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Method for a fluxless molten solder bump process

IP.com Disclosure Number: IPCOM000019061D
Publication Date: 2003-Aug-27
Document File: 3 page(s) / 70K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for a fluxless molten solder bump process. Benefits include improved reliability and improved performance.

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Method for a fluxless molten solder bump process

Disclosed is a method for a fluxless molten solder bump process. Benefits include improved reliability and improved performance.

Background

Microvoids within solder bumps are a root cause of electrical open failure at die-to-package controlled collapse chip collect (C4) joints. As product power demands increase and with the copper (Cu) stud-bump architecture, electrical open failure has shifted from die under-bump metallization (UBM) to C4 solder joints.

         Conventionally, this problem is solved by using a flux-inclusive solder paste application. It minimizes microvoiding by optimizing the solder printing conditions and reflow profiles. However, during the reflow, microvoids can be generated by flux reaction with oxidized metal pads and solder particles. Microvoid-free bumps are difficult to produce (see Figure 1).

Another problem is that solder application within a vacuum chamber is technically difficult because the tin (Sn) composition evaporates.

Fluxless solder is conventionally considered a void-free solution. However, solder is difficult to wet onto the metal pad without flux application.

General description

         The disclosed method is a fluxless molten solder bump formation process, which ensures microvoid-free C4 bump formation to prevent electrical open failure.

The key elements of the disclosed method include:

•         Using a flux less molten solder

•         Using thermal pressure within a vacuum chamber to form the C4 bump

The disclosed method includes applying thermal pressure wi...