Pressure spraying under immersion

The rate of etching under diffusirMi-controlled kinetics is therefore increased by spraying the etchant onto the substrate as opposed to immersing it in a static bath of etchant. This is the reason that commercial PCM is carried out in a spray etching machine (Fig. 1) where etchant is sprayed from nozzles at typical pressures of 2-4 bar. Due to the size limitations of such machines, typically CHM applied to large parts is carried out in large tanks that can hold as much as 44,0001 of etchant (Dini 1984). 

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