Electrode of printed circuit board and method for forming electrode of printed circuit board

Abstract

[Problem] The purpose of the present invention is to provide: an electrode of a printed circuit board for improving the yield of soldering of the printed circuit board; and a method for forming the electrode of the printed circuit board. [Solution] An electrode (1) of a printed circuit board is provided with a region (3) and a region (5) on the surface thereof. The region 3 and the region 5 have different solder wettability.

Description

Electrode of Printed Circuit Board and Method for Forming Electrode of Printed Circuit Board

[0001] The present invention relates to an electrode of a printed circuit board and a method for forming an electrode of a printed circuit board.

[0002] Conventionally, in soldering of a printed circuit board, there is a problem that it is desired to suppress soldering defects. In particular, in applications where high reliability is required, in soldering of a printed circuit board, the occurrence of defective products (yield) due to the occurrence of voids, balls, bridges, etc. has been a problem. Also, not limited to such applications, various techniques for improving the quality of soldering and preventing defects in soldering of printed circuit boards have been developed. (Patent Documents 1, 2).

[0003] Japanese Patent Application Laid-Open No. 2022-115105

[0004] Haiyan Chen,Jianke Peng,Li Fu,Xincheng Wang,Yan Xie “Solder wetting behavior enhancement via laser-textured surface microcosmic topography”Applied Surface Science 368(2016)208-215

[0005] The invention shown in Patent Document 1 is a bump forming device that supplies ball-shaped solder onto an electrode pad formed on a substrate, and includes a plasma generating device that irradiates the supplied ball-shaped solder with plasma to remove the oxide film of the solder, and a laser generating device that irradiates the ball-shaped solder with a laser to melt the solder. It is characterized in that the oxide film of the solder is removed by the plasma irradiation means, and at the same time, the solder is melted by the laser irradiation means to form a solder bump on the electrode pad. However, the invention of Patent Document 1 prevents the oxidation of ball-shaped solder, and the effect of increasing the yield of soldering of an electronic circuit board is limited. The invention shown in Non-Patent Document 1 enhances the wettability of solder by forming a concavo-convex shape on the electrode. However, since the entire surface of the electrode has a structure that uniformly enhances the wettability of solder, there is a problem that the behavior of solder cannot be controlled, and the effect of increasing the yield of soldering of an electronic circuit board is limited. [[ID=十六]]

[0006] The present invention has been made in view of the above, and the object of the present invention is to provide electrodes for printed circuit boards and a method for forming electrodes for printed circuit boards that improve the soldering yield of printed circuit boards.

[0007] The above objective is achieved by electrodes 1, 10, and 20 of a printed circuit board, wherein the surface of the electrode comprises a first region 3 and a second region 5, and the first region and the second region have different solder wettability.

[0008] Furthermore, the above objective is achieved by the electrodes 1, 10, and 20 of the printed circuit board, which have an uneven pattern formed on their surface.

[0009] Furthermore, the above objective is achieved by a method for forming the electrodes 1, 10, and 20 of the printed circuit board, wherein the uneven pattern is formed by laser processing or plasma processing.

[0010] According to the present invention, it is possible to provide electrodes for printed circuit boards and a method for forming electrodes for printed circuit boards that improve the soldering yield of printed circuit boards.

