Flexible printed circuits (FPC) is a circuit wiring flexible material. The advantage of flexible printed circuits(FPC) are thin, lightweight, and excellent heat resistance and durability. These contributed to make devices more compact, lighter and thinner. This review will provide a basic assessment of flexible printed circuits (FPC).
Single-sided flexible circuits (FPC)Single-sided flexible circuits (FPC) consist of a single conductor layer on a flexible film with access to circuit-termination features accessible from one side only. Single-sided flexible circuits (FPC) are manufactured with or without coverlays and protective coatings and highly cost effective.
Double-sided flexible circuits (FPC)Double-sided flexible circuits (FPC) is constructed by variou means such as separate conductors on both sides of the base film and printed conductors by printed insulating coverlays. The most popular flexible-circuit through-board interconnectivity technique is the plated through hole (PTH).
Multilayer flexible circuits (FPC)Multilayer flexible circuits (FPC) are conplex to construct and have high costs, and consist of bonded conductive layers that are interconnected by means of plated through-holes. A maxium of 25 layers means that over multiple layers laminate stress can cause through-hole interconnects to barrel and stretch, restricting their reliability.
Rigid-flex circuits are hybrid constructions consisting of rigid and flexible substrates laminated together. Like double-sided and multilayer circuits they make use of PTH interconnects where required.
Manufacturing process for double-sided FPCThe following feature of manufacturing process for double-sided FPC shows a typical manufacturing flow chart for double-sided FPC. After (1) basematerial cutting, (2) NC drilling, and (3) PTH, the process is fundamentally the same as with single-sided FPC. Circuit formation, insulation treatment, plating and other surface treatment steps are called the front-end process or upper process, and manufacturing is implemented in the form of rolls or fixed-sized sheets (worksheets).
Circuit formation is conducted using a photosensitive resin (etching resist) called "dry film" (DF) in a process of exposure, developing and etching. Insulation treatment is conducted by heat lamination with thermosetting adhesive on PI film where holes have been selectively opened as coverlay openings with a die or other device.
The photosensitive covercoat is formed through a process of exposure and developing that is the same as for circuit formation, followed by heat treatment and UV exposure. Nickel/gold, solder, or other material plating is applied to the exposed copper depending on the electroplating or electroless plating method. Anti-oxidation treatment is sometimes used instead of plating.
In the front-end process or lower process, worksheets are divded into sizes the are easy to treat.
Usually, after the application of stiffener and double-sided tape, the product form is finished by punching using a die. When the stiffener requires heat-resistance, heat lamination is done with a thermosetting type adhesive.
When heat-resistance is unnecessary, attachment is done with double-sided tape. Inspection is usually conducted on every piece and includes electrical inspection to detect if circuits are open or have shorts and visualinspection to check other things.
Recently, it has become common to do every step up to parts mounting, so more sophisticated inspection techniques are required.
|Manufacturing process for double-sided FPC|
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