Chemical precipitation of copper on the hole wall
Since almost all PCB designs use perforations to connect different layers of lines, a good connection requires a 25-micron copper film on the hole wall. The thickness of the copper film needs to be achieved by electroplating, but the hole wall is composed of non-conductive epoxy resin and glass fiber board. PCB manufacturer shares with you.
So the first step is to deposit a layer of conductive material on the hole wall, and form a 1 micron copper film on the entire PCB surface, including the hole wall, by chemical deposition. The entire process such as chemical treatment and cleaning is controlled by the machine.
Outer PCB layout transfer
Next, the PCB layout of the outer layer will be transferred to the copper foil. The process is similar to the transfer principle of the previous PCB layout of the inner core board. The PCB layout is transferred to the copper foil by photocopying film and photosensitive film. The only difference is Yes, positive films will be used for the board.
The internal PCB layout transfer uses the subtractive method, and the negative film is used as the board. The PCB is covered by the cured photosensitive film as a circuit, and the uncured photosensitive film is cleaned. After the exposed copper foil is etched, the PCB layout circuit is protected by the cured photosensitive film.
The transfer of the outer PCB layout adopts the normal method, using positive film as the board. The non-circuit area is covered by the cured photosensitive film on the PCB. After cleaning the uncured photosensitive film, electroplating is performed. Where there is a film, it cannot be electroplated, and where there is no film, it is plated with copper and then tin. After removing the film, perform alkaline etching, and finally remove the tin. The circuit pattern remains on the board because it is protected by tin.
Clamp the PCB with clips, and electroplate the copper. As mentioned earlier, in order to ensure that the holes have sufficient conductivity, the copper film plated on the hole walls must have a thickness of 25 microns, so the entire system will be automatically controlled by the computer to ensure its accuracy.
Outer PCB etching
Next, a complete automated assembly line completes the etching process. First, clean the cured photosensitive film on the PCB. Then use a strong alkali to clean the unnecessary copper foil covered by it. Then use the tin stripping solution to strip the tin plating on the PCB layout copper foil. After cleaning, the 4-layer PCB layout is complete.
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