Materials Selection and Design are the two major elements to maximize the life cycle of flex circuit. This Section will cover materials only. A later section will discuss designing.
There are two(2) types of dynamic flex applications:
1)Continuous back and forth bend (a rolling type action)
2)A bend over a radius where the flexing action is at the same focal point.
In the first application, BEST TECH has found that the “Adhesive-less” Flexible Metal Clad Laminate has the longest life.
In the second type application, BEST TECH has found that the Flexible Metal Clad Laminate with “Acrylic Adhesive” has the longest life.
There are common practices that should be employed on both applications:
1)Material construction should be balanced (copper weights, adhesive thickness, Kapton Thickness should be same from the center origin of the material.
2)1 oz Copper performs the best. Durable enough but does not impose thickness.
3)The thickness of the materials at the bend area should be minimized.
4)Electro Deposited Copper (ED Cu) should be avoided in bend areas.
5)Rolled Annealed Copper Foil (RA Cu) should be used.
The following items should be identified on the procurement document:
1)Direction of bend
2)Degree of bend
3)Number of fold cycles
4)Diameter of mandrel
5)Points of application