plate contacts the carrier plate. Thus, in this position, a large-area heat exchange is achieved between the base plate and the component to be welded on the carrier plate, with this heat exchange occurring indirectly through the carrier plate. Therefore, uniform heating of the component can be achieved in this retracted position. The pressure applied by the pressing device can then be reduced, so that the component on the carrier plate is ejected from the carrier plate by the spring load or force exerted by the elastic contact unit, allowing for subsequent cooling.

Preferably, the component holder further comprises at least one heat storage bar capable of thermally conductively contacting the component to be soldered, in particular with an edge region of the component, wherein the pressing device is particularly designed to press the heat storage bar against the component to be soldered via a spring load. Preferably, the heat storage bar is arranged on the side of the component to be soldered opposite the carrier plate. The heat storage bar enables a local increase in the effective heat capacity of the component and, in this way, generates a definable temperature gradient across the surface of the component to be soldered, or alternatively compensates for undesirable temperature gradients caused by increased heat dissipation (e.g., at the edge region of the component). For example, the heat storage bar can be arranged at the edge region of the component to be soldered so that, when the component is cooled by contact with the base plate or the contact unit, the temperature gradient results in the solder in the edge region of the component solidifying more slowly than in the central portion of the component. This allows the still liquid solder to flow from the outside inward during solidification, thereby preventing the formation of cavities or cracks in the solder. Furthermore, the heat storage bar can facilitate the positioning of solder preforms or solder deposits and/or other components. The heat storage strips can adjust the curvature of the base plate.

For example, the component to be soldered can be ejected from the carrier plate in the manner described above to generate the temperature gradient so that cooling occurs solely via the contact element. After the temperature has dropped below the solidus temperature, at which the solder has completely solidified, this ejection can be reversed so that the component is fully seated on the carrier plate again. This results in a reduction in the temperature gradient, so that the component is now largely homogenous and can therefore be cooled further more rapidly.

BRIEF DESCRIPTION OF THE DRAWINGS

Further preferred embodiments of the present invention are apparent from the description and the accompanying drawings.

The present invention will now be described based on exemplary embodiments with reference to the accompanying drawings.

FIG1 is a perspective view of a substrate having a plurality of contact units according to an exemplary embodiment;

FIG2 is a plan view of a contact unit according to another exemplary embodiment;

3 is a perspective sectional view of a heat transfer device having a contact unit according to FIG. 2 , having an alternative embodiment of the contact unit;

FIG4 is a view from the side and from above of a set of contact units according to another exemplary embodiment;

FIG5 is a detailed view of a contact surface of a contact unit according to an exemplary embodiment of the present invention;

6 is a plan view and a perspective view of a carrier plate according to an exemplary embodiment of the present invention;

FIG7 is a perspective view of a substrate according to an exemplary embodiment of the present invention;

8 is a perspective view and a plan view of a substrate according to another exemplary embodiment of the present invention;

FIG9 is various perspective views of components to be welded and heat storage strips;

10 is a plan view and a cross-sectional view of a component holder and a heat transfer device according to another exemplary embodiment of the present invention; and

11 is a perspective view and a cross-sectional view of a component holder and a heat transfer device according to another exemplary embodiment of the present invention.

DETAILED DESCRIPTION

A heat transfer device 10 according to an exemplary embodiment of the present invention includes a rectangular base plate 12 capable of thermally contacting a heat source or heat sink. Six contact elements 14 are arranged on the surface of base plate 12. These six contact elements 14 are also rectangular and are composed of a thermally conductive elastic material, such as epoxy resin containing metal particles or other thermally conductive elastic materials. Base plate 12 can contact a component carrier (not shown) or directly a component, so that contact elements 14 attached to base plate 12 first contact areas of the component carrier where high solder buildup is present, particularly areas to be cooled.

FIG2 shows another exemplary embodiment of a contact unit, which, as shown in FIG3a or FIG3b , can be designed as a spring contact pin 16. According to the embodiment of FIG3a , contact pin 16 comprises a copper, cylindrical, thermally conductive sleeve 18, closed on one side, in which a spring 20, such as a coil spring, is mounted. Sleeve 18 comprises a solid portion and a blind portion for receiving spring 20. The solid portion provides a high thermal capacity for receiving, releasing, and storing thermal energy. The thermal capacity of sleeve 18 is dimensioned to be sufficient to establish the desired temperature gradient upon contact with a component surface. The closed end surface of sleeve 18 forms a contact surface 24, which is capable of thermally contacting the component to be welded. In the uncompressed state shown in FIG2 , spring 20 partially protrudes from the open end surface of sleeve 18 and is in thermal contact with the sleeve. Within spring 20, a thermally conductive stud 22 is retained at the free end of spring 20 protruding from sleeve 18 and is also thermally connected to the spring 20. The end surface of stud 22 is flush with the end surface of the free end of spring 20.

