Surface mount assembly defects for thermally enhanced high I/O,BGAs can range from 0 to 20 ppmj with packages that meet the JEDECcoplanarity specification of 6 mils. Defect levels can be much higherfor packages that exceed 6 mils, however. The ability to put surfacemount components on both sides of the PWB is desirable in someapplications. To facilitate double sided assembly processing, it isrecommended that the BGA package weight be kept below 0.038 gms/solderjoint to avoid defects during the second side surface mount reflowprocess where the package is inverted while the solder joints areliquid. Some high I/O packages assembled to PWBs exhibited “infantmortality” failures during thermal cycling. These failures weretypically at the package/solder ball interface, and were attributed tocopper contamination at the electroless nickel/solder interface. Thermalcycling data show that if package metalization quality problems can beresolved, these high I/O packages can meet the severe requirements oftelecommunications equipment attachment reliability. Further, data showsthat subjecting packages with high temperature solder balls to doubleside renew processing reduces the attachment reliability of thesepackages
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