Pattern nickel/gold plating is one of the most difficult tasks that dry films
are expected to perform. Here are some recommendations that may help:
1. Some dry films are simply not made to withstand the harsh gold plating
environment, so you should choose one that is designed specifically for gold
plating, or, a good universal plating film. There are several on the market;
if you are looking for a recommendation, contact me offline.
2. Optimize your dry film process. Try and follow the manufacturers
parameters as closely as possible. Prelamination cleaning, correct lamination
conditions, and good exposure levels are all critical to good resist adhesion.
Failure to maintain good process controls will result in problems; i.e.,
resist lifting, underplating, and blistering.
3. Understand why dry film breaks down in gold. During plating, hydroxyl
ions are formed at the panel surface. These ions are the same as those found
in hydroxide strippers commonly used to strip resist. Although these ions are
much less concentrated than in resist strippers, they still cause a localized
increase in bath pH at the plating surface, and begin to attack (strip) the
resist sidewalls. Properly controlling the gold process minimizes this
attack.
4. Maximize your gold tank:
a. Vigorously agitate the gold solution under the anode/cathode areas. This
will replace spent solution at the plating surface, while removing hydroxyl
ions and minimizing their attack. Hydrogen gas is a visible by-product of
hydroxyl ion generation.
b. Maintain the highest gold content possible, between 1 to 2 Troy ounces per
gallon (10 to 20 gram/liter). Check the gold content on a regular basis, and
make adds as necessary to maintain gold content.
c. Bath temperature, pH, and current density must be within manufacturers
specifications; typically 90 to 110 F (32 to 43 C), pH 3.0 to 5.0, and 4 to 10
ASF.
d. The bath must be filtered continuously, and regularly carbon-treated to
remove organic contaminants.
I hope this is of help. If you would like to discuss further, please contact
me offline.
Mark Dowding
Technical Service Manager
INSULECTRO
909-943-5758
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