JP2011061105A - Connection structure, power module, and method of manufacturing the same - Google Patents

Abstract

【Task】
Provided is a high-reliable connection technology that has sufficient connection strength and suppresses pad breakage when ultrasonically connecting a lead terminal to a pad on a substrate.
[Solution]
A coating layer 14 that is harder than the pad 8 and the lead terminal 11 is formed on the metal base 9 and the pad 8 on the insulating film 8. At the time of ultrasonic connection, the coating layer 14 is broken by applying ultrasonic waves with the ultrasonic tool 13, and the lead terminals 11 and the pads 10 on both sides of the coating layer 14 are directly connected by plastic flow.
[Selection] Figure 6

Description

  The present invention relates to a technique for connecting lead terminals to a substrate.

  Conventionally, the in-vehicle module has been mounted in a vehicle interior having a relatively low level of reliability requirement. And it connected with the wiring called a wire harness with respect to the unit installed in the engine room etc., and the unit was controlled. However, in recent years, an increasing number of in-vehicle modules are mounted from the vehicle interior to the engine room for the purpose of omitting wire harnesses aimed at reducing weight and cost. In the engine room environment, the maximum temperature is higher than in the passenger compartment, so high heat dissipation is important for in-vehicle modules equipped with many heat generating components. In addition, since the mounting space is limited, there is a high demand for miniaturization of the module.

  In particular, power modules that convert and control power are equipped with many high heat-generating components such as IGBT (Insulated Gate Bipolar Transistor) chips and MOS (Metal-Oxide Semiconductor) chips. In consideration of the module mounting environment temperature and the guaranteed operation temperature of the semiconductor, high heat dissipation is required for the power module.

  In mounting a power module, a high heat dissipation substrate such as a ceramic substrate having a low thermal resistance or a metal base substrate is often used as a substrate for mounting components. The ceramic substrate has a structure in which conductor layers are formed on both sides of a ceramic plate. Heat dissipation is improved by using ceramic with good thermal conductivity for the insulating layer. The metal base substrate has a structure in which a conductor layer is formed on a metal plate serving as a base via an insulating layer. Although the insulating layer has a low thermal conductivity, the thermal resistance is lowered by thinning the insulating layer to establish a heat dissipation path to the base metal having a high thermal conductivity. Conventionally, a highly reliable ceramic substrate is often used as the high heat dissipation substrate, but from the viewpoint of low cost, many power modules using a metal base substrate have been developed in recent years. An example of a power module mounting structure is shown in FIG.

  At this time, Al wire bonding or lead terminals are used for connection of the external terminals. Among these, the lead terminal can easily increase the terminal width and the terminal thickness, which is advantageous in a power module having a large flowing current. When connecting with Al wire bonding, a considerable number of connections are required to reduce the connection resistance. In addition, the influence of the number of devices on mass productivity is large, and when the number of modules produced increases, new capital investment is required.

  However, when solder is used to connect the lead terminals, there are concerns about the following. This power module is connected to other modules by its external terminals. If solder is used for the connection, the solder connecting the power module and the external terminals may be remelted by heating. . Since solders having the same melting point cannot be used, different types of solder are required, and the assembly process is complicated.

  As a solution to this problem, there is a method in which lead terminals are ultrasonically connected to the substrate of the power module. Since the ultrasonic connection is a direct bonding between the lead terminal and the substrate pad, there is no problem of remelting when the other module and the external terminal are bonded by solder.

JP-A-6-169161 JP 10-261664

  A schematic cross-sectional view of ultrasonic connection is shown in FIG. The ultrasonic connection is a technique for connecting a terminal to the pad by causing ultrasonic vibration to be applied to the terminal supplied on the pad of the substrate while applying pressure with a tool. At the interface between the terminal and the pad, the ultrasonic vibration removes the oxide film formed on the terminal and the pad and the attached contaminants, and the new surfaces are brought into close contact with each other to establish a connection. The result of SEM observation of the lead terminal / pad interface after connection is shown in FIG. It can be seen that a plastic flow region is formed in which the lead terminal material and the pad material locally cross at the connection interface.

