JPH04290289A - Flexible printed circuit board with electromagnetic wave shield - Google Patents

Abstract

PURPOSE:To improve bending resistance. CONSTITUTION:Circuits patterns 2, 3, 6 are formed of copper alloy rolled and annealed foil of the following composition: a copper alloy containing 0.02-0.15wt.% of total content of indium and tin, lead or antimony, the content of each is 0.006wt.% or more, and content of oxygen is 0.0001-0.005wt.%. This copper alloy has excellent bending resistance and conductivity corresponding to that of pure copper. Thus, the bending resistance of a flexible printed circuit board is improved without deteriorating its conductivity.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flexible printed board that is used, for example, in a drive system for a printer head, and is bent 10,000 to 1,000,000 times or more.

0002

BACKGROUND OF THE INVENTION In recent years, with the electronicization of electrical equipment, malfunctions caused by electromagnetic waves between the parts have become a problem. Therefore, it is necessary to shield electromagnetic waves from the flexible printed board that connects the parts.

[0003] In response to this request, the present applicant filed a patent application in 1983.
In No. 183774, we proposed a flexible printed board with an electromagnetic wave shielding function having the following configuration.

A circuit pattern is formed on the surface of the plastic film, and an insulating undercoat layer, a shield layer coated with conductive paste, and an overcoat layer are sequentially provided on the circuit pattern, and the ground pattern of the circuit pattern and the shield layer coated with conductive paste are formed. are electrically connected through the undercoat layer at appropriate intervals.

Although this technique was satisfactory in terms of electromagnetic shielding, a problem arose in terms of bending resistance. That is, when used in a drive system for a printer head portion, etc., the bending is repeated 10,000 to 1,000,000 times or more. However, in the above technique, the circuit pattern is formed of pure copper foil, and when the pure copper foil is used, disconnection occurs due to cracks in the circuit pattern.

[0006] The present invention takes the above points into consideration and aims to improve the bending strength.

[0007]

[Means for Solving the Problems] In order to solve the above problems, in the present invention, the above circuit pattern is formed from a rolled annealed foil made of the following copper alloys A to E proposed by the present applicant. This configuration is adopted.

(A) A copper alloy having an indium content of 0.01 to 1% by weight, an oxygen content of 0.01% by weight or less, and the remainder consisting essentially of copper.

(B) Indium content is 0.02
~0.15% by weight, oxygen content 0.0001 ~0
．． 005% by weight, the indium content is 4.0% by weight compared to the oxygen content.
7 times or more, the remainder being essentially copper.

(C) The total content of indium and tin is 0.02 to 0.15% by weight, each content is 0.006% by weight or more, and the oxygen content is 0.000% by weight.
A copper alloy containing 1 to 0.005% by weight, the balance essentially consisting of copper.

(D) A copper alloy in which the total content of indium and lead is 0.02 to 0.15% by weight, each content is 0.006% by weight or more, and the balance is substantially copper.

(E) A copper alloy in which the total content of indium and antimony is 0.02 to 0.15% by weight, each content is 0.006% by weight or more, and the balance is substantially copper.

[0013] In the copper alloys having the above compositions (D) and (E), the oxygen content is preferably 0.0001 to 0.005% by weight, and in this case and in the case of the above composition (C),
The total content of indium and tin, indium and lead, and indium and antimony is preferably 4.7 times or more the oxygen content.

(Japanese Unexamined Patent Publication No. 17039/1983, No. 3858/1983, No. 3858/1983,
JP-A-61-23734 and JP-A-61-237
(See Publication No. 35, etc.)

[0015]

[Function] In the present invention constructed as described above, the copper alloy having the compositions A to E has excellent bending resistance as described in the above-mentioned publication, and is comparable to pure copper in electrical conductivity. For example, in terms of fatigue properties, under the condition of bending strain of 0.306%, the number of bends at break of the copper alloy foil is approximately 16.1.
1,000,000 times, while that of pure copper foil is about 43,000 times, about one-fourth of that.
And, under the condition of bending strain of 0.22%, the above copper alloy foil:
More than 31.5 million times, pure copper foil: about 119,300 times and about 26
Under the conditions of bending strain of 0.18% or less, the copper alloy foil: 62 million times or more, and the pure copper foil: about 218,000 times, which is about 1/280 or less.

[0016]

[Example] As shown in Fig. 1, a 30 μm thick rolled annealed copper alloy foil 2 having the composition A is bonded under heat and pressure on a 50 μm thick polyimide film 1, and this copper alloy foil 2 is etched. the required circuit pattern 2 (1.5 mm
15 stripes (not shown in the drawing) were formed with a width of 1.0 mm. However, among the 15 wires, two at both ends are ground pattern 3.
It is.

Masks are provided on the circuit pattern 2 at regular intervals along the length direction of the ground pattern 3, and a screen (not shown) is provided with masks at fixed portions at both ends of the circuit pattern 2. A paste made of epoxy melamine resin was applied using a printing method to a thickness of 30 mm.
An undercoat layer (UC layer) 4 with a thickness of μm is provided. At this time, a through hole 5 is formed in the UC layer 4 in the longitudinal direction above the ground pattern 3 by the mask of the screen, and no UC is applied to both ends of the circuit pattern 2 due to the mask of the screen, leaving the circuit exposed. Becomes (exposure pattern 6)
.