FIG3 a shows a heat transfer device 110 according to another exemplary embodiment of the present invention. Heat transfer device 110 includes a plurality of contact pins 16 according to FIG2 , with only one of these contact pins 16 shown in the cross-sectional view of FIG3 a . Heat transfer device 110 includes a base plate 112 having a through-hole or recess 30 extending therethrough, in which contact pins 16 are retained. A cooling plate 48 is provided as a heat sink beneath base plate 112. In addition to cooling plate 48, a heating plate or other selectively operable plate can also serve as a heat source or heat sink. Contact pins 16 rest against cooling plate 48 via the free ends of springs 20, with posts 22 in thermal contact with cooling plate 48 or fastened thereto. Sleeves 18 protrude from the upper surface of base plate 112 and extend through channel 32 of carrier plate 26. The function of carrier plate 26 will be described in more detail below.

The contact surface 24 of the sleeve 18 is in thermal contact with a component carrier or base plate 28, on which other components to be soldered can be arranged. These other components can be, for example, high-current semiconductor components that can be used as a half-bridge or full-bridge for rectifying or inverting electrical energy. The semiconductor components can be arranged on a ceramic substrate having a metallized surface on which conductive traces form the electrical connections.

As can be clearly seen in FIG3 a , the sleeve 18 can be fully retracted into the base plate 112 against the elastic force exerted by the spring 20, so that the contact surface 24 is virtually flush with the other side of the base plate 112. The pin 16 stands on the post 22. If the base plate 112 is moved closer to the carrier plate 26, the component and the bottom plate 28 can be ejected from the carrier plate 26.

As an alternative to Figure 3a , Figure 3b shows another embodiment of a heat transfer device 310 having multiple contact units 314. The multiple contact units together form a group that rests against a common contact plate 321. Each contact unit 314 includes a contact pin 316 comprising a thermally conductive post 319. Post 319 has a contact surface 324 and a spring blade 322 axially opposed thereto. Contact springs 320 are mounted on spring blades 323 and rest against contact plate 321. Contact pins 316 are retained in recesses 330 in base plate 312. Recesses 330 have a radially constricted region 327 along the component's direction, and posts 319 have radial protrusions 325 that, in their uncompressed state, rest against the constricted region 327 of recesses 330. Therefore, the spring motion of contact pins 316 is determined by the position of radial constrictions 327 in recesses 330, the length of spring blades 323, and the position of contact plate 321. The contact plate 321 can be in thermal contact with a heating plate or a cooling plate arranged below the base plate 312. Thus, thermal decoupling, or different temperatures between the contact unit 314 and the base plate 312, can be achieved. The contact unit 314 can be pre-assembled on a common contact plate 321 and inserted into the base plate 312, these being individually adapted to the soldering process.

A cooling medium, or a heating medium in the case of a heating plate, can flow through the cooling plate 48 to produce the desired cooling or heating effect. The heating plate can also include a resistive heating conductor and be electrically heated. A cooling medium, which can be a gas or liquid, can still flow through the cooling plate, or the plate can include an electrical cooling element, such as a Peltier element.

FIG4 shows a contact unit assembly according to another exemplary embodiment, which is designed with contact pins 116 of varying lengths. The structure of contact pin 116 corresponds to that of contact pin 16 in FIG2 , with sleeves 118 of contact pin 116 having varying lengths. The length of spring 120 of contact pin 116 can be adapted to the varying lengths of contact pin 116. A thermally conductive stud 122 can be provided at the free end of spring 120 protruding from sleeve 118.

The group of contact pins 116 forms a circular unit, with the length of contact pins 116 decreasing from the center of the circle toward the outside, resulting in a conical profile on the top side of the group of contact pins 116. The contact pins 116 can still have the same length, and the length of the springs 120 can be varied accordingly. When the group of contact pins 116 approaches a component, it first contacts and cools the central area of the component. As it approaches further, the contact area continues to increase. This allows for precise, step-by-step control of the temperature gradient, enabling precise spatial and temporal cooling of the components to be welded.

According to an exemplary variant, the contact region 24 of the contact pin 16 ( FIG. 2 ) or of the contact pin 116 ( FIG. 4 ) can in particular be designed to be elastic and/or curved.

FIG5 shows a contact unit 114 according to another exemplary embodiment, similar to contact unit 14 of the heat transfer device of FIG1 , which can be configured on a substrate (not shown). Contact unit 114 is composed of a resilient and thermally conductive material and, when in an uncompressed state, has an elliptical contact surface 124. As the substrate approaches a component carrier or base plate 128, only a small area of contact surface 124 of contact unit 114 initially comes into thermal contact with base plate 128. As the approach continues, contact unit 114 deforms, causing the area of contact surface 124 in contact with base plate 128 to continuously increase.

A welding machine 200 according to an exemplary embodiment of the present invention will now be described with reference to Figures 10 and 11. The welding machine 200 includes a heat transfer device 110 (see Figures 3a or 3b) and a component holder 36 in which a component to be welded can be secured. The component to be welded includes a base plate 28 serving as a component carrier and another component 46 to be welded to the base plate 28. The base plate 28 has six solder areas 50 arranged in a row, and the component 46 is arranged on the six solder areas 50. Solder (e.g., in the form of solder paste or stamped solder elements known as solder preforms) can be provided between the component 46 and the base plate 28 in a fluxless process. Alternatively, instead of the base plate 28, a carrier frame 38 having an integrally formed, small-area container for the component to be welded or having a correspondingly small base plate can be used, or a base plate 128 or multiple base plates can be used. The press frame 40 can be suspended from the carrier frame 38 by means of pins, i.e., positioned in a floating manner.

7 shows a base plate 112 of the heat transfer device 110. The base plate 112 includes six groups of contact pins 16, wherein each group includes six concentrically arranged contact pins 16. The configuration of the groups of contact pins 16 matches the configuration of the solder areas 50 of the base plate 28.

The component holder 36 includes a carrier frame 38 in which the carrier plate 26 is held. The base plate 28 is placed on the carrier plate 26. The component holder 36 also includes a pressure frame 40, which includes a plurality of resiliently mounted pressure pins 42. The pressure frame 40 can be fixed in place on the carrier frame 38 by means of latches 44 arranged on the carrier frame 38.

In particular, as shown in FIG. 6 , the carrier plate 26 has channels 32 aligned with the contact pins 16 , so that the contact pins 16 can be in thermal contact with the base plate 28 through these channels 32 of the carrier plate 26 .

Thermal storage bars 34 can be positioned at the edge of the base plate 28 and, as shown, can be continuous or spaced apart. The thermal storage bars 34 have locating pins 52 and locating holes 54, which are used to align or secure the thermal storage bars 34 to the base plate 28 or the press frame 40. The thermal storage bars 34 provide a localized increase in thermal storage capacity, thereby compensating for increased temperature loss at the edge of the base plate 28 or creating a temperature gradient across the base plate, causing the edge areas to cool more slowly. As a result of this temperature gradient, the solder in the center of the base plate 28, still liquid, cools and solidifies first during the cooling process. The solder in the outer regions remains liquid and is able to flow inward from these areas, preventing the formation of cavities or cracks. At the end of the cooling process, the solder in the edge areas of the base plate 28 has also reached its solidification point.

In particular, as can be clearly seen in Figures 10b and 11c, the base plate 28 is pre-bent to compensate for the stresses induced by the welding process. The intention is that after the welding process is complete and cooling has occurred, the base plate 28 is flat. This is achieved by virtue of the different coefficients of thermal expansion of the components to be welded. When cooling from the bent shape, the components to be welded deform into flat alignment in a manner similar to a bimetallic strip.

In order to ensure good thermal contact between the carrier plate 26 and the base plate 28, the carrier plate 26 is provided with a convex milling or a recess 56, the curvature of which is designed to complement the curvature of the plate 28 (see, in particular, Figures 6a and 11b). The side of the carrier plate 26 opposite the recess 56 is also preferably flat, similar to the upper side of the base plate 112, to ensure full contact between these plates.

When the base plate 28 is inserted into the component holder 36 and the pressure frame 40 is fastened to the carrier frame 38 by means of the latch 44, the base plate 28 is pressed against the carrier plate 26 by means of the pressure pin 42, wherein the pressure is at least partially transmitted indirectly via the component 46 and the heat storage bar 34, so that the component 46 and the heat storage bar 34 are also pressed against the base plate 28.

