JPS62102590A - Flexible printed circuit substrate - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a flexible printed circuit board used as an internal wiring material for electronic equipment and the like.

[Conventional technology]

Conventionally, flexible printed circuit boards have been made by laminating electrical copper foil with a thickness of about 35 microns to a plastic film with an adhesive, and then etching the copper foil to form the necessary circuits.

Recently, high-density packaging has rapidly progressed, and the demand for flexible printed circuit patterns from 5 lines/ll to 10 lines/fl has increased, and as a solution to this, flexible printed circuit boards using physical vapor deposition or ion blating methods are used. A manufacturing method was developed. With these methods, flexible and printed circuit boards with relatively good adhesion and pinhole-free wiring layers can be obtained by sufficiently performing pretreatments such as heating degassing treatment and ion bombardment treatment. .

On the other hand, in flexible printed circuit boards made by laminating plastic film and copper foil, and in flexible printed circuit boards in which wiring layers are formed using physical vapor deposition methods such as sputtering or ion blating, the connections have particularly high reliability. Because of this requirement, it is common to use gold plating. For example, in a bonded flexible printed circuit board, nickel plating is applied to the copper wiring layer to a thickness of 1.
Gold plating with a quality of 99.7% or higher is applied to a thickness of 0.2 μm or more. The reason why nickel plating is applied here is to prevent copper from being eaten by gold.
This is also to prevent its spread.

[Problem that the invention seeks to solve]

However, the above bonded type flexible printed circuit board has the following problems. ■A special adhesive is required to bond the plastic film and tlA fi, and the types of plastic film used are limited, so only plastic films with relatively good heat resistance can be used. ■It is difficult to produce thin copper foil without pinholes, and bonding technology is also not easy.

Therefore, it is impossible to produce fine patterns.

On the other hand, when nickel plating or gold plating is applied to a flexible printed circuit board formed by a physical vapor deposition method such as sputtering or ion-blating, as in the case of the above-mentioned bonded flexible printed circuit board, the formed copperFli film and plastic The adhesion to the film becomes extremely weak and may peel off in some cases. The cause of these problems is not certain, but it is likely that (in the flexible printed circuit board immersed in the plating bath, water molecule anions and cations absorbed by the W4 thin film pass through the grain boundaries and reach the interface between the copper thin film and the plastic substrate. It is thought that this has some kind of influence.

[Means for solving problems]

The present invention was made as a result of research to solve the above problems, and includes a flexible printed circuit board in which a wiring layer is formed of copper by a physical vapor deposition method with an evaporation particle energy of 1 eV or more. The present invention provides a flexible printed circuit board characterized in that a nickel layer is formed by the physical vapor deposition method, and a gold layer is further formed thereon.

The present invention will be described in detail below with reference to the drawings.

FIG. 1 shows a cross section of a flexible printed circuit board that is an embodiment of the present invention, and shows a plastic film made of polyester, polyimide, polyether sulfone, polyphenylene sulfide, tetrafluoroethylene resin, etc.
A copper wiring layer 2 is formed thereon by physical vapor deposition with an evaporation particle energy of 1 eV or more. The thickness of the copper wiring N2 is appropriately selected depending on the application, but is usually about 1 μm to 5 μm. This is because if the thickness is less than 1μ, pinholes are likely to occur.
Further, if the thickness is 5 μm or more, curling occurs due to the internal stress of the thin copper film, and the flexibility is also poor. After forming the copper wiring layer 2, a nickel layer 3 is formed thereon to a thickness of 0.5 cm by the physical vapor deposition method.
Appropriately attach more than μ.

