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Flexible Circuits

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Flex Circuit Construction - Adhesiveless & Adhesive Based

Tech-Etch manufactures flexible circuits from a variety of materials conforming to the IPC-FC-241 and IPC-FC-232 specifications.

Adhesiveless

Adhesiveless materials fall into 2 general categories – cast dielectric on copper and sputtered copper on dielectric film. These materials have gained popularity for several reasons. The absence of an adhesive layer results in a thinner, more flexible construction and in some cases the ability to manufacture flex using different techniques. Adhesiveless materials generally have superior electrical properties but that advantage is negated if an adhesive based coverlayer is applied.

A. Cast Dielectric
The manufacture of cast dielectric materials starts with .5, 1 or 2 oz. (rolled annealed or electro-deposited) copper and a thin layer of polyimide is cast onto the surface. It is available with copper on one or both sides of .001" or .002" polyimide.

B. Sputtered Cu
Sputtered materials start with conventional .001" or .002" polyimide film. Angstrom thick copper is sputtered over a Ni-chrome or monel barrier layer. Copper is then plated to a thickness of 200 microinches. Sputtered adhesiveless material has a unique advantage in that it can be used in the manufacture of semi-additive circuits.

Adhesiveless Materials


Cast DielectricCast Dielectric on Copper



Sputtered CuSputtered Copper on Dielectric Film


Adhesive Based

Adhesive based materials fall into two main categories, acrylic and epoxy.

A. Cover Layers
Polyimide with acrylic or epoxy adhesive are the most common choices for coverlayer material. Polyimide thickness ranges from .0005" to .005" are available with .001" or .002" thickness as typical. Adhesive thickness is a function of circuit material thickness and is usually left to the discretion of the manufacturer.

Photo imagable coverlayers (PIC) can be used in applications requiring high density access to circuit layer. This material is coated over the conductors and does not require adhesive or lamination. Though not as resilient as polyimide film, it does support very small and dense access openings required by many of today’s electronic components.

Photo Imageable Coverlayer can be tinted with either green or amber pigment as shown on the adjacent parts.

Adhesive Based Materials


Adhesive BasedAdvesive Based

Tinted Flexible CircuitsTinted Flex Circuits


B. Stiffeners
Stiffeners are added to rigidize areas of a circuit to strain relieve component attachment locations, provide a firm surface for mounting, or increase thickness of the circuit to correspond to the mechanical specifications (e.g. ZIF connector).

Plastic Stiffener Polyimide film is used when the additional thickness required is .002"-.009". Polyimide stiffeners can have coincidental edges to the circuit outline. Cirlex ® is also used to produce a range of flexibility or stiffness. FR-4 is used when the additional thickness required is greater than .010". The stiffener features are typically smaller than the corresponding circuit features by .015".

Other materials such as metal or molded plastic components can also be used as stiffeners for specific design requirements. Standard flex circuit adhesives or pressure sensitive adhesives can be used to provide varying performance alternatives.

C. Alternate Materials
Exotic and Thick Metal – Tech-Etch’s photo-etching experience gives us the ability to manufacture flex using a variety of conductor materials, including copper alloys, nickel, kovar, stainless steel, and resistance alloys. Consult with engineering if you have specific requirements. Stainless steel and BeCu circuits pictured below.
Stainless Steel CircuitStainless Steel Circuit BeCu CircuitBeCu Circuit

Stiffener


FR4 Stiffener

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