  However, since this ultrasonic connection is a process of connecting while applying pressure, when using a metal base substrate, the pad is damaged during the connection. An example in which the pad is destroyed after connection is shown in FIG.

  FIG. 5 shows a position where the pad breaks as shown in FIG. In power modules that are highly demanded for miniaturization, it is necessary to connect the lead terminals at a narrow pitch. For this reason, there is a case where the size of the terminal connection portion is made smaller than the head size of the tool. At this time, since the end portion of the lead terminal is connected while being pressed in the connection process, the boundary portion between the lower portion of the terminal pressed by the pad tool and the unpressurized portion without the terminal, that is, the figure Directly under the terminal end shown in FIG.

  To deal with such a problem, it is conceivable to increase the size of the terminal connection part or reduce the head size of the tool. However, increasing the size of the terminal connection is disadvantageous for miniaturization. In addition, when reducing the head size of the tool, there is a concern about the decrease in holding power when applying ultrasonic waves to the mesh part holding the terminals, and ultrasonic energy cannot be effectively transmitted to the interface between the lead terminal and the pad, The connection strength of the lead terminal may be reduced. Therefore, a new development problem such as structural optimization of the mesh portion is generated.

  On the other hand, as another countermeasure, there is a method of reducing the applied pressure and amplitude, which are ultrasonic application conditions, and shortening the application time. However, this simultaneously causes a reduction in the connection strength of the lead terminals, and has the disadvantage of reducing the connection process margin.

  The subject of this invention is obtaining the high intensity | strength connection part which does not destroy a pad, when connecting a lead terminal with the pad of a metal base board ultrasonically.

  FIG. 6 shows an example of a cross-sectional structure after connecting the lead terminals in the present invention. In the present invention, a coating layer is formed on the pad of the metal base substrate. The coating layer is a material harder than the lead terminal or the substrate pad. A lead terminal is connected to this pad by ultrasonic connection. At the time of connection, the coating layer is destroyed, and the lead terminal and the pad are connected.

  According to the present invention, the coating layer is harder than the lead terminal and the pad, and has an effect of suppressing damage to the pad. In addition, a high-strength connection comparable to the case without the coating layer is realized without hindering the formation of a plastic flow region where the thickness is thin and the terminal material and the pad material locally intersect.

It is the cross-sectional schematic diagram which showed the example of the mounting structure of a power module. It is the cross-sectional schematic diagram which showed the example of the ultrasonic connection. It is a cross-sectional observation figure of the lead terminal / pad interface after ultrasonic connection by SEM. It is a cross-sectional schematic diagram which shows the example which the pad destroyed after ultrasonic connection. It is the external appearance schematic diagram which looked at the terminal edge part from which the crack generate | occur | produced seen from the board | substrate upper direction. It is a connection part cross section schematic diagram after the lead terminal connection in this invention. It is a connection section section schematic diagram before lead terminal connection in the present invention. It is the connection part cross-sectional schematic diagram before the lead terminal connection in the past. It is a connection part section schematic diagram after connection when the coating material of a pad is thick. It is the external appearance schematic diagram which showed the example of the connection part at the time of connecting using the board | substrate which has a pad in which the coating material was formed in the position directly under a terminal end part. It is the figure which showed the washing | cleaning conditions and Ni plating conditions which were used in performing the experiment shown in an Example. In Example 1, it is a cross-sectional observation figure of the lead terminal / Cu board interface after carrying out ultrasonic connection of the lead terminal with respect to Cu board (Pure Cu goods, Ni plating goods). In Example 1, it is the figure which showed the shear test result performed after the ultrasonic connection of the lead terminal with respect to Cu board (Cu pure product, Ni plating product).

