JPS6011480B2 - How to manufacture circuit boards - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a novel method for making horizontal circuit boards, more particularly having printed circuits flush with the substrate surface;
In addition, the present invention relates to a method of manufacturing a circuit board in which an insulating resin layer exists under the circuit.

Conventionally, one method for obtaining circuit boards is to screen print a conductive resistor paste containing resin as a binder component on an organic insulating substrate, and then bake and harden it at a predetermined temperature.This method is widely used in the manufacture of variable resistors, etc. It is used. However, although the circuit board obtained by this method is characterized by being a cheap circuit board because it is a simple method, it has various drawbacks, and improvements in these points are strongly desired. That is, the drawbacks are as follows.
{1} Since the circuit obtained on the full-scale substrate protrudes from the horizontal plane of the substrate, it may cause significant wear when used as a sliding circuit, or it may be necessary to apply an additional insulating layer on the circuit. When creating a jumper circuit or the like, there is a drawback that the reliability of the withstand voltage of the insulating layer is lowered.

{21 Since surface smoothness can only be expected from natural stamen ringing when left undisturbed after printing or when cured by heating, it is difficult to obtain smoothness and thickness accuracy of the circuit surface.

Therefore, when used in a sliding circuit or the like, contact with the slider becomes unsatisfactory, causing noise. [3] When silver paste or the like is used to form a circuit directly on the substrate, silver migration occurs under high humidity, causing a circuit short circuit.

For this reason, in the past, complicated methods were used, such as coating the board with an insulating resin or widening the width between the circuits. [4] In order to obtain good conductivity and stable resistance, it is necessary to bake the paste at as high a temperature as possible for a long time, but there is a limit to this due to the heat resistance of the substrate, so we decided to If this is done, the substrate may warp or bulge.

For this reason, the current situation is that high-temperature firing type resin binder pastes with good performance cannot be used even if desired. (2) Since a completed board is used, the cost of the circuit board is inevitably higher than that of the present invention in which circuit processing is performed during the insulating board manufacturing process.

■ Mounting components on a circuit board is more difficult than in the case of horizontal circuits.

In an effort to eliminate some of these drawbacks, we have recently begun printing electrodes and resistors on metal slopes that have been previously subjected to mold release treatment, and then applying adhesive to this surface. However, a method has been proposed in which the adhesive is transferred onto the substrate while being cured, and the metal plate is finally physically peeled off.

However, it cannot be said that this method completely eliminates all of the above-mentioned drawbacks, and the following new drawbacks arise. That is, (1-) Since the metal plate is treated with a molding agent, the ink is repelled by heating and hardening, and if the molding agent treatment is reduced, the final releasability deteriorates.

(2) Since it is a heat-pressure transfer using an adhesive onto a ready-made board, the effect of heat-curing shrinkage of the adhesive layer is large, and the final circuit board is likely to warp.

'3} When the substrate is a hard plate, it is difficult to apply pressure uniformly, and even when high pressure is applied, non-uniformity occurs in the thickness of the adhesive layer.

Therefore, it is difficult to expect reliability due to the homogeneous nature of the insulating layer. '4} There is a problem with workability.

(2) Since the adhesive is in an uncured state, there are problems such as resin entering the conductor resistance circuit during heating and pressurization, impairing conductivity and making it difficult to obtain the desired resistance value.

etc.

We have carried out intensive research to solve the various drawbacks mentioned above all at once and have arrived at the present invention.

That is, a conductive paste and/or a resistive paste is finally printed on a peelable metal foil, completely cured until the desired performance is achieved, and then the circuit and the necessary portions of the board surface are completely covered. Screen print a resin paste to cover it and let it harden. Next, we discovered a method in which the printed surface of this printed foil and one or more sheets of prepreg were brought into opposing contact with each other, and after lamination, heat-pressing was performed to integrate them, and then the metal foil was removed to obtain a circuit board. did. It has been confirmed that the above-mentioned drawbacks of the conventional method can be solved all at once. Further details of the present invention will be described below.

