Choosing Materials for Flexible Circuits

Description

By Mark Finstad, Minco

Introduction
The choice of materials used in the composition of a flexible circuit can have a direct impact on the circuit's ability to bend or flex. The thicker the flexible circuit, the less it will be able to bend without cracking. It is therefore important to identify the end use of the flexible circuit before beginning the design so that materials can be chosen accordingly.

There are a number of material guidelines to follow to ensure the reliability of a flexible circuit:
- Copper Plating
- Circuit Thickness

Here are some commonly asked questions about the selction of materials
- Are flex circuits available with Teflon combustion safe materials?
- What are disadvantages and advantages of using acrylic adhesive and All-Polyimide (AP) film in a flex circuit?
- Does a Liquid Photo-Imageable Coverlay (LPI or PIC) cover layer allow tighter bends?
- Is one-half ounce RA copper more or less flexible than one ounce RA copper?
- What material choices typically exist for plating the bare copper traces as they exist in a window?
- Is it possible to do plating with exotic materials?
- Could the track material be another metal besides copper?
- Regarding solderable finish for a BGA assembly - is OSP a good candidate? Why or why not?
- Are there any tougher materials than pure copper?

About the Author
Mr. Finstad is Principal Applications Engineer for the Flex Circuit Division of Minco. He has 23 years experience in design, process development, and production of flexible printed circuits.

Specs

• The choice of materials used in the composition of a flexible circuit can have a direct impact on the circuit's ability to bend or flex. • The thicker the flexible circuit, the less it will be able to bend without cracking
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