JP2004273990A - Electronic circuit board and its production - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain excellent bonding reliability by improving soldering finish to a through-hole particularly with an inexpensive method in a technique for bonding an electronic component onto a printed wiring board. <P>SOLUTION: The electronic circuit board is produced through the steps of: forming a through-hole in a predetermined place on the wiring board and a plurality of via-holes disposed around the through-hole; forming a solder resist on the wiring board with the through-hole and the via-holes formed thereon; inserting a packaging component into the wiring board with the solder resist formed thereon; and feeding a molten solder from a lower surface of the wiring board wherein the packaging component is inserted. In the step of forming the solder resist, the solder resist is formed to partially expose a pattern from the periphery of the via-holes, so that the solder is infiltrated into the via-holes, thereby further improving reliability in bonding. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a technique for joining an electronic component to a printed wiring board, and more particularly to improving the reliability of joining.
[0002]
[Prior art]
As electronic devices have become smaller and more sophisticated, printed wiring boards have also been required to have more layers and higher densities. In such a printed wiring board, a pattern having a large area is often provided at a plurality of locations in order to allow a large current to flow or to take measures against noise. When an electronic component is joined to this large area pattern by flow soldering or the like, heat applied from the lower surface of the printed wiring board is dissipated from the upper surface pattern, and the temperature of the upper surface pattern may not reach a sufficiently high temperature. As a result, there is a problem that the solder is prevented from going up the through-hole, and the reliability of soldering is reduced in the through-hole connected to the pattern having a large area.
[0003]
Patent Document 1 deals with such a problem and discloses an example in which a plurality of heat conduction pins are provided around a through hole connected to a large area pattern so as to connect upper and lower patterns. To solder the lead of the inserted part to the through hole, insert the lead into the through hole, then transport it to a flow solder bath or a dip type solder bath, supply heat and solder from the lower surface of the printed wiring board, Infiltrate the solder into the through hole.
[0004]
Here, since the heat conduction pin supplies heat to the upper pattern of the through hole during soldering, the upper pattern reaches a sufficiently high temperature even if it is not directly heated during soldering. As a result, the solder that has penetrated into the through-hole can reach the upper pattern without solidifying on the way, so that a highly reliable joint can be obtained.
[0005]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 7-170061
[Problems to be solved by the invention]
[0007]
However, in the above-mentioned conventional method, there is a disadvantage that a step of embedding the heat conductive pins in the printed wiring board is required, and the cost of the pins is added to the manufacturing cost. The present invention has been made to solve such a problem, and an object of the present invention is to improve the solder dipping into a through hole by an inexpensive method and obtain excellent bonding reliability.
[0008]
[Means for Solving the Problems]
An electronic circuit board according to the present invention fills a pattern formed on both sides of a wiring board, a through-hole for conducting the pattern formed on both sides, a mounted component having a lead inserted in the through-hole, and a through-hole. In addition, a bonding member for bonding the pattern and the lead and a plurality of via holes provided around the through hole are provided.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
Embodiment 1 FIG.
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a sectional view showing a configuration of an electronic circuit board corresponding to the first embodiment of the present invention. Patterns 2a and 2b are formed on both sides of the printed wiring board 1. Since the area of the pattern 2b is smaller than that of the pattern 2a, the amount of heat dissipated from the upper pattern during soldering is small.
[0010]
Around the through hole 3a connected to the pattern 2a, a plurality of via holes 8 that conduct the upper and lower patterns 2a are provided concentrically around the through hole 3a (see FIG. 2). The via hole 8 is provided for the left lead 6a of the insertion component 5, but is not provided for the right lead 6b connected to the pattern 2b. The via hole 8 is originally provided for electrically connecting the front and back surfaces of the printed wiring board 1 and an inner layer pattern (not shown). Here, a conductive film is also formed on the inner wall of via hole 8. However, in the first embodiment, since it is not assumed that the solder penetrates into via hole 8, this conductive film can be omitted.
