JP2009099779A - Printed wiring board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a printed wiring board suitable for preventing the generation of shrinkage cavities when using lead-free soldering. <P>SOLUTION: A region which is a part of a through-hole land 16 with solder resist 20 put thereon is turned to a heat conduction pattern 26, and thickness W between an intersection P1 where an axis radiating from the center of the through-hole land 16 to the surface direction of a substrate and the outer periphery of a region 28 which is a part of the through-hole land 16 where solder is wet and spread cross and an intersection P2 where the axis and the outer periphery of the entire through-hole land 16 cross increases as the intersection P1 separates from a boundary part 16b. Thus, a heat dissipation effect increases as a part is separated from the boundary part 16b, cooling is accelerated, cooling of respective parts of the lead-free soldering 22 is not easily biased, and thus the possibility of causing the shrinkage cavities is reduced. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a printed wiring board having a lead-free solder heat dissipation structure, and more particularly to a printed wiring board suitable for preventing the formation of shrinkage nests when lead-free solder is used.

  In a printed wiring board, an electrode of a surface mounting component constituting a circuit is mounted by soldering after being mounted on a land designed according to the electrode shape. Further, the lead of the surface mount component is mounted by soldering after being inserted into a through hole designed in accordance with the lead shape. There are various methods of soldering, such as reflow soldering, flow soldering, iron soldering, and laser soldering, which are properly used depending on the type of components and mounting space.

Conventionally, for example, a technique described in Patent Document 1 is known as a technique for solving problems associated with soldering.
Patent Document 1 includes a circuit board made of an insulating material, a wiring pattern formed on at least one surface of the circuit board, and a semiconductor component. The wiring patterns are arranged at intervals from each other, and terminals of the semiconductor component are provided. A conductive pattern extending from the connecting portion and spaced apart from each other, and extending from the connecting portion to a position in the vicinity of the semiconductor component. A technique formed of a gold material is disclosed. Thereby, migration between wiring patterns can be prevented and a short circuit between wiring patterns can be eliminated.
JP-A-2005-64160

  As in the technique described in Patent Document 1, a lead eutectic solder composed of tin and lead has been conventionally used as a bonding material for a printed wiring board. However, in recent years, it has been pointed out that when devices equipped with these printed wiring boards are discarded, lead contained in the solder elutes and adversely affects the environment and the human body. Therefore, as represented by EU's RoHS (Restriction of Hazardous Substances) standards, there is a growing tendency to legally restrict the use of harmful substances including lead.

Against this background, there has been a shift to lead-free solder that does not contain lead, and among these, Sn3Ag0.5Cu lead-free solder, which provides characteristics close to lead eutectic solder, is frequently used.
However, even Sn3Ag0.5Cu lead-free solder still has various problems such as higher melting temperature and inferior wettability than lead eutectic solder. One such problem is shrinkage, which is a phenomenon that is very likely to occur in lead-free solder. The shrinkage nest is a phenomenon in which when the molten lead-free solder is solidified, the Sn primary crystal and the Ag—Sn alloy form dendritic dendrites on the fillet surface, thereby causing cracks on the fillet surface. Shrinkage tends to occur when the cooling rate (heat drawing) immediately after soldering is slow. In addition, when the shrinkage nest is large, there is a possibility of inducing a crack, and it is an important issue to prevent the occurrence of the shrinkage nest.

FIG. 7 is a top view around the through hole of the printed wiring board.
FIG. 8 is a cross-sectional view in the thickness direction along the line AA ′ in FIG. 7.
As shown in FIGS. 7 and 8, the printed wiring board is formed with a through hole 14 designed in accordance with the shape of the lead 12 of the surface mount component. Through-hole lands 16 are formed on both end surfaces and inner peripheral surface of the through-hole 14. The right side surface of the through hole land 16 is connected to the wiring pattern 18.

The lead 12 is inserted into the through hole 14, and the lead-free solder 22 is heated and melted by soldering or the like and then solidified, whereby the through-hole land 16 and the lead 12 are electrically joined via the lead-free solder 22. The
Thus, in the configuration in which the through-hole land 16 is connected to the wiring pattern 18, the heat of the lead-free solder 22 escapes toward the wiring pattern 18 as shown by the arrows in FIG. As a result, it is difficult for the heat on the side opposite to 18 to escape, and the heat sink becomes slow, resulting in the formation of the shrinkage nest 24.

