GB2217918A

GB2217918A - Method of manufacturing printed circuit boards

Info

Publication number: GB2217918A
Application number: GB8818477A
Authority: GB
Inventors: Ho Yeon Jung
Original assignee: Individual
Current assignee: Individual
Priority date: 1988-04-27
Filing date: 1988-08-03
Publication date: 1989-11-01
Also published as: JPH01278794A; KR910000571B1; GB8818477D0; KR890016887A

Abstract

A method of manufacturing printed circuit boards in which a layer of graphite CL is deposited upon an electrically insulating substrate T and selectively masked with layers of an insulating film IL to form a circuit pattern on to which a metal MC is electrodeposited. The metal MC is coated with an adhesive Bn and transferred to a printed circuit base by subjecting the base and the substrate T to increased heat and pressure. The masked substrate T can be re-used. <IMAGE>

Description

TITLE Method of Manufacturing Printed Circuit Boards DESCRIPTION Field of the Invent ion The invention relates to a method of manufacturing printed circuit boards and particularly to a method involving the transferral of a metal cicuit electriodeposited on a reusuable substrate to a printed circuit base.

Background to the Invention Conventionally, there are two methods of manufacturing printed circuit boards in common use. The first, the photo-etching method involves coating a sheet of copper on to an insulating base and coating the copper sheet with a light sensitive agent. The required circuit patterns on the copper sheet are phosphorized and developed, and then the base is dipped into an etching solution to etch off the unphosphorized portions so as to form a copper circuit on the base. The disavantages of this method are that there is an extreme loss of metal during the etching process, etching agent is consumed in large quantities, and that the etching process inevitably causes environmental pollution.

Furthermore the type of equipment required for photo-etching is expensive, and as the method is complicated, the mass production of the printed circuit boards poses difficulties.

The second method of manufacturing printed circuits, the screen printing method, has the advantages that it eliminates the need for etching, and so avoids the problem of pollution associated with the photo-etching method. But as this method involves the formation of a circuit from a conductive ink, the resistance of the printed circuit is very high Furthermore, depending upon the distribution of the metal particles within the conductive ink, the ratio of metal particles to carrying agent, the size of the metal particles, and the printing conditions, etc. the resistance through the circuits is not uniform and this tends to inhibit the reliability of the circuit.

Therefore, printed circuit boards produced by this method are limited in their applications and accordingly, in the case where a high precision and high reliability are required, only printed circuit boards manufactured by the photo-etching method are used.

The Invention The invention provides a method of manufacturing printed circuit boards comprising depositing a layer of graphite onto an electrically insulating substrate, masking a portion of the graphite layer by screen printing with an electrically insulating film, electroplating the unmasked areas of the graphite layer with a metal, coating a thermosetting adhesive onto the surface of the metal, contacting an electrically insulating base with the surface of the metal, and transferring the metal from the surface of the substrate to the surface of the base by subjecting the adhesive to heat and pressure.

Preferably the masked substrate is repeatedly used.

The substrate may be a plastics material.

The invention includes a printed circuit board manufactured by the method as described above.

The Drawings Figure 1 is a plan view of an insulating substrate with a graphite layer deposited thereon, in accordance with the invention; Figure la is a cross sectional view of Figure 1, Figure 2 is a plan view illustrating the masking of a portion of the graphite layer shown in Figure 1 by means of an insulating film, in accordance with the invention, Figure 2a is a cross sectional view of Figure 2; Figure 3 is a plan view illustrating the electrodeposition of a metal onto the unmasked portions of the graphite layer shown in Figure 2, in accordance with the invention; Figure 3a is a cross sectional view of Figure 3; Figure 4 is a plan view illustrating the film of adhesive which is coated onto the metal circuit shown in Figure 3, in accordance with the invention; Figure 4a is a cross sectional view of Figu-re 4;; Figure 5 is a diagramatic representation of the introduction of the substrate to an insulating base, in accordance with the invention; Figure Sa is a cross sectional view illustrating the process of transferral of the metal from a substrate to a base, in accordance with the invention; Figure 6 is a plan view of a printed circuit board in accordance with the invention; and Figure 6a is a cross sectional view of the withdrawal of a substrate from a printed circuit board, in accordance with the invention.

Best Mode With reference to Figures 1 and la, a conductive graphite layer CL is deposited upon an electrically insulating substrate T made preferably of plastics material. Graphite powder, having graphite particles of a diameter preferably less than 3 Clm. and a carrying agent such as varnish are preferably mixed in a ratio of 10:5 weight percentage. The graphite and its carrying agent are deposited on the substrate T by screen printing, spraying or brushing, to a thickness of preferbly 2-4 mm. The graphite layer CL is cured by heating to 130 0C for 10 minutes.

