Vacuum Brazed Aluminum Thermal Plate Inspection and Joint Quality Testing
Vacuum brazed aluminum plate acceptance demands 100 percent inline ultrasonic C-scan inspection and helium leak validation below 10-6 mbar L/s to prevent field coolant leaks.
Intermetallic Formation
Meaning
Growth of solid-state chemical compounds at the junction between two different metals. Excessive intermetallic formation often creates a brittle layer that reduces the mechanical strength of a welded or soldered joint. This phenomenon is a natural consequence of the thermodynamic drive to reach an equilibrium state at the interface.
Interface Chemistry
Diffusion of atoms across the boundary leads to the creation of distinct phases such as copper-tin or aluminum-nickel compounds. While a thin layer of intermetallic formation is necessary for a strong metallurgical bond, a thick layer acts as a site for crack initiation. The electrical resistance of the joint increases as these non-metallic phases grow over time.
Mechanical Impact
Brittle layers formed by these compounds cannot deform plastically when the battery pack undergoes thermal expansion or mechanical shock. Fracture usually occurs directly through the intermetallic formation rather than through the surrounding base metals. Designers limit the peak temperature during laser welding to keep this layer as thin as possible.
Thermal Growth
Kinetic energy from high operating temperatures accelerates the diffusion process and thickens the brittle interface. Long-term storage of battery modules at elevated temperatures promotes intermetallic formation in the ultrasonic bonds between cells and busbars. Testing for aging effects involves cross-sectioning joints to measure the thickness of these layers under a microscope.
Proper material selection prevents the rapid degradation of electrical conductivity in the interconnect system.