IMPROVING YOUR WAVE SOLDERING

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IMPROVING YOUR WAVE SOLDERING
PEM Technologies BRINGING TECHNOLOGY TO THE
INDUSTRY

• Igmar Grewar
• Technical Director
• PEM Technologies

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Wave Soldering

• Conveyor
• PCB transported over the wave

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The 6 Basic Steps of Wave/Selective Soldering

• Component preparation
• Insert components
• Apply Flux
• Preheat PCB
• Soldering
• Cool down

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Preforming THT components

• Cost saving
• Higher production output
• Quality

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The effect of hole sizes

• Hole size less than 1.5 times lead thickness
  bend of slightly less than 90º
• A dimple is formed on the lead for hole size more
  than 1.5 times lead thickness
• Raised from PCB to allow for cleaning or heat
  dissipation

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Selective Pallets

• Stable support platform for PCB
• Eliminate masking by hand
• Eliminate glue dotting for SMDs
• Reduce solder defects such as skips and bridging
• Pockets and channels promotes solder flow
• Standardize conveyor width reduce setup time
• Multiple PCBs on a pallet higher throughput

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The Wave Soldering Process
Picture courtesy of Cobar/Balver Zinn
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Fluxing

• Why do we need flux?
• Prevents oxidation
• Acts as a wetting agent

Picture courtesy of Cobar/Balver Zinn
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Fluxing Wave Solder

• Two common types of fluxing methods
• in wave soldering
• Foam fluxing
  Spray fluxing

Pictures courtesy of Seho
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Foam fluxing Wave Solder

• Flux control required
• Ideal contact area 20mm
• Ideal flux stone pore size 3um - 10um
• Air pressure 2 - 3bar
• Raise or lower the whole flux station to achieve
  the right contact
• Never use a foam fluxer without an air knife
• Not suitable for water based fluxes

Picture courtesy of Seho
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Flux Control (foam fluxer)

• Critical parameters
• Flux density (solid content)
• Water content
• Temperature
• Contamination from PCB or compressed air
• Replace flux in foam fluxers completely every 40
  hours
• Cleaning of foam pipe

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Spray fluxing - Wave Solder

• Single side PCB requires 100 Micro Gram per Cm2
  of PCB surface (Check Flux Data Sheet)
• PTH PCBs will require 20 more
• Check the spray pattern by wrapping a piece of
  photo sensitive fax paper around a bare PCB and
  let it run through the fluxer
• Combination of airflow, flux flow, moving speed,
  distance of nozzle to PCB
• Paper must be evenly gray from flux, not wet and
  certainly not dripping

Picture courtesy of Seho
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Advantages of Spray fluxing

• Quantifiable application of the flux deposit
  (SPC)
• No in-process QC of the flux
• No thinner consumption
• Direct application from can
• Reduced flux consumption
• No flux drippings over the preheat zone

Picture courtesy of Seho
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Conversion to Spray flux

• The Plug n Spray spray-fluxer
• Stand alone fluxer

Picture courtesy of Cobar/Balver Zinn
Picture courtesy of Seho
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Incorrect Flux Volume

• Too little flux can cause soldering defects such
  as bridging and skips
• Excessive flux can lead to solder balling and
  unwanted and uncured residue left on the PCB

Picture courtesy of Bob Willis
Picture courtesy of Cobar/Balver Zinn
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Flux Classification - IPC-J-STD-004
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Flux Types

• Alcohol based (100 VOC)
• Long history of reliability process know how
• Modest in preheat requirements
• Can be applied by spray or foam
• High residue safety and wide process window
• Hazardous flammable material
• Contributing to the "green-house" effect

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Flux Types

• Low-VOC (40 water / 60 alcohol)
• Modest in preheat requirements
• Safer to the environment
• Can be applied by spray or foam
• High residue safety and wide process window

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Flux Types

• Water based (100 VOC-free)
• More soldering power
• Environmentally safe
• Non-flammable
• Requires more preheat
• Spray fluxing only
• Some process adjustments required
• Risk for corrosion if flux is not properly
  polymerized by the heat of the wave (flux under
  pallets, on topside or just too much flux
  applied)

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Preheat
Functions of Preheating

• Evaporation of the solvent in the flux
• Activating the flux
• Minimizing the Delta T between the PCB and the
  solder wave

Picture courtesy of Cobar/Balver Zinn
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Preheat

• Types of Preheating

Infra Red elements
Quartz elements
Forced Convection
Pictures courtesy of Seho
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The Preheat Profile
Picture courtesy of Cobar/Balver Zinn

• Preheat temperature is measured on the top side
  of the PCB
• Typical max. preheat temperature Sn/Pb 90ºC -
  120ºC
• Typical max. preheat temperature Pb-Free 100ºC
  - 130ºC

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Measuring Preheat Temperature
Temperature Profiler / Thermocouples
Adhesive Temperature Strips
Infrared Thermometer
Picture courtesy of TWS Automation
Picture courtesy of www.tempstrips.com
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Measuring Preheat Temperature
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Incorrect Preheat
Picture courtesy of Cobar/Balver Zinn

• Preheat too high or too long may break down the
  flux activation system and cause shorts / icicles
• Preheat too low may cause problems such as skips
  or unwanted residues left on the PCB

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Soldering Phase

• Wetting Phase
• Wicking Phase
• Drain Phase

PCB ------ gtgt
Wave
Draining
Wicking
Wetting
Picture courtesy of Cobar/Balver Zinn
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Soldering Phase

