Evaluating Thermal Stress Transfer in Silicon MEMS Accelerometer Assemblies
Thermal stress evaluation isolates CTE mismatch across silicon and packaging materials to prevent accelerometer zero-g offset drift and sensitivity shifts.
Die Attach Mismatch
Mechanical Strain
Physical displacement between bonded layers occurs during the thermal processing of multi-material electronic assemblies. Die attach mismatch describes the resulting mechanical stress when the adhesive and the silicon substrate expand at different rates.
Thermal Gradient
Temperature changes during operation or assembly cause each material in the stack to shift its dimensions. Because the coefficient of expansion for the die attach material rarely matches that of the silicon or the ceramic base, the interface undergoes significant shear force.
Reliability Limit
Excessive tension at the bond line leads to delamination or cracking of the sensitive silicon die. In a die attach mismatch scenario, the stress often concentrates at the corners of the chip where the displacement is greatest. Thick bond lines help to absorb some of the energy, but they can also introduce unwanted damping into the system.
Selecting an adhesive with a lower modulus of elasticity allows the material to deform without transferring the full load to the transducer.
Calibration Metric
Qualification of the bond integrity involves acoustic microscopy to detect voids or separations. These tests confirm that the assembly meets the requirements for thermal stability over the intended lifecycle. Maintaining a low stress interface is necessary for preventing zero point drift in high precision inertial sensors.