Rigid Flex PCB Fabrication

Rigid flex pcb is a board that combines flexible and rigid board technology in applications. Most rigid flexible boards consist of multilayer flexible circuit boards that are externally and / or internally attached to one or more rigid boards, depending on the design of the application. The flexible substrate is designed to be in a constant flexure state and is usually formed as a flexure curve during fabrication or installation.

Rigid flex PCB provides a wide range of applications from smart devices to mobile phones and digital cameras. Rigid flexible bonding plates are increasingly used in medical devices, such as pacemakers, to save space and reduce weight. The same advantages of rigid flexible printed circuit board can be applied to intelligent control system.

Rigid flex pcb manufacturing – steps

Rigid flex pcb manufacturers assemble circuit boards according to the following steps.

1. Preparation of the base material – the first step involved in circuit board manufacturing is to prepare / clean the laminate. Laminates containing copper layers (with or without adhesive coating) must be thoroughly cleaned prior to other processing. It is very important that the pre etch ring is provided by the supplier for rust protection. However, this kind of coating is an obstacle to the manufacture of rigid flexible PCB, so it must be removed.

In order to remove the coating, PCB manufacturers usually perform the following steps.

1) First, the copper coil is completely immersed in acid solution or exposed to acid mist.
2) The copper coils were then micro etched by sodium persulfate treatment.
3) Finally, the coil is fully coated with an appropriate type of oxidant to prevent adhesion and oxidation.

2. Generate the circuit pattern – the next step is to generate the circuit pattern and then prepare the laminate. Nowadays, two main techniques are used to complete the exposure of circuit patterns, for example:

1）screen printing – this technology is very popular because it can directly generate the required circuit patterns / deposits on the surface of the laminate. The total thickness does not exceed 4-50 microns.
2）image imaging – image imaging is the oldest method, but it is still the most commonly used technique to depict the routing of circuits on laminates. In this method, the dry photoresist film composed of the required circuit is in close contact with the laminate. The assembly is then exposed to ultraviolet light, which helps to transfer the pattern from the photomask to the laminate. The film is then chemically removed, leaving a laminate with the desired circuit pattern.

3. Etch circuit pattern – after the circuit pattern is generated, the copper laminate containing the circuit pattern is etched. The flex manufacturer can dip the laminate into the etching bath or spray it with an etchant solution. Both sides of the laminate are etched simultaneously to obtain the desired results.
4. Drilling process – it’s time to drill the required number of holes, pads and through holes. High speed drilling tools are used to make precision holes. In order to make ultra-small holes, rigid flexible circuit board manufacturers use laser drilling technology. Excimer YAG and CO2 lasers are usually used to punch holes in substrates.
5. Through hole plating – this is one of the key steps in the manufacturing process of rigid flexible PCB, which must be carried out extremely accurately and carefully. After drilling holes of the required specifications, they are deposited on copper and electroless plated. This is done to form layer to layer electrical interconnects.
6. Capping or capping – it is important to protect the top and bottom of the flexible circuit through the capping. This is to provide comprehensive protection for the circuit from adverse weather conditions, harsh chemicals and solvents. In most cases, manufacturers use polyimide film with adhesive as covering material. The surface material is imprinted on the surface by screen printing, and then cured by ultraviolet exposure. To ensure proper adhesion of the cladding material to the substrate, the cladding is laminated under specified heat and pressure limits. Unlike the coating material used as a laminating film, the coating is a material literally applied to the surface of the substrate. As well as the material used, it must be based on the field of manufacture. Both cladding and cladding enhance the electrical integrity of the entire assembly.
7. Cutting flexible panels – punching or cutting individual flexible panels from the production panel is another important step that must be performed with care. In mass production of rigid flexible PCB, manufacturers usually choose hydraulic drilling method. However, due to the high cost of mold, there is no choice for prototype design or small batch production. When creating a prototype rigid flexible PCB in small batch production, a special blanking knife is used.
8. Electrical testing and verification – the final stage of rigid flexible circuit board manufacturing is testing and verification. The circuit board has undergone strict electrical testing to ensure that it does not violate the continuity, isolation, circuit performance and quality of the design specifications. A variety of test methods are used, including grid test and flying needle test.

Rigid flexible PCB is greatly replacing traditional rigid pcb in many applications. Because the quality of PCB determines the integrity of the entire electrical components, it is necessary to maintain high quality in the manufacturing process. Small design or manufacturing defects can seriously affect the performance, function and durability of the final product. Therefore, PCB manufacturers must be very careful from planning, design to material selection, manufacturing and testing. This helps to produce circuit boards with excellent performance and unparalleled reliability.