JPH10256719A - Soldering method, circuit board suitable therefor and surface mount component - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a surface mount component from lifting from a circuit board in a mounting step by the reflow soldering, making the most of the mount ing structure advantages without adhesives. SOLUTION: Surface mount components 4 are temporarily bonded to a circuit board 1 with a paste solder 3, the board 1 is fed in a reflow furnace to heat the entire board, until the solder 3 melts to solder the components 4 to a conductor pattern 2 on the board 1. The heating of the board 1 is made while letting the heat of the components 4 escape to the board 1 from a bypass heat conduction passage made of a material having a higher thermal conductivity than that of the air, for bypassing the normal heat conduction path of the solder 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit board in which surface-mounted components are temporarily fixed with paste solder, introduced into a reflow furnace and heated as a whole. The present invention relates to a reflow soldering method for bonding to a conductor pattern on a circuit board, and a circuit board and a surface mount component suitable for the method.

[0002]

2. Description of the Related Art Conventionally, surface mounting techniques for joining a surface mounting component to a conductor pattern on a circuit board are roughly classified into (a) a method without an adhesive, and (b) a method without an adhesive.
It is divided into the method with adhesive.

[0003] The mounting structure of a surface mount component to which the former method (a) is applied is, as shown in FIG. 9, after a paste solder 3 is applied to the upper surface of a conductor pattern 2 disposed on a circuit board 1. This is a structure having the surface mount component 4 mounted thereon, and the surface mount component 4 is not fixed to the circuit board 1.

On the other hand, as shown in FIG. 10, the mounting structure of the surface mounting component to which the latter method (b) is applied is such that an adhesive 5 is added to the mounting structure of FIG. The mounting component 4 is fixed.

[0005] For this reason, in the reflow soldering step by hot air heating in which the surface mount component 4 is heated before the circuit board 1 is mounted, the former method (a) is applied. According to the structure, when the solder paste 3 is melted and the surface-mounted component 4 is joined to the conductive pattern 2 on the circuit board 1, a chip floating defect in which the surface-mounted component 4 is lifted without determining the directivity as shown in FIG. FIG.
As described above, a tombstone defect in which the surface mount component 4 rises often occurs.

On the other hand, in the mounting structure of the surface mounting component to which the latter method (b) is applied, the above defect is avoided because the surface mounting component 4 and the circuit board 1 are fixed with the adhesive 5. .

However, in the case of the mounting structure of a surface mounting component to which the latter method (b) is applied, the so-called self-alignment effect of solder cannot be used.

The self-alignment effect of the solder is caused by a self-alignment phenomenon that, when the solder is melted, due to the interfacial tension of the solder, even if the surface-mounted component is misaligned with respect to the circuit board, the component is recovered to a correct position. Effect. If the self-alignment effect of the solder cannot be expected, the following problem will occur.

In order to mount surface-mounted components on a circuit board without displacement, the surface condition of the circuit board as well as the accuracy of the mounting machine is a major factor. A factor related to the displacement of the circuit board is that the substrate material for constructing the circuit board may be a resin-based composite material, and it is relatively difficult to maintain a stable surface state of the circuit board. As a mounting step for soldering, it is more cost-effective to allow a certain degree of inaccuracy in mounting surface-mounted components on a circuit board. As a result, FIG.
In the case of the mounting structure of No. 0, the self-alignment effect of the solder cannot be expected, and the requirement for the mounting accuracy of the surface mounting components on the circuit board becomes strict, and the cost increases. For example, a high-grade circuit board with high heat resistance that does not cause board warpage in the mounting process may be required.

[0010]

From this point of view, the mounting structure shown in FIG. 9, which can expect a self-alignment effect of the solder, is employed. It is more advantageous to carry out a reflow soldering method in which the solder paste is melted by this and the paste solder is melted to join the surface mount component to the conductor pattern on the circuit board.

However, since it is necessary to cope with the phenomenon of chip floating as described above, the mechanism and mechanism of the chip floating were examined and tested. The contents of the study and the experiment will be described.

The chip floating shown in FIGS. 11 and 12 occurs in a reflow furnace for melting and soldering the paste solder. The mechanism of this chip floating is shown in FIG.
The chip floating occurs when the temperature of the surface-mounted component rises faster than that of the circuit board. When the temperature of the surface-mounted component rises faster than that of the circuit board, the flow of heat in the reflow furnace is as indicated by an arrow a in FIG.

