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Why Procuring Flexible Printed Circuitry is Different
June 9, 2014 |Estimated reading time: 1 minute
An article in a previous issue of The PCB Magazine, "How to Select a Flex Circuit Supplier," discussed how to select a flexible printed circuit (FPC) vendor. Herewith two thoughts on why procuring FPC is different from other products.
Firstly, FPC specifications and quality controls tend to be too tight; FPC is, by nature, a flexible, easily formed product of thin sheets of plastic film and metal foils bonded together with flexibilized adhesives. It is not carved out of billets of metal in a machine shop and it is not reasonable to assign thousandths-of-an-inch tolerances to every dimension.
FPC appeared as a commercial product in the late 1950s. Back then, the manufacturing process consisted of fusion-bonding high-performance polymer films onto treated copper foil to form an initial laminate. This was imaged and etched to form the conductor pattern, then subjected to a second fusion bond process in which the covering film had pre-punched apertures to expose terminal pads, sometimes with an added piece of film attached to the backside of the pad to force it upward into the punched openings to stiffen and reinforce the area against solder heat and stress. Typical bonding temperatures reached 530°F or so, and distortion and residual stress were constant problems. But this was a product with outstanding chemical and environmental durability and superb electrical performance. There were no flexibilized adhesives here! Read the full article here.Editor's Note: This article previously appeared in the July 2014 issue of The PCB Design Magazine.