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88 SMT007 MAGAZINE I JULY 2021 Development/ Etching/Stripping ese process steps are oen done in tanks because of the small size of the work piece, small batch sizes, and the use of a variety of dif- ferent chemistries which makes it impractical to set up conveyorized spray units for all these unit operations. Occasionally, environmental and health concerns dictate the use of tanks to avoid aerosols of chemicals such as HF in vented air due to spray action. I have seen resist development in tanks and in vertical or hori- zontal conveyorized spray units. Some tanks and vertical developers are relics from the era of solvent resist processing and give only marginal results with modern aqueous pro- cessable resists. Control of the Production Environment About cleanroom environment, temperature and humidity control, the effort is commen- surate with the need for a particular end-use. One shop I visited has standards that exceed what is common in PWB fabrication in order to meet very stringent medical and aerospace requirements. In summary, the photochemical machin- ing industry is practicing and advancing PWB technologies as it is growing its product mix in the arena of advanced electronic packaging components with fine features and tight toler- ances. is industry's traditional fl exibility in handling a variety of products in small lot sizes with short lead times should be a real asset in the electronics arena. SMT007 References 1. "Aetztechnik—eine Nischentechnologie mit hoher Praezision," Galvanotechnik, D-88348 Saul- gau. 88 (1997), No. 6. 2. "Fine Line Etching of Lead Frames, Don Ball," Printed Circuit Fabrication, Vol. 19, Nr. 12, December 1996, pg. 18. 3. "Results of the 1996 Photo Chemical Machining Survey," The Journal (PCMI), Summer 1996, pg. 10. 4. "The Development of an Aqueous-Working Etch Resist for the PCM Market: Synergy or Sym- biosis?", D. Albin & Walter Striedieck, The Journal (PCMI), Spring 1997, pg. 19. 5. "A New Etch Resist for Photo Chemical Machin- ing," C. Bird & D. Kapp-Schwoerer, The Journal (PCMI), Summer 1997, pg. 8. 6. "New Aqueous Dry Film Photoresist for Pho- tochemical Machining Applications," L. Moyer et al, The Journal (PCMI), Winter 1992, pg. 9. Dr. Karl Dietz had decades of experience in the chemical and electronic industries, and a well- known expert in material and process technology for printed circuit boards and substrates. He was an author and a columnist on PCB topics, as well. Karl passed away in 2020; he will be missed.

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