[0011] This is a schematic diagram illustrating electrode 1 of a printed circuit board according to the first embodiment of the present invention. second embodiment of the present invention. This is a schematic diagram illustrating electrode 10 of a printed circuit board according to the second embodiment of the present invention. This is a flowchart illustrating a method for forming electrode 1 of a printed circuit board according to the first embodiment of the present invention. This is a flowchart illustrating an alternative method for forming electrode 1 of a printed circuit board according to the first embodiment of the present invention. This is a flowchart illustrating a method for forming electrode 1 of a printed circuit board according to the second embodiment of the present invention. This is a flowchart illustrating an alternative method for forming electrode 1 of a printed circuit board according to the second embodiment of the present invention. This is a schematic diagram illustrating electrode 20 of a printed circuit board according to the third embodiment of the present invention. This is a schematic diagram illustrating an experimental example of electrode 1 of a printed circuit board according to the first embodiment of the present invention. This is a photograph used as a substitute for a drawing to illustrate an experimental example of electrode 1 of a printed circuit board according to the first embodiment of the present invention. This is a photograph used as a substitute for a drawing (X-ray image) illustrating an experimental example of electrode 1 of a printed circuit board according to the first embodiment of the present invention. This is a photograph used as a substitute for a drawing (X-ray image) illustrating comparative example 1 of the experimental example of electrode 1 of a printed circuit board according to the first embodiment of the present invention. This is a photograph (X-ray) that serves as a substitute for a drawing to illustrate Comparative Example 2 of an experimental example of electrode 1 of a printed circuit board according to the first embodiment of the present invention.

[0012] The electrodes 1 and 10 of the printed circuit board and the method for forming the electrodes 1 and 10 of the printed circuit board according to embodiments of the present invention will be described below with reference to Figures 1 to 14. In all the following drawings, the dimensions and proportions of each component may be shown differently as appropriate for ease of understanding.

[0013] Figure 1 is a schematic front view of electrode 1 of a printed circuit board according to the first embodiment of the present invention. As shown in Figure 1, electrode 1 of the printed circuit board according to the first embodiment of the present invention comprises region 3 and region 5.

[0014] Figure 2 shows a schematic front view of the printed circuit board with ball-shaped solder placed on electrode 1 (upper figure), and a schematic side view (lower figure). The ball-shaped solder is placed in region 3 of electrode 1. The ball-shaped solder is placed on the upper surface of region 3 of electrode 1. Region 3 of electrode 1 has the uneven pattern shown in Figure 3 formed on its entire surface. The upper figure of Figure 3 is an enlarged front view of region 3 of electrode 1, and the lower figure of Figure 3 is an enlarged side view of region 3 of electrode 1. As shown in Figure 3, region 3 of electrode 1 has a surface in which the pattern of convex 3a and concave 3b is repeated. Region 3 of electrode 1 should have a surface pattern in which the contact angle between the solder and the electrode is reduced due to the uneven shape, thereby increasing the wettability of the solder. The side length of one convex 3a and concave 3b is preferably 10 to 100 micrometers, and the height of the convex 3a is preferably 10 to 100 micrometers. Furthermore, it is preferable that the sides of the convex surface 3a and concave surface 3b are 20 to 40 micrometers, and the height of the convex surface 3a is 20 to 40 micrometers. However, the preferred shape and size of the surface pattern can be appropriately determined depending on the type and size of the solder, the reflow temperature environment, etc. In this embodiment, the convex surface 3a and concave surface 3b are the same shape and size, but the convex surface 3a and concave surface 3b may be different shapes and sizes, and the convex surface 3a and concave surface 3b may be various shapes such as rectangles, triangles and other polygons, circles, ellipses, etc. Ball-shaped solder may be bonded together and stacked by an intermediate agent such as flux.

[0015] The upper part of Figure 4 is an enlarged front view of region 5 of electrode 1, and the lower part of Figure 4 is an enlarged side view of region 5 of electrode 1. Region 5 of electrode 1 should have a surface pattern where the contact angle between the solder and the electrode is large due to the uneven shape, and the wettability of the solder is low. The sides of the convex surface 5a and concave surface 5b are preferably 1 to 20 micrometers, and the height of the convex surface 5a is preferably 3 to 60 micrometers. Furthermore, it is preferable that the sides of the convex surface 5a and concave surface 5b are 2 to 5 micrometers, and the height of the convex surface 5a is preferably 5 to 20 micrometers. However, the preferred shape and size of the surface pattern can be appropriately set depending on the type and size of the solder, the reflow temperature environment, etc. In this embodiment, the convex surface 5a and the concave surface 5b have the same shape and size, but the convex surface 5a and the concave surface 5b may have different shapes and sizes, and the convex surface 5a and the concave surface 5b may have various shapes such as squares, triangles or other polygons, circles, or ellipses. The region 5 of the electrode 1 only needs to be a region where the wettability of the solder is low, so the convex and concave shapes may be changed to a coating such as an oxide film or a fluorine film. In addition, the wettability of the solder may be reduced by making one side of the convex surface 5a and the concave surface 5b longer than one side of the convex surface 3a and the concave surface 3b (for example, 40 micrometers or more).

