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Transient Liquid Phase Bonding Process

IP.com Disclosure Number: IPCOM000036182D
Original Publication Date: 1989-Sep-01
Included in the Prior Art Database: 2005-Jan-28
Document File: 2 page(s) / 13K

Publishing Venue

IBM

Related People

Kang, SK: AUTHOR [+3]

Abstract

A transient liquid phase (TLP) bonding process for attaching metallized pads on components to a matching set of pads on a carrier is disclosed and comprises: applying by vapor deposition, plating or any other deposition process a metal or alloy coating on one or both of the sets of metal pads to be attached; placing the coated pads in intimate physical contact with each other; heating the coated pads to a temperature above the eutectic temperature of the pad metal-coating or coating- coating combination (whichever is lower), for a sufficient period of time to enable diffusion to occur across the contact interface resulting in the formation of the eutectic liquid, at and near that interface; and cooling the assembly to freeze the eutectic liquid thus forming a strong bond between the pads.

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Transient Liquid Phase Bonding Process

A transient liquid phase (TLP) bonding process for attaching metallized pads on components to a matching set of pads on a carrier is disclosed and comprises: applying by vapor deposition, plating or any other deposition process a metal or alloy coating on one or both of the sets of metal pads to be attached; placing the coated pads in intimate physical contact with each other; heating the coated pads to a temperature above the eutectic temperature of the pad metal- coating or coating- coating combination (whichever is lower), for a sufficient period of time to enable diffusion to occur across the contact interface resulting in the formation of the eutectic liquid, at and near that interface; and cooling the assembly to freeze the eutectic liquid thus forming a strong bond between the pads.

In contrast to the conventional reflow soldering of either evaporated solder pads or screened solder paste pads the TLP process has the main advantage that it is fluxless and eliminates the need for the application of flux prior to joining and the subsequent cleaning of flux residues which are often corrosive if left on the parts. This is particularly attractive for low profile surface mount applications where the gap between the component and the carrier is small making effective flux removal difficult. Further, since the eutectic bonding is achieved at a lower temperature than the melting points of the individual coatings on the contacting pads the overall joining temperature can be significantly reduced compared to conventional reflow soldering with the coating alone. This would be advantageous in joining components that are sensitive to higher temperature exposures. As compared to joining with solder paste, the TLP process is less prone to solder bridging and therefore better suited for greater density of pads per unit area.

Copper- or gold-coated copper pads are typically provided on the components and carriers that are to be joined. To attach these by the TLP process, a thin coating of a metal other than copper or an alloy is deposited on either or both sets of contact pads.

The d...