JP2002141658A - Flow soldering method and apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method which effectively reduces the generation of a liftoff as a flow soldering method for mounting an electronic component on a substrate by using a lead-free solder material. SOLUTION: By the flow soldering method for mounting the electronic component on the substrate by using the lead-free solder material, the fused solder material is stuck on a specific place of the substrate, which is then cooled by a cooling unit so that the solder material stuck on the substrate is quickly cooled and solidified.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flow soldering method for mounting an electronic component on a substrate using a lead-free solder material, and an apparatus therefor.

[0002]

2. Description of the Related Art In recent years, with the miniaturization and high performance of electronic devices, it has been strongly desired to improve the reliability characteristics of electronic circuit boards incorporated in these electronic devices. For this reason, in mounting electronic components, there is an increasing demand for improvement in mechanical strength of joints formed by soldering the electronic components to a substrate and improvement in reliability characteristics such as thermal shock strength.

[0003] In addition, as interest in global environmental protection is increasing on a worldwide scale, laws and regulations for industrial waste treatment are being developed. In an electronic circuit board incorporated in an electronic component, a Sn-Pb-based solder material containing Sn and Pb as main components (for example, so-called “63Sn-37P”) is used.
b) eutectic solder material) is commonly used, but lead contained in this solder material may lead to environmental pollution due to improper waste treatment. Research and development on so-called “lead-free” solder materials that do not contain lead are proceeding.

Hereinafter, a conventional flow soldering method for manufacturing an electronic circuit board by bonding an electronic component to a substrate such as a printed circuit board and an apparatus therefor will be described with reference to the drawings. FIG. 3 is a schematic diagram of a conventional flow soldering apparatus.

Prior to soldering, first, a lead (for example, an electrode) drawn from an electronic component was inserted from a top surface side of the substrate into a through hole provided through the substrate, and the electronic component was arranged. Prepare a substrate. Here, in the wall surface (A) of the through hole, the region (B) surrounding the through hole on the upper surface of the substrate, and the region (C) surrounding the through hole on the lower surface of the substrate, lands (A + B + C, for example, 4) connected to a circuit pattern on the upper surface of the substrate.
In addition, portions of the substrate other than the upper and lower lands are covered with a solder resist.

Next, the substrate is pre-treated by applying a flux to the lower surface of the substrate on which such electronic components are not disposed by using a spray fluxer (not shown). This pretreatment is performed for the purpose of removing an oxide film (natural oxide film) unavoidably formed on the land and improving the spread of the solder material on the land surface.

After that, as shown in FIG. 3, the obtained substrate (not shown) is put into a flow soldering apparatus 60 with the upper surface on which the electronic components are arranged (with respect to the drawing) facing upward. The inside of the soldering device 60 is mechanically transported at a substantially constant speed in the direction of arrow 61. In the flow soldering apparatus 60, first, in order to sufficiently exert the activation force of the flux attached to the substrate by the pretreatment, the preheating unit (or the preheating unit) is disposed in the preheating zone located above the preheating unit 62. ) 6
2 heats the substrate.

Next, solder jet nozzles 64 and 65
When the substrate is transported to the solder material supply zone 66 located above the solder material supply unit 63, the solder material (not shown) previously melted by heating is heated by the primary jet nozzle 64 and the secondary jet nozzle 65. To supply the substrate from the lower surface side as a primary jet and a secondary jet, respectively. The solder material wets the annular space between the inner wall of the through hole and the lead inserted into the through hole from the upper surface side of the substrate by capillary action from the lower surface side of the substrate, and then to the atmosphere around the substrate. The natural cooling by cooling allows the temperature to decrease, and as a result, the solder material solidifies (or solidifies) to form a joint (so-called “fillet”) made of the solder material. In the solder material supply step (or the flow soldering step), the primary jet is used to sufficiently wet the surfaces of the leads and the lands with the solder material, and the secondary jet is used when the solder material extends between the lands. Remove the solder material from the area covered with the solder resist so that it does not remain and solidify to form a bridge (which is undesirable because it can cause a short circuit in the electronic circuit) or form horn-like protrusions. ,
This is for adjusting the shape of the fillet.

As described above, the fillet (joining portion) made of a solder material is formed by electrically and physically joining the lead of the electronic component and the land formed on the board, thereby forming the electronic circuit board. Is produced.

[0010]

A fillet made of a solder material as described above has a sufficiently high bonding strength between a lead of an electronic component and a land of the board in order to obtain high reliability of the electronic circuit board. Required. However, FIG.
As shown in FIG. 7, in the conventional flow soldering method as described above, when the electronic circuit board 70 is manufactured using a lead-free solder material, the land 73 (which is formed by the wall surface of the through hole 72 provided in the board 71) is formed. And disposed on the upper and lower surfaces of the substrate 71 surrounding the through hole 72), the solder material that has spread on the surface of the substrate 71 is partially peeled off at its interface when solidified, as indicated by an arrow 80. Fillet 7 made of land 73 and solder material
4 (or simply referred to as a solder material), which causes a problem that the bonding strength between the lead 75 and the land 73 cannot be high.

