ELEC 6740: Electronics
Manufacturing
Chapter 12: Soldering of
Surface Mount Components
R. Wayne Johnson
Alumni Professor
ECE Department, Auburn
University
334-844-1880
johnson@eng.auburn.edu
Subjects
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Introduction
Wave Soldering
Vapor Phase Reflow Soldering
Infrared Reflow Soldering
Convection Reflow Soldering
Soldering Defects
Alternate Soldering Methods
Introduction
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Soldering - Low temperature
Brazing – Medium temperature
Welding – High temperature
Wave Soldering
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Through hole components
SMT resistors, capacitors, diodes, SOTs
SOICs more difficult
PLCCs and PQFPs should be avoided
Wave Solder
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Flux application
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Preheat
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Foam
Spray
Jet
Minimize thermal shock to board
Activate flux
Solder wave
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Provide solder alloy
Form metallurgical connections
Wave Solder
Flux Spray
Pre-heat
Molten Solder Wave
Wave Soldering
Wave Solder
Wave Solder
Technical Issues
Design for Wave Solder
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Outgassing (gas bubbles released from wet
flux can cause solder skip or lack of fillet.
Design for Wave Solder
Design for Wave Solder
Board travel direction over the wave
Wave Soldering
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Bridges can occur beneath small chips
(0805, 0603, 0402, 0201)
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Capillary action between glue dots
Only liquid photoimageable solder mask is
recommended bewteen pads
Machine Control
Wave Soldering
Max.
Nom.
Minimum
6°C /sec
4°C /sec *
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Temperature
Differential
Solder Temperature
135°C
120°C
110°C
260°C
240°C
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Dwell Time @ Max.
4 sec.
3 sec.
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N/A
4°C /sec.
N/A
Ramp up (°C /sec)
Ramp Down
(°C /sec.)
Temperature measured at the component lead area in degrees celcius.
Temperature differential between the final preheat stage and the
soldering stage.
* Will vary depending on board density, geometry and package type.
** Will vary depending on package types and board density
Wave Soldering
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Capacitor cracking
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Delta between the wave and the preheat
should be 100-120oC
Temperature Profile
Dual Wave
Removes excess solder
Forces solder into narrow regions
Dual Wave
Vibrating Wave
50 or 60Hz
vibrations
Vibrating Wave
Vibration said to be more
effective in filling holes
and eliminating solder
skips than the dual wave.
Dual wave and vibrating
wave lead to more Sn loss
(reaction with atmopshere).
Need to replenish Sn.
Modified Wave
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To reduce bridging
and iclicles
Improves top side
fillets
Inert Atmosphere
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Nitrogen cover
over wave
Compensates for
lower flux activity
Inert Atmosphere
Inert Atmosphere
Vapor Phase Reflow
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Q= hA(Tv – Ts)
Q = heat transfer
rate
h = heat transfer
coefficient
Tv = saturated vapor
temperature
Ts = part surface
temperature
A = product surface
temperature
In-line Vapor Phase
Vapor Phase Soldering
Vapor Phase Soldering Profile
Vapor Phase Soldering Profile
Solder Wicking
Solder Wicking
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h is higher for
a vertical
surface than
for a
horizontal
surface
Solder Wicking
Infrared Reflow Soldering
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Class I: Radiant IR dominant system
Class II: Convection/IR dominant
system
Class III: Convection dominant systems
Infrared Reflow Soldering
Infrared Reflow Soldering
Infrared Heat Transfer
(Radiation)
Q = V × E s × At × K (T ⋅ Tt )
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Q = infrared heat transfer rate
V = geometric view factor (0-1)
Es = emissivity factor of the source (0-1)
At =absorption factor of the target (0-1)
K = Stefan-Boltmann constant (5.67x10-12 w/cm2/K4)
Ts = source temperature
Tt = target temperature
Solder Wicking
Convection Heat Transfer
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Q = H x ∆T
Q = heat absorbed per unit area
H = convective film coefficient
∆T = temperature difference between
fluid (air) and the object
Convection Reflow
Pro & Con of IR & Convection
Nitrogen Reflow
Solder Profile Development
Profiling
Common Reflow Defects
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Tombstoning and Part Movement
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If heating rate is too high, the volatiles in
the solder paste will rapidly evolve,
possibly causing tombstoning (standing on
end), drawbridging (standing at an angle)
or lateral shift.
Poor design
Poor solder wetting
Common Reflow Defects
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Thermal shock
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Rapid heating or cooling rates
Part surface temperature is higher than
interior
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Component cracking
Solder mask discoloration
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Especially dry film solder masks in IR
dominant systems
Laser Soldering
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Selective heating for temperature
sensitive components
Heats the solder only and not the
component
Laser Soldering
Laser Soldering
Laser Soldering
Hot Bar Soldering
Hot Bar Soldering
Hot Bar Soldering Profile
Hot Bar Soldering Profile
Soldering Options