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Method for the stencil printing application of a no-flow underfill material to bond wafers

IP.com Disclosure Number: IPCOM000018941D
Publication Date: 2003-Aug-21
Document File: 3 page(s) / 666K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for the stencil printing application of a no-flow underfill material to bond wafers. Benefits include improved functionality, improved process simplification, and improved reliability.

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Method for the stencil printing application of a no-flow underfill material to bond wafers

Disclosed is a method for the stencil printing application of a no-flow underfill material to bond wafers. Benefits include improved functionality, improved process simplification, and improved reliability.

Background

         A requirement exists to perform no-flow underfill (NUF) processing on a stacked flip chip package. The first die has copper pillars on the front and eutectic solder bumps on the back. The thermo-compression bonder (TCB) damages the backside bumps while performing reflow on the front-side bumps. The TCB is applying vacuum to hold the part and can potentially remove the backside bumps during the reflow process and clog the vacuum line over time. (The bonder acts like a solder removal tool.) Enabling no-flow underfill for both the flip chip dice significantly simplifies process and equipment requirements. Removal of deflux and the integration of epoxy and chip attach is a significant process simplification, which cannot be possible with capillary underfill.

No conventional underfill process exists for wafer-to-wafer bonding. Capillary underfill technology does not work on a wafer-to-wafer bond. No application area is available to stage the underfill material to enable it to flow through capillary action across the wafer bump spaces. Even if tooling is modified to provide a staging/dispense area, the capillary action would take a long time to complete the underfill.

General description

         The disclosed method is the application of no-flow underfill material by stencil printing on a base wafer followed by the bonding of a second wafer to the base.

         The key elements of the method include:

•         Application for FC-to-FC interconnect/stacking technologies

•         No-flow material application for wafer-to-wafer bonding by stencil printing

•         Use of wafer and bump alignment to prealign interconnects

•         Use of a thermo-compression bonder to force mechanical interconnection and reflow

•         Use of a varia...