Super Fine Jet Underfill Dispense Technique for Robust Micro Joint in Direct Bonded Heterogeneous Integration (DBHi) Silicon Bridge Packages

Abstract

Heterogeneous integration is becoming a key technical approach to extend Moore's law. A new packaging technology named Direct Bonded Heterogeneous Integration (DBHi) with Si-bridge has recently been proposed [1] [2]. The DBHi package uses mixed pitch interconnections. Standard pitch bumps (150 μm) connect processor chips to a laminate substrate, while fine pitch bumps (75 μm) connect the processor chips to a bridge chip. In the assembly process of this new package, the chip-bridge joining is performed first, then the bridged chips assembly is joined to the laminate. However, during joining of the bridged chips to the laminate, a critical thermo-mechanical stress is generated in the micro joint on the small bridge chip due to the coefficient of thermal expansion (CTE) mismatch between silicon and laminate. In addition, dispensing capillary underfill from the edge of the bridge chip is not possible because the space from the edge of the bridge chip for underfill supply is limited to 250 μm maximum distance due to the standard pitch bumps located near the bridge chip. In this paper, the chip-bridge joining and encapsulating processes for the micro joint are investigated, and material properties of both conventional non-conductive pastes (NCPs) and a capillary underfill (CUF) which can be dispensed by a fine jet dispense tool are compared. We demonstrate a fine jet underfill dispensing technique which significantly increases the bridge micro joint robustness. The jetted micro dots fly through the high-aspect narrow gap (150 μm-width and 800 μm-depth) between the two processor chips, and land directly on the surface of the bridge chip and then flow into the micro joint area by capillary force. The flying dot size and shape of underfill jetting are measured experimentally and monitored by a high-speed camera. The diameter was about 100 μm with an elongated tail. This assembly method provided improved assembly yields and excellent reliability performance of the DBHi modules.