Isolating Micro-Machined Die Packaging Stress during Automated Thermal Calibration
Automated thermal calibration must isolate packaging thermo-mechanical stress shifts from intrinsic silicon sensor signals using real-time compensation.
Mold Compound Expansion Coefficient
Material Property
Volumetric changes in polymer encapsulants describe how much the protective housing expands per unit of temperature. The mold compound expansion coefficient identifies the mismatch between the plastic package and the silicon die. It governs the mechanical stress levels applied to the internal circuitry during operation.
Measurement Point
Measurements typically reveal two distinct rates of expansion separated by the glass transition temperature of the epoxy resin. Below this point, the material is relatively rigid and follows a linear alpha one coefficient. Once the temperature exceeds the transition threshold, the polymer enters a rubbery state with a higher alpha two expansion rate.
Difference Stress
Differences in the expansion rates of the substrate and the lead frame create internal tension. This mold compound expansion coefficient leads to package warping or delamination if the materials are not carefully matched. High stress at the interface can crack the silicon or shift the electrical characteristics of sensitive analog components.
Reliability Requirement
Labs use thermomechanical analysis to verify the material properties after the curing process is complete. The measured value must fall within the tolerance band specified by the assembly house to ensure long term stability. Proper control of the mold compound expansion coefficient reduces the risk of wire bond fatigue during repeated thermal cycling in the field.