Die Attach Material Optimization for Enhancing Package Integrity of Surface Mount Device after Moisture Sensitivity Level 1

Moisture sensitivity level (MSL) is used to classify the capability of surface mount device (SMD) packages against moisture penetration when exposed to environment, and it is quite important for SMD. Compared to conventional through-hole (TH) which typically use wave soldering process for board mounting, the SMD packages are mounted on board by reflow soldering process at a temperature of $260^{\circ}\text{C}$, the moisture content of the SMD packages can lead to delamination risk by popcorn effect, it must be well controlled in order to prevent the delamination during reflow process.The MSL is ranked from level 1 to level 6, package achieves the most robust level MSLI can be interpreted as not sensitive to the moisture, the floor life is unlimited under typical room temperature and humidity, also do not need dry packing as special control. Typically, automotive products require at least MSL3 and most of them require MSLI, zero delamination after MSLI is being established as a solid requirement by the big players of semiconductor customers.The delamination in the interface between epoxy molding compound (EMC) and leadframe (LF) is well known and with quite mature solutions to achieve zero delamination at 0-hr and after MSLI. In previous study [1], a unique MSLI delamination symptom in the area around DA fillet was reviewed and discussed, root cause was identified as the outgas and resin bleed of the die attach material, die attach process optimization, i.e., increasing the die attach curing temperature was proposed and proven as an effective solution to eliminate such a delamination. Meanwhile, higher up the curing temperature will also bring the risk of LF surface oxidation and degradation. In this study, the die attach material optimization and formulation adjustment are proposed, which can solve the issue without changing the die attach curing temperature. The key components of the material are adjusted to another form, with the material manufacturing process optimization as well to increase the homogeneity of the material, it enables the even curing of the die attach system. To avoid potential side effects and negative impacts to the released system, material characterization is used to determine the differences between the optimized and original version and conclude that the output characteristics of both versions are identical. The material optimization is validated by assembled packages subjects to MSLI with 3 times reflow at $260^{\circ}\text{C}$, delamination levels are determined by C-Mode Scanning Acoustic Microscope (C-SAM) to assess the package integrity after MSLI. Its workability is also proven by typical visual inspection like x-ray, bond line thickness, and (BLT) measurement. Finally, a die attach material optimization can be adopted to enhance the SMD package integrity after MSLI, at the same time without the side effects to manufacturing process and workability.