[0016] Next, the electrode 10 of the printed circuit board according to the second embodiment of the present invention will be described with reference to Figures 5 and 6. In the following description, components that are the same as those of the electrode 1 of the printed circuit board according to the first embodiment of the present invention may be given the same reference numerals and their descriptions may be omitted.

[0017] Figure 5 is a schematic front view of the electrode 10 of a printed circuit board according to a second embodiment of the present invention. As shown in Figure 5, the electrode 10 of the printed circuit board according to the second embodiment of the present invention comprises region 3, region 5, and region 7.

[0018] Region 7 is a region located outside region 5. The upper diagram in Figure 6 is an enlarged front view of region 7 of electrode 10, and the lower diagram in Figure 6 is an enlarged side view of region 7 of electrode 10. Region 7 of electrode 10 has a concave shape that provides a trapping structure to prevent ball-shaped solder from overflowing from electrode 1. Region 7 is a solder trapping region. By making it difficult for solder to overflow from the electrode surface before reflow, it is possible to prevent the generation of solder balls. Region 7 has a recess composed of two upper surfaces 7a and a lower surface 7b. The width of the lower surface 7b is preferably such that approximately 1.5 solder a1 can be trapped, but it may also be such that 2 or more solder a1 can be trapped. The height of the upper surface 7a (the height difference between the lower surface 7b and the upper surface 7a) is preferably at least half the height of the solder a1, but it may also be less than half the height of the solder a1.

[0019] Next, a method for manufacturing electrodes 1 and 10 of a printed circuit board according to an embodiment of the present invention will be described using Figures 7 to 11. Note that a commonly available printed circuit board will be used.

[0020] Figure 7 is a flowchart showing a method for forming the electrode 1 of a printed circuit board. In step S1, a laser processing machine is used to form the uneven pattern shown in Figure 3 on the region 3 of the electrode 1, and a solder wettability improvement process is performed. In the next step S2, an uneven pattern shown in Figure 4 is formed on the region 5 of the electrode 1, and a solder wettability reduction process is performed, thereby forming the electrode 1 of the printed circuit board according to the first embodiment of the present invention. Note that the regions 3 and 5 of the electrode 1 may be formed by performing steps S1 and S2 simultaneously, or by dry etching such as RIE.

[0021] Figure 8 is a flowchart illustrating another method for forming the electrode 1 of a printed circuit board. In step S3, a surface oxidation treatment is performed using an acidic liquid. By oxidizing the surface of the electrode 1, an oxide coating is formed. Next, in step S1, a laser processing machine is used to form the uneven pattern shown in Figure 3 on region 3 of the electrode 1. In step S1, a solder wettability improvement process is performed, and the electrode 1 of the printed circuit board according to the first embodiment of the present invention is formed. In step S1, in order to remove the oxide film on the surface, the entire surface of the upper surface 3a is also irradiated with a laser beam to perform a trimming process. The region 5 outside region 3 becomes a region where solder wettability is reduced because an oxide film is formed on the surface.

[0022] Figure 9 is a flowchart showing a method for forming the electrode 10 of a printed circuit board. Steps S1 and S2 are performed. In the next step S4, a recessed pattern as shown in Figure 6 is formed in the region 7 of the electrode 1 using a laser processing machine. In step S4, a trapping process is performed to prevent ball-shaped solder from overflowing, and the electrode 10 of the printed circuit board according to the second embodiment of the present invention is formed. Note that the region 7 of the electrode 10 may be formed by performing steps S1, S2 and step S4 simultaneously, or it may be formed by dry etching such as RIE or ICP.

