fluid flow mechanics: key to low standoff cleaning · fluid flow theory –empty gaps. 7 ......
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Fluid Flow Mechanics:
Key to Low Standoff Cleaning
By:
Umut Tosun, M.S. Chem. Eng. Steve Stach,
Application Technology Manager President AAT Corp.
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Fluid Flow Mechanics:
Key to Low Standoff Cleaning
Table of Content:
1. Introduction
2. Fluid Flow Theory
3. Inline Progressive Energy Dynamics Approach
4. Testing Protocol
5. Overall Conclusion
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� Increased requirements for electronic packages
� This demands even cleaner electronic assemblies
� Current designs have fewer ICs and more discrete
components
� Space under components is shrinking
1. Introduction
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� Transition from: Flux around the component
� To: Flux under the component
Completely filling flux under tightly spaced
components
Flux around surface mount Flux under cap
1. Introduction
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Fluid Flow Mechanics:
Key to Low Standoff Cleaning
Table of Content:
1. Introduction
2. Fluid Flow Theory
3. Inline Progressive Energy Dynamics Approach
4. Testing Protocol
5. Overall Conclusion
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� Depending on: 1 Surface tension
2 Density of the cleaning agent
3 Higher pressure and Higher Temperature
� Tighter gaps or tight spaces with solvent-phobic surfaces require
differential pressure ≥10 psi
� Pump manifold pressures of 40 to 100 psi were used, depending on
the type of nozzle
2. Fluid Flow Theory – Empty Gaps
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� Interfacial pressure differential - planar
Δp = 2γ cosθ / R
γ = surface tension
R = radius meniscus
Θ = contact angle of
liquid at surface
2. Fluid Flow Theory – Empty Gaps
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� Interfacial pressure differential - cylinder
Δp = γ cosθ / R
γ = surface tension
R = radius meniscus
Θ = contact angle of
liquid at surface
NOTE: if θ is greater than 90˚, as with water on waxy surface, the force
becomes negative or repulsive
2. Fluid Flow Theory – Empty Gaps
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� Relationship between gap size and capillary force for water on glass
Planar:
Cylinder:
2. Fluid Flow Theory – Empty Gaps
Interfacial pressure difference at equilibrium
10
1
psi
0.1
0.01
0 20 40 60
Gap/diameter, mils
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� The residue must be softened if fluid path blocked
� Mechanical steps required to remove a fully blocked gap:
1 Solvent depleted zone
2 Liquid jet with sufficient energy forms flow channels
3 Bulk residue is eroded
2. Fluid Flow Theory – Filled Gaps
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Fluid Flow Mechanics:
Key to Low Standoff Cleaning
Table of Content:
1. Introduction
2. Fluid Flow Theory
3. Inline Progressive Energy Dynamics Approach
4. Testing Protocol
5. Overall Conclusion
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� Inline Cleaning Process Schematic
Dosage
Station
Treatment system Treatment system
21 3 4 5 6 7
Pre-
Wash
Chemical
IsolationRinse
Final
RinsingDryer DryerWash
3. Inline Progressive Energy Dynamics Approach
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� New approach to design in-line cleaner
� Requires innovative cleaning fluid technology
� Involves a manifold design
� Use of bigger pumps and more manifolds
3. Inline Progressive Energy Dynamics Approach
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� Wash section equipped with progressive energy dynamics
3. Inline Progressive Energy Dynamics Approach
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A Progressive Energy Design is:
� A fluid delivery system
� Recognizes the 3-step process required to clean flux-filled spaces
� Delivers only what is needed at each step:
1 The availability of the appropriate amount of
energy
2 Avoids wasting energy by directing less energy
3. Inline Progressive Energy Dynamics Approach
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Fluid Flow Mechanics:
Key to Low Standoff Cleaning
Table of Content:
1. Introduction
2. Fluid Flow Theory
3. Inline Progressive Energy Dynamics Approach
4. Testing Protocol
5. Overall Conclusion
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Overall Experimental Variables
� Equipment: � Pressure (psi)
� Spray manifolds
� Belt speed (ft/min)
� Cleaning agent: � Cleaning agent technology
� Concentration (%)
� Temperature (°F)
� Parts to be cleaned: � Component density
� Solder paste
4. Testing Protocol
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� Boards with 0603 chip capacitors
� Average standoff height of 1 mil.
� Maximum component density: 30 / board
� 3 different test phases
� Leaded and lead-free solder pastes – based on highest level of
difficulty to clean
� Soldering performed in a 10-stage reflow oven under air-atmosphere
4. Testing Protocol
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� Overall experimental overview:
�50
�49
�55
Spray pressure
(psi)
���ACleaning agent
���300603 component
density per
board
�3
�2
1
Spray Configuration
Design
Fixed
Parameters
Phase
III
Phase
II
Phase
I
4. Testing Protocol
�
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� Overall experimental overview:
2.0 / 1.5
1.5 / 2.0
1.0 / 3.0
0.6 / 5.0
0.4 / 7.5Conveyor belt
speed (ft/min)
Exposure time
(min)
Total wash section:
3ft.
��150
��140Temperature
(°F)
���15
���10Concentration
(%)
���Leaded
���Lead-freePastes
Variable
parameters
4. Testing Protocol
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Test board area with 30 set series of 0603 components
� Board specification:
4. Testing Protocol
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Findings Phase 1:
� Standard, non-progressive cleaning manifold tested
� For both leaded and lead-free formulations
� Consistent with results in other inline machines
4. Testing Protocol
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(°°°°F)
150
140
130
10 Conc (%) 15
Cleaning agent A, Lead-free
Exposure time (min.)
