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Razor-thin WLCSP streamlines camera modules

Posted: 13 Dec 2006 ?? ?Print Version ?Bookmark and Share

Keywords:WLCSP? CSP? camera module? Tessera? Shellcase?

RT/Tessera.HTM" target="_blank">Tessera Technologies Inc. announced what it says is one of the slimmest surface-mountable wafer-level chip-scale packages (WLCSPs) available for camera modules, MEMS and optical detectors.

The Shellcase Razor Thin (RT) package uses a thin polymer on one side, instead of the previous two-sided, glass sandwich, to decrease the package profile to 0.5mm from the 0.9mm of the previous Shellcase package. The RT version also sheds heat more easily than its predecessor, is insensitive to moisture and is more rugged overall, making it suitable for automotive, aerospace and military applications as well as CE, according to Tessera.

"The LCD used to be the limiting factor in how thin you could make a handset," but now that distinction belongs to the camera module, said Craig Mitchell, VP of business development and sales at Tessera. "Our thinner packaging can enable the camera module to be thinned down, too."

WLCSP caps the entire wafer with glass before the wafer is diced into chips. Capping the wafer ensures that no particles contaminate the image array or MEMS device when the wafer is finally diced. Tessera estimates that image sensor yields can be upped as much as 40 percent by going to its glass-on-wafer solution.

44 percent thinner
After the wafer is capped, the electrical contacts are relocated to the backside of the wafer. Previously, Tessera's Shellcase technology capped both the top and bottom of the wafer with glass, but the new technology substitutes a polymer on the bottom that is 0.4mm thinner. The change not only makes the overall package 44 percent thinner but makes it more rugged, raises its thermal conductivity and ups its moisture sensitivity level to the industry's highest rating (MSL1, compared with MSL2 for the glass package).

The RT also supports scribe line widths as small as 100?m, compared with 220?m for the previous version, so that more chips can be squeezed onto the same-sized wafer. The bond pad area has been cut by more than 50 percent, and the bond pad pitch has been reduced to 180?m from 350?m. "With our smaller design rules, an image sensor manufacturer can reduce the size of its device, freeing up board space for OEMs," said Mitchell.

For customers who want a chip-on-board solution, Tessera announced its Shellcase CF earlier this year.

Tessera acquired the technology for its Shellcase line when it purchased Shellcase Ltd in December 2005. Tessera's technologies are available for licensing only.

- R. Colin Johnson
EE Times

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