JPH0284793A - How to improve solder through-hole - Google Patents

Abstract

PURPOSE:To ensure reliability on the connection of a through-hole while eliminating the need for solder repair, etc., by printing solder onto the land of the end face of the through-hole in a printed wiring board by using a solder mask with a specific hole, heating and fusing solder and conducting flow solder. CONSTITUTION:Solder is printed onto the land 12A of the end face of a through- hole 12 in a printed wiring board 10 by using a solder mask 2c with a discoid section 21, which is approximately equal to the external shape of the land 12A and a central section of which is approximately uniform to the inside diameter A10 of the land 12A, and a hole 23 divided by a bridge section 22 continuing to the discoid section 21, the solder is heated and fused, and flow solder is performed. Consequently, a proper quantity of solder is printed, and the solder is melted when it is heated, and spread and fixed thinly on the surface of the through-hole as plating. When flow solder is executed, a solder rise is generated easily in the through-hole, wettability of which is improved, the inside of the through-hole is filled with flow solder while the land is also coated completely, and a gas evoluted from flux is removed readily.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for improving solder performance in through holes, and particularly to a method for improving solder performance in through holes in double-sided printed wiring boards.

[Conventional technology 1] Generally, in double-sided printed wiring boards used to realize high-density mounting of electronic components, through holes are formed to conduct the circuits on both sides, and these through holes are plated with copper foil. ing.

Such through holes may be destroyed by heat stress or the like applied to the printed wiring board, leading to disconnection. Especially,
There is a high possibility that the shoulder portion, which is a continuous portion between the cylindrical portion of the through hole and the land portion, will be destroyed. Therefore, in order to improve the connection reliability of the through-hole, conventionally, after components are mounted inside the through-hole, solder is applied in a flow soldering process to fill the solder and cover the land.

In order to make this solder rise efficiently, before mounting the component, creamy solder is printed using a solder mask with holes that are approximately the same as the land outline of the through-hole, and this creamy solder is heated and melted onto the surface of the through-hole. I'm trying to put it on.

[Problems to be Solved by the Invention] However, in this conventional method, when printing creamy solder using a solder mask, the hole shape of the solder mask was approximately equal to the land outline of the through hole. In some cases, this creamy solder C/S was printed in large quantities and even penetrated into the through hole T/H as shown in FIG. After mounting the components in this state, this creamy solder is heated and fused, and then the printed wiring board P/
When the bottom surface of B is flow soldered, the gas F/G generated from the flux accumulates under the through hole T/H and the solder is repelled, as shown in Figure 6. There was a problem in that the side lands L and their shoulders were not soldered, and the connection reliability of the through holes was reduced.

In order to improve the connection reliability of this through-hole, there is also the problem that soldering rework after flow soldering is required, which increases the number of man-hours.

SUMMARY OF THE INVENTION An object of the present invention is to solve such conventional problems and provide a method for improving solder through-holes that ensures connection reliability of through-holes and does not require re-soldering.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a land on the end face of a through hole of a printed wiring board, the central part of which is approximately equal to the outer diameter of the land and approximately the inner diameter of the land. printing solder using a solder mask having holes divided by equal disc-shaped parts and bridge parts connected to the disc-shaped parts;
The method is characterized in that flow soldering is performed after the solder is heated and fused.

[Function] According to the present invention, on the land of the end face of the through hole of the printed wiring board, there is provided a disk-shaped portion that has an outer shape that is approximately equal to the outer diameter of the land and whose center portion is approximately equal to the inner diameter of the land; Solder is printed using a solder mask having holes divided by a bridge portion connected to a disk-shaped portion.

When this printed solder is heated, it melts and spreads like a thin layer of plating on the surface of the copper foil in the through hole, fixing it.

Thereafter, when flow soldering is performed, solder easily rises in the through holes with improved wettability, and the through holes are filled with flow solder and the lands are completely covered. Furthermore, since the through holes are not completely covered, gas generated from flux can easily escape.

[Embodiments] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

First, FIG. 1 and FIG. 2 show a printed wiring board 10 on which the present invention is implemented. Reference numeral 11 designates a printed wiring, and 12 designates a through hole to which the printed wiring 11 is connected and is provided passing through both the front and back surfaces.

The through hole 12 is formed by plating the surface of a hole drilled in the printed wiring board 10 with copper or the like, as is well known, and has a land portion 12^ and a cylindrical portion 12B.

Now, the outer diameter of the land portion 12 is Dl. , when the inner diameter is AIO, in this example, the beam is o-1,3 or 1.4111
m % A+o-0.6 or 0.8 mm.

