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Stacked ICs talk directly
Joseph Rajendran, Contributing Editor -- Design News, May 21, 2001
Singapore—Ball grid array technology is not new. Neither is wire bonding technology. But ST Assembly Test Services (STATS) has engineered a new package called Stacked Die Ball Grid Array (SDBGA) which delivers the best of both worlds.
Many of today's portable devices feature distinct IC groups performing a variety of functions such as amplification and mixed signal scanning. In this design world, signals typically start from one IC, like a SRAM, and pass to another IC, like flash memory, by way of the motherboard. To enhance functionality, circuit designers have tried to either embed logic capability into memory or vice versa. But there are always tradeoffs in this process in terms of performance.
STATS chose a different route for development of the SDBGA. By stacking one IC on another and empowering direct signal transfer, the company was able to enhance functionality while simultaneously reducing space requirements. On the SDBGA, ICs are directly connected so there is no need for signals to go through the motherboard and back to the IC. The result? No signal delay for faster communication.
The key design challenge, says STATS Chief Technology Officer B.J. Han, was to enable the smooth communication between the ICs via IC-to-IC wire bonding. Because ICs are generally of different materials, and because they need to be attached without breaking the passivation, overcoming sensitivity during the attachment process was critical. Optimizing wire bonding with the die attachment material, explains Han, involved proprietary processes and materials engineering. This work, he says, was done in conjunction with materials suppliers who helped develop custom-tailored materials.
With its two-in-one feature, the total SDBGA package height typically measures 1.4 mm. Popular SDBGA sizes are 8 × 8 mm to 14 × 14 mm with pin counts between 80 and 140. Weight and mounting area are only 30% that of conventional packaging.
The product is now in beta customer qualification and shipping should commence shortly once confirmed orders are in.
For more information about SDBGAs from STATS: Enter 538
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