The land 73 of such a fillet 74
The phenomenon of detachment from Sn is generally called "lift-off"
This hardly occurred when a Pb-based solder material was used, but frequently occurred when a lead-free solder material was used. In particular, when a lead-free solder material containing Sn and Bi (for example, Sn-Ag-Bi-based material) is used,
Lift-off occurs remarkably when a lead-free solder material is used to join the Sn-Pb plated leads.

Generally, the cause of the lift-off is that when a solder material used for flow soldering and / or a metal material (eg, plating of a lead) that can be dissolved in the solder material solidifies from a molten state, A low-melting-point fragile alloy having a composition different from that of the original solder material is formed.

The molten high-temperature solder material loses heat mainly through the leads 75 drawn from electronic components (not shown). A temperature gradient is formed inside the solder material 74 attached to the substrate 71 due to the flow of heat through such leads 75. The solidification of the solder material 74 progresses according to this temperature gradient. The lowest temperature portion of the solder material 74 is the upper end portion thereof (indicated by an arrow 81), and the highest temperature portion is the portion between the land 73 and the fillet 74 which are good heat conductors. Since it is near the interface, solidification starts from the upper end portion, reaches the interface between the land 73 and the fillet 74, and ends. At this time, since the low melting point alloy as described above is more distributed (or segregated) to the molten solder material portion that has not yet solidified, the low melting point alloy moves to the molten portion as solidification progresses. It is concentrated. That is, during the solidification of the solder material, a segregation phenomenon occurs in the solder material,
As a result, the land 73 and the fillet 74, which are the slowest to solidify, are obtained.
The low-melting alloy 76 gathers at the interface with. At the time of such solidification, first, the upper end portion of the fillet 74 is fixed (or restrained) by solidification, and a solidification contraction of the solder material generates a tension in a direction indicated by an arrow 82. Thermal contraction occurs in the direction shown to generate tension. The fragile low-melting alloy 76 concentrated near the interface between the land 73 and the fillet 74 as described above cannot withstand these tensions, and it is considered that interfacial peeling in the direction indicated by the arrow 80 occurs.

The present invention has been made to solve the above-mentioned conventional problems, and an object of the present invention is a flow soldering method for mounting an electronic component on a substrate using a lead-free solder material. Accordingly, an object of the present invention is to provide a method for effectively reducing the occurrence of lift-off, and an apparatus for performing the method.

[0015]

SUMMARY OF THE INVENTION The present invention provides a flow soldering method for mounting an electronic component on a substrate using a lead-free solder material (hereinafter, also simply referred to as a solder material). In the zone, after applying the molten solder material to a predetermined portion of the board, the solder material attached to the board is rapidly cooled and solidified,
The substrate is cooled by the cooling unit in the cooling zone.

More specifically, the cooling of the substrate in the cooling zone (more specifically the rapid cooling of the solder material) is at least achieved by actively (or forcibly) cooling the substrate by using a cooling unit. It may be performed between the time when the temperature of the molten solder material attached to the substrate reaches a temperature equal to its melting point and the time when the solder material completely solidifies (or over the entire solder joint). Can be performed over any suitable period using any suitable cooling unit. Also, how to cool the substrate in the cooling zone by actively (or forcibly) cooling the substrate by the cooling unit as long as the solder material attached to the substrate is rapidly cooled and solidified. May be done. For example, the substrate may be entirely cooled or at least a portion thereof (for example, only a necessary portion thereof) may be cooled.

According to the method of the present invention as described above, by actively cooling the substrate using the cooling unit,
The lead-free solder adhering to the substrate is quenched, and the time required for the solder to start solidifying and completely solidifying is reduced. In the conventional method, since the substrate is not actively cooled, a segregation phenomenon occurs in the solder material due to a temperature gradient inside the solder material (fillet), and the fragile low-melting alloy eventually becomes near the interface between the fillet and the land. However, in the method of the present invention, since the solder is completely solidified in a shorter time, the segregation phenomenon in the solder material can be mitigated, and more specifically, a low number of low enough to cause lift-off. It is possible to prevent the melting point metal from moving to the vicinity of the interface and to be collected, whereby it is possible to effectively reduce the occurrence of lift-off.

Furthermore, conventionally, when the solder material solidifies, a hard and brittle metal phase (for example, a Bi phase or a lump of Bi) is formed inside the fillet, giving brittleness to the fillet and lowering the mechanical strength. However, according to the method of the present invention, since the solidification time of the solder material is shortened, the growth time of such a metal phase is shortened, and the metal structure of the fillet is refined, thereby increasing the mechanical strength. Can be improved.

In a preferred embodiment, the lead-free solder material is cooled at a cooling rate of 200 ° C./min or more in the cooling zone. The cooling rate is preferably as high as possible, but may be, for example, about 200 to 500 ° C./min, preferably about 300 to 500 ° C./min.

