Preparation And Properties Of Spherical Silica-epoxy Compounds For IC Package

As the core of modern integrated circuits, silica chip from its design to package is a high degree integration of multiple disciplines of human knowledge and technology. Chip package and testing is the final and key procedure in chip production process. The quality of packing materials has an vital effect on the performance of the packaged device. For the high reliability, low cost and simple production technology suitable for large scale production, epoxy molding compounds (EMC) have accounted for the majority of materials market so far beyond the metal packaging materials and ceramics packaging materials, and been widely used in many military and civilian electronics field.The rapid development of VLSI made more strict requirements for packaging materials, including spherical silica filler, high performance epoxy resin and halogen-free flame retardant and so on. As for epoxy encapsulation material, this paper has made some breakthroughs in the preparation and grade of spherical silica and the intrinsic flame retardant epoxy resin system, and laid a solid foundation for further development of environmentally friendly epoxy molding compound. The main results are as follows:1. Large scale synthesis of spherical silica hydrate was conducted by using industrial grade raw materials and turbulent flow cycle method. Micron spherical silica were obtained after heat treatment and the quality indexes of products were characterized in detail, the results show that the rate of spherical balls is above 95%, the purity of silica has achieved 99.98%, and the particle size can be adjusted and controlled between 1～10μm (d50). The effect of five kinds of spherical silica on the flowability of several kinds of epoxy resin system was studied, and the results showed that the system filled with SS2 (d50= 2.5μm) component exhibited better flowability than the other kinds of spherical silica in the same epoxy system. Through the establishment of close packing spherical particles model according to the particle size distribution of five kinds of spherical silica, we know that the closest packing can be achieved when the model parameters n=0.44. The reasonable solution was obtained by multiple linear regression of the actual size distribution. Experiments proved that the grading of spherical silica is effective to improve the content of spherical silica filler in the epoxy resin system, and the grade solution has been used in our following experiments.2. A laboratory preparation process of epoxy molding compound was designed and established according to the actual industrial production, and a set of mold was designed for the of testing EMC performance. The blending process of raw material, process of melting & softening and molding process were all improved in our experiments. The testing procedures of the spiral flow length, thermal expansion coefficient, flame retardant and moisture of epoxy molding compound were further improved. A set of quality testing method for the raw materials of epoxy molding compound was established, including the epoxy equivalent, hydroxyl equivalent, chloride content of resin and the testing methods of silica filler.3. The effect of the coated triphenylphosphine accelerator (EPCAT-TPP) on the curing reaction of the o-cresol formaldehyde epoxy resin and phenolic resin was studied by means of thermal analysis and the curing conditions of 150℃2h+180℃6h was determined. When the spiral flow length of o-cresol formaldehyde epoxy resin system is 100 cm, the appropriate filled loading of this system is 62%, the thermal expansion coefficient (CTE) of this cured system was 70.91×10-6 K-1, and the bending strength was 132.56 MPa (30℃). The curing behavior of two-component system made of o-cresol formaldehyde epoxy resin by adding lower viscosity resin was studied. The filler loading could reach 73% when the spiral flow length was 100 cm, The system made from o-cresol formaldehyde epoxy and biphenyl epoxy resin exhibited best performance:the CTE reached 47.81×10-6K-1, bending strength was 237.05 MPa (30℃), flame retardant properties reached the FV-1 level and the moisture absorption was 0.345%.4. The single crystal and powder of a new flame retardant containing nitrogen and phosphorus AEDPH4 are synthesized and characterized. We can find from the DSC figure that the curing temperature is lower and the viscosity increases after adding 1wt% AEDPH4 to the o-cresol formaldehyde epoxy resin system. The new curing process of 130℃4h+180℃4h was determined. The E5-1 system containing 1 wt% AEDPH4 was prepared, the CTE of this cured system was 49.14×10-6 K-1, the bending strength was 225.13 MPa (30℃), the flame retardant grade reached the FV-0 degree and the moisture absorption was 0.398%. The results showed that in addition to the increased levels of flame retardant, the bending strength, water absorption and coefficient of expansion was not as good as E5-1 system, and the processing behavior was getting even worse.5. The characteristics of the curing reaction of the intrinsic flame retardant biphenyl resin system were studied by the method of thermal analysis. The catalyst and control action of the coated triphenylphosphine accelerator EPCAT-TPP on the curing process of the system was further confirmed. When the spiral flow length of this biphenyl system is 100 cm, the appropriate filled loading of this system is 76%. The CTE of this cured system was 45×10-6 K-1, and the bending strength was 139.68 MPa (30℃), the flame retardant properties reached the FV-0 level and the moisture absorption was 0.68%. The filler loading reached 78% when this system modified by other low viscosity epoxy resins, and the CTE and bending strength of the four cured system got the same results. The N3-1 system adding dicyclopentadiene ring epoxy resin got the best performance:the CTE was 42.72×10-6 K-1, the bending strength was 190.53 MPa (30℃), the flame retardant properties reached the FV-0 level and the moisture absorption was 0.47%.