JPS61182942A - Substrate for heat-resistant flexible printed wiring and manufacture thereof - 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 (Industrial Application Field) The present invention relates to a heat-resistant flexible printed circuit board and a method for manufacturing the same, and particularly relates to a heat-resistant insulating film and a metal foil with a silicone adhesive layer. The purpose of the present invention is to provide a substrate having an integrated laminated structure through which the adhesive strength between the heat-resistant insulating film and the silicone adhesive is significantly improved by using low-temperature plasma treatment of an inorganic gas. .

(Prior Art) With the diversification and miniaturization of electronic devices, the use of flexible printed wiring boards that are lightweight and can be mounted three-dimensionally is increasing. This flexible printed wiring board is made by etching metal foil pasted onto a plastic film to form a circuit, and then attaching resistors, capacitors, coils, ICs (holders), individual transistors, switch terminals, etc. with solder to form a flexible printed circuit. . The flexible printed circuit (~ wiring board) used in this flexible printed circuit is made by laminating an insulating film and metal foil (mainly copper foil) together using an adhesive, and the insulating film is a polyethylene terephthalate film. However, polyethylene terephthalate film lacks heat resistance, and flexible printed circuits that require soldering are limited to heat-resistant films such as polyimide film.

The adhesive must have flexibility, and N 1
3 R-based adhesives, polyamide-based adhesives, acrylic rubber-based adhesives, etc. are used, but even if acrylic rubber-based adhesives, which have relatively good heat resistance, are used, the heat resistance when used as a substrate is only 250°C. About one minute is not enough to stably perform mounting work. For example, when repairing a circuit, it is difficult to repair the defective part because it cannot withstand the required heating time.
Furthermore, there is an increasing demand for wiring materials that are used under high temperatures, either permanently or temporarily, and there is a demand for improved heat resistance of flexible printed circuits. It is thought that such heat resistance problems can be solved by using silicone resin or silicone rubber with excellent heat resistance as an adhesive, but silicone resins or silicone rubber generally lack adhesive properties. Therefore, in order to obtain sufficient adhesive strength, pretreatment or plasma treatment of the adherend is required, and it has not been put to practical use as a flexible printed wiring board.

(Structure of the Invention) The present invention significantly improves the adhesive strength of silicone adhesives by subjecting heat-resistant insulating films to low-temperature plasma treatment using inorganic gas. The present invention provides a printed wiring board. In particular, by using self-adhesive silicones as silicone adhesives, remarkable improvements in adhesive strength have been achieved, and flexible adhesives with excellent mechanical strength can be made highly heat resistant and flammable. Succeeded in manufacturing printed wiring boards.

That is, the present invention relates to a heat-resistant flexible printed wiring board formed by laminating a heat-resistant insulating film whose surface has been treated with low-temperature plasma of an inorganic gas and a metal foil through a silicone adhesive layer, and a method for manufacturing the same. be.

The present invention will be explained in detail below.

The heat-resistant insulating film used in the present invention includes polyimide film, polyphenylene sulfide film,
Examples include polyvaradic acid film, heat-resistant polyester film, polyether sulfone film, and polyether/ether ketone film. Thickness is 12-1
Thicknesses of about 35 μm are often used. Electrolytic copper foil and rolled steel foil are generally used as metal foils, but
Aluminum foil is also used.

In the present invention, the above-described insulating film and metal foil are laminated and integrated using a silicone adhesive layer, and the insulating film is previously subjected to surface treatment using low-temperature plasma of an inorganic gas.

In this low-temperature plasma treatment method, the insulating film is placed in a low-temperature plasma treatment device that can reduce the pressure, and the pressure is maintained at 0.001 to 10 Torr, preferably 0.01 to 1 Torr, with the inside of the device being an atmosphere of inorganic gas. In this state, a direct current or alternating current of about 0.1 to 5 kV is applied between the electrodes to cause a glow discharge, thereby generating low-temperature plasma of an inorganic gas, and continuously plasma-treating the surface while sequentially moving the insulating film. Plasma treatment time is approximately 10
It is preferable to set it as 100 seconds.

Inorganic gases used include inert gases such as helium, neon, and argon, oxygen, nitrogen, carbon oxide, carbon dioxide, ammonia, and air, but these are not limited to one type, but two or more types can be mixed. It is also done to use.

Next, as a silicone adhesive, a viscous liquid with excellent flexibility and adhesive properties, or a solid material diluted with a solvent is continuously applied to the adherend, dried, and laminated for 10 minutes.
It is preferable that sufficient adhesive strength can be obtained by heating at a temperature of 0 to 200° C. for several seconds to several tens of minutes. Liquid silicone rubber (RTV, L
The most suitable adhesives are self-adhesive silicone rubbers commercially available as heat-cured silicone rubbers (also referred to as TV silicone rubbers), and silicone resin adhesives are also included.

