Flex PCB Fabrication process

Almost all of the flex PCB fabrication was done using the etching method. Commonly, a copper-covered foil plate is used as the starting material to form an anti-corrosion layer by photolithography, and the circuit conductor is formed by etching away the unnecessary copper surface. Due to problems such as side erosion, the etching method has a restriction on machining fine circuits.

The flex PCB fabrication method is difficult to fabricate or maintain a high qualification rate of microcircuits. It is an effective method for flex PCB fabrication to pass the half-addition method, which is the step to form the first layer of circuits.

When Flex PCB Fabrication is coated with photosensitive polyimide resin on the first circuit layer, the hole and protective layer or insulating layer used for the second circuit layer are formed by photolithography, and then the crystalline layer is sputtered to form the substrate conductive layer for the second circuit layer. If the above process is repeated, a multilayer circuit can be formed.

Flex PCB Fabrication Engineers used this semi-addition method to create ultrafine circuits that were key to the performance of the photosensitive polyimide resin used as an insulating layer.

Common defects in flex PCB fabrication

The unclean pressing environment in Flex PCB fabrication may result in bottom material sag and road break, and debris in the air may stain the surface of Flex PCB. Therefore, the timely removal of dirt during flex PCB fabrication is the first priority to keep the environment clean.

In the process of Flex PCB fabrication, poor dry film operation resulted in thin lines and high road breaks in some small areas. Screen printing positioning is not firm, under-exposure will lead to FPC gaping and cracking, screen printing does not pay attention to the printing paper, does not get rid of residual ink, and so on, resulting in an uneven FPC surface. You need to fix the paper with positioning pins, control the exposure time, and timely remove the ink from the screen. Strictly following the Flex PCB fabrication process is the second priority.

In flex PCB fabrication, it is also necessary to control the current in the plating process to avoid bubbles and flickering. After the Flex PCB fabrication is completed, the pre-factory test phase is entered to ensure that the Flex PCB reaches the applicable standard. The use of the shrapnel microneedle module can greatly improve the test efficiency of the FPC and provide a stable connection and conduction.

What is the process of double-sided flex PCB fabrication?

1. FPC opening material
With the exception of some materials, Flex PCB materials are basically rolled. Flexible copperioclad laminate has poor bearing capacity for external forces and is easily injured. If Flex PCB fabrication is a small order, manual shears or hob cutters could be used, and automatic shears could be used for large quantities.

2. FPC drills through holes
As with rigidly printed boards, you can drill through holes digitally for Flex PCB fabrication, but not for winding double-sided metallized circuits. These new drilling techniques include plasma etching, laser drilling, micro-hole drilling, chemical etching, etc. These drilling techniques are easier to meet the requirements of the winding process than CNC drilling.

3. Hole metallization
Hole metallization for flexible PCB fabrication is basically the same as hole metallization for rigid printed circuit boards. In recent years, the direct electroplating process using carbon conductive layer technology has been developed instead of electroless plating. This technology was also introduced in the metallization of holes in Flex PCB fabrication.

4. Cleaning of the copper foil surface
In order to improve the adhesion of the anti-corrosion mask, the copper foil surface should be cleaned before applying the anti-corrosion mask. Even such a simple process requires special attention for flexible PCB fabrication.

Flex PCB fabrication is different from copper plating

Copper deposition in Flex PCB fabrication is a chemical reaction, and copper plating is an electrolytic reaction. In Flex PCB fabrication, copper plating is mainly used to conduct wiring, while copper plating is also used to thicken board surfaces and hole walls. The difference between copper plating and copper plating for flex PCB fabrication is:
1. The electroless copper plating for Flex PCB fabrication was on a surface with catalytic activity, and copper ions were reduced and precipitated through the role of a reducing agent. In addition to thermodynamics, the chemical reaction must meet the dynamic conditions.

2. The smooth electroplating process of Flex PCB fabrication needs to meet such conditions as an electroplating power supply, plating solution, workpiece, and plate. With the above-mentioned things, assembly is sufficient.

What are Flex PCB fabrication materials?

With the development of electronic products toward being short, small, light, and thin, the demand for FPC is on the rise. What are the raw materials required for Flex PCB fabrication?

1. Raw materials in Flex PCB fabrication include:
(1) Glue material exists or does not exist.The copper on the material is divided into electrolytic copper and calendered copper. The calendered copper without glue has better flexibility and foldability.
(2) Material thickness: PI + copper thickness

2. The covering film is composed of PI and glue.

3. Reinforcement for Flex PCB fabrication is generally as follows: PI reinforcement, PED reinforcement, FR4 reinforcement, steel sheet reinforcement, etc. Generally, the thicknesses of reinforcement include PI1/2, PI11, PI21, PI31, and PI91. The two-digit values after PI respectively represent the thickness of PI and the thickness of adhesive, in mils, according to customer requirements.

4. Pure adhesive is primarily used in the fabrication of multi-layer Flex PCBs, as well as bonding and reinforcement. 

5. The screen-closing film in Flex PCB fabrication mainly plays the role of signal screen-closing and should be grounded.

6. 3M adhesive reinforcement and FPC fixation in Flex PCB fabrication.

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