PCB Tech - Rigid flexible circuit board processing technology

As the name suggests, rigid-flex printed circuit boards undergo a manufacturing process that combines rigid and flexible circuit boards. The two boards are then permanently interconnected to form various types of PCBs. In the manufacturing process of rigid-flex circuit boards, certain factors and precision must be considered in order to produce a perfect final product.
Some of the more important considerations are:
l Laser contour cutting
l Selective pad plating
l Material size tolerance
l Thin material handling capacity and procedures, and
l Plasma decontamination and etchback
Compared with traditional rigid PCBs, flexible substrate materials used to manufacture rigid-flex PCBs have more advantages. they are:
l Lighter weight
l can be used to interconnect components,
l Smaller thickness
l Dynamic bending
l Save more space,
l has excellent electrical and thermal properties,
l Just to name a few, it has a high degree of freedom in electronic design and mechanical design.

The steps involved in the rigid Flex design and manufacturing process
1. Preparation of basic materials:
The first step in the rigid-flex manufacturing process is to prepare/clean the laminate. The laminate contains a copper layer (with an adhesive coating) and must be thoroughly cleaned before proceeding to the next step. Basically, the pre-cleaning is to remove the anti-rust layer of the copper coil that the supplier uses to prevent oxidation. To remove the coating, the manufacturer performs the following steps:
l First, immerse the copper coil in a concentrated acid solution.
l Sodium persulfate treatment is used for micro-etching copper coils.
l Use a suitable oxidizer to coat the copper coils to provide adhesion and anti-oxidation protection
2. Circuit pattern generation
After preparing the basic materials, the next step is to generate circuit patterns. This is done using two main techniques:
l Screen printing: This is the most popular technology. It creates the desired pattern directly on the surface of the laminate. The maximum total thickness is 4-50 microns.
l Photographic imaging: This technology is the oldest technology, usually used to describe the circuit traces on the laminate. The pattern is transferred from the photomask to the laminate using a dry photoresist film and ultraviolet light.
3. Etching the circuit pattern
After generating the desired pattern, the copper laminate is then carefully etched. This process can be done by immersing the laminate in an etching bath or by exposing it to an etchant spray. In order to obtain perfect results, both sides of the laminate must be etched at the same time.
4. Drilling process
High-speed tools with 100% accuracy can be used to make a large number of holes, pads and through holes. Laser drilling technology is used for ultra-small holes.
5. Through hole plating
This process is very precise and careful. The drilled holes are precisely deposited with copper and electrolessly plated to form an electrical interconnection layer.
6. Apply a covering layer or covering layer.
A cover layer is applied to protect the top and bottom sides of the rigid-flex circuit board. Its main purpose is to provide comprehensive protection for the circuit board from harsh physical and chemical conditions. Usually a polyimide film is used and it is imprinted on the surface using screen printing technology.
7. Cut out the flex Carefully cut and unload a single flexible PCB board. For PCB mass production, hydraulic drilling is used, while special knives are used in small batch production.
8. Electrical testing and verification.
Testing and verification is the last and final step. The integrity of the rigid-flex circuit boards must be evaluated, because even the slightest defect can seriously affect the function, performance and durability of the final rigid and flexible circuit.