[0023] Figure 10 is a flowchart showing another method for forming the electrode 10 of the printed circuit board. Steps S3 and S1 are performed. In the next step S4, a recessed pattern as shown in Figure 6 is formed in the region 7 of the electrode 1 using a laser processing machine. In step S4, a trapping process is performed to prevent solder from overflowing, and the electrode 10 of the printed circuit board according to the second embodiment of the present invention is formed. In step S1, the entire surface of the upper surface 3a is also irradiated with a laser beam to remove the oxide film on the surface and perform trimming. In step S4, a resist and etching solution may be used to form the recessed shape.

[0024] Next, the electrode 20 of the printed circuit board according to the third embodiment of the present invention will be described with reference to Figure 11. In the following description, components that are the same as the electrode 1 of the printed circuit board according to the first embodiment of the present invention and the electrode 10 of the printed circuit board according to the second embodiment of the present invention may be given the same reference numerals and their descriptions may be omitted.

[0025] Figure 11 is a schematic front view of the electrode 20 of a printed circuit board according to a third embodiment of the present invention. As shown in Figure 11, the electrode 20 of the printed circuit board according to the third embodiment of the present invention comprises regions 3, 5, and 7, and is arranged in the order of region 3, region 7, region 5, region 7, and region 5 from the center outward.

[0026] The electrodes of the printed circuit board according to the above embodiment may have the following configuration: (1) Region 3 may be any region with higher solder wettability than region 5. For example, if region 3 has a structure that increases solder wettability (a solder wettability improving treatment is applied to the electrode surface), region 5 may not have a structure that decreases solder wettability (no solder wettability reducing treatment is applied to the electrode surface), or conversely, if region 5 has a structure that decreases solder wettability (a solder wettability reducing treatment is applied to the electrode surface), region 3 may not have a structure that increases solder wettability (no solder wettability improving treatment is applied to the electrode surface). (2) The number of regions 7 (solder trap regions) may be 0, 1, or 2 or more. Region 7 is located between region 3 and the edge of the electrode. (3) Region 3 is created by laser or plasma processing. (4) Region 5 may be formed by laser or plasma processing, or by coating with an oxide film or fluorine film. (5) Region 7 may be formed by laser or plasma processing, or by wet etching. (6) In an electrode pad with different metals stacked, region 3 and / or region 5 are formed by irradiating the electrode pad surface with a laser and sublimating the surface. For example, if there is a metal with high solder wettability on the surface and a metal with low solder wettability stacked underneath, the laser is not irradiated onto region 3, but region 5 is irradiated with a laser to sublimate the surface metal and expose the metal layer with different solder wettability underneath. Also, for example, it can be applied to an electrode with gold plating (pure gold plating, ENIG, ENEPIG, etc.) on the surface and different metals such as palladium, nickel, copper (or alloys thereof) stacked underneath. (7) When the electrode surface is made of a metal that oxidizes relatively easily, the degree of oxidation of region 3 and region 5 is different. For example, region 3 is created by irradiating it with a laser to remove the oxide layer on the surface.

[0027] The electrode 1 of the printed circuit board according to the first embodiment of the present invention has the following effects: (a) Because the electrode has regions where solder wettability is high and regions where solder wettability is low, the movement of solder during soldering can be controlled, thereby suppressing defects such as voids and solder balls. (b) Because regions where solder wettability is high can be formed by creating an uneven shape using a laser processing machine or the like, it is low cost.

[0028] The electrode 10 of the printed circuit board according to the second embodiment of the present invention has the following effects: (a) The electrode has a trapping region that prevents solder from spilling outwards, which allows for control of solder movement during soldering, thereby suppressing defects such as voids and solder balls.

[0029] The electrode 20 of the printed circuit board according to the third embodiment of the present invention has the following effects: (a) The electrode has multiple trapping regions facing outward to prevent solder from spilling out, which allows for control of solder movement during soldering, and in particular, suppresses defects such as solder balls and bridges.

