pH Neutral Process Solutions Case Studies

FEB
2015
pH Neutral Process Solutions
Innovative pH neutral solutions since 2009
pH NEUTRAL PRODUCTS
SEMICONDUCTOR
APPLICATIONS
▪▪ Aqueous based
▪▪ pH neutral
▪▪ For use in immersion and
ultrasonic processes
▪▪ Removes flux residues from
leadframes, discrete devices,
power modules, power LEDs,
flip chips, and CMOS following
die attach process
▪▪ Optimal surface characteristics
for subsequent processes
SMT AND PCB
APPLICATIONS
▪▪ Aqueous based
▪▪ pH neutral
▪▪ For use in spray-in-air inline
and batch processes
▪▪ Removes leaded and lead-free
flux residues from electronic
assemblies
▪▪ Excellent compatibility with
sensitive metals and polymers
including aluminum, brass,
nickel, and plastics
POWER ELECTRONIC
APPLICATIONS
▪▪ Aqueous based
▪▪ pH neutral
▪▪ For use in spray-in-air
equipment
▪▪ Removes flux residues from
leadframes, discrete devices,
power modules, and power
LEDs
▪▪ Excellent ability to remove oxide
layers from copper surfaces for
subsequent processes
Case Studies
pH Neutral Cleaning Agents - Market Expectation and Field Performance
An excerpt from the technical paper as originally published in the proceedings of IPC APEX, San Diego, CA,
Feb 24 - Feb 26, 2015.
At SMTA International 2010, a study titled “Benchmark Study: pH neutral vs.
Alkaline Cleaning Agents” was presented. This study documented the material
compatibility and cleaning effectiveness of an alkaline cleaning agent with that of a
pH neutral cleaning agent. Based on the results of this study, pH neutral cleaning
agents held the promise of offering superior material compatibility, comparable
if not improved cleaning performance and lower concentrations as compared to
alkaline alternatives for cleaning No Clean, RMA and OA flux residues. This paper
presents three customer case studies whereby the specific customer explored the
option of employing a pH neutral cleaning agent due to issues with their current
cleaning processes and is excerpted within this edition of ZESTRON News.
Contents
pH Neutral Process Solutions
Case Studies
pH Neutral Cleaning Agents Market Expectation and Field
Performance
ZESTRON Academy
Americas Personnel Update
more than chemistry...
pH Neutral Cleaning Agents - Market Expectation and Field Performance
Case Study Review – Customer A
Company A, a global OEM, acquired a new customer and was
tasked with manufacturing newly designed lead-free double-sided
PCBs populated with capacitors, microprocessors, and various size
resistors and connectors. The substrate also included pluggable press
fit cages or shields with nickel silver coating. As the plant currently
uses an aqueous cleaning process with an alkaline cleaning agent
within their current SMT process, this was employed for cleaning the
new substrates. These substrates were exposed to multiple heat cycles
resulting in burnt-in fluxes thereby requiring two passes through
the cleaning process. Satisfactory cleaning was realized, however,
material compatibility issues arose. The shield surface was degraded
and a conformal coated subassembly exhibited peeling as a result of
the cleaning process. A Design of Experiment (DOE) was developed
to address shield material compatibility (Part 1) and conformal
coating compatibility (Part 2).
Fig 3. Bottom of Substrate
Reference Figures 29 and 30 for cleanliness comparison.
Fig. 7. Top of Substrate (Shield)
Design of Experiment
Part 1: Identify an alternate aqueous based cleaning agent and
develop optimized cleaning process parameters.
Due to the material compatibility requirements, a pH neutral cleaning
agent was selected. The current cleaning system was optimized in
order to achieve the desired cleaning results. Optimum cleaning
process parameters developed are detailed in the table below.
Cleanliness assessment was evaluated through visual inspection and
ion chromatography analysis.
Equipment
Spray-in-air inline cleaner
Cleaning Agent / Concentration
pH neutral micro phase / 20%
Conveyor Belt Speed
0.5 ft/min
Wash Pressure (Top / Bottom)
65 PSI / 65 PSI
Wash Temperature
145°F / 62.78°C
Rinsing Agent / Temperature
DI-water / 101°F / 38.33°C
Drying Method
Hot Circulated Air, 102°F-111°F /
38.89°C-43.89°C
Visual inspection indicated that all substrates were found to be fully
cleaned and the shield surface was unaffected. Additionally, all
boards passed ion chromatography analysis confirming that the
desired cleanliness level was achieved with the pH neutral cleaning
agent. Reference Figures 3 and 7.