The cooling rate refers to the rate at which the temperature of the solder joint (more specifically, the temperature at which the solder material solidifies to form a joint (or fillet) made of the solder material) decreases, and is originally intended. The average rate at which the temperature of the molten solder material attached to the substrate is reduced to a temperature equal to its melting point until the solder material solidifies completely (or throughout the entire solder joint). However, when the substrate enters the cooling zone, and when it comes out, it is substantially acceptable to use the average rate of change of the solder joint temperature obtained as the average value of the measured values, so that the present specification, In, the average rate of change obtained in this manner is used for convenience as the temperature decrease rate (that is, the cooling rate). The temperature of the solder joint is determined by, for example, bringing a thermocouple into contact with (for example, pasting) a predetermined portion of the substrate to which the solder material adheres (for example, a land located on the surface of the substrate to which the solder material adheres), It can be measured by recording the data obtained from this thermocouple over time.

Active cooling of the substrate in such a cooling zone can be performed by, for example, gas cooling or liquid cooling, and a unit using gas cooling or liquid cooling is used as a cooling unit for cooling the substrate. be able to. The gas cooling means a temperature lower than the temperature of a substrate (more specifically, a solder material attached to the substrate), generally much lower than this, for example, -20 to 30 ° C.
Preferably air (atmosphere) at -10 to 10C, nitrogen gas,
Using a gas such as an inert gas as a coolant, contacting the substrate with the gas atmosphere (eg, by passing the substrate through such a gas atmosphere or blowing such a gas onto the substrate). Say to do. Also,
Liquid cooling refers to water at a temperature lower than the temperature of the substrate (more specifically, the solder material attached to the substrate), and generally much lower than this, for example, water at 1 to 30 ° C, preferably 1 to 10 ° C.
Using a fluid such as liquid nitrogen and other liquids as a coolant, the fluid is brought into contact with the substrate at least partially, for example, with a solder joint of the substrate or the entire substrate (e.g.,
Cooling (by immersing the substrate in such a fluid or spraying such a fluid onto the substrate). Liquid cooling has the advantage that the latent heat of vaporization of the liquid can be used and the solder material can be rapidly cooled.

More specifically, the gas cooling unit includes a blower, a gas flow device (for example, a pump, etc.) capable of supplying and extracting a low-temperature gas to and from a cooling zone so as to provide a gas atmosphere through which a substrate passes. Or a unit having a nozzle, a fan, a spot cooler, or the like that can blow a low-temperature gas onto a substrate. As the liquid cooling unit, a bath containing a liquid for cooling the substrate by immersing the substrate in the liquid, an atomizer capable of spraying the liquid onto the substrate surface, a relatively small amount of liquid, A unit having a nozzle or the like which can be supplied to the substrate can be used. Such a cooling unit,
Depending on the type, it may be arranged inside the cooling chamber, or may be connected to the cooling unit and a part or the whole may be arranged outside. Of course, it is also possible to use these units in combination. To achieve a higher cooling rate, it is preferable to actively cool the solder material using liquid cooling rather than gas cooling.

The desired cooling rate is, in the case of gas cooling,
In the case of liquid cooling, such as the temperature of the ambient gas supplied to the cooling zone, the flow rate of the ambient gas, the heat capacity of the components and the substrate placed on the substrate, and the transport speed of the substrate, the temperature of the liquid brought into contact with the substrate, It can be obtained by adjusting the heat capacity of the components and the board to be arranged, the transfer speed of the board, and the like. For example, while blowing a gas of about 25 ° C. at a flow rate of 2 liters / minute onto a substrate of glass epoxy resin having a size of 200 mm × 200 mm × 0.8 mm, the substrate is 1000 mm × 500 mm × 5 mm.
By passing through a 00 mm sized chamber at a rate of 1.2 m / min, a cooling rate of about 210 ° C./min is obtained.

Further, the active cooling of the substrate in the cooling zone is preferably performed by gas cooling with nitrogen gas using a gas cooling unit. The use of gas cooling with nitrogen gas suppresses the oxidation of the solder material and the wettability of the solder material (particularly the wettability to the land)
Can be improved, whereby the occurrence of lift-off can be further reduced.

In a preferred embodiment, the method of the present invention comprises the steps of: applying a molten solder material to a predetermined portion of the substrate in a solder material supply zone; and cooling the substrate in a cooling zone. And placing the substrate in an adjustment zone having an atmosphere having a temperature that can ensure that the solder material attached to the substrate is completely melted. The state in which the solder material attached to the substrate is completely melted may be ensured at least immediately before the substrate is cooled in the cooling zone. Those skilled in the art will readily understand that such an adjustment zone is located downstream of the solder material supply zone and upstream of the cooling zone in the substrate transport direction.

The "adjustment zone" is for adjusting (conditioning) the state of the substrate before the substrate is rapidly cooled after the solder material is applied to the substrate. Prior to quenching the substrate, the solder material is substantially completely melted at any location on the substrate (i.e., uniformly within the plane of the substrate) so that the Is for adjusting the state of the solder material attached to the substrate. More specifically, if some of the solder material attached to the substrate cools naturally before entering the conditioning zone and has already begun to partially solidify, the substrate (and thus the solder material) is heated Any solder material adhering to the substrate is again, preferably completely melted, at least before the substrate is cooled in the cooling zone. Alternatively, if substantially all of the solder material adhering to the substrate enters the conditioning zone while maintaining a molten state, at least to the extent that the solder material solidifies before entering the cooling zone (more specifically, Place the solder material in a temperature atmosphere such that heat does not escape too much from the solder material), and preferably heat the solder material to maintain all the solder material adhering to the substrate in a molten state (thus, In some cases, no active heating is required). Thus, the conditioning zone is a "heating zone" for heating the substrate by supplying heat to the substrate, or at a constant temperature throughout the zone, until the substrate passes through the conditioning zone. By providing some heat (or until entering the cooling zone) or thermally isolating the conditioning chamber, excessive cooling (and thus excessive cooling) of the solder material (and thus the substrate) can be prevented. It may also be referred to as a "constant temperature zone" to prevent.

