Quantifying Initial Contact Resistance Baseline Degradation in High Frequency Sockets
Initial contact resistance degradation in RF test sockets increases insertion loss and alters impedance matching, requiring dry-circuit Kelvin monitoring.
Intermetallic Diffusion
Meaning
Solid state transport of atoms across the boundary between two adjacent metals creates new alloy phases at their interface. This phenomenon, known as intermetallic diffusion, occurs when copper and tin or gold and aluminum migrate into one another under thermal or mechanical stress. It forms brittle intermetallic compounds that can compromise both the mechanical strength and the electrical conductivity of the junction.
Material Migration
Metal atoms move through the crystalline lattice of neighboring materials when in direct contact. In printed circuit board assemblies, intermetallic diffusion occurs predominantly at the solder joint interface between copper pads and tin-based solder. This process leads to the formation of specific compounds like copper-tin alloys, which are harder but more brittle than the individual metals.
If these compounds grow too thick, the joint is prone to mechanical fracturing.
Thermal Influence
Temperature accelerates the rate at which atoms cross the material boundary. High operating temperatures in power electronics accelerate intermetallic diffusion, which can cause premature failure of solder joints or wire bonds. In wire bonding, the migration of gold and aluminum can create voids that disrupt the electrical connection.
Thermal management strategies help limit this movement by keeping junction temperatures within safe limits.
Solder Reliability
Mechanical shock and vibration pose a higher risk to assemblies with thick intermetallic layers. When intermetallic diffusion is uncontrolled, the solder joint loses its ductility and cannot absorb physical stresses. This brittleness often leads to micro-cracks that propagate along the interface during thermal cycling.
Design standards specify barrier layers, such as nickel plating, to slow this atomic migration and extend the operating life of the device.