  Embodiments of the present invention will be described with reference to the drawings. FIG. 7 shows a cross-sectional structure of the connection portion before connection in the present invention. The substrate is a metal base substrate. An insulating layer 8 is formed on the lowermost metal base 9, and a wiring layer (not shown) is formed thereon. The lead terminal 11 is connected to the pad 10 which is a part of the wiring layer, and the coating layer 14 which is harder than the lead terminal 11 and the pad 10 is thinly formed on the pad 10. Here, “hard” means that the elastic modulus of the material is high.

  FIG. 6 described above shows a cross-sectional structure after connection. The lead terminal 11 is pressed by the tool 13 and slides at the interface with the pad 10 due to ultrasonic vibration. At this time, the oxide film of the lead terminal 11 and the contaminants existing at the interface are removed at the connection interface, and at the same time, the coating layer 14 on the pad is destroyed. Then, a plastic flow region in which the lead terminal material, the pad material, and the broken coating material are locally mixed is formed, and the connection is completed.

  For comparison, FIG. 8 shows a cross-sectional structure after connection in a conventional case without a coating layer. Other configurations are the same as those in FIG. An insulating layer 8 is formed on a metal base 9, and a lead terminal 11 is ultrasonically connected to a pad 10 which is a part of the wiring layer on a metal base substrate on which a wiring layer is formed. . At the interface between the lead terminal 11 and the pad 10, oxide films and contaminants are similarly removed by ultrasonic vibration, and a plastic flow region 101 in which the lead terminal material and the pad material are locally mixed is formed. However, a crack as shown in FIG. 4 is generated in the pad just below the terminal end as shown in FIG.

  On the other hand, FIG. 9 shows an example of a cross-sectional structure after connection when the coating layer 14 is thick. When the coating layer 14 is thick, the coating layer 14 is not destroyed and the state before connection is maintained. In this case, since the plastic flow region is not formed, the connection strength is reduced as compared with the case where the coating layer 14 is not provided. Therefore, the coating layer 14 needs to be thin enough to be broken by ultrasonic bonding.

  As can be seen by comparing FIGS. 6, 8, and 9, the formation of the coating layer 14 on the pad 10 of the metal base substrate can prevent the substrate pad from being destroyed. Further, by making the coating layer 14 thin, a plastic flow region in which the lead terminal material, the pad material, and the coating layer 14 are locally mixed is formed at the connection interface, and a high-strength connection can be obtained. Although the coating layer 14 is formed on the pad 10 side in the above, the same effect can be obtained even if the coating layer 14 is formed on the surface of the lead 11 instead of the pad 10 side.

  6, 7, and 8, the thickness of the metal base 9 is 2 mm, for example, the thickness of the degreased layer 8 is 0.1 mm, the thickness of the wiring layer (pad 10) is 0.1 mm, for example, The thickness is 0.6 mm, for example. The thickness of the coating layer formed on the wiring layer is 100 nm or less.

  As specific examples of each member, the metal base 9 is made of, for example, Al or Al alloy (Al alloy as the main material. The main material is an element occupying 50% or more), Cu or Cu alloy (Cu as the main material). Alloy), Fe and Fe-based alloys (alloys mainly composed of Fe) are desirable. The insulating layer 8 is suitably made of resin or ceramic. When using a resin, it is preferable to mix a heat dissipating filler in the resin. For the wiring layer, Al, Al alloy, Cu, Cu alloy, Fe, Fe alloy, etc. are also good. It is appropriate to select the same type of member as the wiring layer for the lead terminal 11. If possible, the wiring layer may be softened by annealing or the like.

  Further, it is necessary to select a material harder than the lead terminal 11 and the wiring layer as the material of the coating layer 14. When Cu or Cu alloy is selected as the material of the wiring layer and the lead terminal 11, Cr, Fe, Mo, Ni, Pt, Ta, V, W, etc. are suitable. When both the wiring layer and the lead terminal 11 are made of Al or Al alloy, Pd and Ti can be applied in addition to the above. Examples of the manufacturing method of the coating layer 14 include plating, vapor deposition, and sputtering.