By arranging the board in such an adjustment zone, the temperature distribution (or temperature difference) of the solder material in each solder joint and the temperature distribution of the solder material in the entire board can be reduced. In other words, the substrate (more specifically, the solder material attached to the substrate) can be soaked. Without the conditioning zone, the solder material may begin to partially solidify before cooling the substrate in the cooling zone, in which case the quenching start temperature in the cooling zone may be Although there is some variation in individual joints or all joints, providing such an adjustment zone and soaking the substrate before cooling can reduce the variation in the quenching start temperature and reduce the solidification time of the solder material. Variation can be eliminated, thereby making it possible to further reduce the occurrence of lift-off.

The temperature of the atmosphere in the adjustment zone is a temperature at which the solder material attached to the substrate can be completely melted before entering the cooling zone.
Any temperature may be used as long as the temperature is lower than the heat-resistant temperature of the electronic component in order to avoid heat damage to the electronic component placed on the board, but to ensure complete melting of the solder material, The ambient temperature of the adjustment zone is preferably set to a temperature within the range of the melting point of the solder material or more and less than the heat resistant temperature of the electronic component. More preferably, the ambient temperature of the conditioning zone is at least about 10 ° C. above the melting point of the solder material,
The temperature is within a range of about 5 ° C. or less from the heat resistant temperature of the electronic component. However, the invention is not limited to this, for example, if the solder material attached to the substrate has a temperature higher than its melting point when the substrate enters the conditioning zone (or if the solder material has not begun to solidify). If the temperature of the soldering material attached to the substrate can be prevented from dropping too low before the substrate enters the cooling zone through the conditioning zone, the temperature of the atmosphere in the conditioning zone is necessarily necessarily equal to the soldering temperature. The temperature does not need to be higher than the melting point of the material. Of course, even in this case, from the viewpoint of reliably melting the solder material, it is preferable to set the ambient temperature of the adjustment zone to a temperature within the range from the melting point of the solder material to the heat resistance temperature of the electronic component.

It is preferable that the adjustment zone is maintained in a nitrogen atmosphere. This can prevent the solder material and the land from being oxidized, and can prevent the wettability of the solder material from being reduced.Therefore, a sufficient bonding area between the solder material and the land can be ensured and the peeling of the solder material can be prevented. It becomes possible to suppress.

The atmosphere in the conditioning zone and the cooling zone is
Although they can be selected independently of each other, it is more preferable that both are in a nitrogen gas atmosphere.

According to another aspect of the present invention, there is provided an apparatus for mounting an electronic component on a substrate by a flow soldering method using a lead-free solder material. A solder material supply unit that supplies the solder material to the predetermined location of the substrate by supplying the solder material, and a cooling chamber that is located downstream of the solder material supply chamber in the substrate transport direction. An apparatus is provided, wherein the substrate is cooled by a cooling unit so as to rapidly cool and solidify the solder material attached to the substrate.

In a preferred embodiment, the substrate is cooled by the cooling unit such that the lead-free solder material is cooled at a cooling rate of 200 ° C./min or more in the cooling chamber. As such a cooling unit, a unit (or apparatus) as described above in relation to the flow soldering method of the present invention using gas cooling or liquid cooling, preferably gas cooling with nitrogen gas can be used. .

[0033] In a preferred embodiment, the apparatus of the present invention further comprises a conditioning chamber between the solder material supply chamber and the cooling chamber in the substrate transfer direction,
The atmosphere in the conditioning chamber has a temperature that ensures that the solder material attached to the substrate is completely melted. The temperature of the atmosphere in the adjustment chamber is preferably a temperature within the range of the melting point of the solder material or more and less than the heat resistant temperature of the electronic component. The atmosphere in the adjustment chamber is preferably a nitrogen gas atmosphere.

In this specification, the term "chamber" means a space that partitions a space to some extent, the term "zone" means a space inside (or defined by) the chamber defined by the chamber, and the term "atmosphere". Means a gas atmosphere in a space inside (or defined by) the chamber defined (or defined) by the chamber (thus, the above-mentioned “atmosphere in the zone” is synonymous with “atmosphere in the chamber”). For example,
The “solder material supply chamber” defines the “solder material supply zone” in the flow soldering method of the present invention described above, and the same applies to the “cooling chamber” and the “adjustment chamber”.

