PCB Tech - Talking about PCB etching process and its measures

Talking about PCB etching process and its measures

First look at what is called the PCB board etching process, which uses a traditional chemical etching process to corrode unprotected areas. It's a bit like digging a trench. It's a feasible but inefficient method. The etching process is also divided into positive film process and negative film process. The positive film process uses a fixed tin protection circuit, and the negative film process uses a dry film or a wet film to protect the circuit. Using traditional etching methods to the edge of the line or pad is deformed. Every time the line increases by 0.0254mm, its edge will have a certain slope. In order to ensure sufficient spacing, the wire gap is always measured at the closest point of each pre-set wire.

In order to create a larger gap in the vacancy of the wire, it takes more time to etch an ounce of copper. This is the so-called etching coefficient. Under the premise that the manufacturer does not provide a clear list of the minimum gap per ounce of copper, understand the manufacturer's etching coefficient. It is very important to calculate the minimum capacity per ounce of copper. The etching factor also affects the manufacturer's ring hole. The traditional ring hole size is 0.0762mm imaging + 0.0762mm drilling + 0.0762 stacking, a total of 0.2286. Etching or etching coefficient is one of the four main items of the specified process level.

In order to prevent the protective layer from falling off and meet the process spacing requirements of chemical etching, traditional etching stipulates that the minimum spacing between wires should not be less than 0.127mm. Taking into account the phenomenon of internal corrosion and undercut during the etching process, the width of the wire should be increased. This value is determined by the thickness of the same layer. The thicker the copper layer, the longer it takes to etch the copper between the wires and under the protective coating. Above, there are two data that must be considered for chemical etching: the etching coefficient --- the number of etchings per ounce of copper; the minimum gap or pitch width per ounce of copper.
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