  Accordingly, the present invention has been made paying attention to such an unsolved problem of the conventional technology, and is suitable for preventing the occurrence of shrinkage nest when lead-free solder is used. The purpose is to provide a board.

  [Invention 1] In order to achieve the above object, a printed wiring board of Invention 1 is a lead-free solder heat dissipation structure in which a wiring pattern and a land connected to the wiring pattern are formed on a substrate and soldered to the land. A heat conductive pattern was formed around the lands so that when lead-free solder was soldered to the lands, heat conduction of each part of the lead-free solder was equalized.

  With such a configuration, when lead-free solder is soldered to the lands, the heat conduction pattern is formed around the lands so that the heat of each part of the molten lead-free solder is even. The heat at the location opposite to the boundary portion between the land and the wiring pattern escapes along the heat conduction pattern, and the heat pulling of each part of the lead-free solder is not easily biased.

  [Invention 2] Furthermore, the printed wiring board of Invention 2 is the printed wiring board of Invention 1, wherein the thermal conductive pattern is formed adjacent to the outer periphery of the land, and the center of the outer periphery of the thermal conductive pattern is centered. The land is located on the opposite side of the land from the boundary with the wiring pattern.

  With such a configuration, the heat conduction pattern is formed on the outer periphery of the land so that the center of the outer periphery of the heat conduction pattern is located on the opposite side of the land wiring pattern from the center of the land. Since they are formed adjacent to each other, the heat dissipating effect becomes higher as the distance from the boundary with the land wiring pattern increases, so that the heat sinking is promoted and the heat sinking of each part of the lead-free solder is less likely to be biased.

  [Invention 3] Further, the printed wiring board of Invention 3 is the printed wiring board of Invention 1, wherein the thermal conduction pattern is formed adjacent to the outer periphery of the land, and the surface of the substrate from the center of the land. The thickness between the first intersection point where the axis radiating in the direction and the outer periphery of the land intersects, and the second intersection point where the outer periphery of the axis and the heat conduction pattern intersect, the wiring pattern of the land is the first intersection point As the distance from the boundary portion increases, the distance increases.

  With such a configuration, the heat conduction pattern includes a first intersection where the axis radiating from the center of the land in the surface direction of the substrate and the outer periphery of the land, and a second intersection where the axis and the outer periphery of the heat conduction pattern intersect. Is formed adjacent to the outer periphery of the land so that the first intersection point increases as the distance from the boundary portion with the land wiring pattern increases. The heat dissipating effect becomes higher as the distance is increased, the heat pulling is promoted, and the heat pulling of each part of the lead-free solder is not easily biased.

[Invention 4] The printed wiring board according to Invention 4 is the printed wiring board according to Invention 1, wherein the thermal conduction pattern is formed adjacent to an outer periphery of the land, and the land with respect to the center of the land. These are formed at symmetrical positions with respect to the boundary with the wiring pattern.
With such a configuration, the heat conduction pattern is formed adjacent to the outer periphery of the land so as to be symmetric with respect to the boundary portion of the land wiring pattern with respect to the center of the land. The heat dissipating effect on the opposite side of the land and the boundary with the wiring pattern is enhanced, heat sinking is promoted, and the heat pulling of each part of the lead-free solder is less biased.

[Invention 5] The printed wiring board according to Invention 5 is the printed wiring board according to Invention 1, wherein the thermal conductive pattern covers a peripheral edge of the land and extends outward from the outer periphery of the land for a predetermined length. Has been.
With such a configuration, the heat conduction pattern covers the peripheral edge of the land and is extended to the outside from the outer periphery of the land by a predetermined length, so that it is opposite to the boundary portion with the land wiring pattern. The heat dissipation effect at the point is increased, heat drawing is promoted, and heat drawing at each part of the lead-free solder is less likely to be biased.

