Printed wiring board and pad

Abstract

To effectively prevent soldering defects such as solder bridges between pads arranged along the circumference.SOLUTION: A printed wiring board 1 includes a plurality of pads 11 arranged along a circumference S and a through hole 12 formed on top of each pad 11, the pads 11 extending radially along the circumference S and having a shape in which their width increases the further away from the center of the circumference S, the through hole 12 is formed close to one of the side ends of each pad 11 along the radial direction of the circumference S and spaced apart from the other side end, one side end 11A is divided by the through hole 12, and the through hole 12 dividing one side end 11A of one pad 11 and the other side end 11B of another pad 11 adjacent to that pad 11 are spaced apart and face each other.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a pad to which a plurality of leads of a laser diode or the like are soldered, and to a printed wiring board on which a plurality of such pads are arranged. [Background technology]

[0002] In a printed circuit board, when the spacing between multiple leads of a laser diode or the like is narrow, the spacing between the pads to which each lead is soldered becomes narrow, making it easier for solder bridges and other soldering defects to occur between the pads.

[0003] In the pattern shape of the printed wiring board described in Patent Document 1, the rectangular arrangement portion of the flat package IC on the printed wiring board is tilted with respect to the direction in which soldering in the solder bath proceeds, and a group of soldering lands is provided along each edge of the rectangular arrangement portion, and each solder drawing land is provided at the corner where each edge intersects, and each member that attracts solder is provided in the hole of each solder drawing land to prevent solder bridging.

[0004] In addition, in the printed wiring board described in Patent Document 2, pattern lands are formed around a pair of insertion holes in the substrate into which terminal leads of components are inserted, and protruding lands are formed from each pattern land facing inward toward each other, and the number of wiring patterns formed between each protruding land is restricted, thereby preventing solder bridges on the printed wiring board. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 08-242067 [Patent Document 2] Japanese Patent Application Publication No. 10-261864 Summary of the Invention [Problem to be solved by the invention]

[0006] As described above, in Patent Document 1, a group of soldering lands is provided along each edge of the rectangular arrangement portion, a solder drawing land is provided at each corner where the edges intersect, and a member for attracting solder is provided in the hole of each solder drawing land.

[0007] However, when multiple leads such as those of a laser diode are arranged along the circumference, the pads to which the leads are soldered are also arranged along the circumference, so there is no point corresponding to the corner where the edges of the soldering land groups intersect as in Patent Document 1, and the technology of Patent Document 1 cannot be applied.

[0008] Furthermore, as described above, in Patent Document 2, the protruding lands are formed from each pattern land so that they face inward, and the number of wiring patterns formed between the protruding lands is restricted.

[0009] However, when a plurality of pads are arranged along the circumference as described above, no wiring pattern is formed between the pads, and the technique of Patent Document 2 cannot be applied.

[0010] The present invention has been made in consideration of the above circumstances, and aims to reliably prevent soldering defects such as solder bridges between pads when multiple leads and the respective pads to which each lead is soldered are arranged in a line along a circumference. [Means for solving the problem]

[0011] A printed wiring board according to one aspect of the present invention comprises a plurality of pads arranged along a circumference and respective through holes formed on top of each of the pads, the pads extending radially around the circumference and having a shape that widens the further away from the center of the circumference, the through holes being formed close to one of the radial side ends of the pads and spaced apart from the other side end, the one side end being divided by the through holes, and the through hole dividing one side end of the pad and the other side end of another pad adjacent to the pad are spaced apart and facing each other.

[0012] A pad according to one aspect of the present invention is a pad used for soldering, which extends radially along the circumference and has a shape that widens the further away from the center of the circumference, and the through hole is formed close to one of the side ends of the pad along the radial direction of the circumference and spaced apart from the other side end, the one side end being divided by the through hole, and the through hole dividing one side end of the pad and the other side end of another pad adjacent to the pad are spaced apart and facing each other. [Effects of the Invention]

[0013] According to the present invention, when a plurality of leads and the respective pads to which the leads are soldered are arranged in a line along a circumference, soldering defects caused by solder bridges between the pads can be reliably prevented. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a plan view showing a printed wiring board according to an embodiment of the present invention; [Figure 2] FIG. 2 is an enlarged plan view showing pads and through holes in the printed wiring board of the present embodiment. [Figure 3] (A) is a photograph taken from above showing the state in which each lead of the laser diode is soldered to each pad on the printed wiring board of this embodiment, and (B) is a photograph of the same state taken from diagonally above. [Figure 4] (A) is an image showing an enlarged cross section of the pads, leads, and solder fillets in the printed wiring board of this embodiment, and (B), (C), (D), and (E) are images showing further enlargements of parts A, B, C, and D in (A). [Figure 5] (A) is an enlarged image showing the cross section of a lead and a solder fillet in the printed wiring board of this embodiment, (B) is a further enlarged image of part A in (A) taken with a scanning electron microscope (SME), (C) is an image showing elemental mapping of part A for each of the elements Sn, Cu, Ni, Ag, Bi, Au, Fe, and Co. Also, (D) is an enlarged image showing the cross section of a land and a solder fillet in the printed wiring board of this embodiment, (E) is a further enlarged image of part B in (D) taken with an SME, and (F) is an image showing elemental mapping of part B for each of the elements Sn, Cu, Ni, Ag, Bi, Au, Fe, and Co. [Figure 6] FIG. 10 is a plan view showing a printed wiring board of a comparative example. [Figure 7] 10 is a photograph taken from above showing the state in which the leads of a laser diode are soldered to the respective pads on a printed wiring board of a comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0015] An embodiment of the present invention will be described below with reference to the drawings. Fig. 1 is a plan view showing a printed wiring board according to one embodiment of the present invention. Printed wiring board 1 of this embodiment is a board on which, for example, an 8-beam laser diode (not shown) is mounted, and here, a form in which 10 leads of the 8-beam laser diode (hereinafter simply referred to as the laser diode) are soldered is shown.

[0016] The printed wiring board 1 has a plurality of pads 11 arranged along a circumference S, through holes 12 formed on each pad 11, and a through hole 13 formed at the center o of the circumference S.

[0017] Each through hole 12 is arranged such that the center of the respective through hole 12 overlaps with the circumference S. Each pad 11 extends radially along the circumference S and has a shape that widens in width as it moves away from the center o of the circumference S. For each pad 11, the through hole 12 is formed close to one side end 11A of each side end 11A, 11B of the pad 11 along the radial direction of the circumference S and spaced apart from the other side end 11B, with one side end 11A being divided by the through hole 12.

[0018] Here, the radius a of the laser diode is approximately 5 mm, the radius b of the circumference S is set to 2.35 mm, and the center of the laser diode coincides with the center o of the circumference S.

[0019] There are ten pads 11 and ten through holes 12. The pads 11 and through holes 12 are formed at positions spaced apart by a fixed angle α (=36°) in the circumferential direction around the center o of the circumference S. The through hole 12 dividing one side end 11A of a pad 11 and the other side end 11B of another pad 11 adjacent to that pad 11 face each other with a distance c = (0.3 mm) between them.

[0020] The through hole 13 is provided at the center o of the laser diode and the circumference S. For example, the diameter d of the through hole 13 is set to 0.3 mm, and the diameter e of the land 14 formed around the through hole 13 is set to 0.7 mm. This through hole 13 is provided so that it can be recognized by a robot of automatic equipment that mounts the laser diode on the printed wiring board 1. This robot recognizes the through hole 13, aligns the center of the laser diode with the center of the circumference S of the printed wiring board 1, and inserts each lead of the laser diode into each through hole 12 of the printed wiring board 1.

[0021] Fig. 2 is an enlarged plan view showing pad 11 and through hole 12 in printed wiring board 1 of this embodiment. As shown in Fig. 2, pad 11 has a contour shape that includes a large circular arc 11C that protrudes outward at a position away from center o of circumference S, a small circular arc 11D that protrudes inward at a position close to center o of circumference S, side ends 11A and 11B that extend from both ends of small circular arc 11D toward both ends of large circular arc 11C, and a portion 11E of the inner periphery of through hole 12 that divides one side end 11A. By being divided by through hole 12, a missing portion 11F is formed in pad 11.

[0022] For example, the radius f of the large circular arc 11C is set to 0.65 mm, the radius g of the small circular arc 11D is set to 0.23 mm, and the radius h of the through hole 12 is set to 0.4 mm. Furthermore, for example, the radial distance k from the center i of the small circular arc 11D to the center j of the through hole 12 is set to 1.12 mm, and the radial distance n from the center j of the through hole 12 to the center m of the large circular arc 11C is set to 0.24 mm. The center i of the small circular arc 11D and the center m of the large circular arc 11C are on a line L1 passing through the center o of the circumference S, and for example, the distance p from the line L1 to the center j of the through hole 12 in a direction perpendicular to the radial direction is set to 0.16 mm. Furthermore, the missing portion 11F of the pad 11 is open outward at an angle β (e.g., 31°) and inward at an angle γ (e.g., 61°) relative to the center i of the through hole 12. The line L1 extends radially through the center of the pad 11 in the circumferential direction of the circumference S.

[0023] As described above, each through hole 12 is formed overlapping with a corresponding pad 11. Each pad 11 is divided into an outer region OR and an inner region IR on the circumference by a straight line L2 that is perpendicular to the radial direction of the circumference S and passes through the center j of the through hole 12 that overlaps with the pad 11. For each pad 11, the area of ​​the inner region IR is set larger than the area of ​​the outer region OR, and the ratio of the areas of the inner region IR and the outer region OR is the same.

