Step 5 in PCB mass production: Lamination

　　As the name suggests, lamination refers to bonding the various layers of a PCB together, connecting the outer layers to the inner layers. This process is divided into two steps: layering and bonding. This step is a practical PCB manufacturing process, meaning that the green board (or other color) we see is formed after lamination. The basic form of a PCB consists of a laminate, the core material of which is epoxy resin and fiberglass, also known as the substrate material. Copper-clad laminate is a specific type of laminate used in PCB production, as mentioned above. In this step, we need to use a new raw material - prepreg. This material has good insulation properties and can help bond the core board to the outer copper foil.

　　Layering

　　In the inner layer structure of the PCB, the lower copper foil and two layers of prepreg are pre-fixed through alignment holes and the lower iron plate. Then, the prepared core board is placed in the alignment holes, and two layers of prepreg, one layer of copper foil, and one layer of pressure-resistant aluminum plate are covered on the core board.

　　Bonding

　　After lamination, the printed circuit board clamped by the iron plate is placed on a fixture and then sent to a vacuum press for lamination. High temperature melts the epoxy resin in the prepreg, and finally, under atmospheric pressure, the core board and copper foil are fixed together.

　　After the above procedures are completed, the upper iron plate and pressure-resistant aluminum plate of the PCB are removed. At this time, both sides of the PCB will be covered with a layer of smooth copper foil, and the lamination process is completed. It should be noted that in addition to its pressure-bearing function, the aluminum plate also plays the role of isolating different PCBs and flattening the outer copper foil of the PCB.

　　Step 6 in the PCB manufacturing process: Drilling

　　First, it is necessary to drill through the entire printed circuit board, and then metallize the hole walls to conduct electricity. To find these tiny holes, precise X-ray drilling equipment is needed to accurately locate the PCB core. After finding the hole position on the copper-clad laminate, positioning holes need to be drilled on the PCB to ensure that the drill passes through the center of the hole. In addition, in order to prevent tearing the copper foil on the PCB during drilling, a layer of aluminum plate needs to be covered on the upper and lower layers of the circuit board. Finally, the entire board is placed in a punching machine for punching. To improve the efficiency of PCB manufacturing, we usually stack several identical PCBs together for drilling.

　　Step 7 in the PCB manufacturing process: Panel Plating

　　The connection between different layers of the circuit board is achieved through holes. After drilling, plating is required. A good connection, in the opinion of Feixiang Technology, is a copper film thickness greater than 25 microns on the hole wall. However, since the hole wall is composed of non-conductive epoxy resin and fiberglass board, this poses great difficulties for plating. Therefore, we need to put the PCB into a copper plating tank containing sulfuric acid and copper sulfate, so that a layer of conductive material is deposited on the hole wall. When we pass electricity into the solution, copper is deposited on the surface of the conductive material of the circuit board. After copper plating, tin plating is also required. The plating on the surface of the PCB is an etching barrier.

　　The process of transferring the outer layer PCB layout to the copper foil requires the use of a photoresist film and a photosensitive film, similar to the principle of transferring the inner layer copper-clad laminate layout. The difference is that in the outer layer PCB layout transfer, the solidified position of the photosensitive film is not the circuit. Copper plating is required first, and then tinning is performed on the uncoated areas. After electroplating, the film and tin are removed. Due to the protection of the tin, the circuit pattern is retained on the PCB.

　　Step 8 in the circuit board manufacturing process: Secondary Inspection

　　For circuit boards, after production, the important thing is the wiring. We know that bare boards cannot work independently. The working principle of a PCB is to achieve electrical connection between components through wiring to complete various instructions, so secondary AOI inspection of the wiring is required. The secondary inspection of the PCB is the same as the previous AOI inspection method, so it will not be introduced here.

　　The final step in the PCB manufacturing process: Outer Layer Processing

　　The layers that make up a PCB include the silkscreen layer, the solder mask layer, the copper layer, and the substrate layer. The content of the inner layer has been described above, but this section mainly explains the external part of the PCB layer - the silkscreen layer and the solder mask layer.

　　Applying the solder mask is an important part of the PCB manufacturing process because it protects the PCB. Before applying the solder mask to both sides of the board, the PCB must first be cleaned and covered with epoxy solder mask ink.

　　In terms of cleaning, Feixiang Technology uses cleaning processes such as acid washing and ultrasonic cleaning to remove oxides from the board surface and increase the roughness of the copper surface. After the cleaning process is completed, the production of the PCB solder mask begins, and the process flow is as follows:

　　Cover the areas where no soldering is needed with solder mask ink → Dry the solvent in the solder mask ink → Use a UV lamp to irradiate the hardened solder mask ink to form a polymer → Remove the unpolymerized ink with a sodium carbonate solution → Secondary drying.