Non-Pressure Ag Sinter Paste without Residual Bleed-out: Studied on Different Au Based Substrates

In package assembly, one of the issues faced during die attach is bleed-out. Separation of some formulated ingredients in the paste flowing onto the surface of the substrate surrounding the die is referred to as bleed-out. Commonly, die-attach paste consists of resins, epoxies, solvents, fillers, additives, etc., where any one or more of these materials are expected to flow on the surface of the substrate during bleed-out. Upon thermal sintering, these materials remain on the substrate causing risk for subsequent processing such as wire bonding, encapsulation, etc. Non-pressure silver (Ag) sinter is a die attach process practiced in semiconductor packaging. The present study explains the mechanism of two types of Ag sinter paste (i) polymer-based silver sinter and (ii) pure silver sinter and their impacts on bleed-out. This study focuses on a non-pressure pure silver sinter paste without residual formations on thermal curing, eliminating further risks for subsequent processing. Thermo-gravimetric analysis (TGA) shows the novel formulation to possess weight loss at 50 °C to 220 °C range, while polymer-based paste exhibits a two-step reaction of weight losses between 80 °C to 220°C and 250 °C to 400 °C. Noteworthy observation of novel formulated non-pressure pure silver sinter revealing minimal to no bleed-out residues after sintering and when examined for different Au-based substrates. The paper enumerates and discusses in detail on the non-pressure pure silver sinter paste bleed-out on sintering. Despite the presence of bleed out phenomenon of the pure sinter paste in this article on certain substrate surface, no organic residue or silver particles are detected within bleed out area after sintering, which is confirmed by SEM-EDX and FTIR, demonstrating high ball shear and stitch pull, with riskless device functioning.