Method for manufacturing printed wiring boards and printed boards

Abstract

The present invention provides a method for manufacturing a printed circuit board that reduces the thickness of the solder layer while forming the solder layer over the entire surface of the pad. [Solution] A method for manufacturing a printed circuit board according to one aspect of the present disclosure is a method for manufacturing a printed circuit board having a solder layer on the surface of a pad, comprising the steps of printing a plurality of solder paste portions containing solder particles on the surface, and reflowing the plurality of solder paste portions after the printing step, wherein in the printing step the plurality of solder paste portions are formed scattered on the surface, and in the reflowing step the solder particles contained in the plurality of solder paste portions are solidified on the surface.

Description

Technical Field

[0001] The present disclosure relates to a method for manufacturing a printed wiring board and a printed board.

Background Art

[0002] Printed wiring boards having a solder layer on the surface of pads are widespread (see Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

[0004] A method for manufacturing a printed wiring board according to an aspect of the present disclosure is a method for manufacturing a printed wiring board having a solder layer on the surface of a pad, the method including a step of printing a plurality of solder paste portions containing solder particles on the surface, and a step of reflowing the plurality of solder paste portions after the printing step, the plurality of solder paste portions being formed scatteredly on the surface in the printing step, and the solder particles contained in the plurality of solder paste portions being solidified in a solid state on the surface in the reflowing step

Brief Description of the Drawings

[0005] [Figure 1] FIG. 1 is a flowchart showing a method for manufacturing a printed wiring board according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is a schematic plan view showing a state in which a plurality of solder paste portions are formed on the surface of a pad in the printing step of FIG. 1. [Figure 3] FIG. 3 is a schematic cross-sectional view showing a cross-section taken along line III-III in a state in which a plurality of solder paste portions are formed on the surface of a pad in the printing step of FIG. 1. [Figure 4]Figure 4 is a partially enlarged view illustrating the arrangement of multiple solder paste areas in Figure 2. [Figure 5] Figure 5 is a schematic cross-sectional view corresponding to the cross-section in Figure 3, illustrating the printing procedure in the printing process shown in Figure 1. [Figure 6] Figure 6 is a schematic plan view showing the printing plate used in the printing procedure shown in Figure 5. [Figure 7] Figure 7 is a schematic cross-sectional view corresponding to the cross-section in Figure 3, illustrating the next printing step in Figure 5 during the printing process of Figure 1. [Figure 8] Figure 8 is a schematic plan view showing the printed circuit board obtained by the reflow process shown in Figure 1. [Figure 9] Figure 9 is a schematic cross-sectional view showing the cross-section of the IX-IX line in the printed circuit board shown in Figure 8. [Modes for carrying out the invention]

[0006] [Issues this disclosure aims to address] Patent Document 1 describes a method of forming a solder layer by applying solder paste to the surface of a substrate while masking is applied, and then curing the solder paste. Conventionally, the masking material used has openings that match the shape of the pad.

[0007] However, when using the conventional masking method described above, the solder layer is formed by curing the solder paste applied to the entire surface of the pad, which tends to result in a large solder layer thickness.

[0008] On the other hand, nowadays, it is sometimes desirable to form a thin solder layer that covers the entire surface of the pad.

[0009] This disclosure is made in accordance with the above circumstances and aims to provide a method for manufacturing a printed circuit board that reduces the thickness of the solder layer while forming the solder layer over the entire surface of the pad.

[0010] [Effects of this disclosure] A method for manufacturing a printed circuit board according to one aspect of this disclosure makes it possible to reduce the thickness of the solder layer while forming the solder layer over the entire surface of the pad.

[0011] [Description of Embodiments in this Disclosure] First, the embodiments of this disclosure will be listed and described.

[0012] (1) A method for manufacturing a printed circuit board according to one aspect of the present disclosure is a method for manufacturing a printed circuit board having a solder layer on the surface of a pad, comprising the steps of printing a plurality of solder paste portions containing solder particles on the surface, and reflowing the plurality of solder paste portions after the printing step, wherein in the printing step the plurality of solder paste portions are formed scattered on the surface, and in the reflowing step the solder particles contained in the plurality of solder paste portions are solidified on the surface.

[0013] The method for manufacturing the printed circuit board involves forming multiple solder paste areas on the surface of the pads in a scattered manner during the printing process, thereby reducing the amount of solder particles applied to the surface of the pads. Furthermore, the method for manufacturing the printed circuit board involves reflowing the multiple solder paste areas formed on the surface of the pads to solidify the solder particles into a solid layer on the surface of the pads, thereby forming a solder layer over the entire surface of the pads. Consequently, the method for manufacturing the printed circuit board allows for a reduced thickness of the solder layer while simultaneously forming the solder layer over the entire surface of the pads.

