1. Radian Corporation Report: MP-100 Line 28 February 92
Bruce F. Stacy, Consultant
INTRODUCTION
The MP-100 system is an overhead conveyorized deep tank nickel/gold printed
circuit plating system. Its main benefits are high production with less labor than
conventional automatic or manual plating lines. The equipment was set up at Radian
Corporation during November/December 1991. Nickel and gold plating processes were
then installed by Engelhard and formulated to their specification (see Appendix I).
Product plated on this equipment since start up, in December 1991, exhibited deposit
pitting.
PITTING ON VERTICAL VS. HORIZONTAL TABS
It was discovered that only vertical tab configured product (product with finger
tab rows perpendicular to the direction of travel in the MP-100) exhibited pitting when
plated. Product with horizontal tab rows (product with finger tab rows parallel to the
direction of travel) did not pit. Qualification and production of boards having only
horizontal tab arrays commenced immediately after this discovery.
The following test matrix was run to help isolate the cause of the pitting:1
1) 3521 circuit boards were turned 90 and then plated. Regardless of board design,
those tab arrays plated vertically pitted, those plated horizontally did not.
2) 3521's were plated at Radian, pits were present on the vertical tab arrays, but not
the horizontal arrays. This same product was also plated on Endicott's Deep Tank
line and no pitting was present on any of the tab configurations.
3) 3521's were plated in the nickel and gold strike. They were then removed from
the line, turned 90, and plated with hard gold. Both vertical and horizontal tab
configurations exhibited pitting.
4) 3521's were plated at four feet per minute. The current density in the nickel was
reduced from 156 ASF to 52 ASF and in the gold from 80 ASF to 27 ASF. The degree
of pitting decreased noticeably, though gold and nickel thicknesses were below
specification (a mean of 75u" Ni and 45u" Au).2
EQUIPMENT VARIABLES
Radian's MP-100 is unique in many respects. First, it was built as a "drop in" type
cell. This means that solution flows over the sides of the cells as well as where the
product for plating enters and exits. This leads to excessive aeration of the electrolyte,
1 Unless stated otherwise line speed = 4'/min., hard gold current density = 80 ASF, nickel current density = 156 ASF
2 This test was originally designed with only the gold current density decreased to better isolate the problem, these instructions
were not followed by production. Follow up tests were requested, where only one variable would be changed at a time, but the
decision was made to dump the nickel and gold chemistry before these could be carried out.
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Radian Corporation Report: MP-100 Line 28 February 92
Bruce F. Stacy, Consultant
pitting. It was remarked that these were the best 3521's seen off the line yet. Gold
thickness averaged 54u".
c) The line speed was reduced to three feet per minute and 3521's were plated at 100
ASF in the nickel, 10 ASF in the gold strike, and 40 ASF in the hard gold. Average gold
thickness was 60u" and average nickel thickness was 162u". There was virtually no
pitting on vertical or horizontal tab arrays. A nitric acid vapor test was done according
to IPC specifications on three sections of vertical tab areas. No pores were observed.
d) A Blue Bonnet─a board highly sensitive to pitting, because of its vertical tab
arrays─was plated under the same conditions as the previous test. Gold thickness
ranged from 50 - 60u" and nickel thickness ranged from 95 - 135u" (lower than
specification). Visual inspection at 30x revealed a marked decrease in the amount of
pitting. When tab sections were subjected to nitric acid vapor testing, some pores less
than 1 mil in diameter were found at 20x. This test was to be repeated to determine
whether low nickel thickness caused the porosity.
CATHODE EFFICIENCY STUDIES
Cathode efficiency testing was done in the lab on 1 liter samples of the old gold
and nickel electrolytes (see Appendix III). Results showed the nickel chemistry to be
performing at 100% cathode efficiency, these results were confirmed by Engelhard. The
gold bath was 60% efficient at 40 ASF and 30% efficient at 75 ASF.
Cathode efficiency in the actual plating cell was estimated for both nickel and gold
(see Appendix IV) on both old and new bath chemistries. At 40 ASF the new gold was
20% more efficient than the old gold and at 80 ASF was 87% more efficient. From 100 to
156 ASF the new nickel bath is approximately 60% efficient, the old nickel from 75% to
60% over the same range.
CONCLUSIONS
Tests to verify which process, both nickel and gold or just one of them, was responsible
for the pitting, though requested, were never run. Only one experiment came close (see
New Plating Baths Made to IBM/Endicott Specification, page 4, experiments a & b), the
current density on only the new hard gold bath was decreased 25% from the previous run
and there was virtually no pitting on any tabs.
Old bath formulations may have been capable of producing non-pitted deposits at lower
line speeds and current densities, but requests to evaluate this were never met (see Pitting
on Vertical Vs. Horizontal Tabs, page 1, test #4).
Current densities exceeding chemical/equipment capabilities may have caused
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Radian Corporation Report: MP-100 Line 28 February 92
Bruce F. Stacy, Consultant
Appendix III
DETERMINATION OF CATHODE EFFICIENCY
OF NICKEL & GOLD CHEMISTRY IN THE LABORATORY
Cathode efficiency testing of nickel and gold electrolytes was done off line in one liter
samples of the actual plating bath.