These commercially available self-adhesive silicone rubbers include KE45, KE67 and KE as condensation type liquid silicone rubbers.
68 etc. (all product names manufactured by Shin-Etsu Chemical Co., Ltd.), KE1212A, B, C, KE as addition type liquid silicone rubber
1800A, B, C, KE1251 (all trade names manufactured by Shin-Etsu Chemical), organic peroxide flow type KE701Bu (
(trade name manufactured by Shin-Etsu Chemical Co., Ltd.), etc. are exemplified. These are diluted with a solvent as necessary and adjusted to a viscosity that is easy to apply.One-volume preparations for this purpose include acetone, toluene, methyl ethyl ketone, methyl cellosolve, tetrahydrofuran, dimethylformamide, dioxane, and mixtures thereof. The following is an example.

Specific examples of methods for manufacturing a flexible printed wiring board include the following methods 1) to 1ii).

1) A heat-resistant insulating film is treated with low-temperature plasma of inorganic gas, a silicone adhesive layer is provided on the plasma-treated surface, and a metal foil is then pressure-bonded at high or room temperature to harden the adhesive layer to form a substrate. Method ii) Method 1ii) A silicone adhesive layer is provided on metal foil, and a heat-resistant insulating film surface-treated with low-temperature plasma of inorganic gas is bonded to this at high temperature or room temperature, and the adhesive layer is cured to form a substrate. A heat-resistant insulating film is treated with low-temperature plasma of inorganic gas, a silicone adhesive layer is provided on the plasma-treated surface, and a silicone adhesive layer of the same or different type is also provided on the metal foil, and both are heated at high temperature or room temperature. These methods will be explained in more detail, mainly focusing on the method i), by applying an adhesive composition in which the silicone rubber composition is dissolved in a solvent if necessary. 10 to 15% on the low temperature plasma treated surface of the heat resistant insulating film using a dryer.
Apply with a thickness of 0μm, and apply at room temperature to around 120℃ from 0.5~
Heat for 20 minutes. A metal foil such as copper foil or aluminum foil is placed on the adhesive side of this adhesive-coated heat-resistant insulating film and bonded by pressing and heating with a heat press or by pressing and heating between the rolls of a laminator. After cure. Crimping conditions are 80-170℃, pressure 1-100kg
f/a# and heating time of 0.2 seconds to 60 minutes are preferred. If after-curing is required, it is preferable to gradually raise the temperature to a predetermined temperature at 50 to 200° C. for 1 to 30 hours without applying pressure or under roll pressure. The above method is
The structure is such that a silicone adhesive is applied to an insulating film and a metal foil is laminated thereon, but the silicone adhesive is applied to the metal foil surface as described in methods ii) to 1ii). Alternatively, a method may be used in which the insulating film and the metal foil are both coated and the two are laminated using an adhesive layer as an intermediate layer.

The purpose of the flexible printed wiring board of the present invention is to increase heat resistance, but silicone adhesives generally have excellent flame retardancy, and if necessary, even higher flame retardance can be imparted. It is also easy to do so, and suitable means for improving flammability include the addition of nonflammable inorganic substances, powders such as silicon dioxide and titanium oxide, frome-containing compounds, phenol derivatives, and antimony dioxide.

Next, a specific example will be given.

Example 1 A polyimide film (trade name: Kapton) of 25 mm square and 25 μm thick was placed in a low-temperature plasma processing apparatus, oxygen was introduced at a vacuum level of 0.1 Torr, and the temperature was 110 kHz and 2.5 kV.
Apply an alternating current voltage to the electrode to generate a glow discharge 6
Low temperature plasma treatment was performed for 0 seconds. The polyimide film was placed on the lower electrode of the upper and lower opposing electrodes, and the distance between the electrodes was 120. Similarly o, 1 Torr pressure Ha, Ar, N2, co
, co□, NH, alone or mixed gas (02 and Ar
) Alternatively, low-temperature plasma treatment was performed in an air atmosphere.

A liquid silicone rubber adhesive solution (Shin-Etsu Siri: I-N KE1212A, B, C) was applied to these plasma-treated films.
was applied using a test coater, and then heated at 80'C for 5 minutes to volatilize the solvent and bring it into a semi-cured state. The coating thickness was adjusted so that it was dry and @@25μ. 2 for this film
Electrolytic copper foils of 5 cm square and 35 μm thick were layered and heat-pressed using a roll method, and after-cured to form a copper-clad board. The pressure bonding conditions were a temperature of 170°C and a pressure of 5 kgf/d, and the after-cure conditions were 150°C for 1 hour. The temperature was increased to 150°C at a rate of 20°C per hour. Table 1 shows the characteristics of each flexible printed wiring board thus obtained.

