A breakdown of a flexible circuit shows that it consists of 3 basic elements: copper foil, dielectric material and adhesive. Most of the manufacturing proceses, i.e. imaging transfer, plating and etching , are quite similar to those used when producing plated-through boards. However, there're differences due to the thin and floppy material used in flexible circuits.
Purpose of Flexible Circuits
1) To provide interconnections between printed circuit boards and other components.
2) To serve as three-dimensional substrates for the mounting of SMT components, e.g., in
photographic and video cameras.
3) To establish interconnections capable of withstanding dynamic flexing.
4) To form part of rigid-flex circuit boards.
2) Volume decreases
3) Weight reduces
4) Consistency of SMD mounting
5) Reliability increases
6) Controllability of electrical design of parameters
7) Tin soldered overall on the FPC end
8) Material optional (PI, PET)
9) Low cost
10) Continuity of processing
Thin-film switch, capacitive touch screen / panel, keypad FPC, laser head FPC,
General purpose LED soft light strip, mobile phone built-in antenna FPC Touch screen,
Telephone receiver / earphone FPC, contact belt of inkjet printer, Toy lamp strip,
LCD module, instrument panel, flexible flat cable, display backlight etc.
Flex PCB Capability
|1||Board Type||Single layer, Doulbe layer, Multilayer, Rigid-Flex|
|2||Base Material||PI, PET|
|3||Copper Weight||0.5oz, 1oz, 2oz|
|4||LED Maximum Size||250 x 5000mm|
|5||General Maximum Size||250 x 2000mm|
|8||Mininum Drill Hole||0.05mm|
|9||Maximum Drill Hole||6.5mm|
|10||Tolerance of Drill Hole||±0.025mm|
|11||Thickness of Hole Wall||≧ 8 um|
|12||Minimum Track/Gap of Single Layer Board||0.025/0.03mm|
|13||Minimum Track/Gap of Double Layer and Multilayer Board||0.03/0.040mm|
|15||Minimum Width of Silk Legend||≧ 0.125mm|
|16||Minimum Heigh of Silk Legend||≧0.75mm|
|17||Distance from Legend to Pad||≧0.15mm|
|18||Distance from Opening Solder Mask of Drill Coverlay to Track||≧0.03mm|
|19||Distance from Opening Solder Mask of Punching Coverlay to Track||≧0.03mm|
|20||Thickness of Immersion Nickel||100-300u"|
|21||Thickness of Immersion Gold||1-3u"|
|22||Thicnkess of Immersion Tin||150-400u"|
|23||Minimum Electrical Testing Pad||0.2mm|
|24||Minimum Tolerance of Outline(Normal Steel Mould Punch)||±0.1mm|
|25||Minimum Tolerance of Outline (Precision Steel Mould Punch)||±0.05mm|
|26||Mininum Radius of Bevel Angle (Outline)||0.2mm|
|27||Stiffner Material||PI, FR-4, 3M Adhesive, PET, Steel Sheet|
|29||Solder Mask Colour||Yellow, White, Black, Green|
Payment & Shipping Terms:
|Board Material:||Polyimide 25µm||Board Thickness:||0.15 Mm|
|Surface/Inner Layer Cu Thickness:||35 µm||Surface Finish:||Immersion Gold|
|Coverlay Colour:||Yellow||Color Of Silkscreen:||White|
|Function:||100% Pass Electrical Test||Number Of Layers:||1|
Single Sided Flexible PCBs Made On PI Material With 3M Tape and Immersion Gold for Keypad Application
(Flexible printed circuits are custom-made products, the picture and parameters shown are just for reference)
This is a type of flexible printed circuit for the application of calculator keypad. It’s a single layer FPC at 0.15mm thick. The base laminate is from ITEQ, It’s fabricated per IPC 6012 Class 2 using supplied Gerber data. Polyimide stiffener is applied on the inserting part.
Parameter and data sheet
|Size of Flexible PCB||30.53 X 59.37mm|
|Number of Layers||1|
|Board Type||Flexible PCB|
|Board Material||Polyimide 25µm|
|Board Material Supplier||ITEQ|
|Tg Value of Board Material||60℃|
|PTH Cu thickness||N/A|
|Inner Iayer Cu thicknes||N/A|
|Surface Cu thickness||35 µm|
|Number of Coverlay||2|
|Thickness of Coverlay||25 µm|
|Type of Silkscreen Ink||IJR-4000 MW300|
|Supplier of Silkscreen||TAIYO|
|Color of Silkscreen||White|
|Number of Silkscreen||1|
|Peeling test of Coverlay||No peelable|
|Legend Adhesion||3M 90℃ No peeling after Min. 3 times test|
|Surface Finish||Immersion Gold|
|Thickness of Nickle/Gold||Au: 0.03µm(Min.); Ni 2-4µm|
|Thermal Shock Test||Pass, -25℃±125℃, 1000 cycles.|
|Thermal Stress||Pass, 300±5℃,10 seconds, 3 cycles. No delamination, no blistering.|
|Function||100% Pass electrical test|
|Workmanship||Compliance with IPC-A-600H & IPC-6013C Class 2|
Features and benefits
Reducing the volume
Consistency of assembly
The end can be whole soldered
Continuity of processing
Professional and experienced engineers
More than 15 years of experience
Touch screen, LED display soft board, Tablet antenna soft board
Structure of FPC
According to the number of layers of conductive copper foil, FPC can be divided into single layer circuit, double layer circuit, multi-layer circuit, double sided and so on.
Single-layer structure: the flexible circuit of this structure is the simplest structure of the flexible PCB. Usually the base material (dielectric substrates) + transparent rubber(adhesive) + copper foil is a set of purchased raw materials(semi-manufactures), the protective film and transparent glue are another kind of bought raw material. First, copper foil must be etched to obtain the required circuit, and the protective film should be drilled to reveal the corresponding pad. After cleaning, the two are combined by rolling. Then the exposed part of the pad electroplated gold or tin to protect. In this way, the big panel board will be ready. Generally also it’s stamped into the corresponding shape of the small circuit board. There is also no protective film directly on the copper foil, but printed resistance soldering coating, so that the cost will be lower, but the mechanical strength of the circuit board will become worse. Unless the strength requirement is not high and the price needs to be as low as possible, it is best to apply the protective film method.
Double layer structure: when the circuit is too complex to be wired, or copper foil is needed to shield the ground, it is necessary to choose a double layer or even a multilayer. The most typical difference between a multilayer and a single plate is the addition of a perforated structure to connect the layers of copper foil. The first process of transparent rubber + base material + copper foil is to make holes. Drill holes in the base material and copper foil first, clean and then plated with a certain thickness of copper. The subsequent fabrication process is almost the same as the single-layer circuit.
Double sided structure: both sides of the double sided FPC have pads, mainly used to connect other circuit boards. Although it and monolayer structure is similar, but the manufacturing process is very different. Its raw material is copper foil, protective film and transparent glue. The protective film should be drilled according to the position of the pad first, then the copper foil should be affixed, the pad and track lines should be etched and then the protective film of another drilled hole should be affixed.