  And the coating layer 14 should just exist in the part which is easy to generate | occur | produce a crack, ie, the terminal edge part shown in FIG. Since the lower portion of the lead terminal is a portion to be connected by forming the plastic flow region, the coating layer 14 is not essential. Therefore, a substrate having a pad on which a coating layer 14 is formed at a position immediately below the terminal end as shown in FIG. 10 may be used. In this case, since the connection is made at a portion where the coating layer 14 below the lead terminal is not present, the coating layer 14 may be 100 nm or more.

  In JP-A-6-169161, a connecting member is formed by forming an ultrafine particle film on at least one connecting surface of a connecting member and a connected member, and ultrasonically connecting the connecting member and the connected member via the ultrafine particle film. Proposes ways to reduce damage to Since the connection by this method is a connection structure through the ultrafine particle film after the connection, it is considered that the connection strength of this connection part depends on the breaking strength of the ultrafine particle film itself. Since the connection energy can be reduced by using this ultrafine particle film, it can be imagined that this ultrafine particle film is equivalent or softer than the connection member and the connected member, so the connection strength may be reduced. There is.

  Similarly, Japanese Patent Laid-Open No. 10-261664 proposes a method of reducing element damage by ultrasonically connecting a metal stud to the electrode pad with a metal layer interposed therebetween. Since the metal layer interposed between them is a material that is equivalent or softer than the metal stud, there is a possibility that the connection strength similarly decreases due to the above-described reason.

  In the present invention, since the lead terminal material and the pad material are directly connected, the connection strength does not decrease.

An experiment was conducted to connect the lead terminal 11 to the Cu plate as the pad 10 to verify the effect of the present invention. A 0.6 mm thick Cu plate was prepared by acid cleaning (solid Cu product) and by acid cleaning and Ni plating (Ni plated product: about 30 nm thick). The pure Cu product was subjected to pickling and water washing on the Cu plate, and the Ni plated product was further subjected to Pd activation, water washing, Ni plating, and water washing. Details of the cleaning conditions and Ni plating conditions are shown in FIG. The lead terminal used was a Cu lead having a length of 5 mm, a width of 0.6 mm, and a thickness of 0.6 mm. The Cu lead was similarly subjected to acid cleaning, and then ultrasonically connected to the prepared Cu plate (solid Cu product and Ni plated product). Connection conditions are applied pressure: 80 N / mm ² , amplitude: 9? m, application time; 0.1 s, 0.2 s, 0.4 s. The head size of the tool used for this ultrasonic connection was 2 mm square larger than the Cu lead width of 0.6 mm.

  Cross-sectional observation was performed after ultrasonic connection. After cross-section polishing, the polished surface was wet etched and SEM observation was performed. The observation results are shown in FIG. From FIG. 12, there was a crack in the Cu plate at the end of the Cu lead of the solid Cu product. On the other hand, for the Ni-plated product, although the connection interface was sunk from the Cu plate surface due to ultrasonic vibration, there was no crack. Further, in the Ni plated product, a plastic flow region where Cu of each of the Cu lead and the Cu plate and Ni of the Ni plating cross each other was formed at the connection interface.

  On the other hand, the connection strength was measured by performing a shear test on the Cu leads that were ultrasonically connected. Shear test condition is shear rate 200? m / s, shear height 60? I went at m. The shear test results are shown in FIG. From FIG. 13, the shear strength of the Ni-plated product was similar to that of the pure Cu product. From the above, it was found that even when Ni plating was formed, a high strength connecting portion was obtained, and the effect of the present invention was confirmed.

  An experiment was conducted to connect the lead terminal to the Cu plate, and the effect of the coating layer thickness was verified. A Cu plate having a thickness of 0.6 mm was prepared by performing nickel plating after acid cleaning. The Ni plating was experimented by changing the thickness to 30 nm, 100 nm, and 150 nm. As the lead terminal, a Cu lead having a length of 5 mm, a width of 0.6 mm, and a thickness of 0.6 mm, as in Example 1, was used. Similarly, after acid cleaning, ultrasonic connection was made to the prepared Cu plate. The cleaning conditions, Ni plating conditions, and ultrasonic connection conditions were the same as in Example 1. Similarly, the head size of the tool used for this ultrasonic connection was 2 mm square larger than 0.6 mm which is the width of the Cu lead.

