PCB Technical - What is the material and function of the flexible PCB?

Early flexible circuit boards (hereinafter referred to as soft boards) are mainly used in the fields of small or thin electronic mechanisms and connections between hard boards. In the late 1970s, it was gradually applied to electronic information products such as computers, cameras, printers, car stereos, and hard disk drives. At present, the Japanese FPC application market is still dominated by consumer electronic products, while the US has gradually shifted from past military use to consumer use for people's livelihood.

The functions of the soft board can be divided into four types: Lead Line, Printed Circuit, Connector, and Integration of Function. The use covers computers and computer peripherals. Scope of systems, consumer household electrical appliances and automobiles.

COPPER Clad Laminater (CCL)

CU (Copper foil): E.D. and R.A. copper foil

Cu copper layer, the copper skin is divided into RA, Rolled Annealed Copper and ED, Electrodeposited. The two have different characteristics due to different manufacturing principles. ED copper has low manufacturing cost but is fragile. The copper surface is easy to break when making Bend or Driver. RA copper has high manufacturing cost but good flexibility, so the FPC copper foil is mainly RA copper.

A (Adhesive): Acrylic and epoxy resin thermosetting adhesive

Adhesive is two major systems: Acrylic and Mo Epoxy.

PI (Kapton): Polyimide (polyimide film)

PI is the abbreviation of Polyimide. In DuPont called Kapton, the unit of thickness is 1/1000 inch lmil. The characteristics are thinness, high temperature resistance, strong chemical resistance, and good electrical insulation. The current FPC insulation layer has welding requirements. Kapton.

Features:

has a high degree of flexibility, can be three-dimensional wiring, change the shape according to space constraints.

High and low temperature resistance, flame resistance.

can be folded without affecting the signal transmission function, can prevent electrostatic interference.

Stable chemical changes, high stability and reliability.

is conducive to the design of related products, can reduce assembly man-hours and errors, and increase the service life of related products.

The size of the application product is reduced, the weight is greatly reduced, the function is increased, and the cost is reduced.

Polyimide Resin

Polyimide resin is a general term for heat-resistant resins represented by polypyromellitic acid imide produced by the reaction of an oxygen-containing layer base and anhydrous pyromellitic acid and possessing five negative imine rings.

Polyimide resin is the most versatile of all high heat-resistant polymers. It can create various sensors such as polypyromellitic acid imide and other kinds of sensors, and it can also make it multifunctional, so its use is so wide. Although the use of polypyromellitic acid imine is greatly restricted because it does not melt, it has been successfully developed and only needs to sacrifice its heat resistance slightly to create a polyamide that can be melted or melted with a solvent. After the amine, its use soon became widespread.

For the polyimide resin used in PCB printed circuit boards, in addition to heat resistance, attention should be paid to issues such as formability, mechanical properties, dimensional stability, electrical properties, and cost. Therefore, there are many restrictions on its use. For these reasons, only a few addition polymerization type thermosetting polyimides are currently used for multi-layer printed circuit boards with more than ten layers.

However, it is believed that the dosage will continue to increase in the future, as shown in the table below. In addition, the bottom protective film of the flexible circuit board is still polypyromellitic acid imide currently used.

The conductors used in printed circuit boards are all made of thin foil-like copper. It is the so-called copper foil. According to its manufacturing method, it can be divided into electrolytic copper foil and rolled copper foil.

Function Purpose Purpose

Leading circuit The connection between rigid PCBs, three-dimensional circuits, movable circuits, and high-density circuits. Commercial electronic equipment, car dashboards, printers, hard disk drives, floppy disk drives, fax machines, car mobile phones, general phones, notebook computers, etc.

Printed circuit High-density thin three-dimensional circuit Cameras, camcorders, CD-ROMs, hard disks, watches, etc.

Connector Low-cost connection between hard boards Various electronic products

Multifunctional integration system, integration of hard board lead wires and connectors, computers, cameras, medical equipment.