JP2007150100A - Circuit board and electronic equipment using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a circuit board which prevents the exposure phenomenon of the land at lead-free soldering, and to provide electronic equipment that uses this circuit board. <P>SOLUTION: The circuit board 1 has a circuit wiring (not shown), a component surface land 2 formed in a component surface side 1a, a solder side land 3 formed in the solder surface side 1b, and a through-hole 4 which connects these lands. A component surface land end 2a and solder surface land end 3a are covered by solder resists 5 and 6, respectively, so that the diameter (c) of the component surface resist used as the diameter of an exposed component surface 2b of the component surface land 2 respectively differ from the diameter (f) of the component surface resist, used as the diameter of an exposed component surface 3b of a component surface land 3. Consequently, oxidization of the lands can be prevented, by making lead-free soldering 8 spread over to the exposed sections of the lands. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a circuit board compatible with lead-free soldering and an electronic apparatus using the circuit board.

  In order to apply the EU's RoHS Directive (prohibition of the use of hazardous substances), green procurement is accelerating in Japan, and in the future it will not be possible to sell electronic devices that use lead-containing solder. Accordingly, lead-free solders such as tin-zinc-based, tin-silver-based, tin-copper-based solders, etc., which replace lead-containing solders, are becoming widespread. However, lead-free solder (lead-free solder) still has various problems, one of which is land peeling. Land peeling occurs when a large amount of stress is applied to the joint with the land as the molten solder solidifies and contracts when flow soldering is performed using lead-free solder. There is a circuit board disclosed in Patent Document 1 as a circuit board in which the land peeling is suppressed.

  Hereinafter, the basic configuration of the circuit board disclosed in Patent Document 1 will be described with reference to FIG.

  11 is a circuit board having circuit wiring, such as a printed circuit board, and the surface on which the insertion component is mounted is the component surface 11a, for example, the flow soldering by solder jet or the soldering by hand The surface becomes the solder surface 11b. On the component surface 11a, an annular component surface land 2 formed by coating a metal foil such as a copper foil is formed. On the solder surface 11b, a metal foil such as a copper foil is disposed at a position facing the component surface land 2. An annular solder surface land 3 formed by coating is formed, and a through hole 4 serving as a communication hole for connecting the component surface land 2 and the solder surface land 3 is formed in the circuit board 11. A plated layer made of, for example, copper or the like is formed in a hollow tubular shape on the inner peripheral surface of the through hole 4 and is integrated by being coupled to the component surface land 2 and the solder surface land 3.

  Solder resist 15 is covered on the component surface land end 2a which is the outer peripheral end of the component surface land 2, and similarly, the solder resist land end 3a which is the outer peripheral end of the solder surface land 3 is also solder resist. 16 is covered. Of the component surface land 2 and the solder surface land 3, the component surface exposed portion 2b and the solder surface exposed portion 3b which are portions not covered with the solder resists 15 and 16 are generally exposed to the copper foil surface. Is subjected to substrate surface treatment with heat-resistant preflux. The lower limit of the overlap between the component surface land 2 and the solder resist 15 is basically such that the opening range of the solder resist 15 (the diameter of the exposed portion 2b) is such that the solder resist 15 covers the component surface land end 2a. However, the width of the overlapping portion between the land 2 and the solder resist 15 is desirably 0.01 mm or more, and more desirably 0.02 mm or more. On the other hand, the upper limit of the overlapping width is determined in such a range that a solder fillet 8 a described later can be formed and the opening range of the solder resist 15 is larger than the diameter of the through hole 4. The overlap between the solder surface land 3 and the solder resist 16 is also determined within the same range as described above.

  Reference numeral 7 denotes an electronic component lead as an insertion component, which is inserted into the through hole 4 from the component surface 11a side of the circuit board 11, and is subjected to flow soldering using lead-free solder from the solder surface 11b side. In the flow soldering process, when the circuit board 11 on which various insertion parts are mounted is passed through, for example, a jet solder bath, lead-free solder melted in the jet solder bath wets the solder surface land 3 and through-flows due to the surface tension. The inside of the hole 4 is soldered up, and the component surface land 2 on the opposite surface is also wetted. When the circuit board 11 passes through the jet solder bath, the lead-free solder 8 accumulated in the through hole 4 is cooled and solidified, and solder fillets 8a, 8b made of lead-free solder 8 are formed on the component surface land 2 and the solder surface land 3. Is formed. The radius of the solder fillets 8a and 8b is equal to or smaller than the opening radius of the solder resists 15 and 16.