When heat transfer device 110 approaches carrier plate 26, initially only contact pin 16 is in thermal contact with base plate 28, thereby achieving localized cooling in the area of contact pin 16. As the approach continues, the distance between contact surface 24 of contact pin 16 and base plate 112 decreases, ultimately allowing contact pin 16 to remain largely within recess 30 of base plate 112. Finally, full contact is established between heat transfer device 110 and carrier plate 26, and thus base plate 28 is also in thermal contact with carrier plate 26, achieving large-area cooling of base plate 28. As heat transfer device 110 approaches carrier plate 26, base plate 28 can be ejected from carrier plate 26.

To interrupt the thermal contact between carrier plate 26 and base plate 28, latches 44 can be partially or completely released, reducing or even eliminating the pressure exerted by pressure pins 42. Alternatively, the pressure of pressure pins 42 can be selected so that, when heat transfer device 110 approaches carrier plate 26, base plate 28 is ejected once contact pins 16 are fully retracted and base plate 112 moves against carrier plate 26. When heat transfer device 110 approaches component holder 36, base plate 28 is ejected from carrier plate 26 by contact pins 16 because, from this point on, the reaction force of springs 20 compressing contact pins 16 disappears, or is at least so minimal that contact pins 16 only slightly enter recesses 30. Without thermal contact between base plate 28 and carrier plate 26, cooling can be more precisely controlled, or a greater temperature gradient can be achieved in the region of the contact point with contact pins 16.

FIG8 illustrates a heat transfer device 210 according to another exemplary embodiment of the present invention. Heat transfer device 210 includes a rectangular substrate 212, on the upper surface of which a large number of schematically illustrated contact units 214 are arranged. Contact units 214 can correspond to contact pins 16 (FIGS. 2 and 3) or contact units 114 formed of an elastic material (FIG. 5). The density of contact units 214 arranged on substrate 212 is greatest along the edges of substrate 212 and decreases inward, i.e., the spacing between contact units 214 increases from the outside inward. The interior of substrate 212 is devoid of contact units 214.

To prevent temperature gradients on a base plate (not shown) in thermal contact with heat transfer device 210 during the heating process, a heat transfer device 210 of this type can preferably be used as a heating plate or heat source. The goal here is to prevent naturally occurring temperature gradients. Typically, a heating body in a colder environment is cooler at the edges—in this case, the edges of carrier plate 26 or base plate 28—than in the center. Due to the higher heat transfer at the edges, this temperature drop can be offset, resulting in a more uniform heat distribution during heating. This generally has little effect on the cooling process.

When using the heat transfer device 10 according to FIG. 1 to cool a base plate 28 ( FIG. 9 ) equipped with heat storage strips 34 , six rectangular contact elements 14 can contact the central region of the base plate 28, while components arranged on the base plate are connected to the base plate 28 via heat storage strips 34 arranged at the edges. From an initial temperature of approximately 280°C, selective cooling in the region of the contact elements 14 can achieve cooling to approximately 200°C, while the outer regions, particularly the heat storage strips 34, have temperatures approximately 5°C to 20°C higher. After a considerable period of time, the individual components have cooled to temperatures below 100°C, while the edge regions, particularly the heat storage strips 34, can still have significantly higher temperatures. Within this temperature range, controlling the gradient is no longer crucial, except that the temperature difference between the central and edge regions decreases with decreasing absolute temperature. As a result, the soldered connections cool and solidify from the inside out, preventing mechanical stresses from occurring. Any cavities or cracks that may occur can be filled by the still-hot solder flowing in from the outside. This significantly improves the quality of the soldered connections.

Preferably, contact elements 214 are used which are arranged at the edge of the component to be heated or the base plate 28, 128 for heating. Contact elements 14, 114 or contact pins 16, 116 can be arranged at the central region of the component or base plate 28 wetted by the solder for cooling.

Preferably, the contact unit 214 for the heated substrate 212 and the contact unit 14 , 114 or the contact pin 16 , 116 for the cooled substrate 12 , 112 can be configured complementarily with respect to the component or base plate 28 , 128 .