As described above, according to the printed wiring board of the first aspect, the heat of the portion opposite to the boundary portion with the land wiring pattern escapes through the heat conduction pattern, and the heat of each part of the lead-free solder is absorbed. Since it becomes difficult to be biased, it is possible to obtain an effect that the possibility of shrinkage cavities can be reduced as compared with the conventional case.
Furthermore, according to the printed wiring board of the invention 2 or 3, the heat radiation effect becomes higher as it is away from the boundary portion with the land wiring pattern, the heat dissipation is promoted, and the heat dissipation of each part of the lead-free solder is not easily biased. Therefore, the effect that the possibility that a shrinkage nest will generate | occur | produce can be reduced is acquired.

  Furthermore, according to the printed wiring board of the invention 4 or 5, the heat dissipation effect at the portion opposite to the boundary portion with the land wiring pattern is enhanced, the heat sink is promoted, and the heat pull of each part of the lead-free solder is increased. Since it becomes difficult to bias, the effect that the possibility that a shrinkage nest will generate | occur | produce can be reduced is acquired.

Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. 1 and 2 are views showing a first embodiment of a printed wiring board according to the present invention.
First, the configuration of the present embodiment will be described.
FIG. 1 is a cross-sectional view in the surface direction around a through hole of a printed wiring board.
FIG. 2 is a cross-sectional view in the thickness direction along the line BB ′ in FIG.

As shown in FIGS. 1 and 2, the printed wiring board includes an insulating material 10 and a wiring pattern 18. The printed wiring board has a through hole 14 designed in accordance with the shape of the lead 12 of the surface mount component.
Through-hole lands 16 are formed on both end surfaces and inner peripheral surface of the through-hole 14. The right side surface of the through hole land 16 is connected to the wiring pattern 18.

  A solder resist 20 is formed adjacent to the outer periphery of the surface of the through-hole land 16. A region that is a part of the through-hole land 16 and is covered with the solder resist 20 is defined as a heat conduction pattern 26 that promotes heat extraction. In the through-hole land 16, the center of the outer periphery of the through-hole land 16 is located on the opposite side of the center of the through-hole 14 from the boundary portion 16 b of the through-hole land 16 with the wiring pattern 18. Therefore, an intersection point P1 where the axis line radiating from the center of the through hole 14 in the plane direction of the substrate and the outer periphery of a part 28 of the through hole land 16 where the solder wets and spreads (area other than the heat conduction pattern 26) intersects, The wall thickness W between the axis and the intersection P2 where the outer circumference of the entire through-hole land 16 intersects increases as the intersection P1 moves away from the boundary portion 16b. The area of the through hole land 16 including the heat conduction pattern 26 is preferably equal to or larger than the area of the normal through hole land.

The lead 12 is inserted into the through hole 14, and the lead-free solder 22 is heated and melted by soldering or the like and then solidified, whereby the through-hole land 16 and the lead 12 are electrically joined via the lead-free solder 22. The
Next, the operation of the present embodiment will be described.
The through-hole land 16 has an intersection P1 where an axis radiating from the center of the through-hole 14 in the surface direction of the substrate and an outer periphery of a part 28 of the through-hole land 16 where solder spreads, and the axis and the through-hole. Since the thickness W between the intersection P2 where the entire outer periphery of the land 16 intersects is formed adjacent to the outer periphery of the through-hole land 16 so that the intersection P1 increases as the distance from the boundary portion 16b increases, The more distant from the portion 16b, the higher the heat dissipation effect. As a result, the heat of each part of the lead-free solder 22 escapes almost uniformly radially from the center of the through-hole land 16 toward the surface of the substrate, as shown by arrows in FIG. Therefore, heat sinking is promoted and the heat sinking of each part of the lead-free solder 22 is less likely to be biased.

  In this way, in this embodiment, a region that is a part of the through-hole land 16 and is covered with the solder resist 20 is used as the heat conduction pattern 26 and radiates from the center of the through-hole land 16 toward the surface of the substrate. The wall thickness W between the intersection point P1 where the outer periphery of the region 28 where the axis and a part of the through-hole land 16 are spread by the solder and the intersection point P2 where the outer periphery of the entire through-hole land 16 intersects is The intersection P1 increases as the distance from the boundary portion 16b increases.