Next, FIG. 3 shows a solder mask 20 used to implement the present invention. The solder mask 20 is in the form of a flat plate that is superimposed on the printed wiring board 10, and holes are provided at locations where creamy solder is to be printed.

Therefore, in the present invention, as a hole corresponding to the through hole 12, a disk-shaped portion 21 having an outer diameter of 0.2 mm and a central portion having an outer diameter of A2 degrees, and a bridge portion 22 connected to this disk-shaped portion 21 are provided.
A hole 23 divided into two is provided. and,
The width of this bridge portion 22 is assumed to be W. Further, the thickness of the solder mask 20 is assumed to be t.

Thus, the solder mask 20 shown in FIG. 2 is superimposed on the printed wiring board 10 shown in FIG. Print solder. and,
After mounting electronic components on other parts, paper phase soldering (VPS) is performed. Then, the creamy solder melts due to heating, and the through hole 1 is formed as shown in Figure 4.
The thin film layer 13 is fixed to the surface of the copper foils (12A, 12B) of No. 2.

Thereafter, the printed wiring board IO is sent to a jet-type automatic soldering device, and flow soldering is applied to one side of the board.

Then, as shown in FIG. 4, the gas generated from the flux easily escapes from the open through hole 12 as shown by the arrow X, and also easily enters the through hole 12 whose wettability has been improved by the thin film layer 13 Solder rises and the inside of the through hole 12 is filled with flow solder. Further, the upper and lower land portions 12A are also completely covered with flow solder.

In addition, in the above-mentioned embodiment, through-hole! Although the second land 128 is circular, it goes without saying that the present invention is also applicable to square lands.

[Experiment example] (1) First, the land outer diameter of the through hole 12 []+o−
1.3mm, land inner diameter A1゜-0.6mm printed wiring board! For O, the outer diameter of the hole 23 is D20 - 1.3 mm
, outer diameter A of the disc-shaped part 21, owO, 6 mm, width W of the bridge part 22 - 0,3 mm, thickness t - 300 μm.
When the solder mask 2o was used, a thin film layer 13 was formed in a portion of the through hole 12.

(2) For the same printed wiring board 1o as in (1),
The outer diameter of the hole 23 was set to 010.1.21, and the other parts were made using the same solder mask 20 as in (1).
In No. 2, the thin film layer 13 and the clogged portion coexisted.

(3) Printed wiring board 1 same as (1) and (2)
0, the thickness was set to t-200 μm, and the other parts were the same as in (2) using the solder mask 20. As a result, through hole 1
A thin film layer 13 was formed on the entire surface of 2.

(4) Next, change the shape of the hole 23 of the solder mask 20,
The bridge portion 22 shown in FIG. 3 is shaped like a cross and the hole 23
When we used a plate in which the plate was divided into four parts, it was impossible to use because of the plate omission when printing creamy solder.

[Effects of the Invention] As is clear from the above description, according to the present invention, a disk-shaped portion is provided on the land of the end face of the through-hole, the disk-shaped portion being approximately equal to the outer diameter of the land and the center portion thereof being approximately equal to the inner diameter of the land. Since we printed solder using a solder mask that has holes divided by a bridge part connected to a disc-shaped part, an appropriate amount of solder is printed, and when heated and fused, there is no through-hole. A thin film layer of solder is formed on the surface of the hole, and during flow soldering, flux gas can completely escape and complete solder can be obtained.

[Brief explanation of the drawing]

FIG. 1 is an enlarged plan view of a part of a printed wiring board on which the present invention is implemented, FIG. 2 is a sectional view taken along the line II--II of FIG. 1, and FIG. FIG. 4 is a cross-sectional view showing the formation of a thin solder film layer obtained by implementing the present invention and how flux gas escapes; FIG. 5 is a cream-like solder mask. FIG. 6 is a cross-sectional view showing how solder has entered the through hole, and FIG. 6 is a cross-sectional view showing how flux gas is trapped. DESCRIPTION OF SYMBOLS 10... Printed wiring board, 12... Through hole, 12A... Land, 20... Solder mask 21... Disk-shaped part, 22... Bridge part, 23... Hole. Figure Figure

Claims (1)

[Claims] 1) On the land of the through-hole end of the printed wiring board,
Using a solder mask having a hole divided by a disc-shaped part whose center part is approximately equal to the outer diameter of the land and approximately equal to the inner diameter of the land, and a bridge part connected to the disc-shaped part. A method for improving solder build-up of through-holes, which comprises printing solder, heat-sealing the solder, and then performing flow soldering.