You're looking at a section of a 3-mil thick nickel grid with 6-mil lattices. The entire part is about 4 inches in diameter. How would you make this part?
Electroforming is certainly a possibility. A photo resist pattern would be created on a stainless steel substrate using a phototool and photo resist. To build a pattern of photo resist to accommodate a .003" (about 75 microns)thick deposition of nickel will require two coats of 1.5 mil resist. When the pattern is printed and developed, the mandrel will show a pattern of raised areas of resist for the holes and narrow traces of exposed metal for the lattice. With the patterned substrate immersed in the nickel sulfamate bath, electrodeposition will occur at a rate of about 1.5 microns per minute. So, in about 50 minutes, a 3 mil thick electroform will be produced. The nickel part is peeled off the substrate, and the process can be repeated.
Photochemical etching will start in a similar manner. In this case, the actual nickel substrate will be coated with photo resist and then imaged with a phototool that occludes the holes and exposes the lattices. Ferric chloride will etch nickel at about 1 mil (25 microns) per minute total (.5 mil per side). The nickel will etch through in about 3 minutes.
Assuming the same size sheet and number of parts per sheet, photo chemical etching will produce 16 times as many parts per hour as electroforming. Even with the additional process steps of of having to laminate, image, develop, strip and cut-out for every sheet, chemical etching has a higher overall through rate compared to electroforming.
Photochemical etching and electroforming have some distinctive characteristics when working with very thin substrates. In photo etching, the minimum hole size must always be fractionally greater than the material thickness. In electroforming, however, the hole size may be substantially smaller than the thickness of the metal deposition, sometimes under 10 microns.
Photo etching can utilize a wider range of alloys, including stainless, carbon and silicon steels, copper alloys including brass, bronze, beryllium copper, nickel silver; nickel, aluminum, molybdenum, & sterling silver. Electroforming is most usually accomplished in pure nickel, although copper, silver and gold are used in specialized applications.
Both photochemical etching and electroforming processes are finding growing applications as the world of digital technology demands ever-smaller and more powerful devices. Conventional metal fabricating processes, including stamping, fine blanking, laser, water and plasma cutting do not have the detail resolution to create the extremely fine structures needed for micro-scale electronic interconnects.
High resolution imaging technologies now allow the creation of phototools with sub-10 micron features. Ultra thin film and aqueous liquid resists are able to develop exceptionally fine detail. These advances in imaging are enabling new opportunities in many industries including electronics, medical, MEMS and more.
Although both photochemical etching and electroforming are technologies that have been around for more than 50 years (electroforming actually goes back the mid-1800s), neither process is well known or well understood by the engineering design community.
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