Silica-filled epoxy molding

Fig. 31. Comparison of the profile of the apparent mean viscosity vs, time for the silica filled epoxy molding compound, measured by RPA. (O denotes conventional crushed fused silica and denotes spherical fused silica)...

Because of the thermal contraction mismatch of a silicon chip, metal lead-frame and silica-filled epoxy molding compound integrated circuit (IC) packages bow or warp when cooled to room temperature after manufacture. The magnitude of the bow in an IC package can be determined quantitatively by... 

Silica-filled epoxy molding compounds use an epoxysilane for such a reason. In some cases, special epoxysilanes that have low chloride and low ionic content are used to further minimize negative effects on electrical properties. 

A part, consisting of a carbon fiber composite tube, was initially adhered to the inside of a short titanium coupling by a silica-filled epoxy. The bond failed and a fluorinated mold release was believed to be the cause of the failure and was the purpose for this investigation. A sample of the epoxy (Sample A) and the part (Sample B) were submitted for X-ray photoelectron spectroscopy (XPS) to analyze for the presence of both fluorine and silicon. 

The moisture resistance properties of filled molding compounds are enhanced by the treatment of the fillers with silane adhesion promoters prior to compounding. Silane promoters on wollastonite fillers in thermoplastic polyester molding compounds (50 percent filled) will improve the flexural strength after 16 h in 50°C water by as much as 40 percent. Silane-treated silica fillers have been found to significantly increase the moisture resistance of epoxy adhesives used in the electronics industry for chip, surface-mounted, and printed-circuit processes.8... 

Epoxy polymers (including epoxy novolacs) have been designed to meet most of these requirements and are almost universally used in such encap-sulant applications. Epoxy polymers exhibit superior adhesion that in many cases eliminates the need for a barrier or junction coating. They have a low coefScient of thermal expansion low shrinkage and low injection velocity, which means that low transfer or injection pressures can be used. These polymers also possess excellent mechanical properties coupled with low moisture and gas permeability. Above all, they are cheap and readily available. Other transfer-molding materials used to a limited extent include silicones, phenolic materials, and even polyesters. Most molding formulations are highly filled (70-75%) with materials such as quartz, fused silica, short... 

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