The Etchant of Photo Chemical Machining Industry Ferric Chloride

The 1980s saw the end of ferric chloride as a significant etchant in the printed circuit industry. The PCM industry remains reliant on lerric chloride for the majority of its etching requirements. Ferric chloride etchants became a commodity in the 1980s as a suitable product was made available by many producers. The disposal of spent etchant replaced specialty formulation and process technical service as concerns for which the PCM industry looked to etchant suppliers for assistance. These trends are expected to continue in the 1990s.

A supplier often sees an industry’s needs and practices from a much different perspective. It might be useful for photochemical machine manufacturer to see their industry’s developments from a vendor’s viewpoint, just as it was useful for us to see the customer’s view of the ferric chloride industry.

A major development in the ferric chloride etchant business was the completion of the printed circuit industry’s switch away from ferric chloride in the 1980s. It meant the end of what had once been a major market for ferric etchants.

The photo chemical machining (PCM) industry stayed with ferric chloride etchants, because, unlike the printed circuit industry, PCM requires the ability to etch a wide range of metals. This need made it impossible to develop simple, steady state, automatically replenished etchants with applicability to the who le PCM industry economically.

The etchant regeneration systems which had been widely adopted by larger PCM facilities by the 1980s fall short of the indefinitely regenerable goal unless only low alloy steels are etched. These regeneration systems have had a significant impact on the industry’s consumption of ferric chloride and on the quantity of waste generated. They have also changed the nature of the waste: lower volume with significantly higher heavy metal contents.

Another approach, but not in widespread use, has been a bleed and feed system in which ferric chloride is constantly fed into an etcher as excess volume is bled off. This method allows one to maintain a relatively constant etch rate, but at much higher etchant consumption and waste generation rates than traditional batch practice.

The use of recirculation, mildly acidic, rinses after etching to minimize drag out to the rinse water waste treatment system has led to an interesting opportunity for solving an environmental problem along with extending etchant life.

It is well known that just increasing because of ferric chloride in itself reduces etching rate. Evaporation, as well as the increased metal content resulting from etching raises baume further depressing etch rate as ferric chloride is used. Using the acidified drag-out rinse to reduce the baume or the etchant to hear its initial fresh value helps maintain the etch rate at a higher rate. This does cause volume growth, with more spent etchant volume than fresh etchant purchased, but it does also help consume the recirculation rinse and prolongs its life as fresh water and acid are added to it.

This has been done by a number of facilities, and is especially effective for those with modest etchant requirements, where evaporation from intermittently used etchers is substantial.

The 1980s also saw the ready availability of ferric chloride which was suitable for etching from manufacturers who had traditionally served only the much larger water and wastewater treatment application.

This commoditization of the ferric etchant market had the expected effects of lowering the etchant price and causing the specialty ferric etchant suppliers to reduce their investment in technical service and R & D. Overall, the PCM ferric application had matured enough that there had been no clamor for higher priced ferric chloride proprietary with vendor technical service. The PCM industry is now in its own hands for etching know-how, and seems to be in good hands. In-house experience is the backbone of this self reliance on what product to order for a given job and how to best use it. (Which does put a price on employee turnover.)

Commoditization of former specialty businesses is nothing new. A trend which may affect the availability of outside process technical assistance is the tendency of specialty suppliers of related products or equipment, which still have above average margins, to develop the expertise in order to facilitate their own sales and service efforts.

As PCM became almost entirely self reliant in etching process know-how, new headaches grew to almost full size in the 1980s: environmental compliance and spent etc haut disposal.

Fortunately, the metals being etched in ferric chloride and ferric chloride itself do not pose a serious problem for rinse water effluent treatment techniques. PCM has avoided the problems with complex agents, etc., which plague metal finishers and printed circuit producers because of the composition of their processing chemistries.

Pick-up or spent ferric chloride, available as a matter of competitive necessity from many suppliers in the ’70s and early ’80s became less available as regulations grew on the transporting and processing of the spent with a sharp increase in the costs associated with such services.

The relatively small volume of PCM etchant spent limits the investment that this waste stream can support, and compliance costs forced the smaller ferric recyclers out of the market. We’ve been fortunate to have an existing ferric recycling unit in a TSD facility which can spread its overhead costs over a broader base of activities.

To recap: etchant itself has become cheaper as environmental costs increased. Process technology has become a lower priority to environmental compliance.

The outlook is for environmental factors to become even more significant in determining where shops axe located, how they will be designed, and how they’ll be run. Environmental regulations can be expected to go through a prolonged refining process, during which time their focus can be expected to become much more specific-and expensive- for each generator.

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