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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