By John McHale
AUSTIN, Texas - Engineers at Austin Semiconductor Inc. used masking technology from Cubic Memory in Scotts Valley, Calif., and eliminated wiring in developing a low-cost 3-D package-free wafer stack for a data storage memory board in NASA`s New Millennium Earth Orbiter program at Goddard Space Flight Center in Greenbelt, Md.
"We took out about 2,000 wires from the system and got rid of 70 pins," says Lloyd Rodenbeck, operations manager of modular development at Austin Semiconductor in Austin, Texas. "The only drawback is that we have to produce the product with wafers as opposed to die, because die is so difficult to obtain."
But Austin`s competitors in this arena such as Irvine Sensors of Costa Mesa, Calif., use die but their product is more expensive and more difficult to redesign, Rodenbeck claims. Austin`s product cost 10 times less to redesign, he adds.
The densities available in a silicon 3-D stack provide more memory per cubic inch than previously possible, say Austin officials. "We mounted the stack on a ball grid array," Rodenbeck says.
Pins usually operate in parallel, resulting in a significant reduction in pin count per layer. If the resulting stack has eight layers, the overall reduction in pin count will be approximately 10 to 1, which improves reliability and performance, and reduces power consumption.
"We can also cut out a figment of bad wafer, fuse out the bad die, and leave it as baggage with the wafer still able to function," Rodenbeck explains.
This project is part of NASA/Goddard`s Chip-On-Board program, which will also develop processes for assembly of package-free stacks on printed circuit boards.
