Mechanical Fracture
A structural failure mode involves the formation and slow propagation of microcracks in materials subjected to sustained mechanical tension and environmental exposure. In electronic packaging and printed circuit board fabrication, stress cracking causes brittle fracture in plastic encapsulation resins and copper traces under internal residual or thermal stress. This failure mechanism ceases to develop when tensile stress levels fall below the endurance limit of the material.
Stress Concentration
Residual internal stress develops during manufacturing processes such as plastic molding and reflow soldering cooling. Differential thermal expansion between silicon die and organic resin substrates creates permanent tensile stress fields within assembly components. Environmental exposure to solvents, cleaning agents, or ambient moisture lowers the threshold energy required for crack initiation along polymer chains.
Microscopic surface flaws or sharp geometric corners concentrate localized stress, initiating microcracks that grow under cyclic or constant loading conditions. Over time, microcracks coalesce into macrocracks, severing copper trace connections or breaking encapsulation seals. Broken encapsulation allows moisture and ionic contaminants to penetrate active die regions, causing short circuits and corrosion failures.
Controlling cure cycles, reducing thermal gradients, and optimizing package geometry minimize residual tensile stress concentrations within microelectronic assemblies.
Material Integrity
Relieving internal residual stress prevents slow crack propagation in rigid packaging resins. Controlling processing temperatures maintains material structural integrity under long-term operational loading.