Part 2: Assess the compatibility through visual inspection of the pH
neutral cleaning agent with conformal coating materials using the
optimized parameters from Part 1.
Three conformal coating types (parylene, acrylic and polyurethane)
were compared for the initial compatibility analysis with the pH neutral
cleaning agent and parylene was found to be most compatible.
Three test vehicles were coated with a 33 µm layer of parylene-based
conformal coating material and subjected to the optimized cleaning
process parameters including two passes through the inline cleaner.
Through visual inspection of the coated test vehicles following the first
and second pass through the inline cleaner, the coating was found to
be intact. Reference Figure 13.
Conclusion
The pH neutral cleaning process resulted in:
▪▪ Fully cleaned double-sided substrates assembled with lead-free
solder paste and flux
Fig 13. After 2nd Pass
▪▪ Excellent material compatibility with nickel silver coated shields
and parylene conformal coated subassemblies
Case Study Review – Customer B
Customer B, a value-added EMS provider, planned to qualify a new
manufacturing process for a high reliability electronic assembly for a
medical application. The SMT process utilized no clean solder paste
and flux in an aqueous based inline cleaning process. There were
sensitive materials on the substrate surface and aluminum carriers to
hold substrates as they were conveyed through the cleaner. A DOE
was formed to develop a cleaning process for their qualification.
Based on the process and material compatibility requirements a pH
neutral aqueous based cleaning agent was selected.
Design of Experiment
The substrate was designed as a panel and each panel included 18
boards, double-sided. A spray-in-air inline cleaner was selected
for the cleaning process. Cleanliness was assessed using visual
inspection, ionic contamination, and ion chromatography analyses.
All panels were passed through the inline cleaner utilizing the
aluminum carrier and inspected for surface integrity. The optimized
inline cleaner operating parameters are detailed in the table below.
Fig 29. Underneath Component
After Cleaning using DI-water
Fig 30. Underneath 1812 Component
After Cleaning using pH neutral
An additional panel was cleaned and used for ion chromatography
analysis. The board passed the ion chromatography test as the ion
species were below the maximum recommended contamination
level.
Part 2: Utilizing cleaning process parameters from Part 1, and the
customer’s test boards, assess cleanliness level achieved through
visual and ion chromatography analyses. Additionally, assess the
effect of the cleaning agent on the sensitive materials.
Conclusion
The pH neutral cleaning agent:
▪▪ Successfully cleaned all substrates
▪▪ Exhibited excellent material compatibility with all substrate
components as well as the anodized aluminum carriers
▪▪ 10% concentration, 1.5 ft/min belt speed and 145°F wash
temperature minimizing operating costs
The customer provided five boards for cleanliness assessment.
These boards were double-sided increasing the cleaning challenge.
Therefore, the wash temperature was increased to 150°F as
compared to 140°F in Part 1. All other batch cleaner operating
parameters remained the same.
Case Study Review – Customer C
Customer C is a high reliability OEM for the aerospace and energy
industry. For one application, substrates were manufactured with
water soluble solder paste and flux and cleaned with DI-water.
Through visual analysis, they confirmed that residues were left
untouched underneath low standoff components potentially leading
to reliability issues. They wanted to explore the use of a water based
engineered cleaning agent provided it was compatible with their
component materials including anodized aluminum and olive drab
cadmium. A DOE was developed to explore the option of using a
chemically assisted batch cleaning process. A pH neutral cleaning
agent was selected.
Design of Experiment
Part 1: Utilizing ZESTRON® populated test vehicles and a batch
cleaner, develop optimized operating parameters and compare results
to those achieved with the DI-water cleaning system. A cleanliness
assessment was made through visual analysis on the surface as well
as undercomponent and ion chromatography analysis. Due to the
material compatibility requirements, a pH neutral cleaning agent
was selected.
Eight boards were populated with low standoff components at the
customer location using the selected water soluble paste and flux.
Two of these boards were cleaned at the customer site using their
current DI-water cleaning process and returned to ZESTRON for the
cleanliness assessment. The remaining six boards were also returned
to ZESTRON for cleaning trials using the pH neutral cleaning process
and cleanliness assessment. The optimized cleaning parameters
used are detailed below.