Equipment:
1) 25 AMP Rectifier
2) 1 liter beaker
3) 1" teflon coated stir bar
4) Hot plate/magnetic stirrer
5) 4 in2 platinized titanium anode
6) 12 gauge copper wire (cathode)
7) minimum 4 in2 soluble nickel anode
8) thermometer
9) 1/2" mandrill
10) timer
11) 500 ml of 5% sulfuric acid solution
12) analytical balance
13) positive and negative rectifier leads
Take 12 gauge copper wire and cut into 12" lengths. Coil the bottom 9" around a 1/2"
mandrel to make springs (slinkies)─ these are better suited when testing high current
density capabilities of solutions in a beaker. Weigh the coils on an analytical balance and
record the tare weights.
Place the one liter beaker with the bath to be tested and a stir bar on a hot plate/magnetic
stirrer. Set the stir setting to 7, or until there is a 1/2" deep vortex on the solution surface
and bring the bath to operating temperature. Submerge the anode in the solution, secure
to the side of the beaker, and attach it to the positive rectifier output using a wire. Take
one of the pre-weighed coils, activate in 5% sulfuric acid, rinse, secure on opposite side of
beaker, and attach it to the negative rectifier output using a wire. Set amperage (to
predetermined current density) and plate for ten minutes. When plating completed,
thoroughly dry and reweigh on analytical balance.
To calculate cathode efficiency (CE):
1) plated weight (mg) - tare weight (mg) = weight of deposit (mg)
Then:
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Radian Corporation Report: MP-100 Line 28 February 92
Bruce F. Stacy, Consultant
2) # amperes x # minutes = ampere minutes (AM)
Then:
3) weight of deposit/AM = mg/AM = electrolyte CE
To calculate as a percentage:
4) electrolyte CE (mg/AM)/ # mg/AM of metal @ 100% CE = % CE
Note: 100% CE Ni = 18.3 mg/AM, Au = 122 mg/AM
The above test procedure yielded the following results when run on old nickel and gold
solutions from the MP-100:
Current Density (ASF) %CE Ni % CE Au
18.5 79 83
37 NA 52
50 117 NA
75 NA 30
95 108 23
151 102 NA
The conditions were as follows:
Cathode size: 1.5 in2
Nickel Bath:
Ni - 150 g/l
pH - 3.8
Temp. - 130F
Gold Bath:
Au - 7.5 - 8 g/l
Co - 800 - 900 ppm
pH - 4.5
Temp.- 130F
Note: This test should be repeated on new gold bath to develop a base line.
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Radian Corporation Report: MP-100 Line 28 February 92
Bruce F. Stacy, Consultant
Appendix IV
DETERMINATION OF CATHODE EFFICIENCY
OF NICKEL & GOLD PLATING SYSTEM ON MP-100
Introduction
Cathode efficiency testing of plating baths in the lab measures the plating rate of
electrolytes under optimum conditions. This type of testing is only a measure of chemical
performance and not a true indication of what is occurring on line where equipment influences
performance. A method was developed to measure the performance of the system─ both
chemistry and equipment. There are limitations to this method: i.e., distribution, number
of readings, location of readings, etc. which diminish its use as a quantitative method, but
when coupled with standard cathode efficiency test methods (see Appendix III) can
define whether a plating performance problem is chemical or equipment related.
Procedure
3521's plated on the MP-100 line were subjected to thickness testing using XRF
equipment. Fifteen readings were taken per panel from identical tab array locations
across each board. A mean thickness reading was obtained and a total weight of deposit
per board was generated using the following equation:
Mean thickness (u") x wt. of deposit (mg)/u"/in2* x in2 of plated area = total deposit
weight in milligrams
* Nickel deposit wt. = 0.145 mg/u"/in2; Gold deposit wt. = 0.28 mg/u"/in2
Ampere minutes (AM) were calculated:
# of amperes x # minutes boards were in the cell = AM
Deposition rate was calculated:
deposit weight in milligrams/AM = CE in mg/AM
And knowing nickel @ 100% CE = 18.3 mg/AM and Au @ 100% = 122 mg/AM
we calculate a cathode efficiency on actual product on line to determine the performance
of the MP-100 plating system.
(Continued on next page)
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Radian Corporation Report: MP-100 Line 28 February 92
Bruce F. Stacy, Consultant
Results
Current Density CE Old Nickel Bath CE New Nickel Bath
26 ASF 83% NA
52 ASF 88% NA
100 ASF NA 63%
117 ASF NA 64%
156 ASF 60% 61%
302 ASF 19% NA
Current Density CE Old Gold Bath CE New Gold Bath
27 ASF 53% NA
35 ASF NA 42%
40 ASF 33% 40%
60 ASF 26% 34%
80 ASF 15% 28%
Conclusions
Using this test method, coupled with the laboratory efficiency test (Appendix III)
demonstrates overall CE of old baths in the beaker is higher than on line, this is
particularly true for nickel where the difference is 40%. To increase the CE in the nickel
cell we either have to optimize equipment (anodes, sparger, etc.), related parameters, or
drastically reformulate the nickel bath.
Comparison of old vs. new gold baths shows an overall higher and more uniform
CE on the new bath across the current density range.
Further data needs to be gathered to confirm this method. More points are
needed at lower and higher current densities in the new nickel and the new gold baths.
These new solutions should also be tested for CE in the laboratory to develop a base line
for later comparison of electrolyte performance.