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Analysis: Tessera banks on imaging, optics biz

Posted: 13 Oct 2009     Print Version  Bookmark and Share

Keywords:image sensor  Tessera optics IP  CMOS  DRAM 

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One of the emerging costs is the IC-packaging process. Traditionally, camera module image sensors use chip-on-board (COB) packaging technology. In a rival technology, Tessera offers its Shellcase wafer-level chip scale packaging scheme, said to provide lower costs and better yields.

"Wafer-level packaging (WLP) is an alternative approach where the die are packaged while still in wafer form and the wafer is then singulated to free individually packaged die. WLP has the advantage that the costs of packaging are shared among the good die on the wafer, greatly reducing packaging costs per die," according to a paper from Tessera.

To propel Shellcase technology in the market, Tessera has licensed the technology to several manufacturers: Advanced Wafer Level Packaging, China Wafer Level CSP, Nemotek, as well as Xintec, a joint venture between TSMC and OmniVision.

CSP now accounts for about 40 per cent of the image sensor market, according to Barclays. Omnivision uses the Shellcase CSP technology, but others don't. For example, Aptina, the CMOS image sensor spin-off of Micron Technology Inc., uses CSP technology, but not from Shellcase. One of Aptina's biggest handset customers is Motorola.

Two other image sensor players—STMicroelectronics and Toshiba Corp.—also makes use of CSP, but not from Shellcase. Nokia primarily uses CMOS image sensors from ST and Toshiba, according to the report.

There is still no simple formula for OEMs. "While chip scale packaging for image sensor reduces cost, form factor, and is overall more efficient, several large image sensor vendors including Samsung continue to use COB packaging because they already have the infrastructure in place, including the associated equipment and an established supply chain," according to Barclays.

"Industry checks suggest that currently CSP packaging is used primarily for sensors with resolutions in the VGA"1.3 MP range, while COB packaging is used for the higher resolution sensors, as CSP packaging is only economical for high-volume packaging needs and higher-resolution image sensors have not yet reached the critical mass," according to the report.

In addition to CSPs, Tessera is moving to disrupt another piece of the puzzle. Instead of the traditional lens stack using traditional optics technology, the company is pushing its OptiML wafer level optics (WLO). This allows manufacturers to build thousands of lenses on a single wafer for camera modules, which saves board space and cost.

Using reflow-compatible materials to build the optical elements of the camera module enables it to be efficiently mounted directly onto a phone board, leveraging the same solder reflow process used for assembling other electronics on the same board.

This is still a work in progress. Tessera has completed a VGA-based module based on the technology, with 3Mpixel technology in the works. "Wafer level optics is a relatively newer phenomenon and the technology has yet to be proven on a volume scale," said Barclays' Muse. "As such, wafer level optics currently account for only about 10 per cent of the handset camera lens market."

Tessera is also moving forward with another promising technology: The integrated camera module. This is when the module manufacturer integrates the wafer level packaged image sensor with the wafer level optics.

There are issues with that approach. "Note that ST also developed wafer level camera technology internally. The company had traditionally manufactured the image sensor and the image processor, purchased the lens stack externally, and then assembled the entire camera module," according to Barclays.

"And with Nokia—ST's largest camera module customer—pushing for very low-cost modules and wafer level camera technology adoption, ST also began developing wafer level optics. In light of the challenges, checks suggest that the ST's wafer level camera was not reaching the same level of image quality, causing Nokia to become less aggressive in pushing its vendors to adopt a wafer level camera approach," the report said.

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