Long Term Interconnect Creep and Weld Fatigue under Cyclic Thermal Load in Heavy Formats
Thermal expansion and cell swell induce cyclic shear stresses that trigger weld fatigue and interconnect creep, requiring compliance flexure loops.
Interconnect Creep
Meaning
Resistive growth within a conductor junction refers to the gradual increase in electrical impedance at the mechanical interface between two metallic surfaces. Interconnect creep occurs when oxidation or surface deformation forces a shift in the microscopic contact area over time. This phenomenon reduces the effective conductive path and generates localized heat during high current discharge cycles.
Resistance Stability
Thermal expansion cycles drive the physical displacement of mating contacts within high density connectors. Interconnect creep results in a permanent loss of tension in spring loaded mechanisms which allows non-conductive oxides to infiltrate the contact zone. Persistent contact degradation eventually leads to localized melting or catastrophic failure of the interconnect assembly under sustained load.
Failure Mechanism
Material degradation stems from the diffusion of contaminants into the micro-cavities of the contact interface. Interconnect creep manifests as a slow rise in voltage drop across the connection even when the external environmental conditions remain stable. Corrosion accelerates this process by filling the contact gaps with insulating mineral deposits.
Mechanical vibration further exacerbates the situation by wearing down the remaining conductive asperities on the contact surfaces.
Market Impact
Procurement specifications for battery packs often include stringent contact pressure requirements to mitigate the impact of long term degradation. Interconnect creep forces engineers to calculate derating factors for current carrying capacity over the intended service life of the hardware. System reliability depends upon selecting contact plating materials that resist oxidation to prevent the inevitable rise in junction temperature.
Higher resistance at the interconnect interface ultimately shortens the usable life of the energy storage module.