The process of PCB manufacturing can be complex which involves a lot of steps. The PCB can be single layer, double or multi-layer based on their usage and applications and depending on this there can be multiple steps that are involved in creating the PCBs. Skipping any one step can prove costly to the final electronic product but when done properly it can fulfill the needs in an electronic application.
What are the parts of PCB?
PCB has 4 main parts
Substrate: Substrate act as the skeleton in the final product. They are mainly made of high-quality fiberglass, that provides the strength to the PCB and prevents breakage.
Copper layer: Copper layer or coper foil can be used depending on the type of application and like metal, its primary use to carry electrical signals to and fro the PCB.
Solder Mask: Solder mask is a layer of polymer on the top of copper to prevent any short circuit that happens if the copper comes in contact with the outer environment.
Silkscreen: Silkscreen is given on the top of solder mask and is primarily for nomenclature details like number, logos, settings symbols, test points etc.
How is the PCB manufactured?
Now that we know the parts of PCB, its time to know more about the process of manufacturing the same. As told above, depending on the complexity and application the process steps differs and its mandatory to follow each and every step for the best results.
The inside of the PCB uses
Black Ink-For copper traces and circuits of PCB
Clear Ink- For the nonconductive areas like fiberglass.
The outside
The outside of the PCB the color trend will be reversed.
Each PCB layer & accompanying solder mask will get its own film. After the film is printed the sheets are lined up and a hole called registration hole is punched through them, which is used as a guide to align the films later on.
Once the resist and laminate are lined up using the registration hole they receive a blast of UV light, the light passes through the translucent material which helps to harden the photoresist. The black ink doesn’t prevent the light from getting into areas that shouldn’t be hardened.
After the board has been prepared its washed with alkaline solution to remove any photoresists and the board is pressure washed to remove anything left on the surface of the board and left to dry. After drying the only resist should be on the top of copper. Finally, the technical looks over the PCB for any flaws or errors.
Once the outer and inner layers are ready, they should be sandwiched together to get the final picture. For this a special type of table is used on which each layer is secured with a pin and special metal clamps are used. A layer of pre-impregnated epoxy resin is placed followed by a layer of substrate then a copper foil layer. The copper layer is followed by many layers of pre-impregnated resin, finished off with a copper plate called press plate.
Pins are pressed through the sheet to ensure that the layers stay intact. After the copper plate is placed next step is to the stack to be pressed which is done using a mechanical press. The stack is then taken to the laminating press where heat and pressure is applied to the stack. Heat causes the resin to melt and pressure applied causes the layers to press and fuse together. After the layers are pressed together the top press plates & pins are removed.
10. PCB plating- Plating uses different types of chemicals to fuse the layers together. The process called as bathing is carried out where the PCB layers are bathed in a series of chemicals. In bathing process, the panel is coated with a micron thick layer of copper.
11. Outer Layer Imaging- In step 4, a photo resist was applied to the PCB panel, similarly here also a photoresist coating needs to be applied. But this time only the outer layer needs to be coated as they are the ones to be imaged and plating is done using tin to secure the copper of outside layer.
12.Outer layer etching- The outer tin covering act as a covering for the copper layer from etching. Any unwanted copper is removed using the solvent as before. Previously for inner layer etching dark ink is used for conductive areas and light ink for non-conductive areas, these ink are reversed for outer layers. The non-conductive area has dark ink and conductive area has light ink. The light ink allows the tin plating to cover and protect the copper.
13. Outer layer AOI- As done with the inner layer, the outer layer too must go through the set of inspections. Any unwanted coating is checked along with the design specifications. It will only go through the next steps if all the conditions needed to perfect the design are met.
14. Solder mask application- Once the panel is clean, they will now go through solder mask application. Each panel has epoxy resin and solder mask fil covering. UV light is used to check where the solder mask need to be removed. Once the unwanted solder mask is removed, its taken to an oven to cure the mask, this mask provides extra protection for the copper from corrosion and oxidation.
15.Silk screen application- All the vital data should be written on the board itself for better convenience and is also called legend printing. The data to be given include
Using an inkjet printer the information is printed on the board and is proceeded for further steps.
16.Finishing the PCB- Finishing requires to be done using conductive material like below ones
17. Electrical reliability test- Once the coating and curing is done, different electrical tests are conducted to check the reliability. Electrical testing should adhere to standards of IPC-9252. One test is circuit continuity test and other one is isolation test. The continuity test checks for any circuit disconnections. The isolation test checks for isolation values of PCB parts to check for any shorts.
18.Profiling & route out- profiling will identify shape & size of the PCBs. Routing out or scoring allows the easier separation of boards. A router or CNC machine creates several small pieces along the edge of the board so that it can quickly break off without damage.
19.Quality check and inspection- PCB again undergoes final inspection. It checks for whether the hole size are matching for all layers, the board have its specific dimensions, clean and dust free, not having sharp edges.
20.Packaging & Delivery- Packaging involves material that seals the board from dust and foreign particles. The sealed boards are then put in containers that protect them damage from shipping.
PCB manufacturing is no piece of cake, it involves a lot of articulate steps that need to be followed. We design our processes to accommodate all type of printed circuit board assembly, whether they are thin, thick, or flexible, small or large, single sided or double sided, single layered or multi-layered or even mixed technology. With our connections to the large PCB manufacturers in the Far East we can provide you with PCB assemblies that use the best quality PCB’s at the lowest cost New Paragraph