Structural Rupture
Mechanical separation occurring at the boundary layer between bulk solder and the printed circuit board pad finish marks a critical point of failure in electronic assemblies. This failure, classified as intermetallic fracture, occurs because the intermetallic compound layer is inherently brittle compared to the surrounding metals. It often happens when the assembly is subjected to mechanical shock, vibration or intense thermal cycling, stripping the joint of its physical load-carrying capacity and causing an open circuit that disables the board.
Solder Joint Failure
Reflow soldering creates a copper-tin intermetallic layer that is necessary for a strong metallurgical bond. However, if this layer grows too thick from excessive heat or prolonged storage, the joint becomes vulnerable to an intermetallic fracture. This degradation is often hidden from visual inspection because the crack runs parallel to the board surface and beneath the bulk of the solder joint.
Brittleness Impact
Lead-free solder alloys like SAC305 are stiffer than traditional leaded alloys, and they transmit more mechanical force directly to the boundary layer. Using nickel-gold or organic solderability preservative pad finishes can help control the growth rate of this brittle layer. Controlling compound growth improves the long-term shock resistance of the board.