In this case, the paste solder is used for the surface mount component 4.
The temperature is highest at the part in contact with the solder paste, and a difference in temperature distribution appears in the paste solder, and the solder is gradually melted from the point where the melting temperature is reached. Then, the paste solder portion that has started to melt expands the melting region while attracting surrounding unmelted solder particles due to the interfacial tension of the solder, and eventually all the paste solder is melted.

Therefore, when the above-mentioned molten portion draws in the surrounding unmelted particles, the surface-mounted component itself receives the reaction. This reaction causes the surface mount component to float.

From the above, it can be concluded that the lifting of the surface-mounted component is caused by an excessive temperature distribution difference in the paste solder.

For the above-mentioned reason, in the case of the mounting process by the conventional reflow soldering method without using the adhesive, a chip floating defect that the surface mounting component is lifted from the circuit board in the mounting process occurs. There was a problem.

Along with this, the presence or absence of chip floating is inspected in the final step of the mounting process, and if there is chip floating, the solder is melted, and the surface mounting component is positioned at a predetermined position, and then re-soldering is performed. There was a problem that required work.

The present invention has been made in view of such a conventional problem.
A soldering method capable of preventing the occurrence of chip floating failure, in which surface mounting components are lifted from a circuit board in a mounting process using a reflow soldering method, while taking advantage of the mounting structure without an adhesive, and suitable for the same method. To provide a simple circuit board and a surface mount component.

[0019]

According to a first aspect of the present invention, a circuit board having surface-mounted components temporarily fixed by paste solder is introduced into a reflow furnace and heated as a whole.
This is a reflow soldering method of melting the paste solder and joining the surface mount component to the conductor pattern on the circuit board, wherein the heating of the circuit board bypasses a heat transfer path via the paste solder and The soldering method is characterized in that the heat of the surface mount component is released to a circuit board by a bypass heat transfer path made of a substance having a higher thermal conductivity than air.

According to the first aspect of the present invention, it is possible to prevent an excessive difference in temperature distribution from occurring in the molten solder, thereby preventing a chip floating defect.

According to the invention described in claim 2 of the present application, in the area where the surface mount component is to be mounted, heat conduction is higher than air that contacts the lower surface of the surface mount component to be mounted and releases the heat to the circuit board. In a circuit board, a heat conductive member having a high rate is disposed.

According to the invention as set forth in claim 2 of the present application, the occurrence of an excessive temperature distribution difference in the paste solder is prevented by the circuit board, and the occurrence of chip floating failure is prevented. Can be.

According to a third aspect of the present invention, there is provided a circuit board according to the second aspect, wherein the heat conductive member is a flux applied to a predetermined thickness.

According to the third aspect of the present invention, when the flux is applied to the circuit board, the flux is simultaneously applied to the circuit board as a heat conductive member for preventing the occurrence of chip floating defects. Can be formed.

According to a fourth aspect of the present invention, there is provided the circuit board according to the second aspect, wherein the heat conductive member is a conductor pattern having a predetermined thickness.

According to the invention described in claim 4 of this application, the heat conduction capability of the conductor pattern can be changed in accordance with the heat capacity of the surface mount component, and the conductor pattern can be used exclusively for heat conduction or a signal line or the like. Can also be used.

According to a fifth aspect of the present invention, in the circuit board according to the second aspect, the heat conductive member is a resist film having a predetermined thickness.

According to the invention as set forth in claim 5 of the present application, when a resist film is formed on a circuit board, the resist film is simultaneously formed as a heat conductive member for preventing occurrence of chip floating failure. can do.

According to the invention described in claim 6 of the present application, when mounted on a circuit board, a portion corresponding to a lower surface thereof has a heat projecting portion protruding to an extent of contacting the surface of the circuit board. A surface mount component characterized by the following.

According to the invention as set forth in claim 6 of the present application, an excessive temperature distribution difference is prevented from being generated in the paste solder by the heat transfer portion of the surface mount component. The occurrence of floating failure can be prevented.

[0031]

Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 shows a mounting structure of a surface mounting component to which a preferred embodiment of the present invention is applied.

FIG. 1 shows a mounting structure without an adhesive capable of expecting a self-alignment effect of solder. As shown in FIG. 1, a paste solder 3 is applied to a conductor pattern 2 on a circuit board 1 for bonding a surface mount component 4, and a paste solder 3 is applied to a region where the surface mount component 4 is to be mounted. A heat conductive member 6 having a higher thermal conductivity than air that contacts the lower surface of the surface mount component 4 to be mounted and releases the heat to the circuit board 1 is disposed. Specifically, the place where the heat conductive member 6 is arranged is right below the surface mount component 4 and in the area A where the conductor pattern 2 is not formed. In other words, the heat conducting member 6 is located in a gap between the lower surface of the surface mount component 4 and the upper surface of the circuit board 1.

