Two companies have developed alternatives to traditional methods of shielding thermoformed parts from electromagnetic interference. 3M Co., based in St. Paul, Minn., has introduced its 6100 thermoformable EMI shielding. The material is a thin laminate of two porous, nonwoven layers - one metal and one of ethylene vinyl acetate polymer that functions as a hot-melt adhesive. It comes on rolls 2 feet wide by 50 feet long, can be cut with scissors and does not stick to other surfaces until the activation temperature of the polymer layer has been reached.
The material is cut to size and laid on top of a sheet of plastic in the clamp frame at the start of the thermoforming cycle. As the heat increases, the material bonds to the sheet and the metal fibers elongate to create a conductive grid over the part.
3M 6100 can be used with thin- or heavy-gauge plastic, and with either male or female molds in vacuum and pressure forming. 3M is touting the product as an alternative to secondary spraying of the parts with conductive paint or plating.
Dixon Gleeson, marketing development manager for 3M's Electrical Specialties Division in Austin, Texas, said the one-step processing allows the thermoformer to keep control of the part.
Sending parts to a subcontractor for shielding means that the thermoformer becomes dependent on that vendor's reliability to maintain scheduled delivery dates.
In addition, Gleeson said, ``We anticipate [thermoformers] will realize a significant cost saving.''
Jack F. Gabower, an engineer in Mauston, Wis., has devised a way to use thermoformed, vacuum metalized plastic inserts to provide EMI shielding. The inserts function like internal metal shrouds, but can be made in more complex shapes, and are lighter and less expensive, Gabower said.
The use of plastic inserts also allows recycling of molded housings without removing a coating, he said.
Gabower, president of family-owned Vacuum Platers Inc., has applied for a patent for the inserts, which also protect against radio frequency interference and electrostatic discharges.
The aluminum used in the process can be recovered easily via a process of immersion in caustic solutions. The resulting waste solution presents no disposal problem, he said.