TOKYO - NEC Corp. announced a breakthrough in the recycling of mold residues produced during the manufacture of epoxy-resin, multilayer printed circuit boards. The new recycling method, announced March 18 at the Cir-cuitry Engineering Convention in Tokyo, was developed at NEC's Resources and Environment Protection Research Laboratories in Kawasaki, Japan.
NEC researchers devised a two-step process of crushing, followed by fine pulverizing. Both cutting and shearing forces are applied during the crushing step, and shearing and impact forces are combined during pulverizing. Printed circuit board wastes are reduced to particles smaller than 1 millimeter.
Major Japanese companies that produce most of the world's consumer electronics products have been chipping away at the recycling problem for years. Wastes resulting from the manufacture of printed circuit boards have presented one of the most difficult challenges because circuit boards include glass, epoxy resins and metallic copper.
The copper and resin components exist in multiple layers, so they are not easily separated for recycling and the epoxy resins cannot be remelted. Moreover, the glass fiber and copper elements are too hard to pulverize using conventional processes.
Because of these difficulties, most of the residues from the process of molding printed circuit boards end up in landfills. In Japan alone, the electronic industry dumps more than 22 million pounds of printed circuit board mold residues every year.
Metallic copper, epoxy resin and glass fiber respond to pulverizing differently, so particle size varies. Because of size and density differences, researchers experimented with both screen-and gravity-separation techniques.
Gravity separation using a centrifugal classifier with a high-air vortex system was found to be most effective, achieving a recovery rate for copper as high as 97 percent by weight. The balance of the mixture is a glass-fiber and resin powder used as a high-quality filler for resin-based coating materials.
In laboratory tests, impact strength and flexural strength of molds using glass-fiber-resin powder have been found equal or superior to reference molds using silica powder as a filler.
NEC worked with two other firms, IHI Corp. and Nippon Trading Co. Ltd., to develop the coating application. Compared with conventional coating materials, which contain no resin, the new material offers twice the tensile strength and half the thermal expansion rate, NEC said. NEC spokesman Mark Pearce said the firm plans to expand the use of the powder to other resin-based products.