The physical N@ method is used for copper wiring layer 2 and nickel N3.
This is to strengthen the adhesion with the film, and a high-quality film is expected. In addition, using nickel as a thin film layer is difficult when copper, zinc, tin, etc. are made into a thin film by physical vapor deposition, and due to the nature of the thin film, it is vulnerable to moisture etc. (therefore, it increases the surface resistance value and also increases the Although nickel tends to cause peeling, it is relatively chemically stable, and when the gold layer 3 is provided on top of it, the rate of gold diffusion into the nickel is slow, and furthermore, the copper wiring layer 2 and the gold layer 4 Nickel layer 3 between
This is because when provided, it becomes a kind of buffer layer and has excellent mechanical properties, especially in terms of bending properties. Finally, a gold layer 4 is provided to improve the reliability of the connection. This gold layer 4 is not limited to the physical vapor deposition method, but may be formed by an ordinary plating method, and is appropriately selected in consideration of the required characteristics, cost, etc. of the flexible printed circuit board. Note that when forming the nickel layer 3 after forming the copper wiring layer 2, it is desirable that the film be formed in a vacuum without returning to the atmosphere. This is because in the atmosphere, the surface of the copper wiring layer 2 is oxidized and various adsorbed molecules promote interfacial peeling.

[Example 1] A polyimide film (manufactured by DuPont East, trade name: Kapton) with a thickness of 25 μm was coated with an Ar gas pressure of 4×10 −′ T using a flat plate magnetron direct current sputtering device.

Copper was sputtered under the conditions of rr, D, C, 500V x 8A to obtain a 2μ thick copper wiring layer. After that, nickel was sputtered under the same conditions without breaking the vacuum state to 0.5
A nickel layer of μ thickness was formed. Thereafter, it was taken out into the air and a desired conductor circuit pattern was formed by etching, and finally the ends (connection parts) of the pattern were plated with gold to a thickness of 0.3 μm to obtain a flexible printed circuit board. The obtained circuit board was subjected to a bending test using the apparatus shown in Fig. 2 (bending radius 5 m, number of bends 30 times/min).
When the test was carried out, no abnormality was observed up to 100,000 bends, and good characteristics were exhibited. In the test method, one end of the flexible printed circuit board is fixed to the fixed piece 7 and the other end is fixed to the movable piece 6, and the movable piece 8 is moved to the position indicated by the dotted line in the figure and returned to its original position. This was counted as one bending. In addition,
The lead wire 6 is connected to the gold-plated pattern end 4 by solder.

[Comparative Example 1] The same polyimide film shown in Example 1 was coated with an Ar gas pressure of 4 using a flat plate magnetron DC sputtering device.
Xl0-'Torr, D, C, 500V X 8 A
Copper was sputtered under the following conditions to obtain a 2μ thick copper wiring layer.

After that, when it was taken out into the air and nickel plated, the ends (connections) of the underlying copper wiring layer peeled off locally.
Also, the part to which the nickel plating was attached was easily peeled off when rubbed with a finger, and it was not possible to apply the next gold plating.

〔Effect of the invention〕

The flexible printed circuit board according to the present invention is flexible,
The industrial value of the present invention is extremely high, as it can easily form a gold layer that satisfies solder resistance and is indispensable for the reliability of connections.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a flexible printed circuit board according to an embodiment of the present invention, and FIG. 2 is a schematic diagram for evaluating flexibility. 1 - plastic film, 2 - copper wiring layer, 3 - nickel layer, 4 - gold layer, 5 - flexible printed circuit board,
6 - lead wire, 7 - fixed piece, 8 - movable piece. Figure 1 Figure 2 Procedural amendment (voluntary) July 22, 1985 L Display of case Patent application No. 1988-2142549 2,
Title of the invention: Flexible printed circuit board ball Relationship with the case of the person making the amendment Patent applicant 5 Contents of the amendment (1) Figure 1 of the drawings attached to the specification of the present application was incorrect, so the correct Figure 1 was submitted. I will do it. Figure 1

Claims (1)

[Claims] In a flexible printed circuit board in which a wiring layer is formed of copper by a physical vapor deposition method with an evaporation particle energy of 1 eV or more, a nickel layer is formed on the steel wiring layer by the physical vapor deposition method, and a gold layer is further formed on the nickel layer. A flexible printed circuit board characterized by forming a flexible printed circuit board.