[0024] As described above, through hole 12 is formed close to one side end 11A and spaced apart from the other side end 11B, and one side end 11A is divided by through hole 12. When pad 11 is divided into two by a straight line L1 passing through the center of pad 11 (the center o of circumference S, the center of small circular arc 11D, and the center of large circular arc 11C) into a one-side region AR closer to one side end 11A and a one-side region BR closer to the other side end 11B, the area of ​​the one-side region BR closer to the other side end 11B is set larger than the area of ​​the one-side region AR closer to one side end 11A.

[0025] The leads of the laser diode are passed through the through holes 12 of the printed wiring board 1 configured as described above, and the leads of the laser diode are soldered to the pads 11 that overlap the through holes 12 .

[0026] Figure 3(A) is a photograph taken from above showing the state in which each lead of the laser diode has been soldered to each pad 11 on the printed wiring board 1 of this embodiment, and Figure 3(B) is a photograph of the same state taken from diagonally above.

[0027] 3(A) and 3(B), each lead 15 of the laser diode is passed through a respective through-hole 12 and soldered to a respective pad 11. In each pad 11, the area of ​​the inner region IR is set larger than the area of ​​the outer region OR, so that the solder fillet 16 is formed so as to sufficiently extend into the inner region IR without being excessively raised to one side in the outer region OR. Therefore, in each pad 11, the solder fillet 16 is well formed around the entire periphery of the lead 15 that is passed through the through-hole 12.

[0028] In addition, in each pad 11, the area of ​​the one-side region BR near the other side end 11B is set larger than the area of ​​the one-side region AR near one side end 11A, so that the solder fillet is formed in a raised state in the one-side region BR near the other side end 11B, and the raised solder fillet is suppressed in the one-side region AR near one side end 11A. As a result, the solder fillet with a small raised state in the one-side region AR of one pad 11 faces the solder fillet with a large raised state in the one-side region BR of another pad 11 adjacent to that pad 11, making it difficult for a solder bridge to form between the two pads 11.

[0029] A laser diode was mounted on the printed wiring board 1 of this embodiment, and each lead of the laser diode was soldered to each pad 11. After that, a heat cycle test (500 cycles) was performed on the printed wiring board 1 to check for the occurrence of cracks in the solder.

[0030] Figure 4(a) is an image showing an enlarged cross section of the pad 11, lead 15, and solder fillet 16 in the printed wiring board 1 of this embodiment, and Figures 4(b), (c), (d), and (e) are images showing further enlarged views of parts A, B, C, and D in Figure 4(a).

[0031] As is clear from the images of FIGS. 4(a) to 4(e), the solder has good wettability with respect to the leads 15, and no cracks or the like have occurred.

[0032] Figure 5(a) is an image showing an enlarged cross section of a lead 15 and a solder fillet 16 in the printed wiring board 1 of this embodiment, Figure 5(b) is an image showing a further enlargement of part A in Figure 5(a) taken with a scanning electron microscope (SME), and Figure 5(c) is an image showing elemental mapping of part A for each of the elements Sn, Cu, Ni, Ag, Bi, Au, Fe, and Co.

[0033] Furthermore, Figure 5(d) is an image showing an enlarged cross section of the land 14 and the solder fillet 16 in the printed wiring board 1 of this embodiment, Figure 5(e) is an image showing a further enlargement of part B in Figure 5(d) by SME, and Figure 5(f) is an image showing elemental mapping in part B for each of the elements Sn, Cu, Ni, Ag, Bi, Au, Fe, and Co.

[0034] As is clear from the images in Figures 5(a) to (f), Sn, Cu, Ni, and Ag components were observed in the solder fillet 16. It is presumed that the Ag component was contaminated with solder paste (product name S70G). A Sn-Cu-Ni alloy layer was observed at the interface between the lead 15 and the solder fillet 16, and a Sn-Cu alloy layer was observed at the interface between the land 14 (or pad 11) and the solder fillet 16.

[0035] 6 is a plan view showing a printed wiring board of a comparative example. Similar to the printed wiring board 1 of the above embodiment, the printed wiring board 21 of the comparative example has ten leads of a laser diode soldered thereto, and includes a plurality of pads 31 arranged along a circumference S and through-holes 32 formed on each pad 31. However, no through-hole is formed at the center o of the circumference S.

[0036] Furthermore, each through hole 32 is arranged so that the center of the respective through hole 32 overlaps with the circumference S. Each pad 31 extends radially of the circumference S and has a shape that increases in width as it moves away from the center o of the circumference S.

[0037] However, in the comparative example printed wiring board 21, for each pad 31, a through hole 32 is formed in the center of each side end 31A, 31B of the pad 31 along the radial direction of the circumference S, and none of the side ends 31A, 31B are separated by the through hole 32, which is different from the above embodiment.