According to such a mounting structure, the circuit board 1 on which the surface-mounted components 4 are temporarily fixed by the paste solder 3 is introduced into the above-mentioned reflow furnace and is entirely heated. When the solder 3 is melted and the reflow soldering for joining the surface mount component 4 to the conductor pattern 2 on the circuit board 1 is performed, unnecessary heat is released from the surface mount component 4 as follows.

That is, when such reflow soldering is performed, the circuit board 1 is heated by bypassing the normal heat transfer path a passing through the paste solder 3 as shown by the arrow in FIG. In addition, the heat of the surface mount component 4 is released to the circuit board 1 by the heat transfer path b formed of the heat conductive material 6 having a higher heat conductivity than air.

Therefore, the difference in temperature distribution between the surface mount component 4 and the circuit board 1 in the reflow furnace can be reduced. By reducing the temperature distribution difference, the temperature distribution difference in the paste solder 3 is also reduced, and the thrust vector for floating the surface mount component 4 is reduced.

Here, the thrust vector that floats the surface mount component 4 will be described with reference to FIG.

FIG. 3 is a diagram schematically showing a temperature distribution state in the paste solder 3 applied to the conductor pattern 2 on the circuit board 1. The region Y is divided into a region Y in which the temperature distribution difference in the region is steep.

In the region X, since the temperature distribution difference in the region is gentle, there is a stronger tendency to melt in-situ than to attract the surrounding solder particles as in the state X1. Therefore, it is difficult to make the vectors of the force for attracting the surrounding solder particles uniform, and no thrust for floating the surface mount component 4 is generated.

On the other hand, in the region Y, since the temperature distribution difference in the region is steep, the peripheral solder particles are melted while attracting the solder particles as in the state Y1, and the vector of the force is increased as the temperature distribution difference in the region becomes steeper. But it is easy to turn in a certain direction.

If the thrust vector for floating the surface mount component 4 is small, the occurrence of chip floating as shown in FIGS. 11 and 12 can be eliminated.

Next, a circuit board 1 suitable for implementing the present invention will be described.
Each form of the surface mount component 4 will be described.

In the first embodiment of the circuit board 1, a flux 6A applied to a predetermined thickness as shown in FIG. 4 is applied as the heat conducting member 6 in FIG. According to the first embodiment of the circuit board 1, when the flux is applied on the circuit board 1, the flux is formed on the circuit board 1 at the same time as the flux 6 </ b> A for the heat conducting member for preventing the occurrence of chip floating failure. can do. Therefore, it is excellent in terms of workability in arranging the heat conductive member 6 of FIG. 1 on the circuit board 1.

In the second embodiment of the circuit board 1, as shown in a top view (a) and a cross-sectional view (b) of FIG. A heat conductive member 6 to which a conductor pattern having a predetermined thickness is applied is arranged between lands (conductor patterns 2) 7 at positions where the lands are joined to the pattern. The circuit board 1 has an upper surface covered with a resist coating 8, and the heat conductive member 6 and the lands 7 are exposed at respective locations of the resist opening 8a. According to the second embodiment of the circuit board 1, the heat conduction capability of the conductor pattern for the heat conduction member 6 can be changed according to the heat capacity of the surface mount component 4, and the conductor pattern is dedicated to heat conduction or a signal line or the like. Can also be used. Specifically, as shown in FIG. 6, a conductor pattern 6a as a heat conducting member is arranged between the lands 7, and at least a width of the conductor pattern 6a in a region 4a where a surface mount component is to be mounted is set for a signal line or the like. By making the width larger than the width of the conductor pattern, the heat conduction capability of the conductor pattern for the heat conduction member 6 is improved. Also, as shown in FIG. 6, a conductor pattern 6a connected to a conductor pattern for signal lines or the like is provided on the conductor pattern 6a.
b are formed integrally with each other so that the conductor pattern 6
a can be used also as a signal line or the like, and the heat conduction capability of the conductor pattern for the heat conduction member 6 can be improved. If there is no conductor pattern 6b, the conductor pattern 6a is exclusively used as a heat conducting member.

