DE9116280U1 - Rigid, partially bendable printed circuits - Google Patents

Description

91 193 AB Rigid, partially flexible printed circuits and processes for their manufacture

Description:

The innovation concerns rigid printed circuits that can be bent in some areas, consisting exclusively of rigid circuit board materials with one or more conductor track levels.

For many years, printed circuits have been used in devices and vehicles for electronic regulation and control. These are usually rigid circuit boards that electrically connect discrete components and highly integrated modules and act as a carrier for them. The circuit boards usually consist of one or more layers of glass fiber reinforced, hardened epoxy resin boards that are copper-clad on one or both sides to form conductor tracks and can be electrically connected to one another in the various levels.

For several years, printed circuits have been used that have rigid and flexible areas next to each other. This means that a large number of rigid circuit boards can be mechanically and electrically connected to one another in almost any desired spatial arrangement without connector strips or wiring. The flexible areas are usually made of thin polyimide films that are also copper-clad on one or both sides.

The circuit boards, which consist of rigid and flexible areas, are usually made up of superimposed rigid and flexible individual layers that extend over the entire circuit and are glued and pressed together using composite films. These are rigid (e.g. glass fiber reinforced epoxy resin) and flexible insulation carriers (e.g. polyimide film) with one- or two-sided copper cladding into which the conductor tracks are etched. The shape of the rigid layers determines the rigid part of the circuit boards. The flexible areas of the circuit boards are produced by removing the rigid layers in these areas in several process steps. One such process is described, for example, in DE-PS 26 57 212.

The production of such rigid-flexible circuit boards is very time-consuming and costly due to the numerous process steps and the use of relatively expensive polyimide films. In many applications, however, it is not necessary for the flexible areas to be so flexible that they can be subjected to high permanent bending stresses. In many cases, these areas are only subjected to bending when they are installed in the device or vehicle and, if necessary, again during subsequent inspections or servicing. These bending stresses are limited in number and relatively small.

The aim of this innovation was therefore to develop rigid printed circuits that could be bent in some areas.

which consist exclusively of rigid

PCB materials and can be manufactured cost-effectively with as few process steps as possible.

This task is solved in accordance with the innovation in that the rigid circuit board material in the areas that are bendable has a lower thickness, entirely or partially, than in the other areas, and the lower thickness is created by material removal.

Preferably, the rigid circuit board material has a thickness of 0.05 to 0.5 mm in the bendable areas, whereby the upper limit depends somewhat on the rigidity or elasticity of the rigid circuit board material.

In certain cases, it may be advantageous to use laminates as rigid circuit board material, in which an outer layer consists of a material with slightly higher flexibility and in the bendable area the other layers are completely or partially removed by material removal.

The production of such rigid circuit boards, which have flexible areas, is carried out in such a way that the circuit boards are made thinner by removing material in the areas that are to be flexible. The material can be removed using known methods such as milling, broaching or laser methods.

The material removal in the bendable areas does not have to be carried out evenly over the entire surface, but if the bending stress is not too great, it is sufficient if, for example, several grooves are made perpendicular to the bending direction.

Surprisingly, it has been shown that even rigid circuit board material can be bent if it is removed to a sufficiently thin layer thickness.

The illustration shows a schematic longitudinal section of a rigid circuit board that has a flexible area (3). It consists entirely of a rigid material (1), for example glass fiber reinforced epoxy resin, which has a conductor track pattern (2) made of copper on one side. In the area (3) that is to be flexible, the rigid material is removed from the back of the conductor track support (2) to a remaining layer thickness of 0.05 to about 0.5 mm.

The following example should explain the innovation in more detail:

2 A circuit board measuring 300 x 100 mm and 1.6 mm thick, made of glass-fiber-reinforced epoxy resin is covered with a 35 μδπα layer of copper. In the middle of this circuit board, on the side opposite the copper layer, a

2
The thickness of the circuit board was reduced to 0.2 mm by mechanical milling in an area of 30 x 100 mm. In this area, the circuit board is then bendable and withstood fifty bendings of 90 degrees each without any noticeable damage in this area.

The conductor tracks are formed using known methods. The relatively few and simple process steps mean that the production of these circuits is cost-effective.

Claims (3)

1. Rigid printed circuits that can be bent in some areas, consisting exclusively of rigid conductor board materials with one or more conductor track levels, characterized, that the rigid circuit board material has a smaller thickness in the areas that are flexible than in the other areas, and that the smaller thickness is caused by material removal. 2. Printed circuits according to claim 1, characterized in that the rigid circuit board material has a thickness of 0.05 to 0.5 mm in the bendable areas. 3. Printed circuits according to claim 1 or 2, characterized in that laminates are used as circuit board material in which an outer layer consists of a material with greater flexibility.