Intermetallic Compound Fracture Mechanics in High Density BGA Latent Defects
Intermetallic growth control and thermal profile validation prevent latent BGA fracture defects before boards leave the line.
Strain Energy Release Rate
Fracture Energy
Energy required to grow a crack by a unit area along the interface of a composite or multi-material structure defines the toughness of that material system. This physical parameter, known as strain energy release rate, is a fundamental metric used to evaluate the resistance of printed circuit board laminates to delamination. It measures the energy available for fracture per unit of new crack surface area.
Laminate Testing
Double cantilever beam or end notched flexure tests measure the load and displacement during crack propagation to calculate this property. When thermal stress from reflow or assembly operations is applied, the strain energy release rate determines whether a micro-crack will grow into a major delamination. If the strain energy release rate of the interface is lower than the critical fracture energy of the resin system, the laminate will fail under thermal cycling.
This failure often occurs at the glass-epoxy or copper-resin boundaries inside the multilayer board.
Reliability Limit
Circuit board designers use this parameter to select the appropriate laminate materials for harsh environment applications. It governs the structural integrity of the assembly during high temperature lead-free soldering processes. It represents a key limit for high layer count boards.
Laminates with high fracture toughness resist delamination during rework.