TBGA substrate for lead-free and halogen-free applications

Green material requirement, i.e., lead-free and halogen-free, recently became a hot topic in IC packaging due to the environmental issues in increasing lead contamination and ozone concern in landfill and decomposition. The critical component on tape ball grid array (TBGA) reliability is heatsink adhesive which will be evaluated for the green material requirements to meet JEDEC moisture sensitivity level 3 (MSL 3) test at lead-free solder reflow condition. Therefore, TBGA package substrate is explored in this paper for lead-free and halogen-free requirements, by evaluating five types of heatsink adhesives. The five types of heatsink adhesives were qualified for eutectic solder applications. In the evaluation, all of the materials besides heatsink adhesives for the TBGA substrate with halogen content less than 900ppm are chosen to meet the halogen-free requirement. Any voids in the packages will be propagated and led to the delamination in the MSL-3 lead-free reliability test, since the package is subjected to high peak solder reflow temperature of 260°C. It is found that the high resin flow or good flowability of heatsink adhesive is crucial for 2-ML TBGA in the lead-free application, where heatsink adhesive is required to laminate onto the ground solder mask without any void. Heatsink adhesive is also observed to be void-free, since any voids in the adhesive will result in the cohesive failure in the reliability test. In addition, moisture absorption of adhesive should be low enough to reduce the hygroscopic stress and then to improve its performance in the lead-free reliability test. In conclusions, adhesives A and B are qualified to be applicable in the lead-free and halogen-free applications for both 1-ML and 2-ML TBGA packages with their higher resin flow and low moisture absorption. With the same chemical structure and properties as adhesive B except lower resin flow, adhesive C is only recommended for I-ML TBGA in the lead-free and halogen-free applications.