7.5
1.5
5.0
2.0
3.0
0
0
0
(°°°°F)
150
140
130
10 Conc (%) 15
Cleaning agent A, Leaded
Exposure time (min.)
7.5
1.5
5.0
2.0
3.0
0
0
0
� Phase 1: Cleaning agent A – Removes lead-free and leaded
4. Testing Protocol
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� Phase 1 – Experimental parameters and results
� Even speeds as low as 0.4 fpm – could not clean the components
� For both – leaded and lead-free formulations
Fixed Parameters
Equipment SpecificationSpray Pressure (psi) 55
Spray bars (top) 5
Board Specification (0603 components) Component density 30
4. Testing Protocol
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� Phase 1 – Experimental parameters and results
Variable Parameters
Cleaning
Agent # % (˚F) (ft./min) / (min)
Cleaning
Result
Lead-free A
1 10 140 0.4 / 7.5 0
3 10 150 0.6 / 5.0 0
5 15 150 0.6 / 5.0 0
Leaded A
2 10 140 0.4 / 7.5 0
4 10 150 0.6 / 5.0 0
3 15 150 0.6 / 5.0 0
+: Clean 0: Partially cleaned -: Not clean
4. Testing Protocol
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Findings Phase 2:
� Same machine but modified
� New manifolds were build in to increase flow
� Results significantly better than in previous study
4. Testing Protocol
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� Phase 2: Cleaning agent A – Removes lead-free and leaded
(°°°°F)
150
140
130
10 Conc (%) 15
Cleaning agent A, Lead-free
Exposure time (min.)
7.5
1.5
5.0
2.0
3.0
++
(°°°°F)
150
140
130
10 Conc (%) 15
Cleaning agent A, Leaded
Exposure time (min.)
7.5
1.5
5.0
2.0
3.0
-0+
4. Testing Protocol
0
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Fixed Parameters
Equipment SpecificationSpray Pressure (psi) 49
Spray bars (top) 5
Board Specification (0603 components) Component density 30
� Phase 2 – Experimental parameters and results
� Effective cleaning under the low standoff components
� belt speeds of 1 fpm – employing a 3 ft. long wash section
� 3-minute exposure time
4. Testing Protocol
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� Phase 2 – Experimental parameters and results
+: Clean 0: Partially cleaned -: Not clean
01.5 / 2.01501514
01.5 / 2.01501512
+1.0 / 3.01501510
+0.6 / 5.0150158
ALeaded
-1.5 / 2.01501513
-1.5 / 2.01501511
01.0 / 3.0150159
+0.6 / 5.0150157
ALead-
free
Cleaning
Result(ft./min) / (min)(˚ F)% #
Cleaning
Agent
Variable Parameters
4. Testing Protocol
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Findings Phase 3:
� New machine was built for Phase 3 testing
� Incorporating the progressive energy dynamics concept
� One additional feature
� Expanded wash tank about 6“
4. Testing Protocol
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� Phase 3: Cleaning agent A – Removes lead-free and leaded
(°°°°F)
150
140
130
10 Conc (%) 15
Cleaning agent A, Lead-free
Exposure time (min.)
7.5
1.5
5.0
2.0
3.0
0 -++ +
(°°°°F)
140
130
10 Conc (%) 15
Cleaning agent A, Leaded
Exposure time (min.)
7.5
1.5
5.0
2.0
3.0
150 0 -++ -
4. Testing Protocol
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� Phase 3 – Experimental parameters and results
Fixed Parameters
Equipment SpecificationSpray Pressure (psi) 50/50
Spray bars (top) 7
Board Specification (0603 components) Component density 30
� Additional improvement
� Effective at belt speeds of 1.7 fpm
� 2.1-minute exposure time
� Two-pump machine
4. Testing Protocol
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-2.2 / 1.61501532
+1.7 / 2.11501531
+1.2 / 2.91501530
-2.2 / 1.61501029
-1.7 / 2.11501028
+1.2 / 2.91501027
ALeaded
-2.2 / 1.61501526
+1.7 / 2.11501525
+1.2 / 2.91501524
-2.2 / 1.61501023
+1.7 / 2.11501022
+1.2 / 2.91501021
ALead-
free
Cleaning Result(ft./min) / (min)(˚ F)% # Cleaning Agent
Variable Parameters
+: Clean 0: Partially cleaned -: Not clean
4. Testing Protocol
� Phase 3 – Experimental parameters and results
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Fluid Flow Mechanics:
Key to Low Standoff Cleaning
Table of Content:
1. Introduction
2. Fluid Flow Theory
3. Inline Progressive Energy Dynamics Approach
4. Testing Protocol
5. Overall Conclusion
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� Component size will further decrease, in contrast board density will
increase
� It will be more difficult to clean the assemblies
� Bigger pumps, longer machines, surfactant based cleaning agents are
not the most effective and efficient cleaning methods
� Progressive energy manifold design to optimize pressure and flow
5. Overall Conclusion
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5. Overall Conclusion
� Main Accomplishments
� Fastest belt speed currently known in the industry
� Optimal Process Definition through adjustment of latest chemical and
mechanical technologies