Polymer Die Attach Selection Criteria for Low Drift Inertial Measurement Units
Polymer die attach selection governs MEMS IMU bias drift by balancing storage modulus, glass transition temperature, and long-term viscoelastic stress relaxation.
Polyimide Film
Polymeric Substrate
High-performance dielectric sheets made of aromatic polyimide are widely utilized as flexible base layers for printed circuits and sensor arrays. Due to its combination of electrical insulation and mechanical strength, polyimide film supports thin-film metal tracks in harsh operational environments. This substrate allows sensors to conform to curved surfaces without breaking the electrical connections.
Thermal Stability
The polymer maintains its physical and electrical properties across a wide temperature range extending from cryogenic levels to over three hundred degrees Celsius. This stability ensures that the polyimide film does not degrade or outgas during the high-temperature solder reflow processes or thermal-vacuum cycles used in aerospace assembly. This performance is unmatched by most other flexible plastics.
Moisture Absorption
Polyimide materials have a affinity for water, which can affect their mechanical dimensions and electrical permittivity. This moisture uptake can cause polyimide film to swell, introducing small strain errors in bonded foil strain gauges or capacitive humidity sensors. Engineers must account for this behavior when designing precision measurement systems that operate in varying humidity.
Metrological Application
Thin sheets of this material are calibrated for thickness uniformity and dielectric constant to minimize the uncertainty of the sensors printed on them. Variations in the polyimide film thickness can cause localized differences in thermal resistance or sensor sensitivity. Measuring these variations with sub-micron resolution before sensor fabrication ensures that each produced unit performs within the specified limits.
This step is critical for high-volume sensor manufacturing where consistency is required to avoid costly calibration of individual units.