ELEC 6740: Electronics Manufacturing Chapter 12: …jevans/elec6740/Chapter12.pdfELEC 6740: Electronics Manufacturing Chapter 12: Soldering of Surface Mount Components R. Wayne Johnson

ELEC 6740: Electronics Manufacturing Chapter 12: Soldering of Surface Mount Components

R. Wayne JohnsonAlumni Professor

ECE Department, Auburn University

[email protected]

Subjects! Introduction! Wave Soldering! Vapor Phase Reflow Soldering! Infrared Reflow Soldering! Convection Reflow Soldering! Soldering Defects! Alternate Soldering Methods

Introduction! Soldering - Low temperature! Brazing – Medium temperature! Welding – High temperature

Wave Soldering! Through hole components! SMT resistors, capacitors, diodes, SOTs! SOICs more difficult! PLCCs and PQFPs should be avoided

Wave Solder! Flux application

! Foam! Spray! Jet

! Preheat! Minimize thermal shock to board! Activate flux

! Solder wave! 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! Outgassing (gas bubbles released from wet

flux can cause solder skip or lack of fillet.

Design for Wave Solder

Design for Wave SolderBoard travel direction over the wave

Wave Soldering! Bridges can occur beneath small chips

(0805, 0603, 0402, 0201)! Capillary action between glue dots! Only liquid photoimageable solder mask is

recommended bewteen pads

Machine Control

Wave SolderingMax. Nom. Minimum

Ramp up (°C /sec) 6°C /sec 4°C /sec * **

Temperature Differential

135°C 120°C 110°C

Solder Temperature 260°C 240°C **

Dwell Time @ Max. 4 sec. 3 sec. **

Ramp Down (°C /sec.)

N/A 4°C /sec. N/A

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! Capacitor cracking

! Delta between the wave and the preheat should be 100-120oC

Temperature Profile

Dual Wave

Forces solder into narrow regions

Removes excess solder

Dual Wave

Vibrating Wave

50 or 60Hzvibrations

Vibrating Wave

Vibration said to be moreeffective in filling holesand eliminating solderskips than the dual wave.

Dual wave and vibrating wave lead to more Sn loss(reaction with atmopshere).Need to replenish Sn.

Modified Wave! To reduce bridging

and iclicles! Improves top side

fillets

Inert Atmosphere! Nitrogen cover

over wave! Compensates for

lower flux activity

Inert Atmosphere

Inert Atmosphere

Vapor Phase Reflow! 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! h is higher for

a vertical surface than for a horizontal surface

Solder Wicking

Infrared Reflow Soldering! 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 = 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

)( 44tsts TTKAEVQ ⋅×××=

Solder Wicking

Convection Heat Transfer! 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! Tombstoning and Part Movement

! 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! Thermal shock

! Rapid heating or cooling rates! Part surface temperature is higher than

interior! Component cracking

! Solder mask discoloration! Especially dry film solder masks in IR

dominant systems

Laser Soldering! 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