Flexible Circuit Boards: A Primer

To be able to understand flexible circuits, one must be familiar with metal foils, plastic films, and adhesives and must understand the interactions of a variety of combinations. Each type of material has a different operating temperature base on the adhesive system.

Below is a list of basic types of flex materials:

Single sided: Having conductors on one side of the base material, coverlay on the same side.

Rigid-Flex: Several layers of a variety of combinations of either single or double sided materials bonded together in a stack configuration, with areas being rigid, and other areas being flexible.

Double-sided: By definition double-sided boards have circuity on both sides of the boards. The have plated through holes to interconnect the two sides. These are the workhorses of consumer electronics, automotive electronics, and the RF/Microwave industry. They are the lowest cost choice of consumer products. Laminate materials range from resin-impregnated paper to blend of low cost Teflon for RF applications. The most common material used is FR-4 because of its proven reliability and its low cost. Even with technology advances in material applications double sides are here too stay.

Electrical interconnections for products are too frequently an afterthought and chosen when many opportunities for true cost reduction have already been lost. The application and use of flex circuits should be evaluated in the beginning. Products made with flexible printed circuits tend to be more reliable because of fewer interconnections and the flexibility of the circuits.