Equipment
Spray-in-air inline cleaner
Cleaning Agent / Concentration
pH neutral micro phase / 10%
Conveyor Belt Speed
1.5 ft/min
Wash Pressure (Top/Bottom)
65 PSI / 65 PSI
Wash Temperature
145°F / 62.7°C
Rinsing Agent / Temperature
DI-water / 145°F / 62.7°C
Equipment
Spray-in-air batch cleaner
Drying Method
Hot Circulated Air, 102°F (D1),
230°F (D2), 240°F (D3)
Cleaning Agent / Concentration
pH neutral micro phase / 10%
Cleaning Time
15 min
Wash Temperature
140°F / 60°C
Rinsing Agent / Temperature
DI-water / Room Temperature
Number of Rinses Required
5 each w/ dwell time of 20 secs
Drying Method
Hot Circulated
150°F /65.5°C
Utilizing the operating parameters as detailed in the table above,
all boards and panels were cleaned in one pass. For the ionic
contamination test procedure, additional scrap boards were used.
These were tested before and after the cleaning process. Although all
boards passed the IC test per the IPC standard, there was a significant
difference in the result of the clean versus uncleaned boards.
Two boards were used for ion chromatography, one cleaned with DIwater and another with the pH neutral cleaning agent. Both boards
passed the test for the ion species and were below allowable maximum
contamination levels. However, the total ionic contamination present
on a board cleaned with the pH neutral cleaning agent was less
than what was present on the DI-water cleaned board. However,
the undercomponent assessment of the DI-water cleaned board
confirmed the presence of untouched flux residue thereby providing
the opportunity for field reliability issues under use.
Air,
15
All boards were cleaned using the optimized cleaning process from
Part 1 resulting in all surfaces fully cleaned and leaving the anodized
aluminum and olive drab cadmium materials unaffected. Of the five
boards, one was used for ion chromatography and the remainder for
undercomponent cleanliness assessment.
For the ion chromatography analysis, all species were below the
allowable maximum contamination limits. For the undercomponent
cleanliness assessment, all components (100 in total) were removed
and the undercomponent surface inspected. Other than light residue
remaining under four components, all others were fully cleaned
underneath.
Conclusion
The pH neutral cleaning agent:
▪▪ Provided excellent cleaning results on the surface and underneath
the components with an optimized batch cleaning system
▪▪ Exhibited excellent material compatibility with anodized
aluminum and olive drab cadmium material
▪▪ 10% concentration, 1.5 ft/min belt speed and 150°F wash
temperature minimizing operating costs
Overall Conclusion
As reviewed in the background and introduction of this study,
pH neutral cleaning agents held the promise of offering superior
material compatibility and excellent cleaning results as compared to
the inhibited alkaline cleaning agents. In this study, three case studies
were presented, each with a different paste/flux vehicle and material
compatibility constraints whereby a pH neutral process cleaning
solution was identified.
In summary, pH neutral cleaning agents can in fact meet the
stringent cleaning requirements expected, even with burnt-in flux
residues from multiple heat cycles, while exhibiting excellent material
compatibility and with lower wash concentrations as compared to
alkaline alternatives. Additionally, pH neutral cleaning agents
are environmentally friendly eliminating the need for waste water
neutralization.
For the paper in its entirety, please contact infousa@zestron.com.
min,
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2015
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Curriculums
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ZESTRON Technical Centers
Workshops
Presented at premier electronics events, published in leading industry
journals addressing the latest in technology and solutions to cleaning
challenges
Technical Articles
Collaborative regional training sessions with industry experts
designed to meet the electronic industry’s cleaning requirements
Ravi Parthasarathy, M.S.Ch.E.
Senior Process Engineer
OUR TEAM OF Experts
ZESTRON Americas’ team of experts have over 80 years of field
experience with high precision cleaning applications within
electronics manufacturing utilizing engineered cleaning agents.
They have conducted numerous technical studies addressing
critical cleaning challenges worldwide publishing their results in
leading industry journals as well as presenting them at key industry
events. Capitalize on their process knowledge through our
workshops, webinars and technical training.
Umut Tosun, M.S.Ch.E.
Application Technology Manager
www.zestron.com/us/academy
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Cleaning Questions? ZESTRON Has Answers.
Phone:
Email:
Web:
+1 (703) 393-9880
infousa@zestron.com
www.zestron.com
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Executive Vice President
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Application Technology Manager
u.tosun@zestronusa.com
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