Cream solder printing method for printed circuit board

Abstract

To solve a problem in which, in the case of double-sided boards, the inner surfaces of the through-holes that interconnect the electronic circuits formed on both sides of the printed wiring board are covered with copper foil, and when the copper foil is protected by covering it with molten cream solder, in a case in which there is a large amount of cream solder, the molten solder will protrude from the opening on the opposite side of the through-hole, and when the cream solder is printed on the opposite side of the printed wiring board, the metal mask will float due to the solder protruding from the opening on the opposite side of the through-hole, preventing it from adhering to the surface of the printed wiring board.SOLUTION: An opening formed in a metal mask for applying cream solder to a land portion formed in communication with a through hole is composed of a plurality of openings sandwiching a bridge portion spanning the through hole.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a method for printing cream solder on a printed wiring board, in which a copper foil portion applied to the inner surface of a through-hole is covered with solder in a reflow process, and the method does not cause the solder to drip and protrude to the opposite side of the through-hole. [Background technology]

[0002] In the case of double-sided boards, through holes are sometimes provided to interconnect the electronic circuits formed on both sides of the printed wiring board. The inner surfaces of these through holes are covered with copper foil to connect the electronic circuits on both sides of the printed wiring board via the copper foil. However, if the copper foil attached to the inner surfaces of the through holes is not protected in any way, problems such as corrosion may occur.

[0003] Therefore, it is known that when cream solder is printed on one side of the printed wiring board, the through-hole is sealed with the cream solder, and when the cream solder is melted, the molten solder is guided into the through-hole, and the copper foil on the inner surface of the through-hole is covered with solder (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2016-46465 A (paragraph

[0022] ) Summary of the Invention [Problem to be solved by the invention]

[0005] In the above-described conventional method, if the amount of cream solder covering the opening of the through-hole is large, the molten solder will drip and protrude from the opening on the opposite side of the through-hole, and when the cream solder is printed on the opposite side of the printed wiring board, the metal mask will float due to the solder protruding from the opening on the opposite side of the through-hole, preventing it from adhering to the surface of the printed wiring board.

[0006] In view of the above problems, the present invention aims to provide a method for printing cream solder on a printed wiring board in which the amount of solder covering the inner surface of the through-hole is adjusted so that the molten solder does not protrude from the opening on the opposite side of the through-hole. [Means for solving the problem]

[0007] In order to solve the above problems, the cream solder printing method for printed wiring boards according to the present invention is a method for printing cream solder on a printed wiring board having through holes whose inner surfaces are covered with copper foil, and then reflow soldering the printed wiring board to deposit solder on the surface of the copper foil on the inner surface of the through holes, characterized in that the openings formed in a metal mask for applying cream solder to land portions formed in communication with the through holes are composed of multiple openings sandwiched between bridge portions spanning the through holes.

[0008] The solder paste is not printed on the bridge portion, but only on the opening portion formed on either side of the bridge portion. Therefore, by increasing or decreasing the width of the bridge portion, the area of ​​the opening portion can be adjusted, and the amount of solder paste printed on the through-hole portion can be adjusted. [Effects of the Invention]

[0009] As is clear from the above explanation, the present invention allows adjustment of the amount of cream solder printed on the through-hole, thereby making it possible to increase or decrease the amount of solder covering the inner surface of the through-hole, and preventing the solder from protruding from the opposite side of the through-hole even if the cream solder melts. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a perspective view showing an example of a through hole to which the present invention is applied; [Figure 2] Diagram showing the opening of the metal mask when one bridge section is formed [Figure 3] Diagram showing the opening of the metal mask when two bridge sections are formed DETAILED DESCRIPTION OF THE INVENTION

[0011] Referring to Figure 1, reference numeral 1 denotes a through-hole formed in a printed wiring board, the inner surface of which is covered with copper foil. Annular lands 2 are formed on both sides of this through-hole 1 so as to surround each side of the through-hole 1, and patterns 21 are connected to the lands 2. The printed wiring board in which this through-hole 1 is formed has various copper foil patterns formed on both the top and bottom surfaces. First, cream solder is printed on one side, and after electronic components are mounted, the cream solder is heated and melted in a heating furnace, and then cream solder is printed on the remaining side of the cooled printed wiring board, a process known as reflow soldering.

[0012] When printing cream solder on a printed wiring board, a metal mask with openings 31 formed as shown in Figure 2 is brought into close contact with one side of the printed wiring board, and in this state the cream solder is spread over the surface of the metal mask with a squeegee, so that the cream solder is printed only in the areas where the openings 31 are formed.

[0013] If a circular opening is formed in the metal mask to match the through-hole 1, a large amount of solder will melt and spread into the through-hole 1. Therefore, a bridge portion 3 is provided, and two openings 31 are formed on either side of this bridge portion 3. By forming them in this manner, cream solder is not printed on the bridge portion 3, and is printed only on the portions where the openings 31 are formed. Therefore, in the embodiment shown in Figure 2, the amount of cream solder printed can be increased or decreased by appropriately adjusting the width of the bridge portion 3.

[0014] Furthermore, the amount of cream solder can be adjusted not only by the width of the bridges 3, but also by the number of bridges 3, as shown in Figure 3. In the embodiment shown in Figure 3, two bridges 3 are formed by crossing each other. This results in four openings 31, but the size of each opening 31 can be set smaller than in the embodiment shown in Figure 2.

[0015] In this way, by increasing or decreasing the width and number of bridge portions 3, the opening area of ​​opening 31 can be increased or decreased, and the amount of solder spreading on the inner circumferential surface of through-hole 1 can be adjusted.

[0016] The present invention is not limited to the above-described embodiments, and various modifications may be made without departing from the spirit of the present invention. [Explanation of symbols]

[0017] 1 through hole 2 rand 3 Bridge section 21 patterns 31 Aperture

Claims

[Claim 1] A method for printing cream solder on a printed wiring board, which includes printing cream solder on a printed wiring board having through holes whose inner surfaces are covered with copper foil and then reflow soldering the printed wiring board to deposit solder on the surface of the copper foil on the inner surface of the through holes, characterized in that the openings formed in a metal mask for applying cream solder to land portions formed in communication with the through holes are composed of multiple openings sandwiched between bridge portions spanning the through holes.

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