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Roboc Dispensing Applicaon? Chances Are We’ve Already Done It!


July, 2011


Through Silicon Vias (TSVs) Continued from previous page


consists of one or more metal inter- connect layers on a silicon substrate, with TSVs connecting one side of the interconnects to the bond pads on the other side. They can be used as a simpler way to connect multiple ICs using fine pitch horizontal wiring, or to connect a high-density IC to a lower-density organic substrate. The


and smaller size, a situation that demands high density and low para- sitic interconnects.


Flip Chips for MEMS Flip chips might be a better


design for MEMS, since, unlike wire arrays, flip chips can be batch fabri- cated and have superior electrical


Dispensing & Punching


Dots 190 Micron Diagram showing TSVs and MFIs connecting a MEMS chip


to a CMOS processor — MEMS sensor IC with three different possible types of sensor arrays, and the use of MFIs and TSVs


to make the high-density, stress-tolerant connections between the sensor IC and the CMOS processor below it.


Step & Repeat RTV, Pick & Place with Scale


latter application — bridging the dimensional in feature sizes in an advanced IC and the printed wiring board — looks particularly attractive. Xilinx used the silicon interpos-


Vision with Assembly From CAD File


er approach late in 2010 when they needed to establish interconnects between a large Field Programmable Gate Array (FPGA) and its organic substrate. They used a silicon inter- poser and, instead of using the large, hard to manufacture and expensive FPGA, they placed on the silicon interposer four smaller, less costly FPGAs having presumably higher yields. This approach very likely had a favorable impact on reliability and costs. In Dr. Bakir’s view, multiple ICs directly stacked with TSVs in fab processes, along with silicon inter- posers, will be areas of significant growth in the use of TSVs in the near future.


performance. But flip chips do not lead to smaller size because they require routing and distribution through the PCB. Flip chips have another drawback: they typically require underfill, which can interfere with performance. They also can be subject to thermomechanical stress, which is sometimes great enough to crack the die. Even without physical damage, thermomechanical stress is hard on MEMS devices. In one test, the performance of a MEMS devices changed by up to 37 percent when thermomechanical stress was applied. “You don’t want the device characteristics to change before and after packaging,” Dr. Bakir says. To solve these problems, Dr.


Bakir’s group has invented, and applied for a patent on, the Mechanically Flexible Interconnect (MFI) — basically a tiny, coiled,


Dispense with Vision & UV Cure


Multiple Valves


Precision Filling


Hot Melt Glue with Robotics


Scanning electron microscope (SEM) image of a group of MFIs after reflow.


Another area of significant TSV Multiple Bio Fills Pick & Place Soldering


815-363-3524 • info@dispenseworks.com www.dispenseworks.com


adaptation will be MEMS (and sen- sor) devices. This area of growth varies from the others because of its diversity: the large and growing number of functions carried out by MEMS devices requires, at the moment, that each pair of ICs — the sensor IC and the processor — be developed individually. This is not a problem as long as they are mounted separately on a board and connected by wires and traces, but the natural evolution of MEMS devices is toward higher density, higher performance,


tapered spring that can be formed at the wafer level. The spring is tapered along its length because modeling showed that this design would more equally distribute stresses. The group is currently fabricating MFIs as small as 50 x 100 microns. In an example of how this


works, a MEMS sensor IC can have three different possible types of sen- sor arrays, and the use of MFIs and TSVs make possible the high-densi- ty, stress-tolerant connections be - tween the sensor IC and the CMOS


Continued on page 59


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