IE46109B1

IE46109B1 - A method of producing composite reigid-flexible printed-circuit boards

Info

Publication number: IE46109B1
Application number: IE254977A
Authority: IE
Original assignee: Schoeller & Co Elektronik
Priority date: 1976-12-17
Filing date: 1977-12-15
Publication date: 1983-02-23
Also published as: FR2374818B1; BE861966A; DE2657212B2; DK142475C; DE2657212C3; CH630202A5; IT1091374B; NL180294C; DK142475B; DE2657212A1; GB1561620A; FR2374818A1; SE7714310L; DK546677A; IE46109L; NL180294B; NL7713431A; SE424132B

Abstract

The printed circuit board is produced by pressing rigid and flexible individual layers (3,1). To remove the rigid outer layer (3) in that area (6) of the printed circuit board which is required to be flexible, grooves (4,5) are made on the inside of the rigid outer layer (3) before pressing and on its outside after the conductor pattern (8a) has been produced and the part (6a) of the rigid outer layer (3) between the grooves (4,5) is broken out. In this way, the flexible area (6) of the printed circuit board is reliably and expediently covered and uncontrollable positional errors in the covering are eliminated.

Description

This invention relates to a method of producing composite rigid-flexible printed-circuit boards.

More particularly the invention relates to a method of producing composite rigid-flexible printed-circuit boards having two or more insulating individual layers wherein the printed-circuit boards have adjacent rigid and flexible areas by pressing together rigid and flexible individual insulating layers with the aid of bonding Sheets and removing the rigid individual layers in the desired flexible areas.

The rapid development of printed-circuit board technology led from one-sided printed-circuit boards to the two-sided through-connected printed circuit board, to multi-layer circuitry and to flexible circuitry.

Rigid and flexible support materials which are adapted to each other and pressed together with bonding sheets have recently allowed printed circuits with rigid and flexible areas to be produced as a circuit unit, known as a rigid-flexible printed-circuit board, independently of the number of circuit planes, by removing the rigid support elements in certain areas.

The rigid-flexible printed-circuit board is composed of rigid and flexible individual layers which are firmly stuck together with the aid of bonding sheets.

These are inflexible and flexible insulating supports which can be provided on one or both sides with a copper laminate. The shape of the rigid layers determines - 3 the rigid part of the circuit. The flexible layers are derived from the rigid part and form the flexible areas of the circuit which join the other parts of the circuit together or produce the connection to external assemblies. The electrical connection between the individual layers is produced in the form of metallised holes.

The rigid-flexible printed-circuit boards were formerly produced by making an opening of the same size as and corresponding to the desired position of the flexible part of the rigid-flexible printed-circuit board in the blank of the rigid outer layers, before laminating the individual layers to form the total circuit. After lamination, these openings have to be hermetically sealed with a resist so as to prevent metallisation on the flexible part and transition area between the flexible and rigid parts. This resist is complicated and expensive and, even when taking great care, errors leading to irreparable damage can arise since a faulty seal and errors in positioning of the resist cannot be avoided. The slight adhesion of the copper deposit on the resist could also interfere with subsequent stages of production owing to loose particles.

Mechanical assembly and soldering processes generally involved rigid printed-circuit boards. Special apparatus therefore generally had to be used in the past for each type of circuit during subsequent processing of rigid-flexible printed-circuit boards. In addition, it was advisable to also cover the flexible part with a resist during the soldering process.

An object of the invention is therefore to provide a method of producing composite rigid-flexible printedcircuit boards having two or more individual layers - 4 which allows the flexible part to be covered reliably and economically with a resist during the subsequent stages of production and allows uncontrollable errors in the positioning of the resist to be avoided.

The present invention provides a method of producing a composite rigid-flexible printed-circuit board having two or more individual insulating layers which comprises pressing together rigid and flexible individual insulating layers with the aid of bonding sheets cut out in a desired flexible area, only the one or two outer layers consisting of rigid supports, and removing the rigid outer layers in the desired flexible areas, grooves being produced in these areas along the separating lines between rigid and flexible parts of the printed-circuit board on the inner face of the rigid outer layers before pressing together and on the outer face thereof after forming the conductive pattern , either on the flexible layers alone or on both the flexible and rigid layers, and the areas between the grooves being broken out in order to remove the rigid outer layers in the desired flexible areas.

In one embodiment of the present invention, the areas of the outer layers to be removed are only broken out after assembly and soldering (as hereinafter defined) by correspondingly regulating the depth of the grooves.

As used herein, the term soldering means the stage in the production of printed circuits which comprises soldering electric components such as resistors and capacitors on to printed circuit boards provided with conductive patterns.

