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Advanced Imaging Magazine

Updated: January 12th, 2011 09:49 AM CDT

Taking a Look at Wafer-Level Packaging

Meeting consumer demand for increased features on camera phones and other mobile devices
An image sensor packaged at wafer level and provided with a ball grid array interface to simplify and reduce the cost of attachment to a printed circuit board.
Comparison of a conventional cell phone camera with an OptiML module from Tessera.
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By Barry Hochfelder

circuit at wafer level, instead of the traditional package of each individual unit after wafer dicing. There are at least four major WLP technology classifications, according to research organizations Prismark Partners LLC (Cold Spring Harbor, N.Y.) and TechSearch International (Austin, Texas). They are Redistribution and Bump technology; Encapsulated Copper Post technology; Encapsulated Wire Bond technology; and Encapsulated Beam Lead technology.

“The advantage of our technology is, first of all, we are working from a wafer,” says Jacky Perdrigeat, CEO of Nemotek Technologie (Rabat, Morocco). “We are making and designing it from an eight-inch glass wafer. We design the lens and to produce it, we go to micromilling equipment to design a master lens shape wafer. We stamp from others to replicate the image of the master on wafer glass. During the process we replicate the image of a network of lenses on wafer glass.”

Perdrigeat says about 3,000 lenses can be produced on the eight-inch wafer, which gives a manufacturer the productivity and capacity that the ever-growing market requires.

The Process

The manufacturing process delivers a more cost-effective and miniaturized wafer level and hinges on the use of reflow-compatible materials. Reflow compatible means the complete camera module can be assembled directly to the phone board and placed on a solder machine withstanding a high degree of heat without damage, making the manufacturing process of the phone board less expense for the device while allowing defective pieces to be easily reworked and sent through the soldering process again. Since this is the same solder reflow process used for assembling other electronics, customers save time by using the same procedure throughout the production cycle. A fixed focus optics feature also eliminates the high costs of manual focus adjustments present in other non-wafer offerings.

The process flow of a typical camera module is that the sensor is shipped to the camera module manufacturer. Generally, it’s chip-on-board. They purchase the lens and put over the sensor.



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