Substrate Distortion
Mechanical distortion represents the localized physical deformation experienced by an integrated circuit die or sensor element due to external forces. This package strain originates from the stresses exerted by the surrounding protective molding compound or ceramic housing. The resulting force alters the electrical characteristics of sensitive semiconductor junctions through the piezoresistive effect.
This deformation dictates the ultimate accuracy of silicon pressure sensors and bandgap voltage references.
Assembly Source
Mismatch between the thermal expansion coefficients of the silicon chip and the surrounding substrate generates stress during the cooling phase of the packaging process. The solder attachment and the encapsulation material shrink at different rates, leaving residual forces in the die. This condition worsens when the completed assembly is mounted onto a printed circuit board.
Metrological Impact
Electrical performance deviates from the unpackaged wafer-level measurements due to these residual stresses. A package strain alters the offset voltage of operational amplifiers and shifts the output of precision voltage sources. This behavior requires calibrated correction in the post-assembly phase.
Mitigation Method
Stress isolation techniques use soft compliant adhesives or die-attach materials with low elastic modulus to absorb the thermal expansion differences. Protective gel fills also replace rigid epoxy caps in sensitive applications.