Before pressing the individual layers together, a groove is produced in the rigid outer layers on the face towards the flexible layer (inner face) 'along the lines - 5 separating the rigid and flexible parts of the circuit wherein the depth of the groove is selected so that the outer faces of these layers are undamaged. The bonding sheet with whose aid the individual layers are stuck together is cut out over the flexible part of the circuit so that the rigid outer layer does not stick over the future flexible part. When using adhesive films which flow when the layers are pressed together, the adhesive may advantageously be prevented from flowing onto the flexible part by inserting separating films in the openings in the bonding sheet.

The individual layers of the blank laminated by this method are stuck together all over, particularly in the edge zones, apart from in the flexible part of the circuit. The flexible part is thus hermetically sealed and the blank has a closed surface to the outer layers allowing the blank to be processed in the same economical manner as that normally used in the production of rigid printedcircuit boards.

Grooves are again formed along the lines separating the rigid part from the flexible part, after forming the conductive patterns, on the outer layers so as to produce a clean transition from the rigid to the flexible part of the circuit. Since there is already a groove at this position on the inner face of the rigid outer layers, the depth of the groove may be regulated so as to definitely avoid damaging the flexible layer. After cutting the shape of the circuit, the rigid part of the outer layer over the flexible part falls out or may easily be removed from the flexible part.

In an advantageous development of the invention, the outer layer is not completely separated in the case 4010® - 6 of the groove on the outer face and thus the part of the rigid outer layer above the flexible part is still joined to the rigid part of the circuit by webs or by the remaining coating of the outer support. The outer layer above the flexible part thus serves as a resist and reinforcement for the rigid-flexible composite printed-circuit board which may thus be assembled and soldered without special apparatus.

The resist may easily be broken off at the perfor10 ation and removed if necessary.

Xn order to illustrate the method according to the invention in more detail, an embodiment is described with reference to Figures 1 to 6 of the accompanying drawings wherein Figure 1 is a diagrammatic plan of a printed15 circuit board and Figure 2 shows a diagrammatic longitudinal section before forming the conductive patterns.

Figure 3 shows a diagrammatic plan and Figure 4 shows a diagrammatic longitudinal section after forming the conductive patterns wherein this printed-circuit board has only one rigid outer layer. Figures 5 and 6. similarly show a printed-circuit board with two rigid outer layers.

The layered structure of the blank shown in Figures 1 and 2 consists of the rigid outer layer 3 provided with a copper foil laminate 8 on one side with a separating groove 4 on the inner face, a bonding sheet 2 cut out to clear the flexible part of the circuit and a flexible outer layer 1 provided on one side with a copper foil laminate 10. Figures 3 and 4 show the blank after forming the conductive patterns and a separating groove 5 on the outer face of the rigid outer layer 3. The printedcircuit board 7 remains after cutting the shape and the rigid part 6 may be removed above the flexible part or - Ί remains as a reinforcement until after the soldering process on the flexible part. The positioning holes 9 serve for orienting the conductive patterns.

Figures 5 and 6 show an embodiment with two rigid 5 outer layers 13. A separating foil 18 is additionally inserted in the cut-out part of the bonding sheet 12 so as to prevent any adhesive from flowing out onto the flexible part. Conductive patterns 16 on the inner anfi outer layers are formed before pressing together. The conductive patterns 16 are oriented in relation to each other and to the grooves 14 and 15 by positioning holes 19. The double-sided flexible layer 11 is also provided with covering foils.

Claims

1. A method of producing a composite rigid-flexible printed-circuit board having two or more individual insulating layers which comprises pressing together rigid and flexible individual insulating layers with t^e aid of bonding sheets cut out in a desired flexible area, only the one or two outer layers consisting of rigid supports, and removing the rigid outer layers in the desired flexibleareas, grooves being produced in these areas along the separated lines between rigid and flexible parts of the printed-circuit board on the inner face of the rigid outer layers before pressing together and on the outer face thereof after forming the conductive pattern, either on the flexible layers alone or on both the flexible and rigid layers, and the areas between the grooves being broken out in order to remove the rigid outer layers in the desired flexible areas.

2. A method as claimed in claim 1, wherein the areas of the outer layers to be removed are only broken out after assembly and soldering (as hereinbefore defined), by correspondingly regulating the depth of the grooves.

3. A method as claimed in claim 1 or 2, wherein a separating foil is inserted in the cut-out areas of the bonding sheet.

4. A method of producing a composition rigidflexible printed-circuit board substantially as described with particular reference to any of the accompanying drawings.

5. A composite rigid-flexible printed-circuit board when produced by a method as claimed in any of claims 1 to 4.