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1999 Pollution Prevention Internship
Final Report
Project Title:
Developing a new copper plating technique
Intern:
Sarah Collette
Home phone: 603-868-5236
4616 Granite Square Station
Durham, NH 03824
e-mail: collette@hopper.unh.edu
Facility:
Teledyne Halco
8 Delta Drive
Londonderry, NH 03053
Contact Person: Marc Filipowicz
Manager, Human Resources
Phone: 603-889-6191
Fax: 603-882-4457
Table of Contents
Executive summary
Introduction
Goals
Approach
Chemical Usage
Waste Management
Accomplishments
Pollution Prevention Benefits
Recommendations
References
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Executive SummaryTeledyne Halco is currently working on a new horizontal copper plating technique
for the printed circuit board industry. The goal is to use electroplating to plate 1 mil. of
copper in the holes of a printed circuit board in 10 minutes. A concept validation
apparatus was created so those tests could be run to evaluate the potential of the new
copper plating technique. Being unique, the combination of mechanical and chemical
aspects of the process needed to be explored to allow for optimization.
Trials were run at different conditions and the results were recorded. The
thickness of the through-hole copper deposit was measured by preparing micro
sections. Based on results from the trials, mechanical and chemical adjustments were
made. The data obtained was used to define our next steps.
I was required to keep a lab notebook. Everyday I documented test activities,
any conditions/adjustments that were made to the machine, trials that were run
observations, and results. This allowed us to keep our research organized so that we
were able to look back on previous changes that were made or trial results.
Given the machine is still in the R&D phase, I can not provide design details, talk
about specific parameters, or show drawings/pictures of the actual machine. In addition,
specific details about the data that we have obtained are not available.
IntroductionTeledyne Halco designs and constructs machines for use in the circuit board
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manufacturing industry. Teledyne is currently working on a new horizontal plating
process that will reduce the time need to achieve standard through hole copper
thickness.
In the printed circuit board industry copper is applied to circuit boards to
interconnect component holes. Copper is the most commonly used metal for the
construction of a printed circuit board because of its conductivity, strength, ductility and
low cost. Electroplating is the production of adherent deposits of metals on a
conductive surface by the passage of an electric current through a conductive metal
bearing solution. It is the most prevalent method used to plate copper on a circuit
board.
The copper plating process is one of the most time consuming stages of PWB
production. Currently a typical plating process takes about 70 minutes to obtain the
desired 1 mil of copper in the hole. This process is performed by dipping boards
vertically into a set of tanks. The deposit thickness depends on the processing time
and on Faraday?s Law which governs the current that is being impressed on the
surface.
GoalsThe goal of my internship was to provide technical support to successfully
research and develop a new horizontal copper plating technique. This new technique
will take less time to plate the required amount of copper, reducing the production time.
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The machine will use less volume of plating solution and have a smaller footprint than
the current methods. The system will be computer controlled, reducing hands on labor
and process contact.
The objective of the new copper plating technique is to plate one mil of copper in
each hole of a printed circuit board in 10 minutes. The machine is intended to provide
selective plating, a method by which more copper is plated in the hole than on the
surface of the board. The quality of the copper deposit must meet relevant printed
circuit industry specifications for purity, percent elongation and tensile strength (IPC and
ASTM specifications). The copper has to be securely attached to the wall of the hole, it
must be uniform from top to bottom of the hole and void free (no holes in the copper).
The appearance of the board is also important; to be acceptable the board must be
shiny and burn (surface roughness) free.
For the past year Teledyne has been researching and testing their new copper
plating technique on a prototype machine that was designed and constructed in their
Halco facility. The observations and results from previous tests using different
iterations of the prototype machine are currently helping the engineers in designing the
Alpha version. This version will eliminate compromises that were made in the prototype
and incorporate the product of test evaluations. The design efforts for the Alpha model
are being worked on at the current time, scheduled to be fabricated by the end of
October. Future, more demanding testing will be performed on the Alpha model, and
any deficiencies that arise will be addressed through re-engineering. The data obtained
from testing done on the Alpha will be used to construct the Beta model.
The Beta differs from the Alpha in that the Alpha will remain within the Teledyne
organization for controlled testing whereas the Beta will be placed at a Customer facility
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for use in daily manufacturing. This will afford an opportunity to obtain ?real world?
performance data. If all goes as planned and the performance goals are met, the
machine will then be ready for production and made available for sale to the printed
circuit board industry.