[0014] (2) In the above (1), the plurality of solder paste portions may be formed in a dot shape during the printing process. According to this embodiment, the thickness of the solder layer can be reduced while making it easier to form the solder layer over the entire surface of the pad.

[0015] (3) In the above (1) or (2), in the printing step, the plurality of solder paste portions may be formed on lattice points. According to this aspect, while reducing the thickness of the solder layer, it is easier to form the solder layer more easily on the entire surface of the pad.

[0016] (4) In the above (3), the lattice points may be lattice points of a triangular lattice. According to this aspect, while reducing the thickness of the solder layer, it is easier and more reliable to form the solder layer on the entire surface of the pad.

[0017] (5) In any of the above (1) to (4), the average interval between the plurality of solder paste portions may be 500 μm or less. According to this aspect, in the solder layer obtained by the reflow step, it is easy to prevent solder non-wetting caused by the gaps between the plurality of solder paste portions. As a result, it is easier to form the solder layer on the entire surface of the pad.

[0018] (6) In any of the above (1) to (5), the average diameter of the plurality of solder paste portions may be 100 μm or more and 1000 μm or less. According to this aspect, it is easy to reduce the thickness of the solder layer easily.

[0019] (7) In any of the above (1) to (6), the occupancy area ratio of the entire plurality of solder paste portions on the surface may be 40% or more and 70% or less. According to this aspect, while reducing the thickness of the solder layer, it is easy to form the solder layer on the entire surface of the pad.

[0020] (8) In any of the above (1) to (7), in the printing step, some of the solder paste portions may be printed so as to protrude from the surface in a plan view. According to this aspect, it is easy and reliable to form the solder layer on the edge portion of the surface of the pad.

[0021] (9) In any of (1) to (8) above, a printing plate having a plurality of openings corresponding to the plurality of solder paste portions may be used in the printing step. According to this embodiment, the plurality of solder paste portions can be easily and reliably formed at desired positions on the surface of the pad.

[0022] (10) A printed circuit board according to another aspect of the present disclosure is a printed circuit board used in the method for manufacturing a printed circuit board described in (9) above, having a plurality of openings into which solder paste is inserted, wherein the plurality of openings are arranged at a distance from each other.

[0023] According to this printed circuit board, a printed wiring board in which the thin solder layer is formed over the entire surface of the pad can be easily manufactured.

[0024] In this disclosure, "forming multiple solder paste areas in a scattered manner" means forming multiple solder paste areas spaced apart from each other. The shape and size of each solder paste area are not specified. "Solid" means that the area ratio is 90% or more of the surface area of ​​the pad. This area ratio may be 95% or more, or 97% or more. "Dot-like" means that multiple circular or approximately circular shapes are arranged. Here, "circular" is not limited to a perfect circle, but includes, for example, an ellipse, an oblong (a shape in which arcs are connected to the ends of two opposing sides). Also, "approximately circular shapes" include, for example, triangles, quadrilaterals, and other polygons.

[0025] "Average spacing between multiple solder paste areas" means selecting any five adjacent solder paste areas (or the maximum number of four or fewer areas if there are fewer than five areas), determining the minimum spacing between each area, and then averaging these minimum spacings. "Average diameter of multiple solder paste areas" means averaging the diameters of any five solder paste areas (or the maximum number of four or fewer areas if there are fewer than five areas). Here, "diameter of solder paste area" means the diameter when converted to a perfect circle of the same area. "Plan view" means a view in the thickness direction of the pad.

[0026] [Details of the embodiments of this disclosure] Preferred embodiments of this disclosure will be described below with reference to the drawings. Note that, regarding the numerical values ​​described herein, it is possible to adopt only one of the upper or lower limits, or to combine the upper and lower limits as desired. This specification includes all possible numerical ranges that can be combined. Furthermore, the figures are schematic and may not correspond to actual shapes, dimensions, proportions, etc.