[0011]
The solder resist 9 is formed by applying an epoxy resin or the like on the upper side of the patterns 2a and 2b, and restricts the solder from freely diffusing on the patterns. The solder resist 9 is applied so that a part of the pattern 2a can be seen around the through hole 3a, but the exposed pattern cannot be seen around the via hole 8.
[0012]
Next, a method for manufacturing an electronic circuit board corresponding to the first embodiment will be described. First, a solder resist is applied to the printed wiring board 1 in which the through holes 3a and 3b and the via hole 8 are formed. Next, the leads 6a and 6b of the insertion component 5 are inserted into the through holes 3a and 3b, respectively. The printed wiring board thus obtained is transported to a flow solder bath or a dip type solder bath, and when heat and molten solder are supplied from the lower surface side of the printed wiring board 1, the solder penetrates into the through holes 3a and 3b. , Leads 6a and 6b are joined to patterns 2a and 2b, respectively. However, since the solder resist 9 covers the periphery of the via hole 8, the solder does not enter the via hole 8.
[0013]
In this method, since a plurality of via holes 8 are provided around the through hole 3a, the area of the pattern 2a having good heat conductivity is reduced in the vicinity of the through hole 3a, and the area from the through hole 3a to the upper pattern 2a is reduced. The amount of heat flowing out and dissipating is suppressed. Therefore, even if the upper pattern 2a is not directly heated at the time of soldering, the temperature around the through hole 3a reaches a high enough temperature for the bonding to progress. As a result, as shown in FIG. 1, the solder that has entered the inside of the through hole 3a reaches the upper pattern 2a without solidifying on the way, and solidifies to become the solder member 7. Also, since the area of the pattern 2b is smaller than that of the pattern 2a, the solder smoothly goes up the through hole even without the via hole.
[0014]
The electronic circuit board thus obtained was put into a temperature cycle test of −40 ° C. (30 minutes) to 125 ° C. (30 minutes) and evaluated up to 2000 cycles. After the test, the cross section of the printed wiring board was observed, and as a result, as shown in FIG. 3, the cracks 10 slightly progressed from the final portion of the solder toward the inner wall of the through hole. However, it was confirmed that there was no particular problem from the viewpoint of joining reliability.
[0015]
In the first embodiment, an example is shown in which the via holes 8 are arranged on one concentric circle centered on the through hole 3a, but the arrangement can be freely designed as appropriate. For example, the via holes 8 may be arranged on a plurality of concentric circles having different radii.
[0016]
Embodiment 2 FIG.
FIG. 4 is a sectional view showing a configuration of an electronic circuit board corresponding to the second embodiment of the present invention. As in the first embodiment, a plurality of via holes 8 are provided around the through hole 3a connected to the pattern 2a and connect the patterns 2a above and below the through hole 3a. However, in the second embodiment, the solder resist 9 is formed such that a part of the pattern 2a is exposed from the periphery of the via hole 8.
[0017]
Next, a method for manufacturing an electronic circuit board according to the second embodiment will be described. First, a solder resist is applied to the printed wiring board 1 in which the through holes 3a and 3b and the via hole 8 are formed. Next, the leads 6a and 6b of the insertion component 5 are inserted into the through holes 3a and 3b, respectively. The printed wiring board thus obtained is transported to a flow solder tank or a dip type solder tank, and when heat and molten solder are supplied from the lower surface of the printed wiring board 1, the solder penetrates into the through holes 3a and 3b, The leads 6a, 6b are joined to the patterns 2a, 2b, respectively. At this time, since the solder resist 9 does not completely cover the pattern 2a, the solder penetrates into the via hole 8.
[0018]
In the electronic circuit board corresponding to the second embodiment, in addition to the effect of dissipating the heat flow in the vicinity of through hole 3 a by providing via hole 8, the solder penetrates inside via hole 8. Therefore, there is an effect that the upper pattern 2a connected to the through hole 3a is directly heated. As a result, as shown in FIG. 4, the solder that has entered the inside of the through hole 3 a reaches the upper side of the lead 6 a without solidifying on the way and spreads to the exposed portion of the pattern defined by the solder resist 9.
