Meaning
Polymerization processes alter the density and volume of thermosetting resins as they transition from a liquid to a solid state. This reduction in volume, known as cure shrinkage, occurs due to the formation of closer chemical bonds during crosslinking. It can induce mechanical stresses within sealed electronic packages.
Stress Generation
Internal mechanical stress develops when the compound is constrained by the rigid walls of a housing or component during curing. High cure shrinkage rates often lead to microcracking at the interfaces between the compound and the metal leads. This delamination allows moisture to enter the package and compromise electronic performance.
It can also cause delicate wire bonds to fracture under tension.
Dimensional Stability
Component alignment can be disrupted during the solidification phase of assembly. Mitigating cure shrinkage is essential when positioning optical sensors or high precision connectors that require sub millimeter accuracy. Changes in dimension can lead to assembly failures in multi part enclosures.
Filler Mitigation
Mineral fillers added to the resin mix help reduce the total volume change. In applications where cure shrinkage must remain below one percent, the formulation is heavily loaded with silica or alumina. This formulation strategy keeps the final dimensions within specified tolerances.
