Manufacture of flexi‐rigid boards

The manufacture of flexi‐rigid multilayer boards poses a number of problems which are not met with in ordinary multilayer production or in the making of plain flexible circuits. Steps have to be taken to overcome the poor dimensional stability of thin polyimide foils during processing and to ensure that those portions of the assembly which need to be rigid are bonded whilst flexible portions are left unbonded other than for a cover coat. Pressure on cover coated flexible areas must be maintained during bonding without allowing resin to now over these areas, and finally the bonded unit must be profiled, often with superimposed flexible areas of different shapes. This article describes some of the techniques used by a leading manufacturer to overcome these problems. Several of the processes described are covered by patents held by Exacta Circuits Ltd. This article is an extract from a forthcoming book ‘Handbook of Multilayer Printed Circuits’ to be published at the end of the year by Electrochemical Publications Ltd., 8 Barns Street, Ayr, Scotland.