SMART Group Lead-Free Wave & Selective Soldering Workshop Dec 5th 2007

Welcome to Wootton Bassett! Wave Solder Process – Back To Basics

Nigel BurttProduction Engineering ManagerDolby Laboratories, Inc. – European HQ

Lead-Free Wave and Selective Soldering

Workshop

SMART Group Lead-Free Wave & Selective Soldering Workshop Dec 5th 2007 2

Dwell time

wetting time

Wave solder process timeline (single-wave)

Flux Applied

Preheat

Wave solder process

Soldering Cooling

Solder contact made Solder contact lost

Solder wetting complete

Flux activated, solvent evaporated, thermal

shock minimised

Solder solidified and joint formed

Complete coverage of PCB and penetration of

PTHs

Solder drainage complete

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Lead-Free No-Clean Wave Solder Process Setup –Five Priorities

1) DWELL TIME

2) CONVEYOR SPEED

3) PREHEAT

4) FLUX APPLICATION

5) SOLDER TEMPERATURE

All these parameters need to be in balance

- some compromises will be required

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Lead-Free No-Clean Wave Solder Process Setup –First Priority = Dwell Time

• Set dwell time in solder wave to be within about 2-4 seconds• Solder wave flow both forwards and backwards over the nozzle as the

PCB comes into contact

• Solder flow velocity should be roughly equal to the conveyor speed

• Dross and flux residue move away from the PCB

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Dwell Time• Solder wave height and conveyor speed control the dwell time

• Approximately a 2-4cm solder contact window is desirable as the PCB passes over the wave.

• Rough rule of thumbDwell time (secs) contact window (cm) / conveyor speed (m/min)

• The wave surface should be exactly parallel to the PCB contact window, contact timing across the wave should be coincident within 0.2 seconds

• Physical adjustment of the machine level, nozzle level and conveyor heights may be necessary to achieve the correct parameter balance.

• Conveyor should present PCB to wave at an angle of around 70

20-40mm

70

Parallel to wave

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Dwell Time must be optimised for each PCB design

From www.wavesoldering.com

SMART Group Lead-Free Wave & Selective Soldering Workshop Dec 5th 2007 7

The Importance of Parallelism

From www.wavesoldering.com

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Lead-Free No-Clean Wave Solder Process Setup –Second Priority = Conveyor Speed

• Set conveyor speed to between 0.7-1.5m/min• Setting must be carefully balanced against dwell time and preheat

requirements for each PCB design

• Faster = less dwell time, less preheat

• Slower = more dwell time, increased preheat

SMART Group Lead-Free Wave & Selective Soldering Workshop Dec 5th 2007 9

Lead-Free No-Clean Wave Solder Process Setup –Third Priority = Preheat

• Set preheaters to provide a topside temperature on the PCB of around 90-1300C immediately before solder contact • Utilise the different types of preheat available to provide an even ramp rate

• Setting must be balanced against solder dwell time

• Preheat requirement depends on flux type and carrier solvent

• Also dependent on PCB thickness and/or fixture thermal mass

• PCB underside should not exceed 1500C before the wave

• Purpose is to activate the flux and allow it time to work

• Also brings the PCB and components up to a suitable working temperature to minimise thermal shock during solder contact and to promote wetting during soldering

• Important that the preheat drives off the flux base solvent, to prevent solder spitting during wave contact. • Especially for VOC-free (water-based) no-clean fluxes

SMART Group Lead-Free Wave & Selective Soldering Workshop Dec 5th 2007 10

Lead-Free No-Clean Wave Solder Process Setup –Fourth Priority = Fluxer

• Set fluxer to give complete and uniform coverage of PCB to be soldered and full penetration of all plated-through holes• Recommended application rate is approx 75ml/cm2, but depends on flux

type and solvent carrier.

• Too little flux will result in bridging and other such defects

• Too much will lead to increased residue and solder balling

• Use old thermal transfer fax paper in a fixture to check on flux coverage

From www.ecd.com

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Lead-Free No-Clean Wave Solder Process Setup –Fifth Priority = Solder Temperature

• Set the solder pot temperature to suit your lead-free alloy• For SnAg3.8Cu0.7, the melting point is 2170C, but the pot will have to run

with superheat above this temperature to optimise the flow characteristics of the alloy

• If run too hot, the topside temperature on the PCB during wave contact may affect SMT solder joints, even causing secondary reflow in extreme cases.

• Don’t rely upon the machine thermocouple to set, use a separate thermocouple directly in the wave to check the solder contact temperature accurately.

• Typically the running wave should measure around 2600C

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Measurement Tools

From www.solderstar.com

From www.intertronics.co.uk

From www.rswww.com

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Example of Dolby Process

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Wetting Test PCB as final check

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Any Questions?

SMART Group Technical Committee

info@smartgroup.org

+44(0) 1494 465217

Nigel Burtt - Production Engineering Manager

Dolby Laboratories, Inc. - European HQ

njb@dolby.co.uk

+44(0) 1793 842132

(c) SMART Group 2007

We accept no liability for the consequence of any action taken on the basis of information provided from us.  

The information is provided in good faith. Any views or opinions presented to you are solely those of the author and reflect their understanding of current good practice and their interpretation of guidance, regulation and standards.