Wednesday, July 20, 2016

FPC flexible printed circuit board material introduction

On the composition of FPC flexible printed circuit board material

Insulating Substrate

Insulating substrate is a flexible insulating film. As the circuit board insulating carrier, flexible dielectric thin film, the heat resistance of the comprehensive survey of the material requirements, covering shape performance, thickness, mechanical properties and electrical properties. Now engineering commonly used is film of polyimide (pi: polyimide with the, the name of the commodity, Kapton), ptfe:ployterafluoroethylene polyester (pet:polyester commodity name Mylar film and PTFE film. The general film thickness selection in the range of o.0127 o.127mm (0.5 ~ 5MIL). Polyimide film, polyester film and poly tetrafluoroethylene film performance comparison.

Adhesive sheet

Bonding sheet is adhesive film and metal foil, or bond films and film coverage (film). For the thin films deposited on different substrates can be used for different types of bonding sheet, such as polyester binder film and polyimide with bonding sheet is not the same, the polyimide substrate bonding sheet with epoxy and acrylic acid. Choose bonding sheet is focused on material flow and thermal expansion coefficient. No bonding sheet polyimide copper clad laminate, resistance to chemical and electrical performance is better.

Due to the low acrylic adhesive sheet of glass transition temperature, a large amount of contamination produced in the process of drilling is easy to remove, effect of metallized hole quality, as well as other adhesive materials to be unsatisfactory place, so multilayer flex circuit layer bonding piece of common polyimide material, since cooperating with polyimide substrate, the CTE (coefficient of thermal expansion (CTE) to overcome the size instability in multi-layer flexible circuit and other properties can satisfactory.

Copper foil

Copper foil is covered with adhesive in the substrate of the conductor insulating layer, after selective etching of the formation of conductive lines. This kind of copper foil most is the rolled copper foil (pcrca copper foil) or electrolytic copper foil (electrodeposited copper foil). The ductility of the wrought rolled copper foil and bending is better than that of the electrolytic copper foil, an extension of the rolled copper foil rate is 20% ~ 45%, the extension of the electrolytic copper foil rate is 4% ~ 40%. The thickness of copper foil is the most commonly used 35um (1oz), thin 18um o.5oz or thick 70UM (2oz), even 105um (for).

Coverage
The covering layer is an insulating protective layer covering the surface of the flexible printed circuit board, which can protect the surface of the conductor and increase the strength of the substrate.

First class is dry film type (coating), polyimide materials selection, without adhesive directly and after etching for the circuit boards in a laminated way pressing. The mulching requirements in the suppression of the pre forming, exposing welding part and therefore cannot meet more fine assembly requirements.

The second category is the photoreceptor development type. Sensitization development type of the first kind is covered dry film by film machine pressed in, by developing photosensitive exposed welding parts, to solve the problem of high density assembly; the second is the liquid screen printing covering materials, commonly used a thermosetting polyimide material, and photosensitive developing type flexible circuit board special solder resist ink.

More info on FPC board

1 comment:

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    SMT

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