ApproachTeledyne Halco created a prototype machine that allowed them to validate the
potential of this unique copper plating technique. There were many fundamental
electroplating concepts that needed to be taken into consideration, and satisfied, to
achieve the theorized results. The chemical composition of the acid copper sulfate bath
used in the new plating process had to be analyzed and maintained within certain
specifications, but first those specifications had to be determined. The specific types
and sizes of power supplies had to be evaluated. Appropriate materials of construction
had to be selected to resist the harsh chemical environment.
Since no one had ever plated copper using this technique, all of the parameters
for the process needed to be determined by research and development. This summer I
helped Teledyne further investigate the capabilities of the prototype device by varying
key parameters, evaluating test samples and organizing the results so that we could
see how different conditions affected the process and what configuration of the
machine yielded the best results.
The acid copper sulfate plating bath contained de-ionized water, copper sulfate
(pentahydrate), sulfuric acid, hydrochloric acid and organic proprietary additives. The
organic additives consisted of a carrier, which helped the overall uniform plating over
the board, and a brightener that made the copper topography smooth and shiny. There
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are a variety of organic additives that could be used in the acid copper-plating bath.
We worked with a specific chemical suppler that helped us to determine which organic
additives would be suitable for our conditions. The chemicals that made up the additive
and carrier were proprietary which made it difficult to understand how they might react
in the bath. There was also no easy way to determine the concentration of the
additives. The concentrations of the bath components need to be optimized to achieve
optimum results.
The copper, sulfuric and chloride concentrations were analyzed through titrations
and Hull cells. A Hull cell is a miniature plating bath that allowed us to quickly evaluate
the bath, at various current densities, prior to running a board through the machine. A
copper plate is put in the Hull cell and a controlled amount of amps is run through the
solution. Depending on if the appearance of the plate is dull, matte, or shiny, each
condition gives us a general idea about what needed to be added to the bath. The
extent of visible burning allowed us to determine how many amps the bath could
handle.
At the beginning of my internship, the copper sulfate plating bath seemed to be
out of our control. We believed that something in the bath was changing and over time
the plating rate in the holes was decreasing. It was thought that possibly the organic
additives were the problem, maybe they had reacted or broken down into other
components. Another possibility was that certain materials that were used in
construction of the model machine could have contaminated the bath. To remove the
organic additives, the bath was exposed to activated carbon in a re-circulating mode.
Looking for assistance with the bath chemistry, we met with a different chemical
supplier in the hope of identifying a new additive that would be better suited for our
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process. They recommended revised specifications for the bath component
concentrations. They also recommended that a heating/cooling loop be added to
control the temperature of the bath more closely. This would allow us to eliminate
another potential variable. The bath chemistry was set to their recommendations with
the exception of carrier and brightener, neither was added to the bath. The bath was
established and maintained at a ?high? acid level and a ?low? copper level. The high
sulfuric acid helps to increase the conductivity of the bath while the low copper
improves the throwing power (propensity for hole plating).
To further improve the machine and determine what the optimum operational
parameters needed to be, many trials were run in the prototype machine while varying
conditions. The results of copper thickness and quality testing were closely monitored.
To run a trial, a board was mounted to a platform that went into the machine and came
back out the same side (FILO). The system was computer controlled with the board
length and the dwell time entered by keypad at the start of the trial. Two rectifiers
supplied the electric current to the bath and were controlled semi-automatically. After
leaving the plating machine the board is run through a rinse to remove any excess
solution.
Each trial, a variable was changed and compared to previous trials to see what
affect it had on the plating rate. Boards were run at various amp settings. The results
were used to determine what the optimum amps needed to be. Boards were also run
at different dwell times.
After a board was run micro-sections (metallurgical cross sections) were used to
measure the through-hole copper thickness and the surface copper thickness. To
prepare a micro-section two holes on the board were cut out using a punch machine.
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The section was then set in an acrylic solution that would harden and hold it in place.
Once it was dry the micro-section was ground down and polished so that only half of
the hole was left. The section was then looked at under a microscope. The copper
thickness in the hole and on the surface was measured through the microscope. The
uniformity (top to bottom, side to side) and quality of the copper was also looked at.