  Cross-sectional observation was performed after ultrasonic connection. After cross-section polishing, the polished surface was wet etched and SEM observation was performed. As a result, no cracks existed in the samples examined this time. In addition, in the 30 nm product and the 100 nm product, a plastic flow region was formed in which the Cu of the Cu lead and the Cu pad and Ni of the Ni plating were mixed with each other at the connection interface, whereas in the 150 nm product, the Ni plating was performed. Although the remaining part was seen, the plastic flow region could not be confirmed.

  Similarly, the connection strength was measured by a shear test. From the result of the shear test under the same conditions, compared with the shear strength of the pure Cu product in Example 1, it was almost the same for the 30 nm product and the 100 nm product. On the other hand, the 150 nm product showed a clear decrease in connection strength. From the above, it has been found that the thickness of the Ni plating needs to be such that the leads and pads on both sides of the plating can be plastically flowed (for example, 100 nm or less) by ultrasonic bonding.

  Experiments for connecting lead terminals to a metal base substrate were conducted to confirm the effects of the present invention. Thickness 105? Cu pads on an Al base substrate (with an insulating film on an Al metal base) with Cu wiring of m were subjected to acid cleaning only (solid Cu product) and Ni plating after acid cleaning A thing (Ni-plated product: about 30 nm thick) was prepared. As the lead terminal, a Cu lead having a length of 5 mm, a width of 0.6 mm, and a thickness of 0.6 mm, as in Example 1, was used. Similarly, after acid cleaning, ultrasonic connection was made to the Cu pad on the prepared Al base substrate. The cleaning conditions, Ni plating conditions, and ultrasonic connection conditions were the same as in Example 1. Similarly, the head size of the tool used for this ultrasonic connection was 2 mm square larger than 0.6 mm which is the width of the Cu lead.

  Cross-sectional observation was performed after ultrasonic connection. After cross-section polishing, the polished surface was wet etched and SEM observation was performed. There was a crack in the Cu pad at the end of the Cu lead of the solid Cu product, but there was no crack in the Ni plated product. Further, in the Ni-plated product, a plastic flow region where Cu of each of the Cu lead and the Cu pad and Ni of the Ni plating cross each other was formed at the connection interface.

  Similarly, the connection strength was measured by a shear test. From the result of the shear test under the same conditions, the Ni-plated product had the same shear strength as the pure Cu product. From the above, it was found that a high-strength connection portion was obtained when Ni plating was formed on a metal base substrate, and the effect of the present invention was confirmed.

In the highly information-oriented society, demand for electrical energy is high, and the demand for power electronics that uses power with high efficiency has been increasing due to demands for energy saving in environmental issues and all electrification by reducing fossil fuels for the purpose of reducing CO ₂ emissions. Roles are expected to become increasingly important. In the field of power electronics, the problem of high heat generation of the module is significant, and it is essential to study a structure with high heat dissipation. Although the module examined this time is for in-vehicle use, it is considered that the structure of the present invention is effective for not only in-vehicle use but also a module that requires miniaturization and high heat dissipation.

1 ... Ceramic substrate
2 ... Wiring layer
3 Ceramic plate
4 ... Solder
5 ... Electronic components
6 ... External terminal
7 ... Metal base substrate
8 ... Insulating layer
9 ... Metal base
10 ... pad
11 ... Lead terminal
12 ... Mesh part
13 ... Ultrasonic tool head
14 ... Coating layer
50 ... Heat generation parts
100: Connection surface in which a plastic flow region is formed where lead terminal material, pad material and broken coating material are locally mixed
101... Connection surface in which a plastic flow region in which the lead terminal material and the pad material locally intersect is formed
200 ... Cracks generated in the pad
201 ... Position of head end of ultrasonic tool
202 ... The part where the end of the lead terminal contacts the pad