Reference Signs List

10, 110, 210, 310 heat transfer device

12, 112, 212, 312 base plate

14, 114, 214, 314 contact units

16, 116, 316 contact pins

18,118 sleeve

319 columns

20, 120, 320 springs

321 contact plate

22,122 columns

323 Spring

24,124,324 contact surfaces

325 radial column protrusion

26 Loading plate

327 Radial concave contraction

28,128 baseboards

30, 330 recess

32 channels

34 heat storage strips

36 Component holder

38 Carrier rack

40 Pressing frame

42 Pressure pin

44 latch

46 parts

48 cooling plates

50 Solder area

52 positioning pins

54 positioning holes

56 recess

200 welding machine

Claims (30)

1. A heat transfer device (10, 110, 210) for thermal coupling of components (28, 128) to be welded, the heat transfer device (10, 110, 210) having a heat source and/or heat sink (48) located in a welding machine (200), the heat transfer device (10, 110, 210) comprising a heat source and/or heat sink (48) and at least one substrate (12, 112, 212), the at least one substrate (12, 112, 212) being in at least thermal contact with the heat source and/or the heat sink (48), wherein the substrate (12, 112, 212) comprises at least two contact units (14, 114, 214), the contact units (14, 114, 214) having corresponding contact surfaces (24, 124), wherein the contact surfaces (24, 124) are capable of thermal contact with the components (28, 128), wherein the contact units (14, 114, 214) have at least two ... at least two contact units (14, 114, 214) having at least two contact units (14, 114, 214) having at least two contact units (14, 114, 214) having at least two contact units (14, 114, 214) having at least two contact units (14, 114, 214) having at least two contact units (14, 114, 214) having at least two contact 114, 214) are designed such that the relative distance between the contact surface (24, 124) and the surface of the substrate (12, 112, 212) facing the component (28, 128) is variable, wherein the distance between the substrate (12, 112, 212) and the component (28, 128) is variable, characterized in that the contact unit (14, 114, 214) is designed such that the relative distance between the contact surface (24, 124) and the surface of the substrate (12, 112, 212) facing the component (28, 128) is variable according to the change in contact pressure of pressing the substrate (12, 112, 212) against the component (28, 128), the contact pressure being caused by the change in distance between the substrate (12, 112, 212) and the component (28, 128). 2. The heat transfer device (10, 110, 210) according to claim 1, characterized in that the contact unit (14, 114, 214) is repositionably held in the recess (30) provided in the substrate (12, 112, 212). 3. The heat transfer device (10, 110, 210) according to claim 1, characterized in that the contact unit (14, 114, 214) is retractable to a retracted position, wherein the contact surface of the contact unit (14, 114, 214) is flush with the surface of the substrate (12, 112, 212) facing the component (28, 128). 4. The heat transfer device (10, 110, 210) according to claim 1, characterized in that the contact unit (14, 114) is formed of an elastic thermally conductive material. 5. The heat transfer device (10, 110, 210) according to claim 4, characterized in that the contact unit (14, 114) is formed of metal paste, epoxy resin containing metal particles and/or conductive elastic material, wherein the metal paste, the epoxy resin containing metal particles and/or the conductive elastic material are disposed on the side of the substrate (12) facing the component (128) to be welded. 6. The heat transfer device (10, 110, 210) according to claim 1, characterized in that the corresponding contact unit (214) includes a contact pin (16, 116) having the contact surface (24) and being adjustable relative to the substrate (112, 212). 7. The heat transfer device (10, 110, 210) according to claim 6, characterized in that an elastic thermally conductive material is coated on the end face of the contact pin (16, 116). 8. The heat transfer device (10, 110, 210) according to claim 7, wherein the elastic thermally conductive material is an epoxy resin containing metal particles and/or a conductive elastic material. 9. The heat transfer device (10, 110, 210) according to claim 6, wherein the contact pin (16, 116) is flexibly installed. 10. The heat transfer device (10, 110, 210) according to claim 9, characterized in that the corresponding contact pin (16, 116) includes a heat-conducting sleeve (18, 118) closed on one side, the closed end face of the heat-conducting sleeve (18, 118) facing the component (28, 128) to be welded, and a spring (20, 120) is accommodated in the sleeve, the spring protruding partially from the open end face of the sleeve (18, 118) and in thermal contact with the sleeve (18, 118) at least in an uncompressed state. 11. The heat transfer device (10, 110, 210) according to claim 10, characterized in that the heat-conducting column (22, 122) is held inside the spring (20, 120) at the free end of the spring (20, 120) protruding from the sleeve (18, 118), and the column is thermally connected to the spring (20, 120). 