Nov. 07, 2019
The fabrication of PCB is very complicated. Take the four-layer printed board as an example. The manufacturing process mainly includes PCB layout, core board fabrication, inner PCB layout transfer, core board punching and inspection, lamination, drilling, and hole wall. Copper chemical precipitation, outer PCB layout transfer, outer PCB etching and other steps.
1, PCB layout
The first step in PCB fabrication is to organize and inspect the PCB layout. Then the PCB fabrication factory engineer will check whether the PCB layout conforms to the manufacturing process and whether there are any defects.
2, the production of core board
Cleaning the copper clad plate, if there is dust, may cause the last circuit to be shorted or open circuit.
3, the inner layer PCB layout transfer
First make the two layers of the most intermediate core board. After the copper clad plate is cleaned, a photosensitive film is placed on the surface. The two-layer PCB layout film and the double-layer copper-clad board are finally inserted into the upper-layer PCB layout film to ensure accurate film stacking position of the upper and lower layers of the PCB layout. The uncured photosensitive film is then washed away with lye, and the desired copper foil line will be covered by the cured photosensitive film. Then use a strong base to etch away the unwanted copper foil.
4, core board drilling and inspection
The core board has been successfully produced. Then, the alignment holes are made on the core board to facilitate alignment with other materials. Once the core board is pressed together with the other layers of the multilayer PCB, it cannot be modified, so the inspection is very important. The machine will automatically compare with the PCB layout drawing to see the error.
The lower layer of copper foil and the two layers of prepreg have been fixed in advance through the alignment hole and the lower iron plate, and then the prepared core plate is also placed in the alignment hole, and finally two layers of prepreg, a layer of copper foil and A layer of pressure-bearing aluminum plate covers the core. The PCB boards sandwiched by the iron plates are placed on the holders and then fed into a vacuum hot press for lamination. The high temperature in the vacuum hot press melts the epoxy in the prepreg and holds the core and copper foil under pressure.
To connect the four layers of copper foil that are not in contact with each other in the PCB, first drill the perforations through the top and bottom to open the PCB, and then metallize the holes to conduct electricity. Place a layer of aluminum on the puncher machine and place the PCB on top. In order to improve efficiency, 1 to 3 identical PCB boards are stacked together for perforation according to the number of layers of the PCB.
7. Copper chemical precipitation of the pore wall
A layer of conductive material is deposited on the walls of the holes, and a 1 micron copper film is formed on the entire surface of the PCB, including the walls of the holes, by chemical deposition.
8, the outer PCB layout transfer
Next, the outer PCB layout will be transferred to the copper foil. The process is similar to the previous inner core PCB layout transfer principle. The photocopying film and photosensitive film are used to transfer the PCB layout to the copper foil, the only difference. It will be a positive film.
9, outer PCB etching
First, the cured film on the PCB is washed away. The undesired copper foil covered by it is then washed away with a strong alkali. The tin plating on the PCB layout copper foil is removed by using tin-removing liquid.