Flexible PCB

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Flexible Printed Circuit
1.    Introduction
Flexible printed circuit is made of polyimide or polyester with high reliability and high pliability. It is mainly used on cell phone, laptop, PDA, digital camera, LCM, PC, telephone, relay, gyroscope, missile, motermeter, and many other products.

2.    Product Type
Flex circuit board is featured with high density, light weight, low thickness, and high pliability. All these features will benefit electronic products in compactness. Its lightness can help reduce the weight of terminal products. The slimness can improve the softness to utilize the limited space. The shortness will help save on connection of cables. And the smallness can effectively reduce the product size which will improve its portability.

In terms of structure, Flex PCB can be grouped into single sided flex PCB, double sided flex PCB, multilayer FPC PCB, and flex rigid PCB.
According to base material technique, there will be 3 types, namely FPC flex PCB, TAB flex PCB, and COF flex PCB.
Based on the appearance, there are 3 categories, film-clad flex PCB, printing ink FPC PCB, fretwork FPC PCB, and crosshatching flex PCB.
According to insulation base film, FPC can be categorized into PET flex PCB, PI flex PCB, polyesterimide flex PCB, flourocarbon ethylene flex PCB, polyimide fiber flex PCB, and polybutylene terephalate flex PCB.
And there are ED flex PCB, RA flex PCB, aluminum-clad flex PCB, and trodaloy-clad flex PCB according to metal conductor foil.
There are different types of adhesive used on flex PCB, including polyester adhesive, acrylic adhesive, epoxy or modified epoxy adhesive, polyimide adhesive, and phenolic butyral adhesive.

3.    Production Flow

A scientific and comprehensive production flow is essential for manufacturing a high quality FPC board. Each step is important from pretreatment before producing to the final delivery. There are around 30 procedures of manufacturing flexible printed circuit, including cut lamination, drilling, PTH, horizontal electrolytic plating, pretreatment, photo process, registration, exposure, developing, etching, striping, surface treatment, pasting covering film, lamination, curing, Ni/Au immersion, legend printing, shearing, electrical measurement, punching, final visual inspection, and packing.

4.  Specifications

Flex PCB is a patterned arrangement of printed circuitry composed of insulating and conducting layers heat pressed by adhesive. The common thickness of insulating basement membrane of flexible printed circuit is 12.5μm, 15μm, 20μm, 25μm, 30μm, 35μm, 40μm, 45μm, 50μm, 75μm, 100μm, 125μm, 150μm, 175μm, 200μm, 200μm, 225μm, 300μm, 350μm, 400μm, 450μm, and 500μm. There are black PI stiffeners, yellow PI cover films, white coverlay, transparent polyimide films, and brown PI copper clad laminates.

The common thickness of metallic conductor of flex PCB is 3μm, 6μm, 9μm, 12μm, 15μm, 18μm, 20μm, 25μm, 30μm, 35μm, 50μm, 70μm, 105μm, 140μm, 175μm, 210μm, 245μm, 280μm, 315μm, 350μm, 400μm, 450μm, and 500μm. There are 4 manufacturing methods for adhesive free copper foil base materials, namely curtain coating, spray plating, electroless deposition/electrolytic plating, and laminating.

The common thickness of flexible printed circuit adhesive is 2μm, 5μm, 8μm, 10μm, 12μm, 15μm, 18μm, 20μm, 25μm, 30μm, 35μm, 40μm, 45μm, 50μm, 60μm, 70μm, 75μm, 100μm, 125μm, 150μm, and 200μm. High chemical durability and processing compatibility should be ensured for flexible printed circuit without any sacrifice of original electrical property, heat-resistant property, and mechanical property.