[0038] Furthermore, when each pad 31 is divided into an outer region and an inner region by a line that is perpendicular to the radial direction of the circumference S and passes through the center of the through-hole 32 that overlaps the pad 31, the area of ​​the inner region is set smaller than the area of ​​the outer region. This point also differs from the above embodiment.

[0039] Furthermore, when each pad 31 is divided into two regions, one near one side end 31A and the other near the other side end 31B, by another line passing through the center of the circumference S and the center of the pad 31, the areas of both the regions are set to be the same. This point is also different from the above embodiment.

[0040] FIG. 7 is a photograph taken from above showing the state in which the leads of the laser diode are soldered to the pads 31 on the printed wiring board 21 of the comparative example.

[0041] As is clear from Figure 7, each lead 35 of the laser diode is passed through a respective through-hole 32 and soldered to a respective pad 31. In each pad 31, the area of ​​the inner region is set smaller than the area of ​​the outer region, so the solder fillet 36 is difficult to form without spreading into the inner region, and instead flows almost entirely into the outer region OR, resulting in an excessively lopsided buildup. As a result, in each pad 31, the solder fillet 36 is not formed around the entire periphery of the lead 35 that is passed through the through-hole 32, and unsoldered areas are noticeable.

[0042] In addition, in each pad 31, the area of ​​one side region near one side end 31A and the area of ​​one side region near the other side end 31B are set to be the same, so that the solder fillets 36 are formed in a raised shape in both side regions. This makes it easy for a solder bridge to form between the side region near one side end 31A of one pad 31 and the side region near the other side end 31B of another pad 31 adjacent to that pad 31.

[0043] As described above, in the printed wiring board 1 of this embodiment, in each pad 11, the through hole 12 is formed close to one of the side ends 11A of the pad 11 along the radial direction of the circumference S and spaced apart from the other side end 11B, so that the one side end 11A is divided by the through hole 12. In addition, in each pad 11, the area of ​​the inner region IR is set larger than the area of ​​the outer region OR. Furthermore, in each pad 11, the area of ​​the one-side region BR closer to the other side end 11B is set larger than the area of ​​the one-side region AR closer to the one side end 11A. This effectively prevents soldering defects such as solder bridging.

[0044] The configurations and processes of the above-described embodiment explained with reference to FIGS. 1 to 7 are merely examples of the present invention, and the present invention is not limited to these configurations. [Explanation of symbols]

[0045] 1 printed wiring board 11 Pads 12 Through holes 13 through holes 14 rand 15 Lead

Claims

1. The device comprises a plurality of pads arranged along a circumference, and through holes formed in each of the pads so as to overlap each other, The pad extends along the radial direction of the circumference and has a shape that increases in width as it moves away from the center of the circumference, the through hole is formed close to one of the side ends of the pad along the radial direction of the circumference and spaced apart from the other side end, and the one side end is divided by the through hole; The printed wiring board has a through hole dividing one side end of the pad and the other side end of another pad adjacent to the pad, the through hole being spaced apart and facing each other.

2. When the pad is divided into two regions, an outer region and an inner region, by a line that is perpendicular to the radial direction of the circumference and passes through the center of the through hole that overlaps the pad, the area of ​​the inner region is larger than the area of ​​the outer region, 2. The printed wiring board according to claim 1, wherein when the pad is divided into two halves, one side region closer to the one side end and one side region closer to the other side end, by another straight line passing through the center of the pad and extending radially around the circumference, the area of ​​the one side region closer to the other side end is larger than the area of ​​the one side region closer to the one side end.

3. 3. The printed wiring board according to claim 1, wherein the pad has a large arc that protrudes outward at a position away from the center of the circumference, a small arc that protrudes inward at a position closer to the center of the circumference, the side ends extending from both side ends of the small arc toward both side ends of the large arc, and a contour shape that includes a part of the inner peripheral edge of the through hole that divides the one side end.

4. 3. The printed wiring board according to claim 1, wherein a through hole is formed at the center of the circumference.

5. 3. The printed wiring board according to claim 1, wherein the pads and the through holes are formed at positions spaced apart at a constant angle in the circumferential direction around the center of the circumference.

6. 3. The printed wiring board according to claim 1, wherein the through holes formed over the pads are holes into which a plurality of leads of a laser diode are inserted.

7. A pad used for soldering, The pad extends along the radial direction of the circumference and has a shape that increases in width as it moves away from the center of the circumference, the through hole is formed close to one of the side ends of the pad along the radial direction of the circumference and spaced apart from the other side end, and the one side end is divided by the through hole; A pad, wherein a through hole dividing one side end of the pad and the other side end of another pad adjacent to the pad are spaced apart and face each other.

Images