Browse Prior Art Database

Integrated Surface Mount Module I/O Attach

IP.com Disclosure Number: IPCOM000103231D
Original Publication Date: 1990-Aug-01
Included in the Prior Art Database: 2005-Mar-17
Document File: 1 page(s) / 61K

Publishing Venue

IBM

Related People

Chen, JP: AUTHOR [+3]

Abstract

Surface mount module packaging entails the placement, alignment and reflow of .035" solder balls to the multilayer ceramic (MLC) substrate bottom surface metallurgy. Current product definition require as many as 9000 solder balls per 5.2" square substrate. The prior art process involves the use of multiple fixtures and alignment tools, which require redesign for each different module form factor. A eutectic solder paste is required to join the solder balls to the substrate. Due to the distortion and camber of the substrate, uneven paste thickness and misalignment occurs, resulting in yield losses and driving up rework, tool downtime and product costs.

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Integrated Surface Mount Module I/O Attach

      Surface mount module packaging entails the placement, alignment
and reflow of .035" solder balls to the multilayer ceramic (MLC)
substrate bottom surface metallurgy.  Current product definition
require as many as 9000 solder balls per 5.2" square substrate.  The
prior art process involves the use of multiple fixtures and alignment
tools, which require redesign for each different module form factor.
A eutectic solder paste is required to join the solder balls to the
substrate.  Due to the distortion and camber of the substrate, uneven
paste thickness and misalignment occurs, resulting in yield losses
and driving up rework, tool downtime and product costs.

      In MLC substrate technology, vias are punched and electrically
conductive molybdenum is screened in the holes. This article proposes
to add one or two additional layers to the bottom of the substrate
depending on the thickness of the individual layer, which are punched
to match the layout of the bottom surface metallurgy layout, but with
empty holes.  When assembled and fired, these empty layers will
create a pocket for the eutectic paste and solder ball.  In effect,
the substrate design now integrates the screening and alignment
tooling, utilizing the substrate process to create counterbores.

      Because the counterbored substrate would allow the paste to be
screened directly onto the substrate, screening steps of the eutectic
paste can be eliminat...