Improving PCBA wave soldering Quality

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IMPROVING YOUR WAVE SOLDERING

S-DS300 Automatic dip soldering machineS-DS300 Automatic dip soldering machine


6 Basic Steps of Wave/Selective Soldering

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


Preforming THT components

• Cost saving• Higher production output• Quality


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


Selective Pallets

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


Wave Soldering Process


Fluxing

Why do we need flux?

• Prevents oxidation• Acts as a wetting agent


Fluxing – Wave SolderTwo common types of fluxing methodsin wave soldering:

Foam fluxing Spray fluxing


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


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


Spray fluxing - Wave Solder

• Single side PCB requires 100 Micro Gram per Cm2 of PCB surface (Check Flux Data Sheet)

• PTH PCB’s 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


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


Conversion to Spray flux

• The ‘Plug ’n Spray’ spray-fluxer

• Stand alone fluxer


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


Flux Classification - IPC-J-STD-004


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


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


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)


Preheat

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

Functions of Preheating


Preheat

Types of Preheating

Infra Red elements

Quartz elements

Forced Convection

Pictures courtesy of Seho


Preheat Profile

• 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


Measuring Preheat Temperature

Temperature Profiler /Thermocouples Adhesive

Temperature Strips

Infrared Thermometer


Measuring Preheat Temperature


Incorrect Preheat

• 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


Soldering Phase

• Wetting Phase• Wicking Phase• Drain Phase

Wetting

Wicking

Draining

PCB ------ >>

Wav

e


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 @ 235ºC solder pot temperature• Dwell time Tin/Lead = 2.5 sec @ 250ºC solder pot temperature• Dwell time Pb-Free = 2 to 5 seconds @ 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

7ºContact width


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


Wave Nozzle ConfigurationChip Nozzle

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


Wave Nozzle ConfigurationDual 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


Wave Nozzle Configuration

Other Nozzles

• For components requiring high wave pressure or high flow dynamics

• For PCB’s with high thermal mass• To optimize contact time


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


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 yourspecific requirements


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


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


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


Solder AlloySnCuNi

• 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


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


Transition to Lead Free Alloys

• Higher preheat temperatures required

• Corrosion of metal parts


Solutions for Lead-Free

• Pause the PCB in the preheater

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


Cooling Phase

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


Nitrogen or Not?

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


Most common causes of problems

XComponent leads too long

XXSolder wave height too low

XXSolder mask properties

XXXFlux density too high

XXSolder wave height too high

XSolder temperature too high

XXXXXConveyor speed too high

XXXXPreheat temperature too high

XXXXSolder temperature too low

XXSolder is contaminated

XXMoisture trapped in PCB

Conveyor speed too low

X

X

X

Blowholes

XXXXUneven or erratic solder wave

XXXXPreheat temperature too low

XXConveyor angle too small

X

X

Solder Balls

XXXPoor solderability of the PCB or component

XXFlux density too low

Excessive flux

XXXInsufficient flux

Insufficient Hole Fill

BridgesSkips


Shenzhen Southern Machinery Sales and Service Co., Ltd

Add:Room 1806 Block 3 Jinyun COFCO, Qianjin 2nd Road， Xixiang, Baoan District, Shenzhen ,China

S-DS300 Automatic dip soldering machineS-DS300 Automatic dip soldering machine

Shenzhen Southern Machinery Sales and Service Co., LtdShenzhen Southern Machinery Sales and Service Co., LtdAdd:Add:Room 1806 Block 3 Jinyun COFCO,Qianjin 2nd RoadRoom 1806 Block 3 Jinyun COFCO,Qianjin 2nd Road，， Xixiang, Baoan District, Shenzhen ,China Xixiang, Baoan District, Shenzhen ,China


* Help you in Long lead insertion welding

* contrast high wave soldering energy saving operation cost nearly 28000USD a year

* contrast double wave soldering save running cost 16000USD each year



7 inch touch screen + PLC intelligent control and temperature control system Intelligent precision step by step +Imported wire rod system Tracking step type automatic spray system 85 kg small capacity lead-free tin

furnace Maintenance free spray system + automatic welding supply system Three sections of transmission system + manual adjustable width Pure tin slag function automatically Tin stove liquid level automatic detection technology New type of far infrared heating technology, high efficiency and energy

saving heating Ductile cast iron heating plate (Energy saving 40%) Strong wind cooling device Automatic into the PCB Tin furnace overtemperature protection +Preheating overtemperature

protection

Product features Product features ::





Far infrared heating technology (more rapid heating rate + hot

air heating system) High quality control

Details of some parts:



Step tracking precision spray system

Precision welding system .The users can control at will, suitable for all kinds of welding length of foot



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Technology

Improving PCBA wave soldering Quality