BGA (ball grid array), one of the structures used for semiconductor packages, involves a laminated structure. BGA inevitably involves significant warpage, owing to differences in shrinkage among constituent materials. The extent of warpage is governed by total shnnkage (= cure shnnkage i-thermal shrinkage ) of the epoxy molding compound that encapsulates the IC chip. In particular, the cure shrinkage exerts great influence on warpage. Cure shnnkage has been understood as the decrease in free volume at the time of curing. However. the cure shrinkage rate cannot be sufficiently explained by the free volume of the cured epoxy resin. We have developed an evaluation method based on the epoxy group reaction ratio, and have eventually confirmed that cure shrinkage depends on the reaction ratio of the epoxy group after curing, and on epoxy group density.
The market for BGA packages is expanding all over the world, owing to the ease of its mounting onto the PC boards. On the other hand, BGA packages possess certain shortcomings compared to QFPs. Anti-solder crack performance on Fine Pitch BGA (=FPBGA) and warpage on Mold Array Package-BGA(=MAP-BGA) are significant disadvantages. To improve the performance of BGA packages, we studied various combinations of materials used for BGA package including molding compounds, die attach pastes, and substrates.
Surface mount packages are subjected to high levels of thermal stress in mounting, which causes problems such as the occurrence of package cracking or the lowering of the humidity resistance after mounting. In this study we examined these deteriorations from the viewpoint of the stress characteristics of molding compounds at high temperature. A s a result, it was confirmed that both low stress at high temperature and high strength at high temperature of molding compounds are important factors causing quality deterioration in mounting. Here we will report the result of the examination of the characteristics required of molding compounds to cope with the surface mounting methods.(iv) Realization of low stress at high temperaon the deterioration of packages in soldering. In particular, we noticed (iii) Realization of high strength at high temperature and (iv) Realization of low stress at high temperature out of (i)-(iv) and examined their influence on the deterioration. In storage ture Molding Chip Die paci4+V Water diffusion through a package 885 05695603/89/0885 $1.00 0 IEEE ___ .
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