The apparatus of the present invention is suitably used for performing the above-described flow soldering method of the present invention. Accordingly, the description of the preferred embodiment described above in connection with the solder material supply zone and the cooling zone and optionally the conditioning zone in the flow soldering method of the present invention is based on the description of the solder material supply chamber and cooling in the flow soldering apparatus of the present invention. Those skilled in the art will readily appreciate that the chamber, and optionally the conditioning chamber, also applies.

In the flow soldering apparatus of the present invention, the solder material supply chamber in the apparatus of the present invention does not necessarily have to strictly partition the solder material supply zone from the space in another apparatus. In the apparatus of the present invention, the cooling chamber only needs to be able to partition the cooling zone from a relatively high-temperature space in another apparatus so that the substrate can be efficiently and actively cooled. Further, the adjustment chamber may be one which divides the atmosphere therein from a relatively high temperature atmosphere (for example, the atmosphere in the solder material supply chamber), but it is not always necessary to strictly divide this inside in the apparatus of the present invention. There is no. However, it is preferable that the adjustment chambers are configured such that the internal atmospheres of the adjustment chambers are partitioned to some extent from the viewpoint of thermal efficiency.

In order to carry out the flow soldering method of the present invention, the above-mentioned solder material supply chamber, cooling chamber and, if necessary, adjusting chamber are not always necessary. It should be noted that other devices may be used where possible.

[0038] Lead-free solder materials that can be used in the flow soldering method and / or apparatus of the present invention include:
For example, Sn-Cu system, Sn-Ag-Cu system, Sn-A
g system, Sn-Ag-Bi system, and Sn-Ag-Bi-
A Cu-based material or the like can be used. Further, as the substrate, for example, a substrate made of a paper phenol-based material, a glass epoxy-based material, a polyimide film-based material, a ceramic-based material, or the like can be used. The electronic component to be bonded to the substrate may be a leaded electronic component of a type that is bonded using a through hole in the substrate, such as a DIP IC, a connector, and an axial component. But,
These are merely examples, and the present invention is not limited thereto.

[0039]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Two embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1) The flow soldering method of this embodiment is carried out by using a flow soldering apparatus 20 shown in FIG.

Referring to FIG. 1A, a flow soldering apparatus 20 according to the present embodiment includes a preheat unit (or preheater) 2 and a molten solder material on a substrate (FIG. 1).
(A) not shown) and a preheat chamber 19, a solder material supply chamber 16 and a cooling chamber 17 through which the substrate passes inside along the direction of arrow 1. The solder material supply unit 3 has a solder material (not shown) preliminarily melted by heating therein, and passes the solder material through a primary jet nozzle 4 and a secondary jet nozzle 5 in the form of a jet.
It can be supplied to a substrate located in the solder material supply chamber 16 (therefore, located in the solder material supply zone 6 described later). The preheat chamber 19, the solder material supply chamber 16 and the cooling chamber 17 have internal spaces as a preheat zone 9, a solder material supply zone 6 and a cooling zone 7, respectively. There is a gap that can be used. As shown in FIG. 1A, the preheat chamber 1
The boundary between 9 and the solder material supply chamber 16 need not be clear, and will be described in detail below.

The preheat chamber 19 defines a preheat zone 9 for preheating a substrate by the preheat unit 2. In the present embodiment, the preheat unit 2 is provided inside the preheat chamber 19, but the present invention is not limited to this, and the preheat unit 2 may be located outside the preheat chamber 19. Further, the preheat unit 2 is not necessarily required for implementing the present invention, but is preferably provided. The solder material supply chamber 16 is located above the solder material supply unit 3 and defines a solder material supply zone 6 where the molten solder material is supplied to the substrate through the solder jet nozzles 4 and 5. Since such a preheat zone 9 and a solder material supply zone 6 each preferably have a high-temperature atmosphere, they need not necessarily be clearly defined. Therefore, the preheat chamber 19 and the solder material supply chamber 16 are These zones (more specifically, the respective internal atmospheres) do not necessarily have to be strictly defined. In the present embodiment, the preheat chamber 19 and the solder material supply chamber 16 are connected without partitions, and therefore, their respective internal atmospheres are also connected. However, the present invention is not limited to this.
The interior atmosphere of each of the solder material supply chamber 9 and the solder material supply chamber 16 may be defined to some extent.

The cooling chamber 17 defines a cooling zone 7 for actively cooling the substrate by a cooling unit so as to rapidly cool and solidify the solder material attached to the substrate. For this purpose, the cooling chamber 17 includes or is connected to a cooling unit (not shown) so as to cool the substrate located in the cooling zone 7 which is the internal space. As the cooling unit, any appropriate device or the like can be used as long as the solder material can be rapidly cooled. For example, a unit that can blow out gas through a nozzle can be used. More specifically, as shown schematically in FIG. 1B, the substrate 13 in the cooling chamber 17 is enlarged and schematically shown, a plurality of nozzles 12
Are arranged above and below a transfer line (a line shown by a dotted line in the figure), and a gas (indicated by an arrow in the figure) is passed through this nozzle 12 using a gas source, a pump, or the like arranged outside the cooling chamber 17, for example. A unit that can blow out the flow schematically) can be used. From each of the nozzles 12, preferably a low-temperature gas is blown toward the substrate 13, whereby the substrate 13 is gas-cooled. The arrangement of the nozzles 12 in the cooling chamber 17 depends on the substrate 1 in the cooling chamber 17.
No particular limitation is imposed as long as the solder material 3 can be actively cooled to completely cool and completely solidify the solder material. Further, the nozzles 12 do not necessarily need to be arranged above and below a substrate transfer line (a line shown by a dotted line in the figure), and may be provided on only one side. In addition, the cooling unit that can be used in the present invention is not limited to a unit having a nozzle as described above, and the substrate is cooled by bringing a gas, a liquid, or a mixture thereof into contact with the substrate, thereby rapidly cooling the solder material. Other suitable cooling units as obtained can be used.

