Evolution of Internal Stress in Epoxy Composite-Based Potting Structures under Thermal Cycling Aging

Abstract

Epoxy resin-based composites are widely used for encapsulating electronic products in high reliability fields such as aerospace and deep sea exploration. However, thermal expansion mismatch between the epoxy and metallic/ceramic components generates alternating thermal stresses under temperature cycling, which limits long-term device reliability. This work establishes a multipoint distributed in situ sensing network using embedded FBG and strain gauge sensors within an epoxy potted structure, enabling internal strain monitoring over 15 thermal cycles from −60 to 90 °C. A coupled thermomechanical finite element model incorporating temperature-dependent constitutive parameters, tension compression asymmetry, and cohesive interfacial behavior is developed and validated against the monitoring data, yielding a prediction confidence of approximately 85%. A stretched exponential evolution law is proposed to quantitatively describe the strain decay and stabilization behavior. These findings elucidate the internal stress evolution mechanism under thermal cycling and provide a quantitative basis for mechanical reliability assessment and lifetime prediction of epoxy encapsulated electronic structures.