cleaning process do's and don’ts. - smta€¦ · evolution of technology – board and...
TRANSCRIPT
Presented by:Scott F. Cain
Original Slides by: Debbie Carboni
Kyzen Corp
Cleaning Process Do's and Don’ts.
Avoiding Common Pitfalls...
Evolution of technology – Board and Equipment
Board Design Considerations
Overcoming Environmental Challenges
Common machine set up blunders
Common Process Control blunders.
Common board fixturing blunders
Is your rinse effective enough?
How to effectively clean to meet the new standards, be reliable and prove it.
The Next 60+ Minutes
GOAL:
Answer your
questions
Modern Cleaning and Equipment
Evolution of Technology, Cleaning Methodology & Validation
Demand
High Frequency Devices
High Impedance Devices
High Voltage Devices
10 year+ life
Conformal Coated PCB
Products functioning in a Harsh
Environment
Component Challenges
Source: Dale Lee of Plexus Source: Bob Willis Consulting
These images are videos – double click to view
Customized tests
No Clean Paste Can Lead to Electrochemical Migration
I 295mA
24.4 mil
In-situ monitoring of
dendritic growth
Flu
x A
F
lux B
Custom-designed board
Bias 12V/mm
Cleaning or Considering Today
Modern Spray-in-Air Cleaning Tools
Factors that impact the rate function
Deflection energy (i.e., pressure at the board surface)
Nozzles type
Coverage
Modern Cleaning Agents
Both Inorganic and Organic in nature Solvent Phase
Targeted at non-polar soils
Aqueous Phase Targeted at polar soils
Functional additives Defoaming
Corrosion Inhibition
Lower surface tension
Bath life and loading
Rinsing
The Cleaning Process is Dynamic
BOARD DESIGN
CONSIDERATIONS
Eliminate ALL BTC’s
Solution #1 – Optimize PCB Design
Engineer For Cleanability
Make It Easy…ier
Access To Flux Residues Component to Component Spacing
Component Standoff Height
Solder Mask Clearance
Silk Screen Clearance
Solder Mask Type
Redirecting Flux Residue Location Between Pins & Thermal Pad (QFN)
Flux Cleanability
Access To Flux Residue
Board Layout
Increase Spacing Between
Components
Low Standoff Component
Large Package Size Components I.E. – High IO BGA’s/LGA’s
Tall Component Packages
Improved Access To Flux Residue
Increased Component Standoff Height
Solder Mask Design SMD, NSMD, No Solder Mask
Pad Design Thicker Copper – 1 oz > 2 oz > etc.
Smaller Lead To Pad Area Aspect Ratio –
Component Package Specific
Use Silk Screen to raise BTC corners
Remove Silk screen body outline to allow
for flow.
Dale Lee, Plexus
BTC Via Holes and Solder Mask
NSMD is better except for BGAs
Solder Mask Selection
Matte Finish Solder Mask Has Increase Surface Energy To Hold Flux To The Board (More Flux For Solder Joint Formation)
Dull/Low Reflection Appearance
More Difficult To Clean
Glossy Finish Solder Mask Has Low Surface Energy to hold Flux To The Board (Less Flux For Solder Joint Formation – Solder Balls, Icicles, Flags, etc.)
Highly Reflective Appearance
Easier To Clean
Not Preferred
Preferred
Dale Lee, Plexus
ENVIRONMENTAL
CONSIDERATIONS
Over coming Environmental Challenges
Global Harmonized System Internationally agreed upon standard
Hazard testing criteria
Universal warning pictograms
Safety data sheets with required information Hazard Classification
Physical Hazards
Flammability
Toxic substances
Health Hazards
Acute toxicity
Chronic toxicity
Environmental Hazards
Air
Water
Classification of mixtures
What does YOUR Local Publicly/Privately Owned Treatment Works considers Environmentally
friendly?
Biochemical oxygen demand (BOD) Limits vary even within same country/state
Chemical Oxygen Demand (COD) Limits vary even within same country/state
Total Solids – Mostly concerned with lead contamination
pH of waste water Generally treatment plants allow a pH range of 6-10
pH neutral does not mean wash solution is Safe to send to drain or to a waste water
treatment
Waste Water Management
Smell (while subjective) has an impact consciously and subconsciously.
Should not be strong
Should NOT Cause Physical reactions: Eye Irritations, skin irritation, Headache, Nausea
Machine Maintenance
Cause excessive scrubbing/rinsing in the wash or rinse tanks to keep the process in the process
limits
Ease of Concentration Monitoring
Real Time concentration Monitoring available
Eliminates operator from having to take taking manual concentration readings
Human Contact/Operator Experience
What’s in the Wash Bath?
Kapton Tape
Solder Balls
Solder Mask Materials
Paste/Flux
Unplanned contamination: Glue, underfill, Thread lock material, RTV,
Epoxy, grease….3rd SHIFT
Its not just Water and SOAP!
pH Balance
Typical Flux: 2 4 Modern Cleaning agents 7.5 10.5
COD/BOD Balance
Typically the lower the pH, the higher the COD
MACHINE SET UP BLUNDERS
Common
3. Water Supply
2. Nozzle Adjustments
1. Exhaust
Top 3 Set up Mistakes
Should be DI water for entire machine ALL the time. Good quality- Minimum 2 megohm (or your Set point)
low level set point.