The conductive paste and resistance paste mainly composed of thermosetting resin used in the present invention are thermosetting resins such as phenolic resin, epoxy resin, polyester resin, acrylic resin, alkyd melamine resin, and polyimide resin. Any so-called conductive/resistance paste can be used, which is obtained by using a conductive resin as a binder and combining it with conductive materials such as carbon, silver, copper, and solder, and these can be combined as needed. It is also possible to use it as appropriate.

These pastes are then used to print a desired circuit on the ultimately removable metal foil. In this case, since the transfer method of the present invention is used, it is necessary to perform overcoating in the reverse order of the actually required pattern. Next, this printed material is generally cured by heating, but if necessary depending on the type of paste, it may be cured at room temperature by using light, ultraviolet rays, electron beams, a room temperature curing agent, or the like.

In addition, resistance paste generally has better resistance stability if it is cured at a relatively high temperature, so by selecting a metal foil that is stable at high temperatures, high temperature firing is possible. Although the upper limit of the firing temperature is limited due to this aspect, another major feature of this method is that the paste firing temperature and the molding temperature can be selected separately, so that the upper limit of the firing temperature can be significantly increased.

Next, a thermosetting resin insulation paste is applied to the circuit surface of the metal foil having the obtained circuit.

Although screen printing application is preferred, other application methods are possible. It is preferable to apply the coating to the entire surface of the necessary circuit board, but it is also possible to apply the coating only partially around the circuit portion. Any resin paste can be used as long as it has a thermosetting resin as its main component, but it is preferable that the cured product has good electrical performance and that the cured silver paste has a high ability to suppress migration. In particular, pastes containing epoxy resin as a main component are preferred because of their good adhesion to the cured prepreg after hot pressing. After coating, this layer is fired until it reaches the desired hardness.
In addition, if a desired beam pigment is added to the paste during this coating, a colored insulating layer will exist between the bottom of the circuit and the insulating substrate (Buripreg heat-pressure hardening layer) in the final circuit board, which is the original color of the board. It can cover all colors and produce a beautiful circuit board. In this way, because of this resin layer, a circuit with almost no silver migration is finally obtained, making it possible to narrow the gap between circuits, making it possible to create fine circuits, and furthermore, making it possible to use it as a multilayer circuit board. will also be available. Furthermore, the finally removable metal foil used in the present invention includes copper foil, aluminum foil, iron foil, etc., and improves printing workability.
In consideration of the final peeling workability, the thickness is 20 to 1
It is preferable that the metal foil be a metal foil having a size of 00.

Further, if necessary, it is preferable to use a foil having a mirror surface in order to obtain surface gloss after transfer. The resulting printed foil with the cured circuit and insulation layer is then
The required number of one or more sheets of prepreg that can be bonded under heat and pressure is laminated on top of the top layer with the printed surfaces facing each other.

As such prepregs, any material made by impregnating paper, glass cloth, nonwoven fabric, fabric, etc. with phenol resin, epoxy resin, polyimide resin, or other varnish and semi-curing it to the B-stage can be used. , it is also possible to use them in combination.

Such a laminate is then hot-pressed, in which case it is sufficient to use the desired hot-press conditions required for prepreg lamination, since the printed circuit has been previously cured.

For example, in the case of conventional printing methods, it is completely unnecessary to cure pastes using resins that require high firing temperatures, such as imide resins, on substrates that have relatively low heat resistance, such as phenolic resins. However, according to this method, since a pre-fired material is used, there is no such restriction at all, and the advantage is that the molding temperature of the phenolic resin prepreg is sufficient. Next, only the metal foil is removed from the surface of the heat-press laminate to which the printed and fired metal foil is integrated and attached, but since the foil is used as is, it can be removed by beer peeling, or the entire surface can be removed by etching. This has the advantage of being possible.

In addition, since the foil surface is used untreated and removed, there is no transfer of mold release agents to the circuit surface, and it has extremely convenient advantages such as the possibility of secondary printing when used for multilayering, etc. In addition, since the insulating layer with a high resin content is also transferred, the layer under the circuit becomes a layer with high insulating performance, and there is no risk of migration even when silver paste is used.Thus, the metal foil is removed by etching. The resulting circuit board has a smooth circuit part, a resin insulating layer under the circuit, and a horizontal circuit with the entire circuit completely embedded in the board surface, and the printing paste meets the appropriate conditions. Because it was fired under the surface, it had excellent performance stability and was unprecedented as a circuit board that required sliding movement.

