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Method for a substrate-based self-leveling mechanism for a no-flow underfill process

IP.com Disclosure Number: IPCOM000132635D
Publication Date: 2005-Dec-28
Document File: 3 page(s) / 85K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for a substrate-based self-leveling mechanism for a no-flow underfill (NUF) process. Benefits include improved functionality, improved yield, and improved reliability

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Method for a substrate-based self-leveling mechanism for a no-flow underfill process

Disclosed is a method for a substrate-based self-leveling mechanism for a no-flow underfill (NUF) process. Benefits include improved functionality, improved yield, and improved reliability.

Background

      The conventional NUF process can have a low yield (10-20%) when a die shifts on die-substrate contact and the die bump and substrate solder provide insufficient horizontal mechanical constraints (see Figure 1). Entrapment is a major cause of reliability and failure risks (not illustrated) when die-bump gap is not in control.

      One solution is to optimize the bump shape and modify the design layout to provide a self-locking mechanism. However, modifying the bump shape increases the size of the defects from entrapment and requires an expensive controlled collapse chip connect plating process.

      Although the best approach is to add horizontal constraint to the die and substrate, using vacuum or other mechanisms, the manufacturing system (tool) and other yield requirements prevent lateral-direction containment.

              The conventional tool design relies on the initial contact between the die and nozzle (bondhead) to activate the force control mechanism on the die holder. This is usually achieved by a gimbal mechanism that could have arbitrary angled plane before force is applied. However, this arrangement can create an offset load on the die. The lack of horizontal constraint fails to stop the offsetting force that causes the die to slide. The subsequent bonding results in a misaligned joint.

General description

              The disclosed method includes an apparatus for bond-head support on the substrate with elastic properties tuned to the dimensions and properties of the die and substrate. When the die holder initially approaches the substrate, a flat nozzle surface becomes parallel to the die surface as the nozzle leg (or bond-head support) contract the substrate first. On contact, an offsetting force is not generated and the die does not shift. The bonding head (nozzle) remains coplanar with the die surface during the NUF bonding step and misalignment is reduced.

      Additional elastic springs and variations are applied to level the substrate and prevent die shifting at bond head-die contact. Adjustable support legs provide precise gap control to maintain the joint quality.

Advantages

              The disclosed method provides advantages, including:
•             Improved functionality due to providing bond-head support on the substrate

•             Improved functionality due to providing elastic springs and variations to level the substrate
•             Improved yield due to maintaining the optimal bump shape

•             Improved reliability due to minimizing underfill entrapment

•             Improved reliability due...