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Before the PCB etching, we should know the types of etching so that we could make out the difference of them.

There are two layers of copper on the board when etched. In the outer layer of the etching process, only one layer of copper must be etched away, and the rest will form the final desired circuit. This type of graphic plating, which is characterized by the presence of copper plating layer only below the lead tin resist layer.

Another method is the entire board are copper, photosensitive film outside the part is only tin or lead tin resist layer. This process is called “full board copper plating”. Compared with the graphics plating, the biggest drawback of the whole board copper plating is plated twice the copper surface and the etching must also be corroded them. So when the wire width is very fine will produce a series of problems.

And there is another way, is to use the photosensitive film instead of metal coating to do corrosion layer. This method is very similar to the inner layer etching process, which can be seen in the inner layer of the etching process.

How to etch a PCB ?

Process Details Etching is usually done by total immersion of the board in the chemical and agitating by bubbling air through the bath. The copper which is to remain on the PCB is protected from the etchant by an etch resist. Etching time has to be carefully controlled to ensure only unwanted copper is removed.

Over etching can cause undercutting of the resist which can result in serious damage to the edges of tracks and pads. Rinse in deionized water and examine the etched pattern for shorts or incompletely etched areas. If you find small isolated shorts, etch for another 30 seconds and re-examine – if shorts persist, remove them with a razor.

Continue this step until etched circuit is totally free of shorts and other defects. After etching the PCB, rinse thoroughly with water Etching Defects Some defects due to etching are: Non-etched Copper: copper areas which have not been removed completely by etching are acceptable if they are not causing short circuits. Immersion etching techniques generally lead to a low etch factor. Several different types of etching chemicals are used industrially including ammonium Persulphate, chromic or sulphuric acid and ferric chloride.

How to make process control of PCB etching?

To carry the process control of PCB etching, we should pay attention to the etching quality and estimate pre-existing problems.

The basic requirement for the quality of the etch is to be able to completely remove all copper layers except the resist layer. In the strict sense, if the precise definition is to be made, the etch quality must include the consistency of the wire width and the degree of lateral erosion. Due to the inherent characteristics of the current corrosion solution, not only down and around the direction of the etching effect, so the side erosion is almost inevitable.

The structure of the etching apparatus and the etching solution of the different components have an influence on the etching factor or the side erosion, or it can be controlled.

The quality of etching is as long as it has existed before the printed circuit board enters the etch machine. Because there are very close internal links between the processes or processes of the printed circuit processing, there is no process that is not affected by other processes and does not affect other processes.

In theory, when PCB is etching, the graphics plating process in the processing of printed circuit, the ideal state should be: after plating copper and tin or copper and lead and tin the sum of the thickness should not exceed plating The thickness of the photosensitive film, so that the plating pattern on both sides is able to block and embedded in the inside.

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