MNS Roger Grace v Final DR 18/12/08 15:12 Page 33
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being used in a wide range of devices including accelerometers
and RF switches.
Wafer level packaging (WLP) using various bonding
techniques is another technology that started as a MEMS
technology. Currently, it is one of the hottest technologies in
both the IC and MEMS areas. Wafer bonding process options
include fusion, plasma activated fusion, anodic, thermo-
compression, eutectic, glass-frit and adhesive. Infotonics uses a
very sophisticated adhesive bonding strategy to create a five
level wafer stack for a micro-fluidic device.[4] Adhesive bonding
techniques are popular when then can be conducted in a batch ack
mode at room temperature. Suss Mictotec has developed a
technique where it spins the adhesive on to glass or Si wafer and
use standard mask alignment techniques with accuracies of less
than 1 micron wafer to wafer. Ultra violet radiation is used to
cure the adhesive. The resulting process is benign and does not
deform heat sensitive optical elements while maintaining high Figure 7: Genetic environmentally resistant package uses
Image courtsey of eP
throughput and low unit cost as a result of its wafer scale WLP and through hole vias to create accelerometers and
format (Fig 6). Its selection was based on a number of factors and Pirani sensors that perform in extreme environments
[5]
including forgiveness of surface non-uniformities, low pressure
(75 psi) and low temperature (170 degree C) application. The decision to create a monolithic versus heterogeneous
An adjunct to wafer level packaging is a unique approach solution requires a stringent and thorough trade-off process. The
taken by ePack. CEO Jay Mitchell said…”We have developed a “poster child” of this MEMS-based system solution concept are
generic environment resistant package that embodies WLP and the tire pressure monitoring systems (TPMS) that are finding
through-hole vias (Fig 7). In many MEMS packaging scenarios, huge and growing applications in the automotive market… even
the device needs to survive extreme shock, vibration and thermal with the current downturn in the economy and its effect on
excursions while still maintaining its high performance. ePack’s worldwide automotive production volumes (the primary cause of
use of a glass suspension protects the MEMS devices and thus the increase in total volumes of TPMS is due to the current
provides the solution. rapid adoption of these systems). I believe that the adoption of
The anti-radiation nano-getter layer allows for low vacuum MEMS-based system solutions by many commercial companies
pressures of less that 10 mTorr which enhances thermal including Axept, Crossbow, LV Sensors, Tronics Microsystems
isolation. This packaging approach accommodates a wide variety and most recently, Acuity is the beginning of a movement whose
of MEMS designs are provide for ultra high performance for time has come. These solutions provide suppliers with higher
accelerometers and resonators that are hyper critical to value-added and higher profit margins. They will also create
changing environmental conditions”.
[5]
truly differentiated products that address the unfulfilled need of
the market to provide total solutions…not piecemeal ones. The
Conclusions infrastructure to support this approach is in place.
The ability of MEMS to find themselves in an increasing number Carpe Diem...Think outside the chip!!!
of high volume/low cost applications including consumer
electronics has driven device suppliers to rethink the way that
they have designed MEMS products. I strongly suggest that for
Roger Grace is a marketing consultant
all functions of the MEMS-based system solution to be
specialising in MEMS and nanotechnology
addressed at the onset of the design so that a design solution
based in the USA. He will organise and
that optimally meets the performance, price and reliability
chair a June 8
th
, 2009 technical session on
requirements of the customer are met. Additionally, the ability
“MEMS-based Systems Solutions:Thinking
to adopt a system- on -a -chip (SOC) as well as a system-in –a-
outside the chip” as part of Sensors Expo
package (SIP) concept so popular in the IC industry is slowly
2009 http://www.sensors
expo.com or
becoming a reality in the MEMS area.
http://www.rgrace.com
REFERENCES
[1] R. Grace, “MEMS:Lessons from Nano”, Mechanical Engineering, pp.24-28, August 2008. (www.rgrace.com)
[2] MEMS Industry Group, “MIG’s Industry Report: Focus on MEMS Packaging”, Pittsburg, PA, July 2008 (only available to MIG
members).
[3] K. Najafi, “Micropackaging Technologies for Integrated Microsystems”:Application to MEMS and MOEMS”, Invited Plenary
Talk, Proceedings of SPIE’s Micromachining and Microfabrication Symposium, pp. 1-19, San Jose, CA, USA, January 27-29,2003
[4] J. Griver et al. , “Fast PCR Thermal Cycling Device”, IEEEensors Journal, Vol. 8, No. 5, pp.476-487, May 2008
[5] S. LKee et al, “ A Generic Environmental-Resistant Packaging Technology for MEMS”, Transducers and Eurosensors’07,
pp.335-338, Lyon France, June 10-14, 2007.
December 2008 / January 2009
www.micronanosystems.info
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