Role of free hydrochloric acid in the low-cost regeneration of ferric chloride etchant by oxygen gas

摘要

This thesis concerns the development of a low cost and environment-friendly method for the regeneration of the most widely used aqueousetchant, ferric chloride, found in photochemical machining (PCM) facilities.In order to implement the above process a comprehensive and automatedchemical analysis and control system was designed to fully investigate thekey parameters which previous research has suggested play a major role inthe analysis of ferric chloride. Monitoring methods have been developedand deployed in a commercial environment such that the etchant could beanalysed remotely across the business network or via the internet. This levelof monitoring has removed much of the `black art' previously associatedwith etching and has allowed proactive control of the etchant and the PCMprocess in general.Detailed analysis of the data captured has resulted in a clear understandingof the role the free hydrochloric acid (HC1) level plays in prolonging the lifeof the etchant. By keeping the free acid level high, dissolved metals remainin solution. The regeneration uses oxygen from the air, combined withsurplus HCI, to regenerate the etchant within the etching machine itself.This environment-friendly system has allowed etching to continue in a verycontrolled way for nearly one year, during which time some 500kg of metalhave been dissolved. This has totally eliminated the need to change theetchant which otherwise would have been carried out every 16 weeks. Thesaving to the sponsoring company has been over £7000 per year.These combined activities are considered as a major advancement inknowledge and will be of considerable benefit to the PCM industry ingeneral. The monitoring systems alone would significantly benefit anyPCM company by reducing rejects and improving product quality andproductivity.