Enhanced adhesion of silica for epoxy molding compounds (EMCs) by plasma polymer coatings

Silica for epoxy molding compounds (EMCs) was coated via plasma polymerization using an RF plasma (13.56 MHz) as a function of the plasma power, gas pressure, and treatment time. The monomers utilized for the plasma polymer coatings were 1,3-diaminopropane, allylamine, pyrrole, 1,2-epoxy-5-hexene, allyl mercaptan, and allyl alcohol. The EMC samples were prepared from biphenyl epoxy resin, phenol novolac, triphenyl phosphine, and plasma polymer-coated silica, and the loading of silica was controlled to 60 wt%. The EMC samples were cured at 175 C for 4 h and subjected to T-g, CTE, and water absorption measurements. The adhesion of silica to epoxy resin was evaluated by measuring the flexural strength of EMC samples and the fracture surfaces were analyzed by SEM. Plasma polymer coatings were also characterized by FT-IR and coating thickness measurements. The plasma polymer coating of silica with 1,3-diaminopropane and allylamine enhanced the flexural strength of EMC samples (167 and 165 MPa), compared with the control sample (140 MPa), and exhibited a higher T-g, a lower CTE, and lower water absorption. The enhanced properties with 1,3-diaminopropane and allylamine plasma polymer coatings can be attributed to the amine functional groups in the plasma polymer coatings.