Study On The Storage Aging Of Epoxy Prepreg And Hygrothermal Aging Of Printed Circuit Board

The performance of printed circuit boards (PCBs) is very crucial to electric devices. Epoxy prepreg is the most widely used PCBs material. The storage aging of epoxy prepreg has proud effects on the electrical and mechanical properties of the cured PCBs. Moreover, the reliability of electrical device depends deeply on the hygrothermal aging of PCBs. It is very important for electrical industry to characterize and improve the resistance of PCBs to hygrothermal aging.In this article, changes in chemical and physical properties of epoxy prepreg during storage aging were investigated to establish a quality control system by several methods. Compared with dynamic scanning calorimetry (DSC) and mid-infrared (MIR), near-infrared (NIR) Fourier transform spectroscopy is found to be more suitable for studying the epoxide group change during curing. The peak of epoxy in 4530cm-1 and the peak of benzene ring in 4620cm-1 are quite clear without peak overlap in NIR. The consumption of epoxy group and the constancy of the benzene ring peak were investigated by the in-situ NIR analysis during curing study of epoxy prepreg at 100℃. The change of curing conversion corresponds well with the variation of storage temperature and time of different epoxy prepregs aged under various conditions. Both the viscosity and the gelation time correlate well with the curing conversion during storage aging. Two glass transition temperatures of epoxy prepregs were identified in some epoxy prepregs by dynamic mechanical analysis (DMA). Time-resolved light scattering (TRLS) and optical microscopy (OM) results proved that phase separation might occur during storage in these prepregs.In the second part of this article, an amphiphilic oligomeric silane was introduced as a coupling agent to improve the interface bonding between resin matrix and glass fiber in order to enhance the reliability of PCBs in hygrothermal environments. The results from Gel permeation chromatography (GPC), MIR and GC-MS showed that the amphiphilic oligomeric silane coupling agent, which was synthesized by 3-isocyanatopropyl trimethoxy silane and nonyl phenol polyethyleneoxide, has little effects on the processability of epoxy prepreg. The contact angel between glass fiber and epoxy solution decreases with the addition of oligomeric coupling agent. Normalized water sorption by gravimetric measurement showed that the interfacial debonding time of composites with the oligomeric silane is increased significantly. The CAF test and SEM/EDX showed that with the addition of the coupling agent to the composite, the reliability of PCBs is improved remarkably due to the formation of a stable interface. In addition, CAF test is also consistent with the water sorption results, which reveals that the gravimetric measurement of water sorption is a cost-effective method to assess the CAF resistance of materials.