Non Local Strain Gradient Cohesive Zone Formulation for Microvia Corner Step Debonding
Non-local strain gradient cohesive zone modeling eliminates mesh-dependent stress singularities at microvia corner steps to accurately predict reflow debonding.
Target Pad Interfacial Fracture
Meaning
Package failure mechanisms involve the separation of a solder joint or metal trace from the underlying target pad on a printed circuit board. Analysis of target pad interfacial fracture is a major focus during technical audits of failed electronic assemblies in consumer and industrial devices. Inspections determine whether the separation occurred due to poor wetting, contamination, or excessive mechanical shock.
This failure results in open circuits and system malfunction. Rigorous diagnostics find pad flaws.
Fracture Location
Microscopic inspection shows that the crack runs directly along the intermetallic compound layer. This thin boundary layer between the copper pad and the solder is naturally brittle. Mechanical stress easily initiates a fracture if the boundary suffers from voiding or contamination.
Stress Concentration
Thermal cycling generates high shear strain at the corners of the ball grid array. Mismatched expansion rates of the silicon chip and the organic substrate focus these forces on the outermost solder joints. The localized stress eventually exceeds the bond strength of the pad interface.
Quality Control
Solderability testing of incoming boards ensures that the surface finish remains receptive to the solder alloy. Surface analysis techniques check for organic residues or oxidation before the boards enter the reflow oven. Eliminating these defects prevents joint degradation in the field.