In the above configuration, the solder fillet 8a is formed on the inner side of the component surface land end 2a, and the tension in the diagonally upward direction along the solder fillet 8a when the lead-free solder 8 contracts, and the solder fillet forming angle The force repelling thermal contraction of the circuit board 11 generated by the relationship is applied not to the land end 2a having the weakest contact with the circuit board 11, but to the inside of the land 2 having the higher contact with the circuit board 11. Therefore, the component surface land 2 can be made difficult to peel off. In addition, since the component surface land end 2 a is not fixed by the lead-free solder 8, the component surface land 2 is easily followed by thermal expansion and contraction of the circuit board 11. As a result, it is possible to suppress land separation that frequently occurs in the lead-free solder 8.
JP 2002-237664 A

  As described above, in the circuit board 11 corresponding to the lead-free solder, the board surface treatment is changed from the solder leveler to mainly the heat-resistant preflux, and the copper foil for forming lands such as the component surface land 2 and the solder surface land 3 is formed. The pattern is exposed. Lead-free solder has poorer solder wettability than lead-containing solder. When flow soldering is performed, the circuit board 11 has insufficient solder rising from the solder surface 11b side to the component surface 11a side. There is a problem that a so-called red-eye phenomenon occurs in which the solder fillet 8a is formed only in the portion, and the component surface exposed portion 2b which is a copper foil pattern around the portion remains exposed in a ring shape. In the above conventional circuit board, this red-eye phenomenon has not been considered, and it has been inclined to suppress land peeling. Therefore, the component surface exposed portion 2b of the component surface land 2 has substantially the same diameter as the solder surface exposed portion 3b of the solder surface land 3 so that a good solder fillet 8a is formed also on the component surface land 2. Due to the poor solder wettability of lead-free solder, it was difficult for the molten lead-free solder 8 to wet and spread to the outer peripheral end of the component surface exposed portion 2b. If the component surface exposed portion 2b remains exposed, it will eventually oxidize, and as a result, the reliability of the electronic device may be reduced.

  SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to provide a circuit board that prevents a land exposure phenomenon during lead-free soldering and an electronic device using the circuit board.

  According to a first aspect of the present invention, circuit wiring, a component surface land formed on the component surface side, a solder surface land formed on the solder surface side, and a through hole connecting the component surface land and the solder surface land In a circuit board mounted using lead-free solder in a state where the insertion component is inserted into the through hole, the diameter of the exposed portion of the component surface land and the diameter of the exposed portion of the solder surface land Are different from each other so that the respective outer peripheral ends of the component surface land and the solder surface land are covered with a protective material.

  In the present invention, focusing on the property that the lead-free solder does not have very good wettability, the diameter of the exposed part of the component surface land is different from the diameter of the exposed part of the solder surface land, so that the exposed part of the land has lead. Free solder can be distributed to prevent land oxidation.

  The circuit board according to claim 2 of the present invention is characterized in that the protective material is a solder resist or a substrate silk.

  If it does in this way, each land can be protected using the existing material generally used for the circuit board.

  According to a third aspect of the present invention, there is provided an electronic apparatus using the circuit board according to the first or second aspect, wherein the insertion component is soldered and mounted with the lead-free solder.

  If it does in this way, even if it is a circuit board corresponding to lead-free solder, a reliable electronic device can be provided.

  According to the first aspect of the present invention, it is possible to provide a circuit board that prevents a land exposure phenomenon during lead-free soldering.

  According to claim 2 of the present invention, the land can be protected at low cost.

  According to claim 3 of the present invention, it is possible to cope with lead-free solder while maintaining the reliability of the electronic device.

  Hereinafter, preferred embodiments of a circuit board according to the present invention will be described with reference to the accompanying drawings. In addition, the same code | symbol is attached | subjected to the same location as a prior art example, and it abbreviate | omits as much as possible since description of a common part overlaps.

  FIG. 1 is a longitudinal sectional view showing the configuration of the circuit board 1 in the present embodiment. The configuration other than the covering amount of the solder resist 5 is substantially the same as the circuit board 11 of the conventional example. That is, the circuit board 1 includes a circuit wiring (not shown), a component surface land 2 formed on the component surface 1a side, a solder surface land 3 formed on the solder surface 1b side, and a through hole 4 connecting these lands. And have. Solder resist 5 is covered on the component surface land end 2a which is the outer peripheral end of the component surface land 2, and similarly, the solder resist land end 3a which is the outer peripheral end of the solder surface land 3 is also solder resist. However, unlike the conventional example, the magnitude relationship between the diameter of the component surface exposed portion 2b and the diameter of the solder surface exposed portion 3b is different.