In addition, all the copper clad boards created in this experiment were UL-9.
4-V- (flame retardancy equivalent to 5).

Table 1 1*1 Immersion in methanol, acetone or methylene chloride for 5 minutes at 25°C Example 2 In a low temperature plasma processing apparatus, a 25cm width 25μ-
A polyimide film (trade name: Kapton) was inserted, oxygen gas was introduced at a vacuum level of 0.05 torr, and the frequency of 110 kHz was introduced into the electrode.

An alternating current voltage of 3 kV was applied to cause glow discharge, and treatment was performed for 45 seconds with the generated low-temperature plasma. The film was placed on the lower electrode of the upper and lower opposing electrodes, and there were 12 marks between the electrodes.

This treatment increased the contact angle of the polyimide film to water from 35 degrees to 55 degrees. Silicone rubber adhesives A-D with the following composition were applied to oxygen-free rolled copper foil (oxygen concentration 0.001% or less) using a test coater equipped with a reverse coater, and then heated at 80°C for 5 minutes. The conditions were set to semi-cure. The coating thickness of silicone rubber is 25 μm after drying.
It was adjusted so that

In addition, the following KE68SB, KE1800A, B, C1
KE 1251 and KE701Bu are both self-adhesive silicone rubbers manufactured by Shin-Etsu Chemical Co., Ltd.

Adhesive A: 100 parts of KE68S B, 3 parts of Catalyst RC, 100 parts of toluene Adhesive B: 100 parts of KE1800A, 10 parts of B, C
2 parts, toluene 100 parts II C: KE1251100 parts/7 D:
100 parts of KE701Bu, 3 parts of Catalyst C-3, 200 parts of toluene The oxygen-free rolled copper foil coated and dried with each of the above adhesives and the above plasma treated film were stacked together and heat-pressed using a roll method, and after-cured to form a copper-clad board. did. The crimping condition is temperature 1
The after-cure conditions were 70°C, 5 kgf/ci, and 150°C for 1 hour. Table 2 shows the characteristics of each flexible printed wiring board thus obtained.

Table 2 Example 3 A 50m roll of polyimide film with a thickness of 25μm and a width of 508rItQ was processed at a rate of 60m per minute using a continuous plasma processing device.
Plasma treatment was performed at a speed of Conditions are vacuum degree 0°5
Oxygen was supplied at IQ/min in Torr, and the applied voltage was 2 kV.

With an input of 110 kllz and 20 klil, the device had 4 electrodes arranged in a cylindrical shape, and the film was moved along the outer periphery of the electrode group at a distance of 40 points outside the electrodes for processing. The film that has undergone the above plasma treatment is used as an adhesive using KE 18.
00 A 100 parts, K E 1800 B 10 parts,
Using a solution consisting of 2 parts of K E 1800G and 50 parts of toluene, it was continuously coated and dried with a small continuous laminator, while the same adhesive solution as above was used as the metal foil, which was continuously coated and dried with a roll coater. using copper foil.

Both were laminated by roll pressure bonding.

The thickness of the applied adhesive was adjusted to a total of 25 μm. Next, the copper-clad plate wound up into a roll was placed in a circulating dryer, maintained at 150° C. for 1 hour, and then allowed to cool.

When this flexible printed wiring board was cut and a test piece was taken to measure its characteristics, the peel strength was 2.2k.
gf/an, soldering heat resistance at 300° C. for 1 minute or more, and solvent resistance with methanol, acetone, and methylene chloride was also good.

Claims (1)

[Claims] 1. A heat-resistant flexible printed wiring board formed by laminating and integrating a heat-resistant insulating film whose surface has been treated with low-temperature plasma of an inorganic gas and a metal foil via a silicone adhesive layer. 2. The heat-resistant flexible printed wiring board according to claim 1, wherein the silicone adhesive is self-adhesive silicone rubber. 3. A heat-resistant insulating film and metal foil that have been surface-treated with low-temperature plasma of an inorganic gas are formed with a silicone adhesive layer on one or both surfaces of the insulating film and metal foil, and then this silicone adhesive layer is A method for producing a heat-resistant flexible printed wiring board, comprising laminating an insulating film and a metal foil as an intermediate layer and curing a silicone adhesive layer.