[0027] [First Embodiment] <Manufacturing method for printed circuit boards> The method for manufacturing a printed circuit board in this disclosure (hereinafter also simply referred to as "the manufacturing method") is a method for manufacturing a printed circuit board having a solder layer on the surface of a pad. As shown in Figure 1, the manufacturing method comprises a step S1 of printing a plurality of solder paste portions containing solder particles on the surface of the pad, and a step S2 of reflowing the plurality of solder paste portions after the printing step S1. In the printing step S1, the plurality of solder paste portions are formed scattered on the surface. In the reflow step S2, the solder particles contained in the plurality of solder paste portions are solidified on the surface.

[0028] In this manufacturing method, the plurality of solder paste portions are formed scattered on the surface of the pad in the printing step S1, so the amount of solder particles applied to the surface of the pad can be reduced. Furthermore, in this manufacturing method, the plurality of solder paste portions formed scattered on the surface of the pad are reflowed to solidify the solder particles on the surface of the pad, so the solder layer can be formed over the entire surface of the pad. Therefore, in this manufacturing method, the thickness of the solder layer can be reduced while forming the solder layer over the entire surface of the pad.

[0029] [Printed wiring board] A printed circuit board manufactured by this manufacturing method comprises, for example, a substrate, pads arranged on the substrate, and a solder layer laminated on the surface of the pads. The solder layer is formed by reflowing a plurality of solder paste portions printed on the surface of the pads. The pads may be part of a conductive pattern arranged on the substrate. The conductive pattern may include one or more wirings. The pads may be connected to the wirings, or they may be separated from them. The planar shape of the pads is not particularly limited, but may be rectangular, for example. As long as the printed circuit board comprises the pads and the solder layer, the other specific structures are not particularly limited.

[0030] In the printed circuit board described above, the pads are used, for example, as terminals for electrical testing, terminals for inserting and removing connectors, and terminals for soldering connections with other printed circuit boards.

[0031] The following describes each step in the manufacturing method.

[0032] (Printing process) In the printing process S1, as shown in Figures 2 and 3, multiple solder paste portions 12a containing solder particles are printed scattered on the surface 10a of the pads 10 placed on the substrate 11.

[0033] The solder paste portion 12a may contain flux in addition to the solder particles mentioned above. Known methods can be used to print multiple solder paste portions 12a, such as screen printing or inkjet printing. The following describes the procedure for printing multiple solder paste portions 12a by screen printing.

[0034] First, in the printing process S1, as shown in Figure 5, the printing plate 20 is placed on the surface 10a of the pad 10. That is, in the printing process S1, a plurality of solder paste portions 12a are printed using the printing plate 20. The printing plate 20 itself is one embodiment of the present disclosure.

[0035] [Printing board] As shown in Figures 5 and 6, the printed circuit board 20 has multiple openings 21 corresponding to multiple solder paste sections 12a. That is, the printed circuit board 20 has multiple openings 21 that correspond one-to-one with multiple solder paste sections 12a. Solder paste 12 is inserted into the multiple openings 21. The multiple openings 21 are also arranged at a scattered rate. The arrangement of the multiple openings 21 in a plan view is the same as the arrangement of the multiple solder paste sections 12a in a plan view. Also, the shape of the multiple openings 21 in a plan view is the same as the shape of the multiple solder paste sections 12a in a plan view.

[0036] In this manufacturing method, by using the printing plate 20 in the printing step S1, multiple solder paste portions 12a can be easily and reliably formed at desired positions on the surface 10a of the pad 10.

[0037] The material of the printing plate 20 is not particularly limited. The printing plate 20 may be made of stainless steel, for example. In this case, the printing plate 20 is provided as a metal mask.

[0038] If the printing plate 20 is a metal mask, the lower limit of the average thickness of the printing plate 20 may be 50 μm, 80 μm, or 100 μm. The durability of the printing plate 20 can be improved by having an average thickness equal to or greater than the lower limit. On the other hand, if the average thickness of the printing plate 20 is equal to or greater than the lower limit, for example, if an opening of the same shape as the pad 10 is formed on the printing plate 20, the thickness of the solder paste printed on the pad 10 will increase. Conversely, if the amount of solder paste printed is adjusted simply by reducing the size of the opening, it becomes difficult to form a solder layer over the entire surface of the pad 10. In this regard, the printing plate 20, having multiple openings 21 scattered throughout, allows for the formation of a thin solder layer over the entire surface of the pad 10 even when the average thickness is relatively large. The upper limit of the average thickness is not particularly limited, but may be, for example, 200 μm or 150 μm. Furthermore, "average thickness" refers to the average value of the thicknesses of any five points.

