As the name implies, rigid-flexible printed circuit boards are manufactured by the combination of rigid and flexible circuit boards. The two boards are then permanently interconnected to form various types of PCBs. In the manufacturing process of rigid and flexible circuit board, some factors and precision must be considered to produce the perfect final product.
Some more important considerations are:
L laser profile cutting
L selective pad plating
L material dimensional tolerance
L thin material handling capacity and procedures, and
L plasma decontamination and etching back
Compared with the traditional rigid PCB, the flexible substrate material used to manufacture rigid-flexible PCB has 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 To name a few, it has a high degree of freedom in electronic design and mechanical design.
Steps involved in the rigid design and manufacturing process of Flex
1. Preparation of basic materials:
The first step in the rigid-flexible manufacturing process is to prepare/clean the laminate. The laminate contains copper layer (with adhesive coating) and must be thoroughly cleaned before proceeding to the next step. Basically, pre-cleaning is performed to remove the rust-proof layer used by suppliers to coat copper coils to prevent oxidation. To remove the coating, the manufacturer performs the following steps:
First, immerse the copper coil in concentrated acid solution.
L Sodium persulfate treatment is used for micro-etching copper coils.
L Apply a suitable oxidant to the copper coil to provide adhesion and oxidation protection.
2. Generation of circuit pattern
After preparing the basic materials, the next step is to generate the circuit pattern. This is done using two main techniques:
L Screen printing: This is the most popular technology. It creates the required pattern directly on the surface of the laminate. The maximum total thickness is 4-50 microns.
L Photographic imaging: This technology is the oldest one, and it is usually used to depict circuit traces on laminates. The pattern is transferred from the photomask to the laminate by using the dry photoresist film and ultraviolet rays.
3. Etching the circuit pattern
After the required pattern is generated, the copper laminate is carefully etched next. This process can be carried out by immersing the laminate in an etching bath or exposing it to an etchant spray. In order to obtain perfect results, both sides of the laminate must be etched simultaneously.
4. Drilling process
High-speed tools with 100% accuracy can be used to manufacture 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. Copper is accurately deposited in the drill hole, and chemical plating is performed to form an electrical interconnection layer.
6. Apply a covering layer or coating layer.
A cover layer is applied to protect the top and bottom sides of the rigid-flexible printed 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 off Flex
Carefully cut and blank individual flexible boards. For batch production, hydraulic drilling is used, while special knives are used in small batch production.
8. Electrical testing and verification.
And testing and verification is the last and final step. Rigidity-the integrity of flexible printed circuit board must be evaluated, because even the slightest defect will seriously affect the function, performance and durability of the final rigidity and flexibility.
