Browse Prior Art Database

Hybrid Brazing/Pretinning of MLC Substrate

IP.com Disclosure Number: IPCOM000099963D
Original Publication Date: 1990-Mar-01
Included in the Prior Art Database: 2005-Mar-15
Document File: 2 page(s) / 62K

Publishing Venue

IBM

Related People

DiPaolo, N: AUTHOR [+2]

Abstract

Disclosed is a process whereby gold-tin (Au-Sn) eutectic paste (or preform), and lead-tin (PbSn) preforms are used simultaneously to braze pins and pre-tin seal band, respectively, on multilayer ceramic (MLC) substrate at 390 + 10oC. At this temperature both alloys form a strong joint with the nickel/gold metallization of the substrate, though the Au-Sn eutectic melts at 280oC and the Pb-60% Sn (used here) melts at 193oC.

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Hybrid Brazing/Pretinning of MLC Substrate

       Disclosed is a process whereby gold-tin (Au-Sn) eutectic
paste (or preform), and lead-tin (PbSn) preforms are used
simultaneously to braze pins and pre-tin seal band, respectively, on
multilayer ceramic (MLC) substrate at 390 + 10oC.  At this
temperature both alloys form a strong joint with the nickel/gold
metallization of the substrate, though the Au-Sn eutectic melts at
280oC and the Pb-60% Sn (used here) melts at 193oC.

      In both cases, the important reaction that leads to bonding
occurs between the Sn and the Ni.  The function of gold is to prevent
the oxidation of the nickel surface and to aid in the process of
wettability.  The reaction product bonding the two surfaces are
nickel-tin intermetallics. Gold-tin intermetallics, which also form,
are usually dispersed in the body of the joint.  The reaction is
controlled by the Ni diffusion through the intermetallic layer, which
is self-limiting.  For this reason, the nickel consumption is not
excessive for the Pb 60% Sn despite the fact that the reflow
temperature (390oC) is about 200oC higher than its melting point.

      The Au-Sn eutectic reaction and process had been well
established and in use.

      The seal band metallization and the solder joint are shown in
the left and right views of Fig. 1.

      The Pb-Sn preform 6 is placed on the seal band after it is
coated with flux which holds the preform in position. The reflow
process is...