Assembly and reliability of thermally enhanced high I/O BGA packages

Abstract

Surface mount assembly defects for thermally enhanced high I/O, BGAs can range from 0 to 20 ppmj with packages that meet the JEDEC coplanarity specification of 6 mils. Defect levels can be much higher for packages that exceed 6 mils, however. The ability to put surface mount components on both sides of the PWB is desirable in some applications. To facilitate double sided assembly processing, it is recommended that the BGA package weight be kept below 0.038 gms/solder joint to avoid defects during the second side surface mount reflow process where the package is inverted while the solder joints are liquid. Some high I/O packages assembled to PWBs exhibited "infant mortality" failures during thermal cycling. These failures were typically at the package/solder ball interface, and were attributed to copper contamination at the electroless nickel/solder interface. Thermal cycling data show that if package metalization quality problems can be resolved, these high I/O packages can meet the severe requirements of telecommunications equipment attachment reliability. Further, data shows that subjecting packages with high temperature solder balls to double side renew processing reduces the attachment reliability of these packages.