JPS6350864Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention particularly relates to an inexpensive printed circuit board that has good bonding characteristics when a semiconductor is placed directly on a printed pattern and wiring is performed using thin metal wires.

Conventionally, semiconductors, especially solid-state display elements such as light-emitting diodes, are placed directly on printed patterns.
When forming a display by wiring with thin metal wires, the surface of the printed pattern is
It has good wire bond properties (good adhesion and strong bonding against tensile loads), and also serves as a reflective surface to reflect the light from the light emitting diode.
The surface was plated with gold. However, gold is expensive, and if all printed patterns were gold plated, the printed circuit board would be very expensive, making the display unreasonably expensive. For this reason, it is necessary to gild only the necessary parts. In this case, the parts that do not need to be plated are covered with a film and then plated, but air bubbles tend to remain at the edges of the film, and it is often the case that only the areas with the air bubbles are insufficiently plated. .

Furthermore, the coating inevitably becomes thinner at the periphery of the printed pattern, but if it becomes extremely thin or the corners of the printed pattern are exposed, dendritic plating growth will occur during plating. This is particularly likely to occur if the printed patterns are close to each other. Such dendritic plating growth may cause a short circuit due to contact with adjacent patterns, but it can be removed by an overcurrent method or the like before parts are mounted. However, in this case, there are many cases in which a short-circuit accident does not occur, but rather occurs during or after the installation work of the parts, and in this case, it is impossible to solve the problem.

This proposal was made to eliminate these inconveniences, and will be explained in detail below.

Figure 1a shows a substrate 2' on which a printed pattern 1 (copper foil) is formed into a desired shape by etching, etc.
In this example, printed patterns 1, 1, . It is composed of lead parts 5, 5, . . . connected to the lead parts 4, 4.

FIG. 1b and FIGS. 2 to 5 are board sectional views showing the manufacturing process for obtaining the printed circuit board 2 of the present embodiment, based on FIG. 1b, which is a sectional view taken along line A-A in FIG. There is. The base 6 of the printed circuit board is made of, for example, paper epoxy resin, glass epoxy resin, etc., and copper foil having a thickness of 20 to 50 μm is laminated thereon as the printed pattern 1. As shown in FIG. 2, a first coating 7 covering the printed pattern 1 of this substrate
is provided by means such as screen printing. The first coating 7 is made of epoxy resin with excellent chemical resistance or UV ink, and is coated and cured to a thickness of 8 to 23 μm. The areas exposed from this first coating 7 are the mounting parts 3, 3, bonding parts 4, 4, and their surrounding areas (several tens of μm depending on the state of the plating bath).
m to several mm), but if necessary, the base surface where no printed pattern exists or the terminal portion to be plated (not shown) are exposed. Thereafter, it is immersed in a plating bath to provide plating layers 8, 8, . . . on the portions of the printed pattern 1 exposed from the first coatings 7, 7, . This plating layer 8,8
...is a nickel layer with a thickness of 3 to 10 μm and a thickness of 0.3 to 10 μm.
It has a two-layer structure consisting of a 1.0 μm gold layer. Thereafter, the dendritic plating growth that causes the short-circuit accident as in the conventional example described above is removed, and second coatings 9, 9, . . . are provided as shown in FIG. Second coating 9, 9...
is printed in a slightly wider area than the first coatings 7, 7 so as to completely cover the first coatings 7, 7, . The material of the second coatings 9, 9, . . . may be any material such as epoxy resin, and the thickness may be as rough as 3 to 30 μm. What is necessary is the areas adjacent to the printed pattern 1, the first coating 7, 7... and the plating layer 8,
8... is to be reliably covered with the second coatings 9, 9, and the other areas can be covered even if the first coatings 7, 7 are present or the second coatings 9, 9 are not present. good.

FIG. 5 shows light emitting diodes 10, 10 placed on the mounting parts 3, 3 of the printed circuit board 2 obtained in this way.
This figure shows a display board on which the wires are mounted and fixed, and wires are wired to the bonding parts 4, 4 using thin metal wires 11, 11 such as gold wires.

As described above, the present invention includes the base 6, the mounting parts 3, 3, and the bonding parts 4, 4, and the printed pattern 1 provided on the base 6 and at least the mounting parts 3, 4.
3 and a first coating 7 that covers the printed pattern 1 except for the bonding portions 4, 4 and the surrounding areas;
7... and plating layers 8, 8 applied to the portions of the printed pattern 1 where the first coatings 7, 7... are not present.
... and second coatings 9, 9, which cover the boundary portions between the first coatings 7, 7... and the plating layers 8, 8, and the first coatings 7, 7,... Since the dendritic plating growth is fixed by the second coating, short circuit accidents do not occur in subsequent processes, and the boundary between the first coating and the plating layer, where the plating is unstable, is also covered by the second coating. Since it is covered, various inconveniences do not occur and the bonding characteristics are kept good, and since the precious metal of the plating is only used in the necessary parts, it is possible to provide an inexpensive printed circuit board.

[Brief explanation of the drawing]

FIG. 1a is a plan view of the printed circuit board, and FIG. 1b and FIGS. 2 to 5 are cross-sectional views showing the manufacturing process of the circuit board according to the present embodiment. 1...print pattern, 2' , 2 ...substrate,
3, 3... (semiconductor) mounting part, 4, 4... (metal thin wire) bonding part, 6... base, 7, 7
...First coating, 8,8... Plating layer, 9,9...
...Second coating.

Claims (1)

[Scope of utility model registration request] a base, a printed pattern provided on the base having a mounting part and a bonding part, and a first coating covering the printed pattern excluding at least the mounting part, the bonding part and the peripheral parts thereof; , comprising a plating layer applied to a portion of the printed pattern where the first coating is not present, and a second coating covering the boundary portion between the first coating and the plating layer and the first coating. A printed circuit board characterized by: