How to Select MEMS Encapsulation Adhesives: Low Stress, Low Shrinkage and Matched Thermal Expansion Are Critical

MEMS pressure sensors, inertial sensors, accelerometers, gyroscopes, microphones and other devices generally incorporate miniature sensitive chips, micromechanical structures and precision electrodes. Such components are extremely susceptible to mechanical stress. Excessive cure shrinkage or high modulus of encapsulation adhesives, or a large mismatch in coefficient of thermal expansion (CTE) between the adhesive and chips, may lead to zero drift, sensitivity deviation and even structural damage. Therefore, when selecting MEMS encapsulation adhesives, bonding strength alone is not sufficient; priority should also be given to whether the material can relieve stress. I. Three Common Adhesive Application Zones in MEMS Packaging 1. Precision Bonding of MEMS Chips Chips need to be accurately fixed onto substrates while avoiding excessive shrinkage stress exerted on chips by cured adhesives. Required material properties: ■ Low cure shrinkage ■ Good positional retention ■ Thermal expansion performance matched with substrates ■ Stable bonding strength ■ Compatibility with precision dispensing or active alignment processes 2. Electrode Protection for MEMS Chips Electrodes and bonding areas require protection against moisture, corrosion and vibration, yet must not be fully constrained by high-hardness materials. Low-modulus silicone gels or flexible silicones can form a protective layer while reserving certain displacement space for chips and bonding wires. 3. Lid Bonding & Housing Sealing MEMS lid sealing must block moisture vapor and contaminants. Additional requirements may include electrostatic discharge (ESD) protection, optical stability and dispensing within narrow gaps. II. Eilian Recommended Adhesive Grades for MEMS Packaging SIPA 3000 One-Part Addition-Cure Silicone One-part semi-flowable silicone adhesive and sealant; viscosity ~40,000 cps; hardness Shore A 28 after curing; elongation >250%. Recommended applications: ■ MEMS lid bonding ■ Housing sealing ■ Flexible reinforcement of solder joints ■ Areas requiring both adhesion and stress buffering High elongation helps absorb displacement induced by vibration and thermal expansion. SIPA 3003 Chip Mounting Adhesive One-part semi-fluid silicone; viscosity ~20,000 cps; hardness Shore A 50;…