Experimental Study on the Underfill Properties for Silicon Die Flipchip Package

초록

The application of an underfill reduces the stress to solder bumps and enhances the reliability of the solder joints. As the packaging density in board level package increases, the chip to chip distance should be decreased. Moreover, as the board thickness decreases, the importance of bending reliability is increases. On these demands, recently, new underfill material was developed to have short fillet width and high flexural toughness. In this study, the filling behavior and reliability of the conventional and new underfills were investigated. Conventional underfills, 3536(Henkel Loctite Co.), 305Y and 3051B(Hitech Korea Co.) and newly developed underfill, 3075(Hitech Korea Co.) were used for experiments. Flipchip silicon die with a pitch of 400um and solder ball of 200um in dia. and glass substrate were used to evaluate filling behavior. Plastic ball grid array(PBGA) with a pitch of 800um and solder ball of 450um in dia. and FR-4 PCB with a thickness of 1mm were used for mechanical reliability tests. Time to fill was measured by CCD camera after double L-line dispense. Mechanical reliability tests were performed under the various condition of static vs. dynamic, no strain vs. free strain and PCB bending vs. package pull. It was considered that, the newly developed underfill showed improved mechanical reliability and fast filling time compared to conventional underfills.