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Flex & Rigid-Flex Circuits

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Flex Circuit Construction - Adhesiveless & Adhesive Based

Substrate Materials

Tech-Etch manufactures flexible circuits from a variety of materials conforming to their respective industry standard IPC specifications.

Flex Circuit substrate materials fall into 2 general categories, adhesiveless and adhesive based.

Adhesiveless

Adhesiveless materials manufactured as either cast dielectric on copper or 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. In addition, adhesiveless materials generally have superior electrical properties.

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 chrome, Ni-chrome or monel barrier layer. Additional 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 are manufactured using a layer of adhesive between the copper and polyimide film to create a mechanical bond. Tech-Etch carries inventory of two main adhesive types, acrylic and epoxy. Other adhesive systems are also available. Please consult the factory.

Rigid-Flex Substrates

Rigid laminate materials are used in conjunction with the flex materials discussed above to crease rigid-flex products. These laminates are typically FR-4 bonded with epoxy pre-preg. Tech-Etch has the ability to work with material from many suppliers conforming to several IPC standards. Contact the factory to review your specific design requirements.

Alternate Circuit Layer 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 CircuitStainless Steel Circuit BeCu CircuitBeCu Circuit

Cover Layers

Polyimide film bonded over the conductor layer with acrylic or epoxy adhesive are the traditional choices for cover layer material. Polyimide thickness ranges from .0005" to .005" are typically available in .001" increments. Adhesive thickness is a function of circuit construction and is usually left to the discretion of the manufacturer.

Adhesive Based Materials


Adhesive BasedAdvesive Based
Photo Imagable Coverlayer (PIC) can be used in applications requiring high density access to circuit layers, most commonly seen on today’s high density SMT designs. This material is coated over the conductors and does not require adhesive or lamination. Though not as resilient as polyimide film, it is better suited to 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.

Rigid-Flex outer layers are typically coated with soldermask. This mask is used to control the flow of solder during component assembly. Vias are typically left open (mask pulled back) in the soldermask layer on Rigid sections. This is the most cost effective manufacturing method however if the soldermask is required to tent over the vias there are techniques that can be employed to achieve this.

Tinted Flexible CircuitsTinted Flex Circuits


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.


Stiffener


FR4 Stiffener

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