Browse Prior Art Database

Permalloy Plating Bath with Improved Composition Control

IP.com Disclosure Number: IPCOM000116019D
Original Publication Date: 1995-Jul-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 4 page(s) / 131K

Publishing Venue

IBM

Related People

Croll, IM: AUTHOR [+2]

Abstract

Disclosed is a plating bath formulation for nickel-iron deposition that gives improved composition and thickness uniformity and control. This bath also extends the range of current densities over which composition and thickness control can be maintained. Disclosed also is the use of sodium sulfite as a plating bath additive that results in the superior performance of this bath, and may be extendable to other Ni alloys systems.

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Permalloy Plating Bath with Improved Composition Control

      Disclosed is a plating bath formulation for nickel-iron
deposition that gives improved composition and thickness uniformity
and control.  This bath also extends the range of current densities
over which composition and thickness control can be maintained.
Disclosed also is the use of sodium sulfite as a plating bath
additive that results in the superior performance of this bath, and
may be extendable to other Ni alloys systems.

      Nickel-iron alloys of the permalloy type (80% Ni - 20% Fe) are
typically electroplated to form the poles of the thin-film recording
head.  When nickel and iron are codeposited from a non-complexing
bath, iron deposition occurs preferentially to nickel deposition, a
phenomenon well-known and referred to as anomalous codeposition (1).
In order to compensate for the preferential deposition of iron, the
composition of typical permalloy plating baths is adjusted so that
the Ni/Fe ratio of the bath is considerably higher than that of the
final deposit.  (2) describes a method for plating permalloy films
of uniform composition that uses Ni/Fe ratio in the electrolyte in
the range of 45:1 to 70:1 at room temperature and pH of 3.  The range
of current densities that produce an acceptable deposit is from 2 to
12 mA/cm(2), with an optimum of 4 to 8 mA/cm(2).  As a result of the
very high ratio of Ni/Fe required in the plating bath to produce the
desired ratio in the deposit, the concentration of ferrous ion in the
bath is typically very low (0.15 to 0.3 g/l in the bath described
above).  As a result, the rate of deposition of iron is much more
strongly influenced by the agitation in the plating cell than that of
nickel.  The consequence of plating over complex geometries, such as
the area of the magnetic poles in the thin-film recording head, is a
further enrichment of iron relative to nickel in the more
geometrically-accessible regions of the device, such as the yoke on
the top of the coils.  This effect is more pronounced at higher
current density, and can be reduced in part by uniform and intense
agitation over the flat plating surface.  Two acceptable agitation
systems for the plating of nickel-iron alloys are an impinging jet
system, as described in (3) and a reciprocating paddle system, as
described in (4).

      The plating bath disclosed here is a variation of the
Watts-type nickel bath typically used for nickel-iron deposition.

This plating bath uses an additive of sodium sulfite, which
dramatically alters the ratio of nickel to iron in the deposit.  The
so-called anomalous deposition of nickel-iron is eliminated, and
nickel and iron codeposit in a ratio which is much closer to the
ratio of the two elements in the plating  bath.  A typical bath
formulation would be:
  200 g/1 NiCl sub 2.6 H sub 2 O
  10 g/1 FeCl sub 2 .4 H sub 2...