[0019]
The electronic circuit board thus obtained was put into a temperature cycle test of −40 ° C. (30 minutes) to 125 ° C. (30 minutes) and evaluated up to 2000 cycles. After the test, as a result of observing the cross section of the substrate, as shown in FIG. 5, cracks 10 were slightly observed in the exposed portions of the pattern defined by the solder resist. However, no crack was recognized on the inner wall of the through hole 3a.
[0020]
Comparative Example FIG. 6 is a sectional view showing a configuration of an electronic circuit board corresponding to the comparative example. In this comparative example, no via hole 8 is arranged around the through hole 3a.
[0021]
Next, a method for manufacturing an electronic circuit board corresponding to the comparative example will be described. The leads 6a and 6b of the insertion component 5 are inserted into the through holes 3a and 3b, respectively. The printed wiring board thus obtained is transported to a flow solder tank or a dip type solder tank, and when heat and molten solder are supplied from the lower surface of the printed wiring board 1, the solder penetrates into the through holes 3a and 3b, The leads 6a, 6b are joined to the patterns 2a, 2b, respectively. However, as shown in FIG. 6, the solder that entered the inside of the through-hole 3a solidified on the way and did not reach the upper pattern 2a at all.
[0022]
The electronic circuit board thus obtained was put into a temperature cycle test of −40 ° C. (30 minutes) to 125 ° C. (30 minutes) and evaluated up to 2000 cycles. After the test, the cross section of the printed wiring board was observed, and as a result, as shown in FIG. 7, the crack 10 remarkably developed on the inner wall of the through-hole and reached the lower pattern. It was confirmed that the joint in this state was electrically disconnected.
[0023]
【The invention's effect】
An electronic circuit board according to the present invention fills a pattern formed on both surfaces of a wiring board, a through hole for conducting the pattern formed on both surfaces, a mounted component having a lead inserted into the through hole, and a through hole. In addition, by providing a bonding member for bonding the pattern and the lead and a plurality of via holes provided around the through hole, the connection reliability of the bonding member is excellent.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a cross-sectional structure of an electronic circuit board corresponding to a first embodiment.
FIG. 2 is a diagram for explaining that a plurality of via holes are formed around a through hole.
FIG. 3 is a diagram for explaining a shape of a crack generated in a temperature cycle test on the electronic circuit board corresponding to the first embodiment.
FIG. 4 is a diagram for illustrating a cross-sectional structure of an electronic circuit board corresponding to a second embodiment.
FIG. 5 is a diagram illustrating a shape of a crack generated in a temperature cycle test on an electronic circuit board corresponding to the second embodiment.
FIG. 6 is a diagram illustrating a cross-sectional structure of an electronic circuit board corresponding to a comparative example.
FIG. 7 is a diagram for explaining a shape of a crack generated in a temperature cycle test on an electronic circuit board corresponding to a comparative example.
[Explanation of symbols]
1 printed wiring board, 2a, 2b pattern, 3a, 3b through hole, 5 insertion component, 6a, 6b lead, 7 solder member,
8 via holes, 9 solder resist, 10 cracks.

Claims (4)

A pattern formed on both sides of the wiring board, a through-hole for conducting the pattern formed on the both sides, a mounted component having a lead inserted into the through-hole, filling the through-hole and filling the pattern with the lead And a plurality of via holes provided around the through-hole. The electronic circuit board according to claim 1, wherein the via hole is filled with a joining member that joins the pattern. Forming a through hole at a predetermined location on the wiring board and a plurality of via holes arranged around the through hole; and forming a solder resist on the wiring board on which the through hole and the via hole are formed; and A method for manufacturing an electronic circuit board, comprising: a step of inserting a mounting component into a wiring board on which a solder resist is formed; and a step of supplying molten solder from a lower surface of the wiring board into which the mounting component is inserted. 4. The method according to claim 3, wherein in the step of forming the solder resist, the solder resist is formed so that a part of the pattern is exposed from the periphery of the via hole.

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