[0039] As described above, the printed circuit board 20 has a plurality of openings 21 into which the solder paste 12 is inserted. Furthermore, the plurality of openings 21 are arranged at scattered points. Therefore, the printed circuit board 20 can be easily manufactured to produce a printed wiring board in which the thin solder layer is formed over the entire surface of the pad 10.

[0040] As shown in Figure 5, in the printing process S1, with the printing plate 20 placed on the surface 10a of the pad 10, solder paste 12 is placed on the printing plate 20. Furthermore, in the printing process S1, the solder paste 12 is pushed out from the multiple openings 21 formed in the printing plate 20 by pressing and moving the squeegee 30 on the surface of the printing plate 20, as shown in Figure 7. After that, the printing plate 20 is removed from the surface 10a of the pad 10, resulting in the state shown in Figures 2 and 3.

[0041] As shown in Figures 2 to 4, in the printing process S1, multiple solder paste portions 12a may be formed in a dot shape. According to this embodiment, the thickness of the solder layer formed by the reflow process S2 can be reduced, while making it easier to form the solder layer over the entire surface of the pad 10.

[0042] The lower limit of the average diameter D (see Figure 4) of the multiple solder paste portions 12a formed in the printing process S1 may be 100 μm or 150 μm, from the viewpoint of preventing solder non-wetting from occurring after the reflow process S2 due to the solder paste portions 12a becoming too small. On the other hand, the upper limit of the average diameter D may be 1000 μm, 600 μm, 300 μm, or 250 μm, from the viewpoint of easily reducing the thickness of the solder layer after the reflow process S2.

[0043] The shape of the solder paste portion 12a formed in the printing process S1 in a plan view can be, for example, a circle or a polygon. If the shape of the solder paste portion 12a in a plan view is circular, it is easier to make the solder paste portion 12a flow evenly in all directions during the reflow process S2. The circle can be, for example, a perfect circle. On the other hand, if the shape of the solder paste portion 12a in a plan view is polygonal, it is easier to make it easier to uniformly adjust the spacing between adjacent solder paste portions 12a when multiple solder paste portions 12a are placed on the surface 10a of the pad 10. The polygon can be, for example, a hexagon.

[0044] The shapes of the multiple solder paste portions 12a formed in the printing process S1 may be different or the same. If the shapes of the multiple solder paste portions 12a are the same, it is easier to control the thickness of the solder layer obtained by the reflow process S2 to be small and uniform.

[0045] The upper limit of the average spacing L (see Figure 4) between the multiple solder paste portions 12a formed in the printing process S1 may be 500 μm, 300 μm, 200 μm, or 150 μm, from the viewpoint of preventing solder non-wetting due to gaps between the multiple solder paste portions 12a after the reflow process S2. On the other hand, the lower limit of the average spacing L may be, for example, 50 μm, from the viewpoint of preventing difficulties in manufacturing the printed board 20.

[0046] The lower limit of the total area occupancy ratio of the multiple solder paste portions 12a on the surface 10a of the pad 10 may be 40%, 45%, or 50%, from the viewpoint of forming the solder layer obtained by the reflow process S2 over the entire surface of the pad 10. On the other hand, the upper limit of the area occupancy ratio may be 70% or 60%, from the viewpoint of reducing the thickness of the solder layer.

[0047] In the printing process S1, multiple solder paste portions 12a may be formed on a grid. According to this embodiment, multiple solder paste portions 12a can be evenly distributed on the pad 10. As a result, the thickness of the solder layer obtained by the reflow process S2 can be reduced, and the solder layer can be more easily formed over the entire surface of the pad 10.

[0048] Examples of the grid points mentioned above include grid points of a triangular grid and grid points of a square grid. The triangular grid may be a regular triangular grid. The square grid may be a square grid. The grid points being of a triangular grid makes it easy to densely arrange multiple solder paste portions 12a. As a result, it is possible to reduce the thickness of the solder layer obtained by the reflow process S2 while easily and reliably forming the solder layer over the entire surface of the pad 10. In particular, when the triangular grid is a regular triangular grid, as shown in Figure 4, it becomes easier to uniformly control the spacing between adjacent solder paste portions 12a, which further promotes the thinning of the solder layer.

[0049] In the printing process S1, as shown in Figures 2 and 3, a portion of the solder paste 12a may be formed so that it extends beyond the surface 10a of the pad 10 in a plan view. According to this embodiment, the solder particles molten in the reflow process S2 are more likely to flow to the outer edge of the pad 10 due to surface tension. As a result, the solder layer obtained by the reflow process S2 can be easily and reliably formed on the edge of the surface 10a of the pad 10.