For example, a cooling unit that can be used to cool a substrate supplies a low-temperature gas to a cooling chamber to lower the ambient temperature of the cooling zone 7 to a considerably low temperature (for example, −).
(At a temperature of 20 to 30 ° C.), thereby rapidly cooling the substrate (more specifically, the solder material attached to the substrate). In this case, the cold gas need not be directed at the substrate.

The solder material supply chamber 16 as described above
From the viewpoint of thermal efficiency, the cooling chamber 17 supplies the molten solder material to the substrate to sufficiently wet up the inside of the through hole and cool the substrate, respectively, to such an extent that each can be efficiently performed. It should be noted that any internal atmosphere can be defined, and it is not always necessary to strictly define each internal atmosphere.

Next, a flow soldering method using the flow soldering apparatus 20 of FIG. 1A will be described.

First, similarly to the conventional method, a flux is applied to the lower surface of the substrate using a spray fluxer to pretreat the substrate. On this substrate, leads drawn from the electronic components are inserted into through holes from the upper surface side of the substrate, and the electronic components are arranged.

Such a substrate is placed in the flow soldering apparatus 20 of FIG. 1A with the upper surface side on which the electronic components are arranged (up to the drawing), and the preheating of the flow soldering apparatus 20 is performed. Through the chamber 19, the solder material supply chamber 16, and the cooling chamber 17, the wafer is mechanically conveyed on a line shown by a dotted line in the drawing in the direction of arrow 1 at a substantially constant speed. In the flow soldering apparatus 20, first, the substrate is heated in the preheat zone 9 by the preheat unit 2 under an air atmosphere, preferably under a nitrogen atmosphere, for about 1 hour.
Heat (or preheat) to 50-160 ° C. Next, when the substrate is conveyed to the solder material supply zone 6, the solder material (not shown) previously melted by heating is soldered from the lower surface side of the substrate by the solder material supply unit 3 into the primary jet nozzle 4 and the secondary jet flow. The liquid is supplied as a primary jet and a secondary jet through the nozzle 5, respectively. So far,
This is almost the same as the above-mentioned conventional flow soldering method.

After the molten solder material is adhered to a predetermined portion of the substrate as described above, the substrate is transferred from the solder material supply chamber 16 to the cooling chamber 17 and placed in the cooling zone 7. In the cooling zone 7, a low-temperature nitrogen gas is blown so that the solder material attached to the substrate is rapidly cooled and solidified, and the substrate is rapidly cooled by nitrogen gas cooling. At this time, the cooling rate of the solder material is preferably 200 ° C./min or more,
For example, about 200 to 500 ° C./min, more preferably about 30
It can be 0-500 ° C / min. In addition, instead of the nitrogen gas cooling as described above, by using any appropriate cooling unit as described above, other gas cooling such as air cooling by blowing low-temperature air (atmosphere), or low-temperature circulating water The substrate may be cooled by liquid cooling such as water cooling which is brought into contact with the substrate.

By positively cooling the substrate using the cooling unit as described above, the solder material solidifies to form a fillet, and the lead of the electronic component and the land formed on the substrate are formed by the fillet. Electrically and physically joined. The obtained substrate is further transported, transported to the outside of the cooling chamber 17, and taken out of the apparatus 20. As described above, the electronic circuit board on which the electronic components are flow-soldered is manufactured.

According to the present embodiment, since the solidification time of the solder material is shortened, the occurrence of lift-off can be effectively reduced. In addition, the metal structure of the solidified solder material (fillet) can be refined, and the mechanical strength of the joint (fillet) made of the solder material can be improved.

(Embodiment 2) The flow soldering method of this embodiment is carried out by using the flow soldering apparatus 30 shown in FIG. Hereinafter, unless otherwise described, it is the same as the first embodiment.

This flow soldering apparatus 30 is different from the flow soldering apparatus 20 described in the first embodiment in that
Between the solder material supply chamber 16 and the cooling chamber 17, except that the adjustment chamber 18 was added and modified,
This is the same as the flow soldering apparatus 20 of FIG.
The conditioning chamber 18 defines the conditioning zone 8. Like the solder material supply chamber 16, the conditioning chamber 18 also effectively reduces the heat loss of the substrate to the extent that the substrate can be efficiently heated (possibly kept warm) from the viewpoint of thermal efficiency. It should be noted that it is only necessary that the internal atmosphere can be partitioned to such an extent that the internal atmosphere can be prevented, and it is not always necessary to strictly separate the internal atmosphere from another high-temperature atmosphere, for example, the atmosphere in the solder material supply chamber 16. It is. In the present embodiment, the adjustment chamber 1
Although 8 is shown as partitioning the solder material supply chamber 16 and each internal atmosphere to some extent, these may be connected in some cases in consideration of thermal efficiency.

