Multilayer Flexible Printed Circuit (FPC) Multi-layer Flexible PCB Board

(FPC’s are custom-made products, the picture and parameters shown are just for reference)

General description

This type of flexible circuit is 4-layer structure built on polyimide (PI) for the application of wireless router, 1oz copper each layer. The base laminate is from Shengyi. Coated by yellow covering layer, immersion gold is plated on pads. A connector is designed at both ends. It’s fabricated per IPC 6012 Class 2 using supplied Gerber data.

Parameter and data sheet

Features and benefits

Excellent flexibility

Reducing the volume

Weight reduction

Consistency of assembly

Increased reliability

Material optionality

Low cost

Continuity of processing

Diversified shipping method

Engineering design prevents problems from occurring in pre production.

Applications

Laser head FPC, medical equipment controller, Tablet antenna soft board

Multilayer Flexible Circuits

For the most part, manufacture of multilayer flexible circuits is based upon processes of single sided flexible PCB and double sided PTH flexible PCB. Both types evolve from the conventional covercoated double-sided flexible circuits that are bonded together. For a number of reasons, it is not recommended to combine too many flexible circuits into a multilayer flexible circuit.

Materials and Thicknesses of Multilayer FPC

It is common practice to use the materials listed below.

Dielectric Substrates

50 µm (2 mil) polyimide because of its higher stability and easier handling compared with 25 µm (1 mil) polyimide.

Copper Foil

35 µm (1 oz.) copper foil, provided this thickness is compatible with the current carrying requirements of the finished circuit.

Covercoat

25 µm (1 mil) polyimide for a 35 µm (1.4 mil) thick copper foil, since it ensures a better encapsulation of the conductors than a 50 µm (2 mil) polyimide.

25 µm (1 mil) acrylic adhesive for achieving a good encapsulation and a low-flow lamination. Too much acrylic adhesive leads to reliability problems, e.g. barrel cracks, foil cracks, and a too deep etchback.

Outer Layers

Outer layers should not be provided with any circuitry (conductors) on the bonding side because of the risk of air entrapment at the interface.

Bonding Materials

When using covercoated flexible circuits as inner layers, the circuits and the rigid parts are bonded together by means of sheet adhesives.

Processes

A simplified flow diagram is shown below.

More Displays of Multi-layer FPC