Commonly used materials specifications
Typical Build-up ( Flexible PCB )
Single Sided Flex PCB
A single sided flexible printed circuit construction with a polyimide cover film laminated to copper allowing access from one side only. One single conductive layer, either bonded between two insulating lamination or uncovered on one side.
Single Side Double Access
Applied with single sided material to make pattern but make some window on base film and add on cover layer on pattern top. The final products will have single layer copper but two side access possibility. This structure we call that single side double access boards.
Double Sided FPC Structure
Double sided flexible circuit consist of double-sided copper clad material with top and bottom cover films (PI or Green/Yellow Oil, etc). Two conductive layers with an insulating layer between, plus convert layers on outer layer. The cover films are pre-routed to access copper from both sides using plated thru holes (PTH).
Multi-Layer FPC Structure
The structure of the multilayer flex board can be different combination of single-sided and double-sided PCB material , such as a 4 layer board that can be made of 2+2 or 1+1+1+1 , it also can be 1+2+1 (2 single-side PCB + 1 double-side ), the structure based on the actual situation.
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).
Typical Build-up (Rigid-Flex Circuits )
Rigid Flex circuits (rigid-flex circuit boards) are boards that are made of Rigid circuits ( FR4 PCB) and Flex circuits & circuitries. The Rigid circuits ( FR4 PCB) are connected with single or multiple flex through PTH (VIA) , inside or outside of Flex circuit layer, so it enjoys the advantage of both Rigid FR4 PCB and Flex circuit.
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