The third mode of the circuit board 1 is a heat conductive member 6
, A resist film having a predetermined thickness was applied. According to the third embodiment of the circuit board 1, when the resist film is formed on the circuit board 1, the resist film can be formed at the same time as a heat conductive member for preventing occurrence of chip floating failure. In particular, according to the relationship shown in FIG. 7, the thickness S of the resist film 8 is set so that the dimension S between the upper surface of the resist film 8 on the circuit board 1 and the upper surface of the land 7 becomes 50 μm or more when ordinary soldering is performed. By increasing the thickness, the surface mount component 4 and the surface of the circuit board 1 are preferably kept in close contact with the resist film 8 even after the surface mount component 4 is mounted on the circuit board 1, which is preferable.

In the first embodiment of the surface mount component 4, a heat conductive member having a heat projecting portion 6a protruding to the extent that it contacts the surface of the circuit board 1 as shown in FIG. 8 is applied.
According to the configuration of the first embodiment of the surface mount component 4, the heat of the surface mount component 4 is dissipated to the circuit board 1 by the heat transfer portion 6 a so that an excessive temperature distribution difference does not occur in the paste solder. Since the substrate 1 can be heated, it is possible to prevent occurrence of chip floating failure.

Since the function of the heat conductive member 6 is provided to the circuit board 1 or the surface mount component 4 in such a configuration, the mounting process using the reflow soldering method can be performed while taking advantage of the mounting structure without an adhesive. Thus, it is possible to prevent the occurrence of chip floating failure, in which the surface-mounted components rise from the circuit board.

[0048]

As is apparent from the above description, according to the present invention, surface mounting components are lifted from a circuit board in a mounting process by a reflow soldering method while taking advantage of a mounting structure without an adhesive. And a circuit board and a surface mount component suitable for the method can be provided.

[Brief description of the drawings]

FIG. 1 is a diagram showing a mounting structure of a surface mounting component to be soldered by a soldering method according to an embodiment of the present invention and a cross-sectional shape of a heat conductive member.

FIG. 2 is a diagram schematically illustrating a flow of heat from a surface mount component to a circuit board which is soldered to the circuit board by a soldering method according to an embodiment of the present invention.

FIG. 3 is a diagram illustrating a state transition of paste solder used for describing a soldering method according to an embodiment of the present invention.

FIG. 4 is a diagram illustrating a configuration of a first embodiment of a circuit board suitable for a soldering method according to an embodiment of the present invention.

FIG. 5 is a diagram illustrating a configuration of a second embodiment of a circuit board suitable for a soldering method according to an embodiment of the present invention.

FIG. 6 is a view used for explaining in detail a second embodiment of a circuit board suitable for a soldering method according to an embodiment of the present invention.

FIG. 7 is a view used for explaining in detail a third embodiment of a circuit board suitable for a soldering method according to an embodiment of the present invention.

FIG. 8 is a diagram illustrating a configuration of a first embodiment of a surface mount component suitable for a soldering method according to an embodiment of the present invention.

FIG. 9 is a diagram illustrating a mounting structure of a surface mount component without an adhesive.

FIG. 10 is a diagram illustrating a mounting structure of a surface mounting component with an adhesive.

FIG. 11 is a diagram illustrating an example of a chip floating defect.

FIG. 12 is a diagram illustrating another example of a chip floating defect.

FIG. 13 is a view used to explain the mechanism of chip floating.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Circuit board 2 Conductor pattern 3 Paste solder 4 Surface mount component 5 Adhesive 6 Thermal conductive member 7 Land 8 Resist coating

Claims (6)

[Claims] 1. A circuit board on which surface mount components are temporarily fixed by paste solder is introduced into a reflow furnace and heated as a whole, whereby the paste solder is melted to convert the surface mount components into conductor patterns on the circuit board. A reflow soldering method for bonding to the circuit board, wherein the heating of the circuit board is performed by a bypass heat transfer path made of a substance having a higher thermal conductivity than air, bypassing a heat transfer path passing through the paste solder. A soldering method, wherein the heat is carried out while radiating heat of a mounted component to a circuit board. 2. A heat conductive member having a higher thermal conductivity than air that contacts the lower surface of the mounted surface mount component and releases heat to the circuit board is disposed in the area where the surface mount component is to be mounted. A circuit board, comprising: 3. The circuit board according to claim 2, wherein the heat conducting member is a flux applied to a predetermined thickness. 4. The circuit board according to claim 2, wherein the heat conductive member is a conductor pattern having a predetermined thickness. 5. The circuit board according to claim 2, wherein the heat conductive member is a resist film having a predetermined thickness. 6. A surface-mounted component having a heat transfer portion protruding to such an extent as to come into contact with the surface of a circuit board, on a portion corresponding to a lower surface when mounted on the circuit board.