The optimization of the composition of non-conductive film and the lamination to wafer

The Non-Conductive Film (NCF) for the wafers in 3D and TSV packages has been more and more developed in recent years. In the lamination step in the NCF process, NCF is laminated to a wafer, the wafer with NCF is diced, and an IC chip is bonded to the NCF. This lamination step and the condition after the lamination affect the following steps. In this research, the relation between the composition of NCF and the lamination property was studied. There are two types of NCF application. One is the application of the NCF thicker than bumps (`over the bump' type), and the other is the application of the NCF thinner than bumps (`under the bump' type). In case of the lamination `over the bump', no void was found, and dicing lines were well-filled after lamination. On the other hand, in case of the lamination `under the bump', bumps did not penetrate the NCF well, their edges became squashed, and the NCF thickness was not even. Moreover voids were found on dicing lines since they were not filled enough. Based on these findings, we attempted to find the optimum composition of NCF for the lamination under the bump. At first, we checked the following. - the effects of the NCF hardness and tackiness - the effects of the viscosity changes at heating As a result, we found that when NCF was harder and less tacky, and its melting viscosity at heating was higher, NCF thickness became more even and voids were well-controlled in lamination. Secondly we checked the effects of a base film, and found that as a base film was softer, bump-squash occurred less and NCF thickness became more even. Furthermore we attempted to optimize the lamination condition, and successfully achieved good results, i.e. bumps penetrated NCF, no bump-squash nor voids occurred, and NCF thickness was even. Lastly, we checked the condition after dicing (e.g. cracks, delamination), the connectivity and voids after bonding, and reliability.