Typical examples will be described below, but the present invention is not limited thereto.

Example 1 {11 A resistance circuit was formed by screen printing on the mirror surface of aluminum foil with a thickness of 30 strands using a carbon-based resistance paste with a phenolic resin as a binder.
Firing was performed at 0qo for 1 hour.

Next, an electrode circuit was screen-printed onto the circuit at the required portions using a silver paste containing a phenolic resin as a binder, and baked at 17,000°C for 1 hour. Furthermore, an insulating resin paste containing an epoxy resin as a main component was screen printed so as to cover the entire circuit portion, and was cured at 130 qo for 1 hour (Step A). '21 Next,
Eight layers of paper-based phenolic resin prepreg and the aluminum foil with the circuit obtained in {1} were arranged so that the top layer of the prepreg and the printed surface were in contact with each other, and hot-pressed at 170°C for 2 hours using a conventional method.
A laminated product with aluminum foil adhered to the surface was obtained (Step B).

'3} Next, the aluminum foil on the surface of the obtained laminate was removed by etching and dried.

(Step C). {4} In the thus obtained circuit board, the printed circuit and insulation coating are completely transferred to the substrate side, and are also completely embedded, the circuit part surface and the substrate surface are horizontal, and the aluminum mirror The surface was transferred to the circuit surface to form a smooth surface, and the area under the circuit was made of hardened insulating resin, making it an excellent circuit board. Example 2 [11 A resistance circuit was formed by screen printing on a 50mm thick aluminum foil mirror surface using a carbon-based resistance base with imide-based resin as a binder, and baked at 300°C for 1 hour. .

Next, an electrode circuit was screen printed on the circuit at the required portions using a silver paste containing phenol resin as a binder, and baked for 1 hour at 150 mm.

Furthermore, an insulating resin paste mainly composed of epoxy resin was screen printed to cover the entire circuit part.
It was cured for 1 hour at 130 qo. ■ Next, eight sheets of paper Kimura epoxy resin prepreg and aluminum foil with circuits obtained by TL were arranged so that the top layer of the prepreg and the printed surface were in contact with each other, and hot-pressed at 170 oo for 2 hours using the usual method, and the aluminum foil A laminated product was obtained in which the surface was closely adhered to the surface.

(3) Next, the aluminum foil on the surface of the obtained laminate was removed by beer peeling.

[4} The circuit board thus obtained was a printed circuit board having excellent performance as in Example 1.

Example 3 A carbon-based resistance paste using a phenolic resin as a binder was printed on a mirror surface of a copper foil having a thickness of 1' and 35 peaks by screen printing, and baked at 150 q○ for 1 hour.

Next, an electrode circuit was printed on desired portions of this circuit by screen printing using silver paste containing a phenolic resin as a binder, and baked at 15,000°C for 1 hour. Furthermore, an insulating resin paste mainly composed of epoxy resin was screen printed to cover the entire circuit part.
It was heated and cured at 20oo for 30 minutes. [21
Next, the printed surface of the steel foil with printed circuit obtained in '1} was placed on the top of the laminate made of 8 layers of glass cloth base epoxy resin prepreg, and 160 qo was
, and heat-cured for 3 hours.

'3} When the copper foil was removed from the surface of the obtained laminate by etching, an excellent circuit board having a horizontal circuit on the surface similar to that of Example 1 was obtained.

Claims (1)

[Claims] 1 Conductive paste containing thermosetting resin as main component and/or
Alternatively, a circuit is printed on a finally removable metal foil using a resistance paste, the paste is cured under desired conditions, and an insulation mainly composed of a thermosetting resin is coated to cover the entire circuit. The process of printing a resin paste and curing it by firing, placing the printed surface of the printing foil in contact with the top layer surface of one or more sheets of prepreg, which is a base material impregnated with thermosetting resin, and heat-pressing this to form a single piece. A laminate having a printed circuit on the same surface as the surface of the laminate, and further comprising a hardened insulating resin below the circuit. Method of manufacturing circuit boards.