As a result, the heat dissipating effect increases as the position is farther from the boundary portion 16b, the heat sinking is promoted, and the heat sinking of each part of the lead-free solder 22 is less likely to be biased, thereby reducing the possibility of occurrence of shrinkage nests. it can.
In the first embodiment, the through-hole land 16 corresponds to the land of the inventions 1 to 3, the intersection point P1 corresponds to the first intersection point of the invention 3, and the intersection point P2 corresponds to the second intersection point of the invention 3. It corresponds.

Next, a second embodiment of the present invention will be described with reference to the drawings. 3 and 4 are diagrams showing a second embodiment of the printed wiring board according to the present invention.
First, the configuration of the present embodiment will be described.
FIG. 3 is a cross-sectional view in the surface direction around the through hole of the printed wiring board.
4 is a cross-sectional view in the thickness direction along the line CC ′ of FIG.

As shown in FIGS. 3 and 4, the printed wiring board includes an insulating material 10 and a wiring pattern 18. The printed wiring board has a through hole 14 designed in accordance with the shape of the lead 12 of the surface mount component.
Through-hole lands 16 are formed on both end surfaces and inner peripheral surface of the through-hole 14. The right side surface of the through hole land 16 is connected to the wiring pattern 18.

  A solder resist 20 is formed adjacent to the outer periphery of the surface of the through-hole land 16. The heat conduction pattern 26 that is a part of the through-hole land 16 and promotes heat absorption is formed in a substantially rectangular shape at a position symmetrical to the boundary portion 16 b with respect to the center of the through-hole land 16. The area of the through hole land 16 including the heat conduction pattern 26 is preferably equal to or larger than the area of the normal through hole land.

  The lead 12 is inserted into the through hole 14, and the lead-free solder 22 is heated and melted by soldering or the like and then solidified, whereby the through-hole land 16 and the lead 12 are electrically joined via the lead-free solder 22. The

Next, the operation of the present embodiment will be described.
Since the heat conduction pattern 26 which is a part of the through-hole land 16 is formed so as to be symmetrical with the boundary portion 16b with respect to the center of the through-hole 14, the portion on the opposite side to the boundary portion 16b. The heat dissipation effect becomes higher. As a result, the heat on the left half surface of the lead-free solder 22 escapes toward the heat conduction pattern 26 as indicated by the arrow in FIG. 3, and the heat on the right half surface escapes toward the wiring pattern 18. Therefore, heat sinking is promoted and the heat sinking of each part of the lead-free solder 22 is less likely to be biased.

Thus, in the present embodiment, the heat conduction pattern 26 that is a part of the through-hole land 16 is formed at a position symmetrical to the boundary portion 16 b with respect to the center of the through-hole 14.
As a result, the heat radiation effect on the side opposite to the boundary portion 16b is enhanced, heat drawing is promoted, and heat drawing of each part of the lead-free solder 22 is less likely to be biased, thereby reducing the possibility of occurrence of shrinkage nests. be able to.

Next, a third embodiment of the present invention will be described with reference to the drawings. 5 and 6 are diagrams showing a third embodiment of the printed wiring board according to the present invention.
First, the configuration of the present embodiment will be described.
FIG. 5 is a cross-sectional view in the surface direction around the through hole of the printed wiring board.
6 is a cross-sectional view in the thickness direction along the line DD ′ in FIG.

As shown in FIGS. 5 and 6, the printed wiring board includes an insulating material 10 and a wiring pattern 18. A through-hole 14 that is slightly larger than the shape of the lead 12 of the surface-mounted component is formed in the printed wiring board.
Through-hole lands 16 are formed on both end surfaces and inner peripheral surface of the through-hole 14. The right side surface of the through hole land 16 is connected to the wiring pattern 18.

  The peripheral edge of the surface of the through hole land 16 is covered with a solder resist 20. The heat conduction pattern 26 that promotes heat sinking is formed to extend a predetermined length outward from a region 28 that is a part of the through-hole land 16 and spreads the solder. The area of the through hole land 16 including the heat conduction pattern 26 is preferably equal to or larger than the area of the normal through hole land.