• Nominal angle 7º
• Contact Width 20 to 40mm wide for Delta Wave
• Contact Width 15mm wide for Chip Wave
• Dwell time Tin/Lead 3.5 sec _at_ 235ºC solder pot
  temperature
• Dwell time Tin/Lead 2.5 sec _at_ 250ºC solder pot
  temperature
• Dwell time Pb-Free 2 to 5 seconds _at_ 260-270ºC
  solder pot temperature, depending on the
  application
• Conveyor speed 0.8 1.5 m/min
• Conveyor speed (m/min) Contact width (cm) x
  Dwell time (sec)
• Wave height 1/3 2/3 of PCB thickness
• High temperature glass plate is used to measure
  contact width and parallelism to the wave

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Wave Nozzle Configuration

• Delta Nozzle
• Standard Nozzle for through hole components
• Fast moving solder moving in the opposite
  direction of PCB for wetting action
• Small volume of solder moving along with the PCB
  for wicking action

Picture courtesy of Seho
Picture courtesy of Bob Willis
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Wave Nozzle Configuration

• Chip Nozzle
• Turbulent wave
• Can be added in addition to the Delta Nozzle
• High Kinetic Energy
• Avoids shadowing

Picture courtesy of Seho
Picture courtesy of Bob Willis
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Wave Nozzle Configuration

• Dual Wave
• Turbulent chip wave combined with a slow moving
  horizontal wave overcomes the limitations of
  other wave types
• Solution for overcoming the shadow effect on SMT
  components not aligned to the wave

Picture courtesy of Seho
Picture courtesy of Seho
Picture courtesy of Bob Willis
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Wave Nozzle Configuration

• Other Nozzles
• For components requiring high wave pressure or
  high flow dynamics
• For PCBs with high thermal mass
• To optimize contact time

Pictures courtesy of Seho
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Solder Alloy

• Lead Containing Alloy Sn/Pb
• Contains Tin / Lead
• Sn63/Pb37
• Melting point of 183ºC
• Solder pot temperatures from 235 - 250ºC
• Eutectic alloy melts and solidifies at the same
  temperature
• Low surface tension good wetting
• Low viscosity great hole fill and top side
  fillet forming

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Solder Alloy

• 4 Popular choices for Lead-Free
• SAC (Tin/Silver/Copper)
• SAC X (Tin/Silver/Copper X)
• SnCu (Tin/Copper)
• SnCuNi (Tin / Copper / Nickel)
• Your choice of alloy will be dependant on your
• specific requirements

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Solder Alloy

• SAC
• Tin / Silver / Copper
• Typical Sn96.5/Ag3.0/Cu0.5
• Melting point of 217 - 221ºC
• Solder pot temperature 260ºC
• High silver content
• Solder joints looks different than Tin-Lead
• Dull joints due to shrinkage

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Solder Alloy

• SAC X
• Tin / Silver / Copper X
• X Co, Fe, Bi, Si, Ti, Cr, Mn, Ni, Ge, and Zn
• Typical Sn98.3 Ag0.3 Cu0.7Bi0.7
• Melting point of 216 - 225ºC
• Solder pot temperature 265ºC
• Lower material costs vs higher silver SAC alloys
• Performance and appearance similar to higher
  silver SAC alloys

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Solder Alloy

• SnCu
• Tin / Copper
• Sn99.3/Cu0.7
• Melting point of 227ºC (Eutectic alloy)
• No silver content - lowers alloy cost
• Lower tendency to leach copper - less loss of
  conductive copper in tracks and pads
• Poor fluidity at typical lead free temperatures
• Poor through-hole filling and forming of solder
  bridges between components

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Solder Alloy

• SnCuNi
• Tin / Copper / Nickel
• Sn99.25/Cu0.7/Ni0.05
• Melting point of 227ºC
• Eutectic alloy free of shrinkage
• Solder pot temperatures from 265ºC
• Does not contain silver - running costs are low
• Small addition of nickel in to the SnCu alloy
  improves fluidity
• Good fluidity less bridges and better hole
  filling
• Dross rate equal or lower than tin-lead solder
• Lower aggressiveness towards stainless steel
• Bright smooth solder joints

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Solder Bath Analysis

• For Tin-Lead, every 3 to 6 months
• For Lead-Free, every 4 6 weeks after initial
  fill during the first 6 months, thereafter every
  3 to 6 months is recommended

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Transition to Lead Free Alloys

• Higher preheat temperatures required

• Corrosion of metal parts

Pictures courtesy of Seho
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Solutions for Lead-Free

• Pause the PCB in the preheater

• Coated parts available, pumps, solder nozzles and
  solder pot

Pictures courtesy of Seho
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Cooling Phase
Picture courtesy of Cobar/Balver Zinn

• Forced cooling or not?
• No improvement in joint quality
• To speed up production

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Nitrogen or Not?

• Displaces oxygen
• Reduced dross formation
• Increase surface tension
• Improved flow of solder
• Better wetting

Pictures courtesy of Seho
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Most common causes of problems
Skips Bridges Insufficient Hole Fill Solder Balls Blowholes
Component leads too long X
Insufficient flux X X X
Excessive flux X X
Flux density too low X X X X
Flux density too high X X X
Moisture trapped in PCB X X
Preheat temperature too low X X X X X
Preheat temperature too high X X X X
Conveyor speed too low
Conveyor speed too high X X X X X
Conveyor angle too small X X
Solder temperature too low X X X X
Solder temperature too high X
Solder is contaminated X X
Uneven or erratic solder wave X X X X
Solder wave height too low X X
Solder wave height too high X X
Solder mask properties X X
Poor solderability of the PCB or component X X X
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Thank you for your AttentionAny Questions?
www.smartgroupsa.org
PEM Technologies BRINGING TECHNOLOGY TO THE
INDUSTRY
www.pemtech.co.za