Combined rigid and flexible printed circuits and method of manufacture

A printed circuit structure having a rigid and a flexible portion comprising:

• a) a sheet of flexible, polyimide, substrate material extending over the entirety of the rigid and flexible portions;
• b) a path of conductive material carried by at least one side of said sheet of flexible substrate material in both the rigid and flexible portions;
• and
• c) a sheet of flexible polymeric over-layer material extending over the path of conductive material in at least the entirety of all the flexible portion in a manner to prevent exposure of at least the conductive path in the flexible portion to the environment;
• d) the structure being at least partially superimposed onto at least one further such structure, the structures being interconnected in their rigid portions;
• e) the plurality of superimposed structures further comprising a layer of polymer prepreg overlying both opposed faces of said plurality at least at the location of a via, formed in the rigid portions, to define the ends of the via;
• and wherein
• f) the polymers in the rigid portion of the structure have a TCE of no more than about 400 ppm/.degree. C. over a temperature range of from 20.degree. C. to 287.degree. C.

A method of assembling a printed circuit comprising multiple circuit layers and rigid and flexible portions, to prevent the formation of voids in adhesive layers thereof and breaks in vias formed therethrough, comprising the steps of:

• a) starting with a sheet of flexible polyimide substrate material extending over the entirety of the rigid and flexible portions;
• with paths of a conductive material on at least one side thereof;
• b) disposing a sheet of flexible polymeric over-layer material over at least the entirety of all of the flexible portion in a manner to prevent exposure of at least the paths of conductive material in the flexible portion to the environment;
• c) disposing a rigid polymeric substrate material over the entirety of all the rigid portions;
• d) disposing the sheet of flexible polymeric over-layer material over the entirety of at least all paths of conductive material in the rigid portions;
• and,
• e) adhesively attaching the sheet of flexible polymeric over-layer material to the polyimide substrate in both the rigid portion the flexible portion and the conductive material it carries, the adhesive in the rigid portion being polymeric adhesive material;
• wherein
• f) the polymeric materials in the rigid portions have a TCE of no more than about 400 ppm/.degree. C. over a temperature range of 20.degree. C. to 287.degree. C.