JPH04299886A - Printed wiring board having electromagnetic wave shield - Google Patents

Abstract

PURPOSE:To improve flexing resistance without deteriorating conductivity, by forming a circuit pattern from a rolling annealed foil composed of copper alloy having specified composition. CONSTITUTION:A rolling annealed copper alloy foil of composition A is compression-bonded on a polyimide film 1 by heating. A necessary circuit pattern 2 is formed by etching the copper alloy foil. The composition A is as follows; Cr of 0.25-10wt.% is contained, and the residue is inevitable impurities wherein the contents of Cu and P are restricted to be lower than or equal to 100ppm. Particles of Cr are extended and dispersed in the machining direction. On the circuit pattern 2, masks are formed at specified intervals along the length direction on a ground pattern 3. Paste composed of epoxy melamine resin is spread by a printing method, and an undercoat layer (UC layer) 4 is formed. Coating material is spread on the whole surface of the UC layer 4 and thermoset, thereby forming a shielding layer 7, which is electrically connected with the ground pattern 3 via through holes 5.

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 or the like 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 adopts a configuration in which the above circuit pattern is formed from a rolled annealed foil made of copper alloy A or B below. be.

[0008] (A) Cr: Contains 0.25 to 10% by weight, the remainder consists of unavoidable impurities with Cu and P content limited to 100 ppm or less, and the Cr particles are elongated and dispersed in the processing direction. A copper alloy that has been wire-drawn and annealed.

(B) Contains Cr: 0.25-10% by weight, further contains Sn 0.001-0.5% by weight, Zr 0
．． 001-0.5% by weight, Mg 0.001-0.5% by weight, Mn 0.001-0.5% by weight, Zn 0.0
01-2.0% by weight, Al 0.001-0.5% by weight
, Ni 0.001-0.5% by weight, Fe 0.001
~0.5% by weight, Ti 0.001-0.2% by weight, C
o 0.001-0.5% by weight, Cd 0.001-0
．． 5% by weight, V 0.001-0.05% by weight, Ag0
．． 001-0.05% by weight, In 0.001-0.2
Weight %, Te 0.001-0.2 weight %, Y 0.0
0.01 to 0.05% by weight, Si 0.001 to 0.01% by weight, any one or two or more types in total 0.
001 to 3.0% by weight, with the balance containing Cu and P at 1% by weight.
A copper alloy with Cr particles elongated in the processing direction, consisting of an alloy with unavoidable impurities limited to 00 ppm or less.

The processing direction mentioned above refers to the casting direction and the wire drawing direction, and by unidirectional solidification casting (OCC), Cr
The particles elongate and disperse in the processing direction. This dispersion density is preferably about 102 to 106 particles/mm2 (number of Cr particles per unit cross-sectional area).

[0011] In addition, in order to improve solderability and/or to avoid adverse effects of gas on the conductor during the formation of the insulating coating, and to reduce contact resistance, Sn, Sn-Pb alloy,
It is preferable to coat with Ag or an Ag alloy. However, if there are no such problems, coating with these metals or alloys is not necessary. Annealing is preferably performed in an N2 atmosphere, and the P content is preferably 10 ppm or less.

[0012] Even in the alloy of the above composition (B), the Cr particles may be separated, and the alloy may be subjected to wire drawing and annealing.

[0013]

[Function] The present invention constructed as described above is characterized in that the copper alloy having the composition A or B has excellent bending resistance and electrical conductivity, as described in JP-A No. 2-304803 and JP-A No. 2-304804. In terms of properties, it is comparable to pure copper. Therefore, the flexible printed board has improved bending resistance without deteriorating its conductivity.

[0014]

[Example] As shown in FIG. 1, a 30 μm thick rolled annealed copper alloy foil 2 having the composition B was bonded under heat and pressure on a 50 μm thick polyimide film 1, and this copper alloy foil 2 was 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 constant 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)
.

[0016] Next, a conductive paint is applied to the entire surface of the UC layer 4 by a screen printing method, leaving a part of 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-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 composition B was slit to form a 1.2 mm wide rectangular foil strip, and this rectangular foil strip was 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, one was also manufactured in which the material of the circuit pattern 2 was pure copper foil, and the other things were the same as those of both examples.

[0021] 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 were obtained between copper alloy foils and pure copper foils based on their fatigue properties (the latter being a few to a few hundredths of the former).

[0022] 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. In addition, almost the same effect can be obtained even if the copper alloy foil with the above composition A is used, and when Cr particles are dispersed in the copper alloy foil with the composition B and wire drawing and annealing are performed, Its effectiveness has improved.

[0023]

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

[Brief explanation of drawings]

[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 (3)

[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. Cr: Contains 0.25 to 10% by weight, the remainder consists of unavoidable impurities with Cu and P content limited to 100 ppm or less, and the Cr particles are elongated and dispersed in the processing direction, and A copper alloy that has been wire worked and annealed. 2. The electromagnetic shielding flexible printed board according to claim 1, wherein the rolled annealed foil is made of the following copper alloy. Contains Cr: 0.25 to 10% by weight, and further contains Sn 0.0
01-0.5% by weight, Zr 0.001-0.5% by weight
, Mg 0.001-0.5% by weight, Mn 0.001
~0.5% by weight, Zn 0.001-2.0% by weight, A
l 0.001-0.5% by weight, Ni 0.001-0.
5% by weight, Fe 0.001-0.5% by weight, Ti 0
．． 001-0.2% by weight, Co 0.001-0.5% by weight, Cd 0.001-0.5% by weight, V 0.00
1 to 0.05% by weight, Ag 0.001 to 0.05% by weight, In 0.001 to 0.2% by weight, Te 0.00
1 to 0.2% by weight, Y 0.001 to 0.05% by weight,
Si in the range of 0.001 to 0.01% by weight, containing one or more of them in a total of 0.001 to 3.0% by weight, and the balance being unavoidable with Cu and P content limited to 100 ppm or less A copper alloy with Cr grains elongated in the processing direction, consisting of an alloy of target impurities. 3. In the flexible printed board with electromagnetic shielding according to claim 2, the copper alloy of the rolled and sintered dull foil has separated Cr particles and has been subjected to wire drawing and annealing. A flexible printed board with electromagnetic shielding.