rework profiles
DESCRIPTION
How to make a electronics board thermal profile for rework and soldering.TRANSCRIPT
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RexPaulMark Todd
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Outline
q Thermal Quality Management (ThQM)
q Solder paste requirements
q Generating the Oven Recipe
q What’s needed to Profile
q Determine points to profile
q Attaching the T/Cs
q Performing the Profile
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Thermal Quality Management
Stage 1 Define RequirementsW h y d o w e p r o f i l e?
– Identify heat sensitive components
– Choose soldering technology
Stage 2 Machine Recipe DevelopmentW ha t i s t h e o v e n r e c i p e ?
– Develop machine settings required for production thatmeet the above requirements
– Assure all solder joints experience the requiredtemperature profile
– Assure sensitive components do not experience longterm damage
Stage 3 Collect DataH o w a r e w e d o in g ?
– Assure the temperature profile developed duringcharacterization is being repeated
– Proof your thermal process is in control
To Reduce Scrap and Increase Yields
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ThQM Definitions
Profile – The graphical plot of temperature as a function of time, asmeasured by one or more thermocouples at points of interest on a PCB
Recipe – Oven settings required to produce the desired profile
Temp
ºC
Time
• Zone set point
temperature
• Conveyor
speed
• Convection rate
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Solder paste requirements
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Solder paste requirements
RSS – “Ramp Soak Spike” profile
RTS – “Ramp to Spike” profile
Temp
ºC
Time
RSS
RTS
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Solder paste requirementsRamp – slope ºC/sec
Soak – time sec
Spike – slope ºC/sec
Time Above Liquidous (TAL) – time sec
Peak – temperature ºC
Cooling – slope ºC/sec
Ramp
Begin Temp
End Temp
Spike
Peak
Cooling
SoakLiquidous Temp
TAL
What makes a good profi le
Red = KPI
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Generating the Oven RecipeInitial recipe – Where do you start?
Software generated recipe
• Based on similar board profile characteristics
• Based on the oven characteristics
Your own recipe experience
• Use a recipe which solders a board of similar size or component density
Best to “under shoot” zone temperature set points rather than over shoot
• Lowers the risk of destroying the board
• It take less time raise the oven’s temperature then to lower it
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Generating the Oven RecipeInitial recipe – What can you control?
Three basic controls
1. Zone Temperature – Controls the profile slope in that zone
• Higher temp increases heating rate• Lower temp reduces heating rate
2. Conveyor Speed – Controls the time spent in ALL Zones
• Slower speed increases the time in all zones
• Faster speed decreases the time in all zones
3. Convection Rate (option) – Controls the flow of heat in ALL zones
• Higher rate increases heating rate at the same temp set point
• Lower rate decreases heating rate at the same temp set point
• Higher rate reduce temp differences between components
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Generating the Oven RecipeInitial recipe – Suggestions
Zone 1 2 3 4 5 6 7 8 9Leaded 150 170 180 180 180 180 205 235 250
No-lead 150 165 180 200 205 230 245 260 270
Conveyor 32 in/min
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What’s needed to ProfileWhat’s needed to prof ile1. Product to profile
2. Thermocouples
3. Profiler
4. Thermal protective barrier5. Carrier for the profiler
6. T/C attachment solder or tapes
7. Soldering iron
8. Solder wick
9. Gloves
10. Cooling fan
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Determine points to profileComponents at risk (J-STD-075)
• Capacitors: Aluminum Electrolitic, Film, Tantalum
• Crystals; Oscillators and Resonators
• Fuses
• Inductors and Transformers
• Non-Solid State Relays
• LEDs
• Connectors
• Switches
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Determine points to profileIdentifying the trouble spots
Conveyor
Direction
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Methods – Solder
High Temp Solder
• SN10 ~ 280 ºC Melting point
• SN5 ~ 305 º C Melting point
• Au80 ~ 280 º C Melting point
4000.00 / lb
Attaching the T/Cshttp://www.ecd.com/blog/index.php/category/thermocouple-attachment/
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Methods – Solder
1. Wick up old solder
2. Add SN5 to T/C
3. Tape down T/C
4. Touch with solder iron
5. Add a little more solder
6. Done!
0.02”
Attaching the T/Cshttp://www.ecd.com/blog/index.php/category/thermocouple-attachment/
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Attaching T/Cs – Where is it?
PCB
T/C
PCB
T/C
PCB
T/C
OK
OK
OK
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Attaching the T/Cshttp://www.ecd.com/blog/index.php/category/thermocouple-attachment/
Methods – Tapes and glues Aluminum Tape (Silicone adhesive)
Pro – Conforms to T/C
Pro – Hold its shape
Con – You can’t see through it
Kapton® Tape (Silicone adhesive)
Pro – You can see through it
Con – Does not hold it shape
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Attaching the T/Cshttp://www.ecd.com/blog/index.php/category/thermocouple-attachment/
Methods – Tapes and gluesEpoxy® (Hi Temp)
Pro – Holds well
Con – Adds insulation
Con – Requires curing (time or UV)
AttachEZ™
Pro – Conforms to T/C
Pro – Reusable!
Con – Semi transparent
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Attaching Thermocouples - BGAs
1. Pre-drill before BGA is placed
2. Post-drill after BGA is soldered
3. Use an existing via Epoxy® Fill
BGA
PCB
Via
T/C 36 to 40ga
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Performing the ProfileLoading the Board and Profiler
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Performing the ProfileLoading the Board and Profiler
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Off Loading the Board and ProfilerPerforming the Profile
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Off Loading the Board and ProfilerPerforming the Profile
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Cooling for the next runPerforming the Profile
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Checking the resultsPerforming the Profile
Ramp
Spike
Peak
Cooling
Soak
TALBegin Temp
End TempLiquidous Temp
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Performing the ProfileUse software tools to "predict" a better recipe
Prediction using actual product profiles is best because it …
… uses the actual oven recipe and its performance (Machine)
… is the actual profile of components or solder joints (Assembly)
… lets you adjust the profile to the desired specification (Process)
… assures your predictive changes will be accurately reproduced
ECD – U Classes MAP 101 or Profiling 201
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Summary
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q ThQM – Thermal Quality Management
q Solder paste requirements
q Generate an oven recipe
q What you need to profile
q Determine what points to profile
q Attach the T/Cs
q Perform a profile
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Thank you for attending today’s class
Questions? Contact: [email protected]
ECD-U Class List: www.ECD.com/ECDU
ECD Sales/Support: 503-659-6100
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Common questionsCan zone temperature setting fix this problem?
• Increasing the set point temp will raise both peaks
• Increase convection and lower the temperature set point
• Add a thermal shield to the hotter profile part
What causes components or traces to heat at different rates?
• Not because of their size or thermal mass
• Mostly because of their thermal resistance to heat flow
How does convection help heat different parts more equal?• It applies heat to the entire surface more or less equal
• Forced air convection is a continuous source of freshly heated air