  The lead 12 is inserted into the through hole 14, and the lead-free solder 22 is heated and melted by soldering or the like and then solidified, whereby the through-hole land 16 and the lead 12 are electrically joined via the lead-free solder 22. The

Next, the operation of the present embodiment will be described.
The heat conduction pattern 26 is formed by extending a predetermined length outwardly from the region 28 where the solder wets and spreads, which is a part of the through hole land 16, so that the heat radiation effect on the side opposite to the boundary portion 16 b is enhanced. . As a result, the heat of each part of the lead-free solder 22 escapes almost evenly radially from the center of the through-hole land 16 in the surface direction of the substrate, as shown by arrows in FIG. Therefore, heat sinking is promoted and the heat sinking of each part of the lead-free solder 22 is less likely to be biased.

In this manner, in the present embodiment, the heat conduction pattern 26 is formed so as to extend a predetermined length outward from the region 28 that is a part of the through-hole land 16 and where the solder spreads.
As a result, the heat radiation effect on the side opposite to the boundary portion 16b is enhanced, heat drawing is promoted, and heat drawing of each part of the lead-free solder 22 is less likely to be biased, thereby reducing the possibility of occurrence of shrinkage nests. be able to.

In the first to third embodiments, the through-hole land 16 is joined with the lead-free solder 22. However, the present invention is not limited to this, and the land for mounting surface mount components and other lands are lead. It can also comprise so that it may join with the free solder 22. FIG.
In the first to third embodiments, the form shown in FIGS. 1 to 6 is adopted as a form of forming the heat conduction pattern 26 that is a part of the through-hole land 16 and promotes heat absorption. Not limited to this, the shape and number of the heat conduction patterns formed on one through-hole land 16 can be arbitrary as long as the heat-drawing of each part of the lead-free solder 22 can be made uniform.

It is sectional drawing of the surface direction around the through hole of a printed wiring board. It is sectional drawing of the thickness direction along the B-B 'line | wire of FIG. It is sectional drawing of the surface direction around the through hole of a printed wiring board. It is sectional drawing of the thickness direction along the C-C 'line | wire of FIG. It is sectional drawing of the surface direction around the through hole of a printed wiring board. It is sectional drawing of the thickness direction along the D-D 'line | wire of FIG. It is a top view of the through-hole periphery of a printed wiring board. It is sectional drawing of the thickness direction along the A-A 'line | wire of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Insulation material 12 Lead 14 Through-hole 16 Through-hole land 16b Boundary part 18 Wiring pattern 20 Solder resist 22 Lead-free solder 24 Shrink nest 26 Thermal conduction pattern 28 Area where solder spreads P1, P2 Intersection W Thickness

Claims (5)

A printed wiring board having a lead-free solder heat dissipation structure in which a wiring pattern and a land connected to the wiring pattern are formed on a substrate and soldered to the land,
A printed wiring board, wherein a heat conduction pattern is formed around the land so that when the lead-free solder is soldered to the land, heat conduction of each part of the lead-free solder is equalized. In claim 1,
The heat conduction pattern is formed adjacent to the outer periphery of the land, and the center of the outer periphery of the heat conduction pattern is opposite to the boundary portion of the land with the wiring pattern from the center of the land. Printed wiring board characterized by being located in In claim 1,
The thermal conduction pattern is formed adjacent to the outer periphery of the land, and includes a first intersection where an axis radiating in the surface direction of the substrate from the center of the land and the outer periphery of the land, and the axis and the heat A printed wiring board characterized in that a thickness between a second intersection where the outer peripheries of conductive patterns intersect increases as the first intersection moves away from a boundary portion of the land with the wiring pattern. In claim 1,
The heat conduction pattern is formed adjacent to an outer periphery of the land, and is formed at a position symmetrical to a boundary portion between the land and the wiring pattern with respect to the center of the land. Printed wiring board. In claim 1,
The printed circuit board is characterized in that the thermal conduction pattern covers the peripheral edge of the land and extends outward from the outer periphery of the land by a predetermined length.

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