Mechanical Deformation
Plastic flow under steady load characterizes this material failure mode. Solder creep occurs when metal alloys experience continuous stress at elevated temperatures, leading to permanent dimensional changes without reaching the nominal yield point. Interatomic diffusion across grain boundaries governs the rate of this process.
Such movement alters the structural integrity of electrical interconnects over long periods of operation.
Thermal Sensitivity
Temperature gradients drive the migration of atoms within the crystal lattice. Increasing ambient heat reduces the resistance of the connection to external mechanical loads. Standardized testing for this phenomenon measures the strain rate against constant stress levels at specific temperatures above the glass transition point.
Verification involves accelerated life testing where components undergo thermal cycling to simulate decades of field exposure.
Interconnect Stability
Reliability hinges on the ability of the alloy to maintain its geometry under weight or vibration. Engineers select materials based on their ability to resist this time dependent deformation during the anticipated service life of the circuit. Tin based solders exhibit different levels of vulnerability compared to leaded counterparts when subjected to constant tension.
Higher melting point alloys provide better resistance to deformation under steady loads.
Failure Criterion
Permanent separation of a joint eventually follows the cycle of grain boundary sliding. Cumulative loss of cross sectional area reduces the load bearing capacity of the terminal. Sudden failure happens once the localized thinning reaches a threshold that exceeds the strength of the remaining metallurgical bond.
Electronic assemblies show total electrical impedance increase as these microscopic fissures propagate through the bulk material.
