Mold Adhesion Force Measurement

During the encapsulation process of IC packages, when epoxy molding compound (EMC) is filling the mold cavity and cured in the mold, adhesion effects occur in the interface between EMC and mold surface. Adhesion effects can cause many problems. For example, too large an adhesion force may damage an IC during ejection and cause the package to fail and thus lower the yield rate and reliability. To get rid of the mold adhesion problems, improving the mold design and applying suitable surface treatments such as mold surface coating are the common approaches. Applying suitable surface coating is a more popular and practical approach. How to evaluate the mold adhesion force and use the data to improve products yield rate are the main issues for packaging. This paper uses a semi-automatic EMC adhesion force test instrument that had been developed and fabricated to measure normal and shear adhesion forces between the mold surface and EMC. By measuring the adhesion force, one can judge how much does a specific type of surface treatment help in reducing the amount of mold adhesion force. Nine kinds of various mold surface coating were tested with this instrument to measure the magnitude of adhesion force between EMC to determine the effectiveness of mold coating. The measured data showed that with different coatings on mold surface, the mold adhesion force can be very different. This paper also discussed the issue of successive normal force test. Engineers would use the most effective mold coating material to execute the continuous normal adhesion experiment. The variation of normal force during successive molding test could be used to predict the time for mold cleaning. By counting the total number of shots when the normal force begins to rise, engineers can accurately predict the number of shots for a specific kind of mold surface coating to be cleaned. This paper also described the effects of defrosting period on mold adhesion force of EMC. Defrosting is a process to increase the frozen EMC temperature to room temperature and stay at room temperature for some time before molding. It was found by molding engineers that increased defrosting time period would increase the frequency of mold cleaning. But there had been no quantitative description on how much mold adhesion force increase during the defrosting process. A semi-automatic EMC adhesion force test instrument was used to evaluate the effects of defrosting period on mold adhesion force of EMC. It was found that increase the defrosting time will increase the amount of adhesion force between EMC and mold surface. The higher is the relative humidity during defrosting on the adhesion force, the higher is the increase of adhesion force.