Friday, June 5, 2015

Silicon Hot Melt Is Alternative to Polyurethane Hot Melt and DS Tape

By Ken Werner

At a Display Week poster session on Thursday, June 4, Ryan Schneider, Glenn Gordon, and colleagues from Dow Corning presented their paper, "Silicon Hot-Melt Adhesive Providing Protection, Waterproofing and Reworkability for Precision Assembly of Electronic Devices" -- a title that leaves little to the imagination.

The material, Dow Corning EA-4600 HM RTV Black, was initially developed as an alternative to double-sided tape (and polyurethane hot melt) in the assembly of cell phones and other electronic devices. In this role, the adhesive can run about 20% of the cost of tape in large-volume applications. Because the material requires dispensing equipment that costs in the vicinity of $100,000, it takes high volumes for the much lower material cost to deliver its maximum savings.

One advantage of the silicon hot melt is that it can be used to make beads of 0.5mm or less in, for example, a peripheral seal on cellphone window glass, where maximum screen visibility is crucial. It is, said Gordon, impossible to cut DS tape that fine.

Although the original conception was to use the hot melt as an adhesive for assembly, if you deposit a peripheral bead on only one surface and allow it to cure, it forms a gasket that can be used to provide water- and dust-proofing to a snap-on cover -- and the cover can be removed and re-snapped indefinitely while still retaining its water-proofing characteristics. This approach was used to waterproof the back cover of a recent, popular smartphone model. Although Schneider and Gordon would not identify the model in question, reliable industry sources tell me it was the Samsung Galaxy S5. Dow Corning is talking to other manufacturers about adopting the technique.

Ryan F. Schneider (R) and  Glenn V. Gordon of Dow Corning seemed pleased at the reception of their poster paper.  (Photo:  Ken Werner)

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