Metallurgical Degradation
Micro-cracking within the barrel of a plated through hole or at the interface between a component lead and the solder fillet characterizes latent interconnect failures. These anomalies occur when thermal expansion forces exceed the ductility of the copper or the bonding strength of the solder alloy during manufacturing cycles or subsequent operation. Such defects frequently pass initial electrical continuity tests because the surfaces maintain physical contact despite the fracture.
The condition escapes detection until environmental stress causes the gap to expand or oxidation increases the resistance to an open circuit.
Thermal Resistance
Differences in the coefficients of thermal expansion between organic substrates and metallic conductors drive the physical separation of joints. High reflow temperatures induce mechanical strain that pushes the material beyond its elastic limit. A localized separation forms inside the joint where the bond remains stable under standard laboratory conditions but fails under vibration or fluctuating heat.
Mechanical shock converts these minor voids into permanent physical gaps.
Diagnostic Verification
Cross-sectional analysis of a circuit board exposes these voids that resist standard functional testing. Specialized inspection regimes utilize micro-resistance measurements to identify potential weak points before the junction fully severs. Temperature cycling accelerates the progression of the defect to ensure the joint reaches a state of absolute failure.
Permanent reliability depends upon maintaining the mechanical integrity of the conductive path throughout the life of the assembly.