  In the figure, a is the T / H diameter representing the diameter of the through hole 4, b is the land diameter representing the diameter of the component surface land 2 or solder surface land 3, and c is the solder resist 5 applied to the component surface 1a side. The component surface resist diameter representing the opening diameter, d is the remaining amount of the component surface land representing the width of the component surface exposed portion 2b of the component surface land 2, and e is the component surface land end 2a of the component surface land 2 and the solder resist 5. The component surface resist covering amount representing the overlapping width, f is the solder surface resist diameter representing the opening diameter of the solder resist 6 applied to the solder surface 1 b side, and g is the solder representing the width of the solder surface exposed portion 3 b of the solder surface land 3. The remaining surface land, h, is a solder surface resist covering amount that represents the overlapping width between the solder surface land end 3 a of the solder surface land 3 and the solder resist 6. Here, the component surface resist diameter c and the component surface resist coverage e are set according to the component surface land remaining amount d, while the solder surface resist diameter f and the solder surface land remaining amount g are set to the solder surface resist coverage h. It is set together. This is because the component-side land 2 always has a land remaining amount d that allows the solder-free lead-free solder 8 to spread and spread. On the other hand, in the solder surface land 3, the resist covering amount h is set to a minimum value at which no land peeling occurs, and the land remaining amount g is increased as much as possible to form a good solder fillet 8b. Thus, the increase amount of the component surface resist diameter c is smaller than the increase amount of the land diameter b, that is, the component surface land remaining amount d is always set to a value smaller than the solder surface land remaining amount g. On the other hand, the solder surface resist diameter f and the solder surface land remaining amount g are increased in proportion to the size of the land diameter b. Conventionally, the component surface land remaining amount d is substantially equal to the solder surface land remaining amount g, and both of them are increased in proportion to the size of the land diameter b.

  Leads 7 are inserted into the through holes 4 from the component surface 1a side of the circuit board 1, and flow soldering using lead-free solder is performed from the solder surface 1b side. In the flow soldering process, when the circuit board 1 on which various insertion parts are mounted is passed through, for example, a jet solder bath, lead-free solder melted in the jet solder bath wets the solder surface land 3, and through the surface tension. The inside of the hole 4 is soldered up, and the component surface land 2 on the opposite surface is also wetted. At this time, since the component surface exposed portion 2b of the component surface land 2 has only an amount that allows the lead-free solder 8 to be sufficiently wet and spread, the exposed surface of the component surface exposed portion 2b is entirely covered with the lead-free solder 8. When the circuit board 1 passes through the jet solder bath, the lead-free solder 8 accumulated in the through-hole 4 is cooled and solidified, and solder fillets 8a and 8b made of lead-free solder 8 are formed on the component surface land 2 and the solder surface land 3. Is formed. The diameter of the solder fillet 8a is always equal to the component surface resist diameter c, and a metal foil such as a copper foil that forms the component surface land 2 is not exposed. Therefore, the red-eye phenomenon can be prevented even if the wet-spreading property of the lead-free solder 8 is not very good.

  Thus, by reducing the component surface exposed portion 2b of the component surface land 2, the red-eye phenomenon can be effectively prevented, but the protective material covering the component surface land end portion 2a is not limited to the solder resist 5. Any material may be used as long as it can cover the component land 2 and prevent oxidation and corrosion. Accordingly, a substrate silk used for displaying a circuit symbol of the circuit substrate 1 may be used as a protective material, and in this case, it can be easily implemented by performing silk screen printing on the component surface land end 2a. .

  FIG. 2 shows a modification of the present embodiment, in which the component surface lands 2 are all covered with the solder resist 5. That is, in the modification, the component surface land 2 is completely free of the component surface exposed portion 2b. In the case of using not only the circuit board 1 of FIG. 1 but also a conventional circuit board 11 having a material with good wettability of the lead-free solder 8, the entire component surface exposed portion 2 b is covered with the solder fillet 8 a. However, there is a possibility that the bottom of the solder fillet 8a is turned up by the occurrence of so-called lift-off and exposed. Therefore, in this modified example, by covering all the component surface lands 2 with the solder resist 5, the possibility that the component surface lands 2 are exposed is completely wiped out. However, in reality, if the solder resist 5 is applied to the entire surface of the component surface land 2, the solder resist 5 may enter the through hole 4 due to a position error of the solder resist 5. It is preferable to leave the land remaining amount d with a value that allows for an error.

  Furthermore, in this modification, so-called shrinkage nests (solidification cracks) can be prevented. This shrinkage nest is distortion generated due to the time difference of volume shrinkage when the metal solidifies, and it is more likely to occur as the volume of the molten lead-free solder 8 increases. Therefore, as shown in the above conventional example, it tends to occur on a double-sided board in which large solder fillets 8a and 8b are formed on both sides of the component surface 1a and the solder surface 1b, but the component surface land 2 is covered with the solder resist 5 on the entire surface. Therefore, the formation of the solder fillet 8a is suppressed, and the volume of the lead-free solder 8 can be reduced by the solder fillet 8a to prevent shrinkage. Therefore, in order to prevent shrinkage, lead formed on the component surface land 2 at least when the component surface resist diameter c, which is the diameter of the component surface exposed portion 2b of the component surface land 2, is not provided with the solder resist 5 is provided. What is necessary is just to cover the component surface land 2 so that it may become smaller than the diameter of the solder fillet 8a of the free solder 8. Then, the solder fillet 8a formed on the component surface land 2 becomes smaller than the conventional one, and the volume of the lead-free solder 8 can be reduced. Here, the solder resist 5 acts as a protective material that covers the component surface land 2 and inhibits wetting by the molten lead-free solder 8. Of course, the protective material may be substrate silk as described above. While obtaining such advantages, there is a concern about insufficient joint strength due to the fact that the solder fillet 8a is not formed on the component surface 1a side, but lead-free solder has joint strength equal to or higher than that of current lead-containing solder. Therefore, this is not a problem at all.