In the flow soldering method using such a flow soldering apparatus 30, after the solder material is applied in the solder material supply zone 6 in the same manner as in the first embodiment, the substrate is removed from the solder material supply chamber 16. It is conveyed to the adjustment chamber 18 and arranged in the adjustment zone 8. This adjustment zone 8 is preferably provided with a temperature within the range of not less than the melting point of the solder material and less than the heat-resistant temperature of the electronic component, for example, about 220 to so as to ensure that the solder material attached to the substrate is completely melted. The atmosphere is kept at 230 ° C. This atmosphere gas may be air, but is preferably nitrogen gas.

Thereafter, the substrate is transferred from the conditioning chamber 18 to the cooling chamber 17 and placed in the cooling zone 7,
Cooling is performed as in the first embodiment. As a result, the solder material solidifies to form a fillet, and the fillet electrically and physically joins the lead of the electronic component to the land formed on the substrate. As described above, the electronic circuit board on which the electronic components are flow-soldered is manufactured.

According to the present embodiment, the temperature distribution of the solder material in each solder joint and the temperature distribution of the solder material in the entire substrate can be reduced, so that the variation in the quenching start temperature and the solidification of the solder material can be achieved. Time variations can be eliminated, thereby making it possible to further reduce the occurrence of lift-off.

[0057]

EXAMPLE In the flow soldering method, the effect of the cooling rate of the solder on the rate of occurrence of lift-off was examined. Using the flow soldering method and apparatus described in the first or second embodiment, electronic circuit boards were manufactured according to various conditions.

Table 1 below summarizes the conditions of each embodiment.
In Table 1, Examples 1 and 2 relate to the flow soldering method and apparatus of Embodiment 1 described above, which uses only the cooling zone and does not use the adjustment zone.
Embodiment 2 relates to the above-described Embodiment 2 using both the cooling zone and the conditioning zone (in other words, the cooling chamber and the conditioning chamber). For all examples, Sn-Ag-Bi material (melting point about 215 ° C) as a lead-free solder material
Was used.

[0059]

[Table 1]

For each of Examples 1 to 8 in Table 1, the cooling rate of the solder material was 50, 100, 200, 300, 40.
0 and 500 ° C./min to be constant,
An electronic circuit board was manufactured by performing flow soldering while cooling by blowing a gas onto the board at an appropriate temperature and flow rate. The rate of occurrence of lift-off was determined from the obtained electronic circuit board. Table 2 shows the results.

[0061]

[Table 2]

From Table 2, it can be seen that in all the examples, as the cooling rate increases, the efficiency with which lift-off occurs decreases. It has been confirmed that when the solder material is rapidly cooled as in the flow soldering method of the present invention, specifically, when the cooling rate of the solder material is set to 200 ° C./min or more, the occurrence of lift-off is effectively reduced. it can. For example, even in the case of Example 1 using only the cooling zone, when the cooling rate of the solder material was set to 200 ° C./min or more, the occurrence rate of lift-off could be reduced to 15% or less.

As can be seen from Table 2, Example 1 using only the cooling zone, and Examples 3, 5, and 7 using the adjustment zone in addition to the cooling zone (each of the adjustment zone temperature 1
50, 220, and 240 ° C.), it can be seen that even under the same air atmosphere,
It can be seen that the rates of lift-off are lower in the cases of 5 and 7. In the third, fifth, and seventh embodiments using the adjustment zone, in the case of the third embodiment in which the atmosphere temperature of the adjustment zone is lower than the melting point (about 215 ° C.) of the solder material used, in this embodiment, the adjustment zone is The solder material attached to the substrate did not begin to solidify by the time it exited, and thus it can be considered that the solder material had been maintained in a substantially molten state.
When the temperature of the atmosphere in the adjustment zone is lower than the melting point of the solder material, whether the solder material attached to the substrate is maintained in a molten state depends on the temperature of the solder material when supplying the substrate, the transfer speed of the substrate, and It should be noted that, depending on conditions such as the length of the adjustment zone, even if the adjustment zone has an atmosphere of 150 ° C., the molten state of the solder material cannot always be guaranteed. Furthermore, comparing the results of Examples 3, 5, and 7, it was found that the higher the temperature of the adjustment zone was maintained, the lower the incidence of lift-off.
In particular, in the case of Examples 5 and 7 in which the adjustment zone was maintained at a temperature equal to or higher than the melting point (215 ° C.) of the Sn—Ag—Bi-based material used as the lead-free solder material, the cooling rate of the solder material was set to 200 ° C./min. By doing so, the incidence of lift-off could be reduced to 8% or less. It can be considered that this is because by passing the substrate through an atmosphere having a temperature equal to or higher than the melting point of the solder material, it is possible to reliably ensure that the solder material attached to the substrate is in a molten state.

