High-accuracy pick-and-place of multiple dies in parallel assisted by capillary self-alignment

Self-assembly of components driven by liquid surface tension presents a compelling complement (and potential alternative) to traditional high-precision pick-and-place methods, offering exceptional accuracy even when robotic placement is imprecise. While capillary self-alignment using liquid solder is the established standard in flip-chip processes, this work introduces self-alignment of dies on wetted receptors positioned on a temporary carrier. Low-viscosity liquid is precisely jetted onto each receptor, with liquid confinement achieved through patterned hydrophilic and hydrophobic regions created via plasma treatment.

Deterministic die placement is performed using low-accuracy pick-and-place for single dies as well as batches of three and nine dies, optimizing equipment for maximum throughput while maintaining both high accuracy and productivity. This industry-ready, fully automated chip-to-wafer pick-and-place process has been successfully integrated into a fan-out wafer-level packaging production flow, demonstrating that self-alignment can significantly relax the stringent robotic alignment requirements typically needed in fan-out packaging at the single-die level.

The self-alignment process has been thoroughly optimized, with failure modes such as poor liquid confinement, surface contamination, and excessive force identified and eliminated. Post-bond placement accuracy better than 3 μm (3σ) is consistently achieved for dies measuring 3.1 mm x 3.1 mm. Furthermore, parallel die handling enables high throughput rates of approximately 10,000 units per hour, combining precision with productivity.