  As described above, in this embodiment, the circuit wiring, the component surface land 2 formed on the component surface 1a side, the solder surface land 3 formed on the solder surface 1b side, the component surface land 2 and the solder surface land 3 are formed. In the circuit board 1 that is mounted using the lead-free solder 8 in a state where the insertion component is inserted into the through hole 4, the diameter of the component surface exposed portion 2 b of the component surface land 2 is provided. The component surface as each outer peripheral edge of the component surface land 2 and the solder surface land 3 such that the component surface resist diameter c and the solder surface resist diameter f which is the diameter of the solder surface exposed portion 3b of the solder surface land 3 are different. The land end 2a and the solder surface land end 3a are respectively covered with solder resists 5 and 6 as protective materials.

  In the present invention, paying attention to the property that the lead-free solder 8 does not have a very good wettability, the lead-free solder 8 is spread over the exposed portions of the lands by making the component surface resist diameter c different from the solder surface resist diameter f. It is possible to prevent land oxidation. Therefore, it is possible to provide the circuit board 1 that prevents the land exposure phenomenon during lead-free soldering.

  Moreover, in the circuit board 1 of the present embodiment, the protective material is solder resist 5, 6 or substrate silk.

  If it does in this way, the component surface land 2 and the solder surface land 3 can be protected using the existing material generally used for the circuit board 1. Therefore, the land can be protected at a low cost.

  Furthermore, in the circuit board 1 of the present embodiment, a solder resist 5 is provided as a protective material that covers the component surface land 2 and inhibits wetting by the molten lead-free solder 8, and the solder resist 5 is a component of the component surface land 2. The component surface land 2 is such that the component surface resist diameter c, which is the diameter of the surface exposed portion 2b, is smaller than the diameter of the solder fillet 8a of the lead-free solder 8 formed on the component surface land 2 when the solder resist 5 is not provided. It is characterized by covering.

  If it does in this way, the solder fillet 8a formed in the component surface land 2 will become small compared with the past, and the volume of the lead-free solder 8 can be reduced to prevent shrinkage.

  Then, by using the circuit board 1 in which the insert component is soldered and mounted with the lead-free solder 8 for an electronic device, a highly reliable electronic device is provided even if the circuit board 1 is compatible with the lead-free solder 8. be able to. Therefore, the lead-free solder 8 can be handled while maintaining the reliability of the electronic device.

  In addition, this invention is not limited to the said Example, It can change in the range which does not deviate from the meaning of this invention. The circuit board 1 of the present invention can be used in any electronic device, and an insertion component and a surface mounting component may be mixedly mounted on the mounting component. The configuration of the circuit board 1 itself can be applied to any circuit board such as material, shape, and number of layers. The shape of the land is not particularly limited, and may be any shape such as an ellipse, a star, or a cross in addition to a polygon such as a triangle or a quadrangle.

It is a longitudinal cross-sectional view which shows the through-hole structure of the circuit board in this invention. It is a longitudinal cross-sectional view which shows the modification of a through-hole structure same as the above. It is a longitudinal cross-sectional view which shows the through-hole structure of the circuit board in the past.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Circuit board 1a Component surface 1b Solder surface 2 Component surface land 2a Component surface land edge part 2b Component surface exposed part 3 Solder surface land 3a Solder surface land edge part 3b Solder surface exposed part 4 Through-hole 5,6 Solder resist (protective material) )
8 Lead-free solder

Claims (3)

Circuit wiring, a component surface land formed on the component surface side, a solder surface land formed on the solder surface side, and a through hole connecting the component surface land and the solder surface land, the through hole In the circuit board mounted using lead-free solder in a state where the inserted component is inserted into the component surface, the diameter of the exposed portion of the component surface land is different from the diameter of the exposed portion of the solder surface land. A circuit board, wherein each of the outer peripheral ends of the land and the solder surface land is covered with a protective material. The circuit board according to claim 1, wherein the protective material is a solder resist or a substrate silk. The electronic device using the circuit board according to claim 1 or 2, wherein the insertion component is mounted by soldering with the lead-free solder.

Images