Claims (14)

A method for manufacturing a connection structure for connecting a second metal layer on a first metal layer, comprising:
Forming a coating layer of a material harder than the first metal layer and the second metal layer on the first metal layer;
Disposing the second metal layer on the coating layer and applying ultrasonic waves to join the first metal layer and the second metal layer;
The manufacturing method of the connection structure characterized by including. In the manufacturing method of the connection structure according to claim 1,
The method for manufacturing a connection structure, wherein the coating layer is destroyed at the time of connection by ultrasonic waves, and the first metal layer and the second metal layer are joined. In the manufacturing method of the connection structure according to claim 2,
A method of manufacturing a connection structure, wherein the first metal layer is connected to the second metal layer by plastic flow. In the manufacturing method of the connection structure in any one of Claims 1 thru | or 3,
The material of the first metal layer or the second metal layer is Cu or Cu alloy,
The method for manufacturing a connection structure, wherein the coating layer is a film of any one of Cr, Fe, Mo, Ni, Pt, Ta, V, and W. In the manufacturing method of the connection structure in any one of Claims 1 thru | or 3,
The material of the first metal layer and the second metal layer is Al or Al alloy,
The method for manufacturing a connection structure, wherein the coating layer is a film of any one of Cr, Fe, Mo, Ni, Pt, Ta, V, W, Pd, and Ti. It is a manufacturing method of the connection structure according to any one of claims 1 to 5,
The method of manufacturing a connection structure, wherein the first metal layer is formed on an insulating layer formed on a third metal layer. A conductive plate;
An insulating layer on the conductive plate;
Wiring and metal pads on the insulating layer;
In the manufacturing method of the power module comprising the metal pad connected terminal,
Forming a coating layer of a material harder than the metal pad and the terminal on the metal pad;
Placing the terminal on the coating layer;
A method of manufacturing a power module, wherein the coating layer is broken by application of ultrasonic waves to connect the metal pad and the terminal. In the manufacturing method of the power module of Claim 7,
On the metal pad facing the terminal, a coating layer made of a material harder than the metal constituting the metal pad and the terminal is disposed in and around the portion where the end of the terminal contacts, and the periphery thereof,
The coating layer is destroyed when connected by ultrasonic waves,
A method of manufacturing a power module having a connection structure, wherein the metal pad and the terminal are connected. In the manufacturing method of the power module of Claim 7 or Claim 8,
A method for manufacturing a power module, wherein the coating layer has a thickness of 100 nm or less. In the manufacturing method of the power module in any one of Claims 7 thru | or 9,
The material of the first metal layer or the second metal layer is Cu or Cu alloy,
The method for manufacturing a power module, wherein the coating layer is a film of any one of Cr, Fe, Mo, Ni, Pt, Ta, V, and W. In the manufacturing method of the power module in any one of Claims 7 thru | or 9,
The material of the first metal layer and the second metal layer is Al or Al alloy,
The method for manufacturing a power module, wherein the coating layer is a film of any one of Cr, Fe, Mo, Ni, Pt, Ta, V, W, Pd, and Ti. In the connection structure in which the second metal layer is connected to the first metal layer,
A coating layer made of a material harder than the first metal layer and the second metal layer is formed on the first metal layer,
The connection structure, wherein the second metal layer is connected to the first metal layer by plastic flow in a region where the coating layer is on the fragments. The first metal layer, the first insulating layer, and the second metal layer are arranged in this order, and the third metal is disposed on the surface opposite to the first insulating layer with respect to the second metal layer. A power module wiring board having a structure for connecting layers,
The second metal layer and the third metal in a region on the second metal layer facing the third metal layer, including a portion where the end portion of the third metal layer contacts. A power module wiring board, wherein a coating layer made of a material harder than the layer is disposed. In the power module wiring board according to claim 13,
The first metal layer is a conductive plate;
The second metal layer is a wiring and a metal pad,
The power module wiring board, wherein the third metal layer is a terminal.

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