With reference to figures 2 and 2a, the surface of the graphite layer CL is screen printed with an insulating ink film IL in order to mask out unwanted portions of the graphite layer CL. The exposed graphite forms a graphite circuit CC. The printed areas are covered with layers of insulating ink film IL, and the whole board serves as a circuit template TP. This template TP is used in order to copy out repeatedly metal circuits.

With reference to figures 3 and 3a the circuit template TP is immersed in an ordinary electroplating electrolyte in order to electrodeposite a metal, such as copper, onto the graphite circuit CC of the circuit template TP, and ultimately to fqrm a matal circuit MC on the circuit template TP. The thickness of the metal circuit MC electrodeposited on the graphite circuit CC can be variable depending upon the specific purpose, but generally 20#m is preferable. Each layer of the metal circuit MC, which is successively deposited, has a slightly longer cross-sectional width than the previously deposited layer.

After the completion of the electrodeposition of the metal circuit MC, a thermosetting adhesive Bn is coated onto the metal circuit MC by means of the screen printing method as shown in figures 4 and 4d. As the screen and the metal circuit MC have the same pattern, the adhesive Bn is printed only on the metal circuit MC. Immediately after the printing, the adhesive layer Bn exhibits no stickiness at all, but if it is subjected to pressure and heat it is capable of bonding strongly.

After the adhesive layer Bn is formed on the surface of the metal circuit MC on the circuit template TP, the adhesive layer Bn is half-cured chemically by heating it to the temperature range of 130-1500C for 5 minutes. This prevents the elution of the adhesive when the metal circuit MC undergoes transferral, as described below.

As shown in figures 5 and 5a, the metal circuit MC of the circuit template TP is contacted with a printed circuit base P which is to form the printed circuit board, and the two abutting boards TP, P are put into a press Pr in which 0 2 a heat and pressure of 130-150 C and 1000-1500N/cm2 respectively are applied on the two boards TP, P for lo minutes. When the two boards TP, P are taken out from the press, and the circuit template TP and the base P are separated, the metal circuit MC is detached from the graphite circuit CC, as shown in figure 6a, and is transferred and adhered solidly onto the base P by the adhesive, thereby obtaining the desired printed circuit board PC as shown in figure 6. The successively increasing width of the layers of metal circuit MC on the template TP provides an area sufficient for firm adherance to the base P.

As the graphite circuit CC remains intact on the circuit template TP, the steps of electrodepositing the metal circuit MC as described above can be repeated and enable mass production of the same printed circuit PC from the same circuit template TP. The substrate T is therefore constructed from a material which can withstand physical pressures, chemical actions, and elevated temperatures.

As the invention provides a manufacturing method in which the metal circuits are successively transferred from a substrate acting as a circuit template to a printed circuit base, it has the advantage that printed circuits of uniform quality can be produced in large quantities. There is also another advantage in that, as the process does not involve etching, no loss of material due to the etching can occur, and no etching chemical is needed. This brings the consequent advantages that no environmental pollution is caused, and the manufacturing costs can be minimised.

As the printed circuits manufactured according to the invention are produced by transferring a metal circuit from a circuit template the actual printed circuit base does not undergo any chemical treatment or any external mechanical stress, and therefore, a wide range of materials can be used for the base. That is, a wide range of materials such as plastics materials, board, glass board, wood board, non-woven fibres impregnated with plastics materails, thick or thin films, paper boards, etc. can be used.

The metal circuit may be transferred onto both sides of the printed circuit base, and therefore, the present invention makes it possible to manufacture double face printed circuit boards, multi layer printed circuit boards, and composite circuit boards.

As no limitation is imposed on the kinds of the material of the printed circuit base, thin film circuit boards can be manufactured, a kind of cheap and small volume circuit boards which are applicable to a wide range of existing or future electronic apparatus.

As final finish work on the metal circuit is not needed, thereby improving the workability, and as the circuit is composed of a metal, the circuit of the circuit board will exhibit an electrical stability and reliability.

Claims

1. A method of manufacturing printed circuit boards comprising depositing a layer of graphite onto an electrically insulating substrate, masking a portion of the graphite layer by screen printing with an electrically insulating film, electroplating the unmasked areas of the graphite layer with a metal, coating a thermosetting adhesive onto the surface of the metal, contacting an electrically insulating base with the surface of the metal, and transferring the metal from the surface of the substrate to the surface of the base by subjecting the adhesive to heat and pressure.

2. A method according to claim 1, wherein the masked substrate is repeatedly used.

3. A method according to claim 1 or claim 2, wherein the substrate is a plastics material.

4. A printed circuit board manufactured according to any preceding claim.

5. A method of manufacturing printed circuit boards substantially as herein described with reference to the drawings.