Investigations on the Batch Fluctuations of an Epoxy Diluent via Encapsualtion Stress Analysis

Reactive diluent plays an important role in epoxy encapsulant formulations. Contents of epoxide and impurities like inorganic chlorine and saponified chlorine are the major chemical parameters for the reactive diluents and have an impact on the property of epoxy, including the curing residue stress which is unavoidable and could be devastating if it is not handled well. In current work, we analyzed the variations of the chemical parameters of a reactive diluent, as well as the major processing and thermos-mechanical properties of the corresponding epoxy resin. Fluctuations of the reactive diluents were demonstrated by the notable content of chloride. One major influence of the batch fluctuations of the reactive diluents was disclosed upon the varying gel time of the epoxy. Furthermore, evolution of epoxy curing stress was monitored by a straightforward strain gage based method, which showed varying evolving behaviors as a function of time due to the batch fluctuations of the diluents. The higher content of saponified chloride of the reactive diluent delayed the curing reaction, leading to a higher curing shrinkage induced stress during the non-isothermal curing process and a lower thermal-induced stress within the following cooling process, which may result in unexpected fracture in the encapsulation potentially. These results demonstrated the critical effect of the saponified chloride content of the raw materials in the epoxy encapsulant on the consistent performance of the encapsulation. Our novel method to measure the curing residual stress appeared to be a simple and efficient way to monitor the batch fluctuations of raw materials by differentiating the curing behaviors.