[0030] Using Figures 12 to 16, experimental examples of the electrode 1 of a printed circuit board according to the first embodiment of the present invention will be explained. In this experimental example, an example using electrode 1 (copper foil) of a printed circuit board, comparative example 1 (fully processed electrode (copper foil) of a printed circuit board), and comparative example 2 (unprocessed electrode (copper foil) of a printed circuit board) were prepared, and soldering (reflow) was performed on each, and the presence or absence of voids or balls was checked by X-ray imaging.

[0031] Figure 12(a) is a schematic diagram of electrode 1 of a printed circuit board according to the first embodiment of the present invention. In this experimental example, a femtosecond laser processing apparatus was used to form cross-shaped grooves with a depth of 1-10 μm at intervals of 0.01 mm in an area of ​​0.15 mm inside the electrode (the hatched area in the figure), as shown in Figure 12(a). Comparative example 1 of this experimental example is shown in Figure 12(b). Comparative example 1 used an electrode in which grooves with a depth of 1-10 μm at intervals of 0.01 mm were formed in a cross-shaped pattern across the entire surface of the electrode using a femtosecond laser processing apparatus. Comparative example 2 of this experimental example used an electrode that was not processed in any way.

[0032] Figure 13 shows a photograph of electrode 1, prepared in this experiment, taken with an optical microscope. As shown in Figure 13, it can be seen that precise grooves with a spacing of 0.01 mm can be formed by using a femtosecond laser processing device.

[0033] The results of this experiment are shown in Figures 14 to 16. Figure 14 is an X-ray image of the electrode 1 of the printed circuit board according to the first embodiment of the invention after soldering. In the electrode 1 of this embodiment, it was confirmed that the occurrence of voids (white circular areas) was suppressed compared to comparative examples 1 and 2. In addition, two ball defects were observed in comparative example 1 and four ball defects in comparative example 2, but no ball defects were observed in the electrode 1 of this embodiment.

[0034] Thus, it was confirmed that by creating two regions with different solder wettability on the electrode, soldering abnormalities were significantly reduced.

[0035] The embodiments described above are preferred examples of the present invention and are subject to various technically preferred limitations, but the scope of the present invention is not unduly limited by the above description. Furthermore, not all of the configurations described in the embodiments described above are essential components of the present invention. Also, the configurations described in the embodiments described above may be added to or combined with each other. For example, region 3 may be formed by laser processing to create a bumpy pattern that improves solder wettability, and region 5 may be formed by exposing a metal with lower solder wettability than region 3, or by exposing a metal with an oxide film, or by doing nothing (not forming a bumpy pattern that improves solder wettability). Region 3 may be left as is, and region 5 may be formed by laser processing to create a bumpy pattern that lowers solder wettability, or by exposing a metal with lower solder wettability than region 3, or by forming a metal with an oxide film that lowers solder wettability. The present invention is sufficient if region 3 has higher solder wettability than region 5.

[0036] The present invention is widely applicable to electrodes for printed circuit boards and methods for forming electrodes for printed circuit boards.

[0037] 1, 10 Electrodes 3, 5, 7 Fields 3a, 5a, 7a Above 3b, 5b, 7b Below

Claims

1. An electrode for a printed circuit board, wherein the surface of the electrode comprises a first region and a second region, and the first region and the second region have different solder wettability.

2. The electrode of the printed circuit board according to claim 1, wherein the surface of the electrode comprises a third region, and the third region has a recess for trapping solder.

3. The electrode of the printed circuit board according to claim 2, wherein the third region is a region surrounding the first region.

4. The electrode of the printed circuit board according to claim 1, wherein the first region is a region with higher solder wettability than the second region, and the second region is a region surrounding the first region.

5. The electrode of the printed circuit board according to claim 4, wherein the first region has an uneven pattern formed on its surface, and the uneven pattern is formed by laser processing.

6. The electrode for a printed circuit board according to claim 1, wherein the electrode is made up of multiple metals with different wettability laminated together, and the first region and the second region are made of different metals.

7. The electrode of the printed circuit board according to claim 1, wherein the first region and the second region are made of the same metal, and the first region and the second region have different degrees of oxidation.

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