MEMS and Microsystem Packaging NMI at INNOS June 2005 CONFIDENTIAL Introduction Background to MEMS and Microsystem Packaging Types of Packaging – “Zero level” packaging – Primary packaging – Secondary packaging [Page 1] CONFIDENTIAL Silicon IC Systems Silicon IC systems have become: – Incredibly complex – Amazingly dense Standard packages have just about managed to keep up – From early single analogue IC – To multiple stacked digital ICs [Page 2] CONFIDENTIAL Packaging Diversification Standard packaging is “fraying at the edges” – System in Package – Complex chips: eg microprocessors – Power – MEMS Package standardisation helped by: – Single input/output media – electric signals – Mature worldwide industry – High volume and demand from products such as mobile phones etc. [Page 3] CONFIDENTIAL MEMS and Microsystems Packaging MEMS and Microsystems packaging is at the opposite side of the spectrum! – Multiple input/output media – Immature, younger, fragmented industry – Only a few high volume products, such as inkjet, air bag sensor Microsystems – Photonics – Sensors – Inkjet print heads – RF switches [Page 4] CONFIDENTIAL MEMS & Microsystems Input Media Heat Light Image: STS Gas Liquid Motion [Page 5] CONFIDENTIAL Microsystems with Inputs and Outputs in Other Medium Micro fluidics Newer photonics are light to light Image: STS, MEMScap, UCLA Image: Illinois University [Page 6] CONFIDENTIAL MEMS Interface Circuitry MEMS devices tend to have low signal levels – Microphones – Motion sensors Or high frequency – RF switches – Photonics MEMS interface circuitry is often layout or package sensitive [Page 7] CONFIDENTIAL Cost Advanced Packaging IC packaging 30 – 90% of item cost MEMS packaging 70 – 90% of item cost [Page 8] CONFIDENTIAL MEMSnet: Current Challenges Most companies….. have very limited options for prototyping or manufacturing devices MEMS packaging is more challenging than IC packaging…. Most companies find that packaging is the single most expensive and time-consuming task in their overall product development [Page 9] CONFIDENTIAL MEMS Packaging is a Challenge! MEMS are difficult to: – Design – Make – Find a supplier for But, usually, packaging is the hardest task! [Page 10] CONFIDENTIAL MEMS Die Packaging Requirements Mechanical structures often need altered environments – RF switches, IR sensors/bolometers need high vacuum – Controlled atmosphere for capacitance sensing – accelerometers Mechanical structures need a cavity Access for input/output medium Sensitive to packaging stresses Wafers can be thicker [Page 11] CONFIDENTIAL “Zero Level” Packaging Additional glass or silicon wafers bonded to MEMS wafer Composite wafer sawn into “die” Glass MEMS Glass Advantages – Cheaper – bulk wafer scale process – Protects MEMS from saw slurry – Compatible with standard IC packages – Provides environmental control, cavity and protects MEMS [Page 12] CONFIDENTIAL Types of “Zero Level” Processes Direct bonding – Anodic bonding of glass – Wafer-to-wafer bonding Indirect bonding using a “glue” – Eutectic bonding – gold/silicon – Solder – Glass frit – BCB, epoxy – polymer [Page 13] CONFIDENTIAL Direct Bonding Anodic bonding – Glass/wafer/glass Wafer-to-wafer bonding [Page 14] CONFIDENTIAL Indirect Bonding Apply “glue” – Sputter/etch eutectic – Screen print glass frit – Spin on/photo pattern BCB Apply cap Heat treat – Reflow/cure [Page 15] CONFIDENTIAL Micro System Often Requires a System in a Package Interface circuitry – Either In primary packaging – Or layout sensitive in secondary packaging “System in a Package” is a Zarlink speciality [Page 16] CONFIDENTIAL Primary Packaging Hermetic ceramic packaging instead of zero level Zero level package thickness Environmental access All levels of packaging merge [Page 17] CONFIDENTIAL Secondary Packaging Usually a mechanical and electronic structure Designed by the customer (or strong input ) Multidisciplinary project – Specialist engineering knowledge for application – Mechanical engineering – Package engineering [Page 18] CONFIDENTIAL What Level of Package Integration Package integration driven by – Cost (NRE or part cost) – Application – Electronic requirements Levels of integration – Fully integrated MEMS + interface circuitry “System on a Chip” – MEMS + interface in Primary packaging “ System in a Package” – MEMS + interface circuitry as components on a PCB [Page 19] CONFIDENTIAL Self-Powered Systems Current systems – Battery: pacemaker lasts 10 years – Photo cell power: supermarket shelf RF driven LCD price labels Future self-powered system components – Micro fuel cells, MEMS energy harvesters – Low-power wireless cells – E grains, intelligent dust [Page 20] CONFIDENTIAL Design and Manufacturing Systems Profusion of medium Non-standard processes Customers who know their business but not Micro systems – Bio-chips: do you understand biology, do they understand silicon ? Multi-company and multi-disciplinary projects Shared design rules, EDA and fabs are a long way off A consultants dream!? Will we have to choose a niche, will it be difficult to swap niches? NO WONDER MEMS PACKAGING IS NON-STANDARD! [Page 21] CONFIDENTIAL SIMPLY COMMUNICATING CONFIDENTIAL