Resin Rigidity
Epoxy mold compound dimensional stability dictates the structural tolerances achieved during high pressure transfer molding. Thermosetting encapsulants shrink predictably during crosslinking reactions, establishing the baseline parameters for creep compliance calculations in packaged microcircuits. Package geometry determines the mechanical strain experienced by underlying solder joints during thermal aging cycles.
Material manufacturers supply volumetric shrinkage data gathered through thermo-mechanical analysis procedures. Board houses utilize these coefficients to predict board warp under reflow conditions.
Stress Relaxation
Viscoelastic deformation occurs under constant mechanical load within encapsulated electronic assemblies over extended operational periods. Creep compliance quantifies this time dependent strain relative to applied stress inside polymeric encapsulants protecting sensitive semiconductor dies. Elevated junction temperatures accelerate molecular chain slippage within epoxy molding compounds.
This internal movement reduces residual clamping forces exerted on fragile bond wires over operational lifespans. Accelerated life testing measures resultant resistance shifts caused by continuous mechanical displacement.
Failure Criterion
Solder joint fatigue resistance depends directly on the mechanical dampening characteristics provided by surrounding encapsulating resins. Creep compliance thresholds establish the boundary where package deformation transitions from elastic recovery to permanent structural damage. Board assembly shear stresses concentrate heavily along the perimeters of large area ball grid array packages during thermal cycling.
Microscopic voiding inside the mold compound lowers localized load bearing capacity. Destructive physical analysis confirms intermetallic compound degradation whenever environmental stress exceeds specific material limits.
