JPH01218092A - Manufacture of printed wiring board - Google Patents

Abstract

PURPOSE:To prevent bridge soldering from being defective by forming a dam whose thickness is equal to the thickness of a resist between adjacent portions of the conductive film in which the soldering resist is filmed so as to cover the conductive film. CONSTITUTION:A soldering resist 12 is covered so that a conductive film 11 corresponding to electronic component leads which are formed at a narrow pitch is exposed. A part of the conductive film 11 is on a lower level compared to the surface of the surrounding soldering resist 12, so that dams D are formed between the adjacent conductive film portions as much as the thickness of the resist. Then, the reflow soldering is performed after first applying a soldering paste on the part to be soldered on the conductive film 11 having the dams D formed and then mounting the component leads 13 on the corresponding conductive film portions. The dams D prevent the melted solder 14 from being overflown from the conductive film 11, thereby preventing bridges from being defective when the adjacent conductive film portions are soldered.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a method for manufacturing a printed wiring board, and particularly to a printed wiring board on which electronic components having a large number of leads formed at a narrow pitch are surface mounted. The present invention relates to a method for manufacturing a substrate.

(Prior Art) Printed wiring boards have been known that are formed by surface-mounting electronic components such as flat package ICs on which a large number of leads are arranged at narrow intervals.

In order to surface-mount the electronic component on such a printed wiring board, solder resist is coated on the exposed portion of the printed wiring board except for the conductive foil portion for soldering the leads of the electronic component on the printed wiring board.

As shown in FIG.
A solder resist 2 shown by diagonal lines is coated on the outside of the entire conductive foil 1 so as to surround the entire periphery of the conductive foil 1, or a fourth
As shown in FIGS. (a) and (b), the resist 2 is coated so as to be placed also between the conductive foils 1.

However, in these conventional methods, the heights of each conductor foil 1 and resist 2 are approximately equal, and there is nothing between adjacent conductive foils 1 to block the molten solder. When paste-like solder is placed on top of this and reflow soldering is performed, there is a problem in that solder bridges tend to occur between the leads.

Also, there is a gap d or d' between each conductor foil 1 and the resist 2.
is formed, and the solder also enters during this time, making it difficult to deal with narrow pitches.

FIG. 5 shows that paste-like solder is applied to the conductive foil 1 portion of the printed wiring board P shown in FIG.
Solder 4 and Bridge 5 when placed and solder reflowed
This shows the state of

(Problems to be Solved by the Invention) As described above, in the conventional method, there was a problem in that solder bridges were likely to occur because there was nothing to block the molten solder between adjacent conductive foils.

Another problem is that it is difficult to handle narrow pitches because the solder adheres to the sides of the conductive foil.

The present invention was made to solve such problems, and an object of the present invention is to provide a method for manufacturing a printed wiring board that prevents defects caused by solder bridges.

[Structure of the Invention] (Means for Solving the Problems) The method for manufacturing a printed wiring board of the present invention provides a method for manufacturing a printed wiring board of the present invention, in which the electronic component is soldered onto a substrate having a conductive foil for soldering the leads of the electronic component. When surface mounting by soldering, a solder resist is coated from the exposed surface of the board to the periphery of the conductive foil for soldering, and a dam of solder resist is formed on the periphery of the conductive foil. The method is characterized in that solder is applied onto the inner conductive foil, the leads of the electronic component are arranged, and the solder is reflowed.

As the solder resist in the present invention, both ink-like and film-like ones can be used.

(Function) As described above, in the present invention, since the solder resist is coated over the conductive foil, a dam corresponding to the resist is formed between adjacent conductive foils, and this dam causes solder bridging defects. is prevented.

Further, by changing the pattern of the solder resist, it is possible to change the shape of the soldering portion of the conductive foil.

(Example) Next, embodiments of the present invention will be described using the drawings.

First, as shown in FIG. 1(a), a solder resist 12 is coated so that the conductive foil 11 corresponding to the leads of an electronic component such as a flat package IC whose leads are formed at a narrow pitch is exposed.

At this time, the solder resist 12 is coated on the substrate P so as to cover the peripheral edge of the conductive foil 11, as shown by diagonal lines.

By covering the peripheral edge of the conductive foil 11 with the solder resist 12 in this manner, the portion of the conductive foil 11 to be soldered becomes lower than the surface of the surrounding solder resist 12, as shown in FIG. A dam D corresponding to the thickness of the resist is formed between the conductive foils 11. The conductive foil 11 with the dam D formed thereon is soldered by applying paste-like solder to the corresponding component lead 1 as shown in FIG.
3 is attached and solder reflow is performed, the molten solder 14 is prevented from flowing out from the conductive foil 11 by the dam D formed by the resist 12, and bridging defects of adjacent conductive foils caused by the solder 14 can be avoided.

Furthermore, since solder does not adhere to the side surfaces of the conductive foil, narrow pitches can be easily accommodated.

[Effects of the Invention] As explained above, according to the method of the present invention, the part of the conductive foil to be soldered is lower than the surface of the surrounding solder resist, and there is a space between adjacent conductive foils equal to the thickness of the resist. Since the dam is formed, molten solder does not flow out from the conductive foil, and a printed wiring board without solder bridge defects can be manufactured.

Furthermore, since the solder does not reach the side surfaces of the conductive foil, narrow pitches can be easily accommodated.

[Brief explanation of the drawing]

FIG. 1(a) is a plan view showing a dam in the method of the present invention;
Figure 1(b) is a cross-sectional view taken along line A-A' in Figure 1(a), and Figure 2 shows the state in which electronic component leads are soldered to the printed wiring board in Figure 1(b). 3 and 4(a) 6 are plan views of printed wiring boards for explaining the conventional method, and FIG. 4(b) is taken along line BB' in FIG. 4(a). 5 is a sectional view showing a state in which leads of electronic components are soldered to the board of FIG. 4(b). 11... Conductive foil 12... Solder resist 13... Lead 14... Solder D... ·········dam

Claims (1)

[Claims] (1) When surface-mounting electronic components by soldering on a board having conductive foil for soldering to which leads of electronic components are soldered, the peripheral edge of the conductive foil for soldering extends from the exposed surface of the board. A dam of solder resist is formed on the periphery of the conductive foil by coating it with a solder resist, and then solder is applied on the conductive foil inside the dam, and the leads of the electronic component are placed, and this solder is applied. A method for manufacturing a printed wiring board, characterized by reflowing.