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Browse Prior Art Database

Temporary Diffusion Barrier

IP.com Disclosure Number: IPCOM000115223D
Original Publication Date: 1995-Apr-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 2 page(s) / 75K

Publishing Venue

IBM

Related People

Gall, TP: AUTHOR [+4]

Abstract

Transient Liquid Phase (TLP) bonding is a joining technology in which a sandwich of two metals of an alloy system containing a eutectic melting reaction are placed in contact, heated, and joined through the formation of a eutectic liquid. Choosing the relative thickness of each metal layer such that the composition of the homogenized joint is outside the eutectic liquid phase region permits the TLP joint to solidify while being held at a constant temperature above the eutectic temperature. See, for example, [*], in which one surface is bonded to another by depositing layers of gold and tin on the first surface then placing it in contact with a second surface which can be wet with a AuSn liquid.

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This is the abbreviated version, containing approximately 52% of the total text.

Temporary Diffusion Barrier

      Transient Liquid Phase (TLP) bonding is a joining technology in
which a sandwich of two metals of an alloy system containing a
eutectic melting reaction are placed in contact, heated, and joined
through the formation of a eutectic liquid.  Choosing the relative
thickness of each metal layer such that the composition of the
homogenized joint is outside the eutectic liquid phase region permits
the TLP joint to solidify while being held at a constant temperature
above the eutectic temperature.  See, for example, [*], in which one
surface is bonded to another by depositing layers of gold and tin on
the first surface then placing it in contact with a second surface
which can be wet with a AuSn liquid.  When this structure is heated,
interdiffusion between the tin layer and the gold layer will produce
a boundary layer at and near the gold-tin eutectic composition.  When
the temperature exceeds the temperature (280 degree C), a AuSn liquid
forms here.  Holding at a temperature above the eutectic temperature,
the gold continues to diffuse into the liquid until the tin
concentration is sufficiently reduced and isothermal solidification
of the liquid occurs.

      In some binary eutectic systems (e.g., Au-Sn, Au-Pb) solid
state diffusion is sufficiently rapid that significant interdiffusion
will occur at room temperature and during the heating cycle.  If this
solid state interdiffusion is sufficient to change the composition of
the constituent bonding layers such that both are on the same side of
the eutectic composition (e.g., both hypoeutectic or both
hypereutectic) then a TLP reaction is no longer possible.  On the
bonding surface plated with both metal layers, one of the base metals
(such as gold) may diffuse excessively into the second metal layer
(such as Bi, Pb, or Sn) prior to joinin...