A CMI, non-destructive test device which operates on an eddy current system,
was used as a quick estimate of the through-hole copper thickness. To use the CMI, a
probe is placed in a hole and the copper thickness is displayed on the screen. I
devised and performed an evaluation that tested how accurate the CMI unit was
compared to a micro-section. I found that the CMI unit was conservative, it always read
less than the actual copper thickness, generally accurate to within 0.1 to 0.2 mils and
would be valid if used only as a quick estimate.
At one point this summer the machine was disassembled for a few week while
we were waiting for new parts to arrive. No trials could be run. Old results were
organized and studied. The fluid supply system and the application of the fluid were
analyzed to see how they changed. The supply system experienced dimensional
changes with use. The same was true of the applicators. The applicators are used to
wet the board with plating solution. If the dimensions of the applicators are not
consistent they might not evenly wet the surface of the board which could cause
problems. At the end of my internship this was one of the variables that was being
looked into but an alternate way to apply the fluid had not yet been found.
Towards the end of the summer the machine was reassembled with new parts.
Many things were changed from the previous phase. A heating/cooling loop was
installed to better control bath temperature. A larger pump was installed to increase the
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fluid flow. The fluid delivery manifolds were redesigned and new fluid applicators were
mounted to give a more uniform flow throughout the system.
When the machine was back together trials were run again. The parameters
were set and a board was run to give a base line to compare future tests to. One
variable at a time was changed and tests were run. I made up data sheets to
consistently record the conditions of the trials and what results they yielded. Based on
the results of the trials both mechanical and chemical adjustments were made in the
hope of optimizing the copper plating in the hole. The data that was gathered helped
us to decide our next step.
Chemical UsageThe copper plating bath contains de-ionized water, sulfuric acid, copper sulfate,
hydrochloric acid and organic additives. The copper, sulfuric and chloride
concentrations were determined by performing titrations. In the copper analysis a bath
sample is mixed with DI water, sulfuric acid, and potassium iodide and then titrated with
sodium thiosulfate. The sulfuric concentration is calculated by mixing a bath sample
with DI water, bromphenol blue and then titrating with sodium hydroxide. The chloride
analysis mixes a bath sample with DI water, nitric acid, and silver nitrate and then
titrates with mercuric nitrate. When preparing micro-sections an acrylic mounting
solution and an acrylic mounting powder were used.
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Waste ManagementThe bath has never been completely replaced so there is no waste to dispose of.
Teledyne Halco has an electrowinning based wastewater treatment system at their
facility for treatment of metals bearing solutions. If a sample was taken and it was
contaminated and could not be returned to the plating bath it was put into the
wastewater treatment. The sink drain in the lab was also hooked up to the wastewater
treatment system. The cooling water for the plating system was used as rinse water for
another machine after it left the plating machine. The boards that we ran trials with
were recycled when they were no longer needed. There was no waste that was
generated by the plating machine.
AccomplishmentsIn the year that Teledyne has been working with the prototype copper
plating device, a number of key elements have been identified and addressed:
Characterization of uniform solution flow patterns
Impact on amperage on plating rates
Characterization of plating rate as related to Faraday?s Law, and how this differs
from traditional technologies
Relationship of fluid and current delivery to plating uniformity and rate
At this time, testing is ongoing, but progress continues to be made each day. Each trial
that was run gives us more information to help us understand what is happening in the
overall process.
Although we were not able to consistently produce the same results time after
time, from the data obtained, we were able to make adjustments to the machine that
improved the plating performance. Teledyne is continuing to run tests trying different
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configurations. The engineers have been very successful in designing the Alpha
model, with construction to start in the next couple of weeks.
The actual results of the trials that were run, and more specific accomplishments
can not be shared at the current time. Likewise, the improvements that were made to
the design of the machine for incorporation in the Alpha system can not be divulged.
Pollution prevention benefitsThe new plating process will use less volume of plating solution per board run.
The system will be computer controlled so that the bath should age at a predictable rate
allowing it to be carbon treated when a new bath is necessary. Therefore, the bath
would never have to be completely replaced so there would be no waste to be disposed
of. The machine will take up less space than the current methods. It will also be more
electrically efficient than the current method.
Recommendations for future effortsIn the future new fluid applicators might need to be used in the machine. The
current fluid applicator change dimensions over time. The acid levels in the plating bath
are too high for the current material that is being used. Alternative fluid applicators
need to be tested.
ReferencesCommunication with Joe Webb, project manager Teledyne Halco.
Joe Webb?s laboratory notebook.
Communication with Gerry Cooper, Teledyne Hudson.
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Communication with Steve Glassman, CFC.
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