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Photoresist Composition for Precious Metal Plating

IP.com Disclosure Number: IPCOM000114859D
Original Publication Date: 1995-Feb-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 4 page(s) / 137K

Publishing Venue

IBM

Related People

Cywar, DA: AUTHOR [+4]

Abstract

SJR-1440 or SJR-11225 Photoresist (Shipley) is modified by addition of a plasticizing agent to make a formulation useful in a process for the pattern electroplating of precious metals such as palladium and gold. The addition of bis-(2-ethylhexyl)phthalate (dioctyl phthalate) as a plasticizer results in an SJR resist image that does not crack during plating processes, as is observed for unmodified SJR. This modification of the resist formulation does not detract from other properties such as coating quality and resolution.

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Photoresist Composition for Precious Metal Plating

      SJR-1440 or SJR-11225 Photoresist (Shipley) is modified by
addition of a plasticizing agent to make a formulation useful in a
process for the pattern electroplating of precious metals such as
palladium and gold.  The addition of bis-(2-ethylhexyl)phthalate
(dioctyl phthalate) as a plasticizer results in an SJR resist image
that does not crack during plating processes, as is observed for
unmodified SJR.  This modification of the resist formulation does not
detract from other properties such as coating quality and resolution.

      SJR photoresist is a positive-tone, novolak-based liquid that
utilizes a diazonapthoquinone compound as the photoactive material.
It is applied by spin coating and is useful for the production of
thick-film (5-20 um) images.  The resolution is better than 1:1 and
vertical sidewalls are obtained.  Exposure is by UV (360 nm) light
and development by dilute aqueous alkali; dilute aqueous base is also
used for stripping.  Use of this resist allows fabrication of
electroplated Au pads on ceramic modules, for example, that are very
well defined and tightly spaced.  The major problem with the use of
SJR is severe cracking that occurs if the resist-imaged part is
allowed to dry following plating.  Cracking has also been observed
during surface pre-treatments prior to plating and during hard-baking
following development.  These problems are solved by adding the
dioctyl phthalate (DOP) plasticizer to the resist formulation.

      Two different SJR formulations as available from Shipley were
used; SJR 11225 and SJR 1440.  They differ only with regard to their
solvent content, not with regard to the resin/photoactive compounds.

The SJR 1440 is a lower percent-solids formulation.  Following are
some examples of the utility of the modified SJR resist.

EXAMPLE 1

      0.94 g DOP was added to 25.53 g SJR 1440 as received from
Shipley and allowed to stir overnight.  A 12-um thick resist film was
applied by spin coating onto a square glass module having Cr/Cu/Cr
metallization, wherein a 75 minute 100ºC soft-bake was used.
Exposure to 500 mJ/cm2 through a glass artwork followed by
development by immersion in 0.42 N aqueous sodium hydroxide solution
for 160 seconds resulted in a sharp, well defined image.  Following
development, the part was hard-baked for 30 minutes at 116ºC.
The top Cr layer was then etched in a permanganate/phosphoric acid
solution (pH=9, 50ºC0, followed by water rinsing and drying.  The
Cu surface was then prepared for plating by dipping in warm dilute
sulfuric acid, microetching with a sodium persulfate solution, and
rinsing with water.  Plating was as follows (in sequence):

NICKEL - 2.5 micron minimum thickness

Nickel sulfamate plating bath, pH 3.5, temp.  140F, DC plating at 10
ASF for 17 minutes.

      PALLADIUM - 2.5 micron minimum thickness Sel-Rex Palladex-600
bath, pH 7, temp.  50ºC, DC plating at 10 ASF for...