Plumbing material: Material
DI water eats copper
Inlines: Enough to provide good flow in final rinse when other
parts of the machine are calling for water. Wash or rinse tank is filling (total of 38-40 liters/10-
12gallon per minute demand)
Water Supply
Nozzle Alignment
Fluid delivery should be across the entire assembly(s)
Spray bar alignment can impact the cleanliness effectiveness
Perpendicular on most spray is recommended
Slightly turn the airknife toward wash section
Deflector Plates on top of wash
Curtains between wash and chemical isolation sections
Inline Spray/Air Alignment
Other Blunders
Original ducting
should sit inside
Demister collar
at top side.
Demister collar
should sit inside
ducting/collar
from cleaning
machine.
Blunders Results
Best Installation Practices
PROCESS CONTROL
BLUNDERS
Common
Semi Automatic/Manual Monitoring
Data logging
Automate as much as possible
Use your machine alarm settings
with a window that meets your
cleanliness needs.
Don’t Ignore Alarms
Don’t forget Rinse and Dry
Process Control
Keep nozzles clean
Keep wash tanks clean
Keep Rinse water clean
PM – Daily/Weekly
PM’s and Alarms are the Key to Repeatability
BOARD FIXTURING AND
POSITIONING BLUNDERS
Common
Inline Top Spray Bars. Vs Bottom
More impingement energy from the top sprays
Place more difficult to clean facing towards the highest energy
Some machines do not have complete spray over entire converyor. The conveyor belt rail can cause a 1” Dead Zone on the bottom side sprays
When possible, clean between soldering processes
Understanding the batch Chamber Some Batch Machines
Not all boards may see the say pressure
Corners may have 2-3” Low pressure/flow
Batch Board Orientation
Avoid tall boards too close to short boards to avoid
Potential Shadowing When loading the basket
Boards should be spaced 1-3 inches apart
depending on potential shadowing and complexity
of assembly
Most complex assembly side down towards bottom
Face Connectors face down
Electrolytic Caps should be faced away from direct
heat source (heating element) if possible Or run
less than 130F
Ensures proper &
repeatable cleaning
Prevents foaming in the
rinse
Reduces costs
Reduces chemical drag-out
Reduces re-cleaning
Bad
Good
Proper spacing between pallets /PCB’s is key
Bad
Batch Fixturing
Inline Fixturing Designs
CONVEYOR BELT SECTIONS TO
PLACE ON TOP OF CONVEYOR
(NOT IN SAME DIRECTION)
A few more Bad Designs
Baskets Done Wrong • Decent open area
• ½” mesh belt is better
• Round wire mesh has
less drag-out.
Stamped metal, causes:
• Small opening shadows
components
• Diffuses impingement energy
(wash and rinse)
• Excessive drag-out
• Foaming in rinse
Top Hold good
Bottom Bad
Basket Board Spacing Improves cleaning by:
Spacing between assembly to prevent PCBs
on top of each other.
Open mesh or no mesh to allow for direct
energy each other
Bad
Pallet Considerations Raised closer to the sprays
increases energy Know what the height
limitation on the sprays
Total Height with pallet needs to be less than sprayable area
Open slots and holes for good drainage and less weight. Reduces excessive chemical
use
Prevents foaming in the rinse
Use the Whole Belt Keep 2-4” between pallets to prevent
excessive wash solution loss
PCB Placement to Improve Through Put
20" Conveyor 26" Conveyor
Assembly Length (in) 9.5"
Assembly Width (in) 3.5"
Spacing between assemblies 4
Multiple lane processing 2
capacity (boards/hour)
Throughput requirement (no. of boards/day) 5000
hours per day 23
boards needed per hour 217
boards needed per min 4
DON’T FORGET RINSING
Rinsing Issues Often observed under low standoff devices, tight spaces/crevices, and
connectors
Worsen with bath loading
Effectiveness on rinsing cannot be analyzed by ionic cleanliness
assessment methods
A common root cause of downstream process problems such as
conformal coating defects by poor adhesion and wetting
Possible intermittent shorts.
Final Cleanliness
Quick and Easy Surface Test
BAD
Poor wetting Poor adhesion
GOOD Clean Surface
Factors that Improve Rinsing Hot DI-water
Rinse zone is as important as the wash zone
Rinse time
Rinse pressure
Understanding the effects of FLUX Soil Loading
BAD
Poor wetting
Poor adhesion
GOOD Clean Surface
BE RELIABLE AND PROVE IT
How to effectively clean to meet the new standards,
On-Site Test Methods to Meet J-STD-001 Rev G.
Without Objective Evidence, Your “Number” does not mean Anything
Qualification vs. Production
Qualification
No flux loading
Visual, IC, Ionograph, and SIR
Rarely include rinse test.
No downstream process impact
assessment.
Single design test assemblies are
used. And may not have the same
components
Production
Heavy flux loading.
Visual/ Ionograph
Adhesion and wetting are critical to
downstream processes.
Wide variety of assembly geometries
(shadowing, entrapment, etc.)
Rework- unexpected work arounds
Cleaning Equipment and Parameters
Wash, Rinse, Dry
Handling
Process Control
Maintenance
Cleaning is A PROCESS
Cleaning Process Do’s and Don’ts
1. Set up your process Correct from the start
2. Understand the cause and effect each setting
3. Pay attention to board position and handling
4. Cleaning is not just the Wash Stage
5. New Process Control Tools are being introduced that can
provide process optimization and monitoring to meet
tomorrow’s challenges
Scott Cain Western Regional Manager [email protected] Debbie Carboni Global Product Manager, Electronics [email protected]
Questions?