12. The heat transfer device (10, 110, 210) according to claim 11, characterized in that the end face of the end of the column (22, 122) is flush with the end face of the free end of the spring (20, 122) or the end face of the end of the column (22, 122) protrudes from the spring. 13. The heat transfer device (10, 110, 210) according to claim 9, characterized in that the corresponding contact pin (316) has a heat-conducting post (319) with the end face of the heat-conducting post (319) facing the component (28, 128) to be welded, and at the post (319), a spring (320) is held on the spring plate (323) of the post (319). 14. The heat transfer device (10, 110, 210) according to claim 13, characterized in that the spring (320) is placed on the contact plate (321) on the side opposite to the spring sheet (323), and the column (319) has a radial protrusion (325) at the base of the spring sheet (323), wherein when the spring (320) is in an uncompressed state, the radial protrusion (325) is placed on the radially contracted portion of the recess (330) of the substrate (312). 15. The heat transfer device (10, 110, 210) according to claim 6, characterized in that the contact pin (16, 116) is mechanically adjustable. 16. The heat transfer device (10, 110, 210) according to claim 6, characterized in that the contact pin (16, 116) is pneumatically adjustable. 17. The heat transfer device (10, 110, 210) according to claim 6, characterized in that the contact pin (16, 116) is hydraulically adjustable. 18. The heat transfer device (10, 110, 210) according to claim 6, wherein the contact pin (16, 116) is electromagnetically adjustable. 19. The heat transfer device (10, 110, 210) according to claim 6, characterized in that the contact pins (116) are configured as at least one set of contact pins (116), each set of contact pins (116) including a plurality of contact pins (116). 20. The heat transfer device (10, 110, 210) according to claim 1, characterized in that, in the uncompressed state, the distance between the contact surface of the contact pin (116) in each group of contact pins (116) and the base plate decreases from the inside to the outside relative to the position of the contact pin (116) in each group of contact pins (116). 21. The heat transfer device (10, 110, 210) according to claim 1, characterized in that the side of the substrate (12, 112, 212) facing the component (28, 128) to be welded is bent. 22. The heat transfer device (10, 110, 210) according to claim 21, characterized in that the substrate is designed to have a shape complementary to the component (28, 128) to be welded. 23. The heat transfer device (10, 110, 210) according to claim 1, wherein the welding machine (200) is a vacuum welding machine. 24. A welding machine (200) comprising at least one heat transfer device (10, 110, 210) according to any one of claims 1-23, and comprising a component holder (36), wherein at least one component (28, 128) to be welded is capable of being fixed, characterized in that, The component holder (36) and the substrate (12, 112, 212) can be reset relative to each other in such a way that the contact surfaces of the contact units (14, 114, 214) can selectively make thermal contact with the component (28, 128) to be soldered, and the relative distance between the contact surfaces (24, 124) and the surfaces of the substrate (12, 112, 212) facing the component (28, 128) can be varied. 25. The welding machine (200) according to claim 24, characterized in that the component holder (36) comprises a support plate (26) and a pressing device, the support plate (26) serving as a support for the component (28, 128) to be welded, the pressing device being designed to press the component (28, 128) to be welded against the support plate (26), wherein the support plate (26) has at least one channel (32) through which the contact unit (14, 114, 214) passes to establish thermal contact between the contact surface (24, 124) of the contact unit (14, 114, 214) and the component (28, 128) to be welded. 26. The welding machine (200) according to claim 24 or 25, characterized in that the component holder (36) and the substrate (12, 112, 212) are positionable relative to each other, wherein the component holder (36) and/or the heat transfer device (10, 110, 210) are designed such that when the component holder (36) and the substrate (12, 112, 212) are close to each other, the contact unit (14, 114, 214) applies force to the component (28, 128) to be welded, such that the component (28, 128) to be welded is ejected from the support plate (26). 27. The welding machine (200) according to claim 24, characterized in that the component holder (36) has at least one heat storage bar (34) which is capable of making thermally conductive contact with the component (28, 128) to be welded. 28. The welding machine (200) according to claim 27, characterized in that the component holder (36) has at least one heat storage strip (34) which is capable of thermally contacting the edge region of the component (28, 128). 29. The welding machine (200) according to claim 28, wherein the pressing device is designed to press the heat storage strip (34) against the component (28, 128) to be welded by means of an elastic load. 30. The welding machine (200) according to claim 24, wherein the welding machine (200) is a vacuum welding machine.