[0018] Next, a conductive paint is applied to the entire surface of the UC layer 4 by a screen printing method, leaving only a portion at both ends, and the paint film is cured by heating at 150°C for 30 minutes. A shield layer 7 having a thickness of 20 μm is formed. At this time, the conductive paint reaches the ground pattern 3 through the through hole 5, and the shield layer 7 and the ground pattern 3 are electrically connected.

The above conductive paint contains a resin mixture (50% by weight of melamine resin, 20% by weight of polyester resin, and 30% by weight of resol type phenolic resin) based on 100 parts by weight of dendritic metal copper powder with a particle size of 5 to 10 μm. 16 parts by weight of a resin mixture consisting of ), 10 parts by weight of a fatty acid or a metal salt of a fatty acid, and 2.5 parts by weight of a chelate forming agent, some butyl cellosolve acetate was added as a solvent, and the mixture was rolled on a triaxial roll for 20 minutes. Knead it to a suitable viscosity.

Furthermore, a one-component thermosetting silicone rubber coating material [TSE 325] is applied on the shield layer 7.
1. manufactured by Toshiba Silicone Corporation] by a screen printing method, and heat cured at 150° C. for 1 hour to form an overcoat layer (OC layer) 8 with a thickness of 20 μm to produce a flexible print with electromagnetic shielding according to the present invention. A plate P was obtained.

Further, a 100 μm thick rolled annealed copper alloy foil having the composition A is slit to form a 1.2 mm wide rectangular foil strip, and this rectangular foil strip is placed on a 100 μm thick polyester film 1. 2. Through a heat-sealing film.
Fifteen stripes were arranged at a pitch of 54 mm and heat-sealed to form a circuit pattern 2. Thereafter, a flexible printed board P with electromagnetic shielding of another example was obtained in the same manner as described above.

On the other hand, as a comparative example, a circuit pattern was also manufactured in which the material of the circuit pattern 2 was pure copper foil, and the other aspects were the same as those of both examples.

[0023] The flexible printed boards P of this example and comparative example were placed on a mandrel 9 with a diameter of 5 mm as shown in Fig. 2.
After repeated bending as shown by the solid line ← → chain line,
In Examples and Comparative Examples, differences in bending properties based on the fatigue properties of copper alloy foils and pure copper foils were obtained, as described in the section on effects above.

[0024] The thin wire made of the above copper alloy was rolled to form a rectangular foil strip with a thickness of 100 μm and a width of 1.27 mm.
When a flexible printed board P was manufactured using the rectangular foil strip in the same manner as in the above embodiment, similar effects were obtained. Further, similar effects could be obtained even when copper alloy foils having the above compositions B, C, D, and E were used.

[0025]

[Effects of the Invention] Since the present invention has the above structure, the bending resistance is extremely excellent.

[Brief explanation of the drawing]

[Figure 1] Partial perspective view of flexible printed board

[Figure 2]
Flexural characteristic test explanatory diagram

[Explanation of symbols]

1 Flexible plastic film 2 Circuit pattern (copper alloy foil) 3. Ground pattern 4 Undercoat layer 5 Through hole 6 Exposure pattern 7 Shield layer 8 Overcoat layer 9 Mandrel P Flexible printed board

Claims (5)

[Claims] 1. A circuit pattern is formed on the surface of a flexible plastic film, and an insulating undercoat layer, a shield layer coated with conductive paste, and an overcoat layer are sequentially provided on the circuit pattern, and the ground pattern of the circuit pattern is In a flexible printed board with electromagnetic wave shielding which is electrically connected to the conductive paste coated shield layer by penetrating the undercoat layer at appropriate intervals, the circuit pattern is formed from rolled annealed foil made of the following copper alloy. A flexible printed board with electromagnetic wave shielding. A copper alloy having an indium content of 0.01 to 1% by weight and an oxygen content of 0.01% by weight or less, the balance being substantially copper. 2. The electromagnetic shielding flexible printed board according to claim 1, wherein the rolled annealed foil is made of the following copper alloy. The indium content is 0.02 to 0.15% by weight, the oxygen content is 0.0001 to 0.005% by weight, the indium content is 4.7 times or more the oxygen content, and the balance is substantially A copper alloy consisting of copper. 3. The electromagnetic shielding flexible printed board according to claim 1, wherein the rolled annealed foil is made of the following copper alloy. The total content of indium and tin is 0.02 to 0.15
% by weight, and each content is 0.006% by weight
Above, the oxygen content is 0.0001 to 0.005% by weight,
A copper alloy in which the remainder consists essentially of copper. 4. The electromagnetic shielding flexible printed board according to claim 1, wherein the rolled annealed foil is made of the following copper alloy. The total content of indium and lead is 0.02 to 0.15
% by weight, and each content is 0.006% by weight or more, and the balance is substantially copper. 5. The electromagnetic shielding flexible printed board according to claim 1, wherein the rolled annealed foil is made of the following copper alloy. The total content of indium and antimony is 0.02 to 0.
．． 15% by weight and each content is 0.006
A copper alloy whose weight percent or more is essentially copper.