Browse Prior Art Database

Nickel Plating onto a Nickel/Cobalt/Iron Alloy

IP.com Disclosure Number: IPCOM000116279D
Original Publication Date: 1995-Aug-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 2 page(s) / 87K

Publishing Venue

IBM

Related People

Boecker, J: AUTHOR

Abstract

This article describes a method for electrolytically depositing nickel on a Kovar* frame using special bath parameters to deposit the nickel without internal stress and with good adhesion.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Nickel Plating onto a Nickel/Cobalt/Iron Alloy

      This article describes a method for electrolytically depositing
nickel on a Kovar* frame using special bath parameters to deposit
the nickel without internal stress and with good adhesion.

      The electrochemical deposition of nickel onto one of its alloys
might not be particular easy, but when the deposit has to withstand
temperatures of almost 600 degrees C without blistering, the
operation
becomes increasingly more difficult.

      Due to the match in thermal expansion Kovar alloy (28% Ni, 18%
Co, 54% Fe) is used in conjunction with Al&sub2.O&sub3.  ceramic.  A
Kovar seal ring brazed on a ceramic chip carrier has to be
electroplated with nickel.  Thereafter, the vias in the chip area are
plated with immersion gold.  For intermetallic contact immersion gold
needs thermal diffusion at 560 degrees C.

      The main requirement is that the nickel plate on the Kovar ring
must not blister, peel or flake following exposure to a temperature
of
560 degrees C.  To achieve this requirement a special pretreatment
and
a special nickel bath is used.

      For activation of the Kovar surface in order to achieve good
adhesion the following pretreatment steps have been found to be
suitable:
  3 min          hot soak clean                     60 degrees C
  3 min          hot rinse                          60 degrees C
  3 min          acid cleaner containing fluoride   room temp.
  2 min          rinse                              room temp.
  0.5 min        nickel strike                      room temp.
  2 min          rinse                              room temp.
  x min          nickel sulphamate                  68-70 degrees C
  4 min          rinse                              room temp.
  4 min          dry

      The plating time x corresponds to the desired nickel thickness
(in 1 min at 20 A/dm2 4 &mu.m nickel is deposited).

      For high efficient activation high hydrogen generation at the
cathode surface is required.  Therefore, the strike solution was
formulated with low nickel and high chloride content:
         42 g/l  NiCl&sub2.  x 6 H&sub2.O
         17 ml/l HCl conc.
         electrolytic nickel as anode

      The current efficiency is very low in the range of less than
10%.

      The bath has to be kept to strength since understrength HCl
will lead to poor plate adhesion due to a reduced scrubbing action
during the cathodic stage.

      Basis is a low-stress nickel sulphamate solution, wid...