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Low Porosity Plating Method for Sintered Powered Metals

IP.com Disclosure Number: IPCOM000116252D
Original Publication Date: 1995-Aug-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 4 page(s) / 158K

Publishing Venue

IBM

Related People

Topa, R: AUTHOR [+2]

Abstract

Metal compacts prepared by the process of powder metallurgy, wherein metal powder is cold pressed into shape and then sintered at a temperature below the melting point of the metal to cause local diffusion and welding of the particles into a homogenous compact, are always porous. This porosity always adds to the difficulty of plating the metal compact.

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Low Porosity Plating Method for Sintered Powered Metals

      Metal compacts prepared by the process of powder metallurgy,
wherein metal powder is cold pressed into shape and then sintered at
a temperature below the melting point of the metal to cause local
diffusion and welding of the particles into a homogenous compact, are
always porous.  This porosity always adds to the difficulty of
plating the metal compact.

      Connector parts made from copper alloy compacts typically have
a nickel layer on their sliding or engaging surfaces.  The nickel
layer prevents the porosity of the underlying copper from reaching
the engaging surface.  Too much porosity at the engaging surface may
lead to corrosion, which in turn, may cause high contact resistance
and even electrical insulation.

      One method of obtaining a relatively nonporous surface is resin
impregnation of the metal's surface pores.  Resin impregnation is a
sealing procedure wherein an anaerobic liquid is forced under vacuum
into fissures of the surface of the metal.  The impregnated metal is
then cured and rinsed with a solvent.  The organic material remains
in the crevices and the top layer of the metal obtains the structure
of a solid material.  Resin impregnation can improve the plating
performance in grounding applications.  However, when the subsequent
plating procedure involves the use of high current and/or elevated
temperature, the organic material may not remain imbedded in the
metal structure, but work its way to the surface causing poor
adhesion of the plated layers.

      Another method of plating a porous surface to obtain a surface
structure that is relatively pore-free is to deposit several
different layers of metal onto the porous base metal.

      This method attempts to take advantage of the grain boundary
and lattice structure differences of the various layers of deposited
metals by closing down the pore path to the top surface.  A
significant disadvantage of this method, however, is the increased
risk of adhesion problems associated with the many different
metal-to-metal interfaces.

      A third method of obtaining a relatively pore-free surface is
to clean the surface and then electropolish the surface as if the
compact base metal is a wrought metal.  This paper will describe a
methodology based upon the above statement.
  1.  Anodically clean the surface of the sintered metal body.
  2.  Electropolish the surface of the sintered metal body.
  3.  Deposit a strike layer onto the surface of the sintered metal
       body.
  4.  Deposit an electroless nickel layer onto the surface of the
       sintered metal body, wherein the metal layer has a porosity of
       less than or equal to 20 pores per square inch.

      The present paper is directed to a low porosity plating
procedure for connector housings fabricated from sintered powdered
metals.  Powdered copper and copper alloys such as berylliu...