Components of a flexible circuit
A flexible circuit consists of copper foil, dielectric substrate+ coverlay and adhesive.
Copper foil is available in two different types of copper: ED Copper and RA copper.
ED copper is an electro-deposited (ED) copper foil produced in the same way as the copper foil used for rigid printed circuit boards. This also means that the copper is “treated”, i.e., it has a slightly rough surface on one side, which ensures a better adhesion when the copper foil is bonded to the base material.
RA copper is a rolled and annealed copper foil produced from electrolytically deposited cathode copper, which is melted and cast into ingots. The ingots are first hot-rolled to a certain size and milled on all surfaces. The copper is then cold-rolled and annealed, until the desired thickness is obtained.
Copper foil is available in thickness of 12, 18, 35 and 70 μm.
The most common available for dielectric substrate and coverlay is polyimide films. This material can also be used as coverlay. Polyimide is best suited for flexible circuits because of its characteristics as stated below:
High temperature resistance allows soldering operations without damaging the flexible circuits
Very good electrical properties
Good chemical resistance
Polyimide is available in thicknesses of 12.5, 20, 25 and 50 μm.
Base laminates for rigid printed circuit boards are copper foils laminated together with the base materials, the adhesive coming from the prepreg material during lamination. Contrary to this is the flexible circuit where the lamination of the copper foil to the film material is achieved by means of an adhesive system. It is necessary to distinguish between two main systems of adhesive, namely thermoplastic and thermoset adhesives. The choice is dictated partly by the processing, and partly by the application of the finished flexible circuit.
FPC Case: Multilayer Flexible PCB With Immersion Gold at 0.2mm Thick
(Flexible printed circuits are custom-made products, the picture and parameters shown are just for reference)
This is a type of 4 layer flexible printed circuit for the application of Wireless Intercom at 0.2mm thick. The base laminate is from ITEQ, It’s fabricated per IPC 6012 Class 2 using supplied Gerber data.
Parameter and data sheet
|Size of Flexible PCB ||70.58 X 120.37mm |
|Number of Layers ||4 |
|Board Type ||Flexible PCB |
|Board Thickness ||0.20mm |
|Board Material ||Polyimide 25µm |
|Board Material Supplier ||ITEQ |
|Tg Value of Board Material ||60℃ |
|PTH Cu thickness ||≥20 µm |
|Inner Iayer Cu thicknes ||35 µm |
|Surface Cu thickness ||35 µm |
| || |
|Coverlay Colour ||Yellow coverlay / Green solder mask |
|Number of Coverlay ||2 |
|Thickness of Coverlay ||25 µm |
|Stiffener Material ||no |
|Stiffener Thickness ||N/A |
| || |
|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 |
|RoHS Required ||Yes |
|Famability ||94-V0 |
|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
Controllability of electrical parameter design
The end can be whole soldered
Continuity of processing
Provide small quantity, prototypes and production.
Engineering design prevents problems from occurring in pre-production.
Touch screen, consumer card reader soft board, tablet keypad flex board
Bicheng has developed series of management procedures and approaches to assure that PCBs are in compliance with the customers' requirements, inclusive of selection of the vendors, work in progress (WIP) inspection, outgoing delivery inspection and customer service etc.
Evaluation and Audit of Suppliers
Suppliers have to be evaluated by Bicheng. In addition, Bicheng will appraise and rank suppliers every year to guarantee the materials supplied are meeting Bicheng’s requirements. Furthermore, Bicheng continuously develop suppliers and supervise them to improve their quality and environment management basing on the systems of ISO9001 & ISO14001.
Bicheng shall review and verify customer's requirements to make sure that we have the capability to satisfy customers' requirements including specifications, delivery and other demands prior to accepting an order.
Making, audit and control of manufacturing data.
When customers' design data and specifications are provided to our market department, Bicheng has to verify all the requirements. Then, convert the design data into manufacturing data by CAM. Finally, a manufacturing instruction (MI) is generated according to the real manufacturing process and technologies for manufacturing department as the basis for actual fabrication. MI must be reviewed by independent engineers and QA engineers before issue.
Incoming Material Quality Control
All materials have to be inspected before warehousing. We established a series of strict inspection procedure and instruction to control the incoming materials. Furthermore, various precise inspecting instruments and apparatus guarantee the capability to judge the material good or not. We issue material with first in first out principle, and give out “alarm” for the material that will reach the shelf life to ensure the materials are used up before expiry.
Control of Production Process
Right manufacturing instruction (MI), comprehensive equipment management and maintenance and process control, strict WIP inspection and monitoring as well as working instruction, all those make the whole fabrication process totally controlled.
Final Control and Inspection
All PCBs have to be gone through the open and short test as well as visual inspection after passed the specified physical tests. We own various advanced test equipment including customized, probe flying test machines to guarantee that each PCB is 100% tested.
Product Delivery Audit
We set up a dedicated FQA department to inspect the PCB products according to the customer's specifications and requirements by sampling. Qualified PCBs are going to be packed.
FQA also has to carry out a 100% audit of the warehouse packing and shipping products, including product number, customer number, product quantity, shipping address and so on prior to shipment.
We sets up a professional customer service team to proactively communicate with customers and timely deal with the customers' feedbacks. We highly focus on customers' needs and to understand customers’ demands, timely to adjust the policy of customer service and PCB product requirements.