In Example 1, which was carried out in an air atmosphere,
Examples 2, 4, 6, and 8, which had the same conditions as Examples 1, 3, 5, and 7, respectively, except that they were performed in a nitrogen atmosphere, as compared with 3, 5, and 7, had a lift-off. It can be seen that the rate of occurrence of is reduced. In other words,
It can be seen that the rate of lift-off can be reduced by performing flow soldering in a nitrogen atmosphere rather than in an air atmosphere.

[0065]

According to the present invention, there is provided a flow soldering method for mounting an electronic component on a substrate using a lead-free solder material, wherein the occurrence of lift-off is effectively reduced. An apparatus is provided for performing the method.

[Brief description of the drawings]

FIG. 1A is a schematic diagram of a flow soldering apparatus according to one embodiment of the present invention.
(B) is a partial schematic diagram of the flow soldering apparatus of FIG. 1 (a) and shows the inside of a cooling chamber.

FIG. 2 is a schematic diagram of a flow soldering apparatus according to another embodiment of the present invention.

FIG. 3 is a schematic diagram of a conventional flow soldering apparatus.

FIG. 4 is a schematic partial cross-sectional view of an electronic circuit board manufactured by a conventional flow soldering method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Arrow (transfer direction) 2 Preheat unit 3 Solder material supply unit 4 Primary jet nozzle 5 Secondary jet nozzle 6 Solder material supply zone 7 Cooling zone 8 Adjustment zone 9 Preheat zone 12 Nozzle (part of cooling unit) 13 Substrate 16 Solder material supply chamber 17 Cooling chamber 18 Adjustment chamber 19 Preheat chamber 20, 30 Flow soldering equipment

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) // B23K 101: 42 B23K 101: 42 (72) Inventor Yoshinori Sakai 1006 Kazama, Kazuma, Kazuma, Osaka Matsushita Electric F term in Sangyo Co., Ltd. (reference) 4E080 AA01 AB06 5E319 AA02 AB01 BB08 CC24 GG15

Claims (16)

[Claims] 1. A flow soldering method for mounting an electronic component on a substrate using a lead-free solder material, wherein a molten solder material is adhered to a predetermined portion of the substrate in a solder material supply zone. And then cooling the substrate by a cooling unit in a cooling zone such that the solder material attached to the substrate is rapidly cooled and solidified. 2. The method according to claim 1, wherein the solder material is in a cooling zone.
The method according to claim 1, wherein the substrate is cooled by a cooling unit such that the substrate is cooled at a cooling rate of 0 ° C./min or more. 3. The method according to claim 1, wherein the cooling unit is a unit using gas cooling or liquid cooling. 4. The method according to claim 3, wherein the cooling unit is a unit using gas cooling by nitrogen gas. 5. In a solder material supply zone, after applying a molten solder material to a predetermined portion of a substrate, and
5. The method of claim 1, further comprising: before cooling the substrate in the cooling zone, placing the substrate in a conditioning zone having an atmosphere at a temperature that ensures that the solder material adhered to the substrate is completely melted. The method according to any of the above. 6. The method according to claim 5, wherein the temperature of the atmosphere in the adjustment zone is a temperature within a range from the melting point of the solder material to less than the heat-resistant temperature of the electronic component. 7. The method according to claim 5, wherein the atmosphere in the conditioning zone is a nitrogen gas atmosphere. 8. The quenching of the solder material mitigates the segregation phenomenon in the solder material that adheres to the substrate and solidifies.
The method according to claim 1. 9. The method according to claim 1, wherein the quenching of the solder material reduces the metal structure of the solder material that adheres to the substrate and solidifies. 10. An apparatus for mounting an electronic component on a substrate while transporting the substrate by a flow soldering method using a lead-free solder material, wherein the solder melted on the substrate located in a solder material supply chamber. A solder material supply unit that supplies a material and attaches a solder material to a predetermined portion of the substrate, and a cooling chamber that is located downstream of the solder material supply chamber in the transport direction of the substrate,
An apparatus, wherein a substrate is cooled by a cooling unit in a cooling chamber to rapidly cool and solidify a solder material attached to the substrate. 11. The method according to claim 1, wherein the solder material is in a cooling chamber.
The apparatus according to claim 10, wherein the substrate is cooled by the cooling unit such that the substrate is cooled at a cooling rate of 00 ° C./min or more. 12. The apparatus according to claim 10, wherein the cooling unit is a unit using gas cooling or liquid cooling. 13. The method according to claim 12, wherein the cooling unit is a unit using gas cooling with nitrogen gas. 14. An adjustment chamber located between a solder material supply chamber and a cooling chamber in a substrate transfer direction, wherein an atmosphere in the adjustment chamber completely melts the solder material attached to the substrate. Apparatus according to any of claims 10 to 13, having a temperature to ensure a state of operation. 15. The apparatus according to claim 14, wherein the temperature of the atmosphere in the conditioning chamber is a temperature within a range from a melting point of the solder material to less than a heat-resistant temperature of the electronic component. 16. The apparatus according to claim 14, wherein the atmosphere in the conditioning chamber is a nitrogen gas atmosphere.