[0050] (The reflow process) In the reflow process S2, the solder particles contained in the multiple solder paste portions 12a formed on the surface 10a of the pad 10 by the printing process S1 are reflow-melted, and then these solder particles are solidified.

[0051] In the reflow step S2, the solder particles are allowed to flow so as to cover the entire surface of the pad 10, thereby solidifying the solder particles into a solid mass on the pad 10. The solidification of the solder particles in the reflow step S2 results in the printed circuit board 50 shown in Figures 8 and 9.

[0052] [Printed wiring board] The printed circuit board 50 comprises a substrate 11 and pads 10 placed on the substrate 11. A solder layer 51 formed by the solidification of the solder particles is laminated on the pads 10.

[0053] The solder layer 51 is laminated over the entire surface 10a of the pad 10. The lower limit of the area ratio of the solder layer 51 to the surface area of ​​the pad 10 may be 90%, 95%, or 97%. The solder layer 51 does not need to have cracks or holes on the surface 10a of the pad 10.

[0054] The upper limit of the average thickness of the solder layer 51 may be 100 μm, 90 μm, or 80 μm. This manufacturing method makes it easy to reduce the average thickness of the solder layer 51. The lower limit of the average thickness of the solder layer 51 is not particularly limited, but from the viewpoint of easily preventing the occurrence of non-wetting, it may be 40 μm or 50 μm.

[0055] [Other embodiments] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of the present invention is not limited to the configurations of the embodiments described above, but is indicated by the claims, and all modifications within the meaning and scope equivalent to the claims are intended to be included.

[0056] In the printing process described above, by forming multiple solder paste portions scattered on the pad, the thickness of the resulting solder layer can be reduced compared to forming a single solder paste portion on the pad, while also making it easier to form the solder layer over the entire surface of the pad. Therefore, the shape and arrangement of the multiple solder paste portions are not limited to the configuration described in the embodiment, as long as the solder particles contained in the multiple solder paste portions can be solidified onto the surface of the pad in the reflow process described above.

[0057] In the above embodiment, a method was described in which the solder paste portion is formed so as to protrude from the surface of the pad in a plan view. However, in this manufacturing method, as long as the solder layer can be formed on the pad with a desired area ratio, all of the solder paste portion may be formed to be contained within the surface of the pad. [Explanation of Symbols]

[0058] 10 pads 10a surface 11 circuit boards 12 Solder paste 12a Solder paste area 20 Printing board 21 Aperture 30 squeegee 50 Printed circuit boards 51 Solder layer D Average diameter of multiple solder paste areas L Average spacing between multiple solder paste areas

Claims

1. A method for manufacturing a printed circuit board having a solder layer on the surface of a pad, The process involves printing multiple solder paste areas containing solder particles onto the above surface, After the printing process described above, there is a process of reflowing the multiple solder paste areas described above. Equipped with, In the printing process described above, multiple solder paste areas are scattered on the surface. A method for manufacturing a printed circuit board, wherein, in the reflow process described above, the solder particles contained in the multiple solder paste portions are solidified onto the surface.

2. The method for manufacturing a printed circuit board according to claim 1, wherein the plurality of solder paste portions are formed in a dot shape during the printing process described above.

3. The method for manufacturing a printed circuit board according to claim 1, wherein the plurality of solder paste portions are formed on grid points in the printing process described above.

4. The method for manufacturing a printed circuit board according to claim 3, wherein the above-mentioned grid points are grid points of a triangular grid.

5. The method for manufacturing a printed circuit board according to claim 1, wherein the average spacing between the multiple solder paste portions is 500 μm or less.

6. The method for manufacturing a printed circuit board according to claim 1, wherein the average diameter of the plurality of solder paste portions is 100 μm or more and 1000 μm or less.

7. The method for manufacturing a printed circuit board according to claim 1, wherein the total area occupied by the plurality of solder paste portions on the surface is 40% or more and 70% or less.

8. The method for manufacturing a printed circuit board according to claim 1, wherein in the above printing step, a portion of the solder paste portion is printed so that it extends beyond the surface when viewed in plan.

9. A method for manufacturing a printed wiring board according to any one of claims 1 to 8, wherein in the printing step described above, a printing board having a plurality of openings corresponding to the plurality of solder paste portions is used.

10. A printed board used in the method for manufacturing a printed circuit board according to claim 9, It has multiple openings into which solder paste is inserted. The multiple openings mentioned above are scattered on the printing plate.

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