Contactless drop-attach adhesive bonding: An experimental study of mounting-pressure effects in microchip assembly

This work presents an experimental investigation of adhesive-based die attachment using the Drop-Attach technique, compared with the conventional pick-and-place method. Drop-Attach is a contactless process that eliminates the mechanical stresses inherent to force-assisted placement. In this method, dies are optically aligned and released—via a short air pulse—from a height of 100–300 μm above a substrate coated with a flat adhesive layer, enabling pressure-free, contactless placement. The process achieves smaller cycle times, potentially improving the throughput over conventional methods that require additional time for deceleration and bonding-force buildup. To assess feasibility and performance, a silver-filled bismaleimide/acrylate adhesive was printed on ENIG-finished pads, and dummy silicon dies with Au-, Ag-, and Cu-coated surfaces were assembled using both techniques. Bond quality was comprehensively analysed through measurements of bond line thickness, die tilt, void formation, die-shear strength, failure mechanisms, and electrical performance. Drop-Attach achieved minimal die tilt (≤0.1°) and uniform BLTs, though higher voiding and ∼9.55% increased electrical resistance were observed. The lower shear strength was primarily attributed to the absence of adhesive fillet formation rather than the lack of applied pressure. While trade-offs remain, this study demonstrates the feasibility of adhesive-based die attachment using the Drop-Attach method, which enables faster cycle times and higher throughput while significantly reducing mechanical stresses. These advantages position Drop-Attach as a promising technique for next-generation semiconductor packaging.