JPH04290284A - 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 three or four types of indium, tin, lead and antimony in such a manner that the total content is 0.02-0.15wt.% and the content of each is 0.006wt.% or more and the residue is substantially copper. 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 such as a printer head part, 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, the present invention provides a structure in which the above circuit pattern is formed of a rolled annealed foil made of a copper alloy having the following composition as proposed by the applicant. was adopted.

Contains three or four of the above-mentioned indium, tin, lead and antimony, the total content of which is 0.02 to 0.15% by weight, and each content is 0.006% by weight % or more, the balance being essentially copper. The substantial copper portion of the copper alloy has an oxygen content of 0.0001 to 0.00.
It is preferably about 5% by weight. (Unexamined Japanese Patent Publication No. 61-523
(Refer to Publication No. 34)

[0009]

[Function] In the present invention constructed as described above, the copper alloy having the above composition has excellent bending resistance as described in the above publication, and is comparable to pure copper in terms of electrical conductivity. For example, in terms of fatigue properties, under the condition of bending strain of 0.306%,
The number of times the copper alloy foil breaks and bends is about 161,000 times, while that of pure copper foil is about 43,000 times, which is about one-fourth of that.
Under the condition of bending strain of 0.22%, the above copper alloy foil: 3150
More than 10,000 times, pure copper foil: about 119,300 times, about 1/260th
Below, under the condition of bending strain of 0.18%, the above copper alloy foil: 6
More than 2 million times, pure copper foil: about 218,000 times, less than 1/280th.

0010

[Example] As shown in Fig. 1, a 30 μm thick rolled annealed copper alloy foil 2 having the above composition is bonded under heat and pressure on a 50 μm thick polyimide film 1, and this copper alloy foil 2 is etched. A required circuit pattern 2 (15 stripes with a width of 1.5 mm and an interval of 1.0 mm, not shown in the drawing) was formed. 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)
.

[0012] Next, a conductive paint is applied to the entire surface of the UC layer 4 by screen printing, 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.

[0013] The above-mentioned 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 above composition is slit to form a 1.2 mm wide rectangular foil strip, and this rectangular foil strip is heated on a 100 μm thick polyester film 1. 2.5 through fusion film
Fifteen stripes were arranged at a pitch of 4 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, one was also produced in which the material of the circuit pattern 2 was pure copper foil, and the other parts were the same as those of both examples.

[0017] 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.

[0018] 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.

[0019]

[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 (1)

[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. Contains three or four of the following indium, tin, lead and antimony, the total content of which is 0.02 to 0.15% by weight, and the content of each is 0.006% by weight or more, the balance A copper alloy consisting essentially of copper.