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: Single Layer Flexible PCB FPC Service Ranging Prototype
to Mass Production
(Flexible printed circuits are custom-made products, the picture
and parameters shown are just for reference)
General description
This is a type of flexible printed circuit for the application of
Embedded System. 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. FR-4 as stiffener is applied on the bottom
side.
Parameter and data sheet
| Size of Flexible PCB | 90.9 X 50.28mm |
| Number of Layers | 1 |
| Board Type | Flexible PCB |
| Board Thickness | 0.15mm |
| Board Material | Polyimide 25µm |
| Board Material Supplier | ITEQ |
| Tg Value of Board Material | 60℃ |
| |
| PTH Cu thickness | ≥20 µm |
| Inner Iayer Cu thicknes | N/A |
| Surface Cu thickness | 35 µm |
| | |
| Coverlay Colour | Yellow |
| Number of Coverlay | 2 |
| Thickness of Coverlay | 25 µm |
| Stiffener Material | FR-4 |
| Stiffener Thickness | 1.0mm |
| | |
| 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
Excellent flexibility
Reducing the volume
Weight reduction
Consistency of assembly
Increased reliability
Controllability of electrical parameter design
The end can be whole soldered
Material optionality
Low cost
Continuity of processing
Diversified shipping method
Customer complaint rate: <1%
Application
Instrument panel, mobile phone module flex board, Tablet PC camera
soft board
Quality Policy
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.
Contract Evaluation
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.
Customer Service
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.
