Due to the hazards associated with the use of hydrofluoric acid, manufacturers are investigating alternatives. Some alternatives for MA TURA-reported uses are discussed in this section.
In metal finishing operations the fluoride ion is often used to accomplish functions such as pickling stainless steel, desmuting high silicon aluminum alloys and die castings, and etching aluminum and some specialty metals.
- The fluoride ion can be introduced either by using hydrofluoric acid or by adding the ion in the form of a salt (e.g., ammonium and sodium fluoride salts).
- For etching, pickling and cleaning other metals, alternative acids (e.g., nitric, hydrochloric, phosphoric) should theoretically accomplish these functions.
Historically metal finishers neutralized their spent acids and landfilled the resulting solid byproduct. Due to increasing material and disposal costs, metal finishers increasingly minimize their acid waste by acid purification and reuse. Although one of the more challenging applications for the technology, diffusion dialysis can be used to recycle spent hydrofluoric acid in mixed acid baths, reducing virgin hydrofluoric acid consumption by as much as 85%. Two Massachusetts manufacturers currently offer diffusion dialysis units: Pure Cycle Environmental Technologies Inc. of Palmer and Zero Discharge Technologies, Inc. of Chicopee.
In other etching processes manufacturers continue to search for alternatives to HF and new processes to minimize HF byproducts.
- In 1999, as part of the Institute's Demonstration Sites Program, ASE Americas Inc. in Billerica demonstrated a hydrofluoric acid vapor acid etch process for silicon wafers using an ultra-small volume chamber. This new process reduced their use of hydrofluoric acid by nearly 99% compared to the liquid batch etching process. However, the use of hydrofluoric acid vapor rather than liquid introduced new safety concerns to the process that had to be addressed by implementing strict procedures.
- Texas Instruments implemented a new metal spraying technique for coating ceramic parts that decreased the need for hydrofluoric acid etching of the ceramic parts prior to metal application.
In another etching process, ASE Americas, Inc. is researching electrochemical etching in an alkaline solution to replace the acid solution. To aid this research, ASE partnered with UMass Lowell Electrical Engineering Department and received funding through the Institute's University Research in Sustainable Technologies Program.
New non-chemical etch processes (e.g., plasma etch) are being developed for processes where acids and other hazardous materials are currently being used to perform functions such as increasing wettability and removing epoxy contamination.
SRI, 1995 (see endnote #2 for full citation); Unknown, "Process Fine Tuning Reduces HF Use," Chemical Engineering Progress, October 1996, pp. 20-22.