wave soldering

IMPROVING YOUR WAVE SOLDERINGIgmar GrewarTechnical DirectorPEM Technologies

PEM TechnologiesBRINGING TECHNOLOGY TO THE INDUSTRY

Wave SolderingConveyorPCB transported over the wave

The 6 Basic Steps of Wave/Selective SolderingComponent preparationInsert componentsApply FluxPreheat PCBSolderingCool down

Preforming THT componentsCost savingHigher production outputQuality

The effect of hole sizesHole size less than 1.5 times lead thickness bend of slightly less than 90

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 PalletsStable support platform for PCBEliminate masking by handEliminate glue dotting for SMDsReduce solder defects such as skips and bridgingPockets and channels promotes solder flow Standardize conveyor width reduce setup timeMultiple PCBs on a pallet higher throughput

The Wave Soldering ProcessPicture courtesy of Cobar/Balver Zinn

FluxingWhy do we need flux?

Prevents oxidationActs as a wetting agent

Picture courtesy of Cobar/Balver Zinn

Fluxing Wave SolderTwo common types of fluxing methodsin wave soldering:

Foam fluxing Spray fluxing

Pictures courtesy of Seho

Foam fluxing Wave Solder

Flux control requiredIdeal contact area = 20mmIdeal flux stone pore size = 3um - 10umAir pressure 2 - 3barRaise or lower the whole flux station to achieve the right contactNever use a foam fluxer without an air knifeNot suitable for water based fluxes

Picture courtesy of Seho

Flux Control (foam fluxer)Critical parameters:

Flux density (solid content)Water contentTemperatureContamination from PCB or compressed airReplace flux in foam fluxers completely every 40 hoursCleaning of foam pipe

Spray fluxing - Wave SolderSingle side PCB requires 100 Micro Gram per Cm2 of PCB surface (Check Flux Data Sheet)PTH PCBs will require 20% moreCheck the spray pattern by wrapping a piece of photo sensitive fax paper around a bare PCB and let it run through the fluxerCombination of airflow, flux flow, moving speed, distance of nozzle to PCBPaper 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 fluxNo thinner consumptionDirect application from can Reduced flux consumptionNo flux drippings over the preheat zone


Conversion to Spray flux

The Plug n Spray spray-fluxer

Stand alone fluxerPicture courtesy of Cobar/Balver Zinn Picture courtesy of Seho

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 PCBPicture courtesy of Cobar/Balver Zinn Picture courtesy of Bob Willis

Flux Classification - IPC-J-STD-004

Flux TypesAlcohol based (100% VOC)

Long history of reliability & process know how Modest in preheat requirements Can be applied by spray or foamHigh residue safety and wide process window

Hazardous & flammable material Contributing to the "green-house" effect

Flux TypesLow-VOC (40% water / 60% alcohol)

Modest in preheat requirementsSafer to the environment Can be applied by spray or foam High residue safety and wide process window

Flux TypesWater based (100% VOC-free)

More soldering powerEnvironmentally safe Non-flammable

Requires more preheat Spray fluxing only Some process adjustments requiredRisk 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)

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

Functions of Preheating


PreheatTypes of PreheatingInfra Red elements Quartz elements

Forced ConvectionPictures courtesy of Seho

The Preheat ProfilePreheat temperature is measured on the top side of the PCBTypical max. preheat temperature Sn/Pb = 90C - 120CTypical max. preheat temperature Pb-Free = 100C - 130C


Measuring Preheat TemperatureTemperature Profiler /Thermocouples Adhesive Temperature Strips Infrared ThermometerPicture courtesy of TWS Automation Picture courtesy of www.tempstrips.com

Measuring Preheat Temperature

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


Soldering PhaseWetting PhaseWicking PhaseDrain Phase

Picture courtesy of Cobar/Balver Zinn WettingWickingDrainingPCB ------ >>Wave

Soldering PhaseNominal angle = 7Contact Width = 20 to 40mm wide for Delta Wave Contact Width = 15mm wide for Chip WaveDwell time Tin/Lead = 3.5 sec @ 235C solder pot temperatureDwell time Tin/Lead = 2.5 sec @ 250C solder pot temperatureDwell time Pb-Free = 2 to 5 seconds @ 260-270C solder pot temperature, depending on the applicationConveyor speed = 0.8 1.5 m/minConveyor 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

Wave Nozzle ConfigurationDelta Nozzle

Standard Nozzle for through hole componentsFast moving solder moving in the opposite direction of PCB for wetting actionSmall volume of solder moving along with the PCB for wicking action

Picture courtesy of SehoPicture courtesy of Bob Willis

Wave Nozzle ConfigurationChip Nozzle

Turbulent waveCan be added in addition to the Delta NozzleHigh Kinetic EnergyAvoids shadowing

Picture courtesy of SehoPicture courtesy of Bob Willis

Wave Nozzle ConfigurationDual Wave

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

Picture courtesy of SehoPicture courtesy of SehoPicture courtesy of Bob Willis

Wave Nozzle ConfigurationOther Nozzles

For components requiring high wave pressure or high flow dynamics For PCBs with high thermal massTo optimize contact time


Solder AlloyLead Containing Alloy Sn/Pb

Contains Tin / LeadSn63/Pb37Melting point of 183CSolder pot temperatures from 235 - 250CEutectic alloy melts and solidifies at the same temperatureLow surface tension good wettingLow 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 AlloySAC

Tin / Silver / CopperTypical: Sn96.5/Ag3.0/Cu0.5Melting point of 217 - 221CSolder pot temperature 260CHigh silver contentSolder joints looks different than Tin-LeadDull joints due to shrinkage

Solder AlloySAC + X

Tin / Silver / Copper + XX = Co, Fe, Bi, Si, Ti, Cr, Mn, Ni, Ge, and ZnTypical: Sn98.3 Ag0.3 Cu0.7Bi0.7Melting point of 216 - 225CSolder pot temperature 265CLower material costs vs higher silver SAC alloysPerformance and appearance similar to higher silver SAC alloys

Solder AlloySnCu

Tin / CopperSn99.3/Cu0.7Melting point of 227C (Eutectic alloy)No silver content - lowers alloy costLower tendency to leach copper - less loss of conductive copper in tracks and padsPoor fluidity at typical lead free temperatures Poor through-hole filling and forming of solder bridges between components

Solder AlloySnCuNi

Tin / Copper / NickelSn99.25/Cu0.7/Ni0.05Melting point of 227CEutectic alloy free of shrinkageSolder pot temperatures from 265C Does not contain silver - running costs are low Small addition of nickel in to the SnCu alloy improves fluidityGood fluidity less bridges and better hole fillingDross rate equal or lower than tin-lead solderLower aggressiveness towards stainless steelBright smooth solder joints

Solder Bath AnalysisFor Tin-Lead, every 3 to 6 monthsFor 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 AlloysHigher preheat temperatures required

Corrosion of metal parts


Solutions for Lead-FreePause the PCB in the preheater

Coated parts available, pumps, solder nozzles and solder pot


Cooling PhaseForced cooling or not?No improvement in joint qualityTo speed up production


Nitrogen or Not?Displaces oxygenReduced dross formationIncrease surface tensionImproved flow of solderBetter wettingPictures courtesy of Seho

Most common causes of problems

Thank you for your Attention

Any Questions?PEM TechnologiesBRINGING TECHNOLOGY TO THE INDUSTRYwww.smartgroupsa.orgwww.pemtech.co.za

Almost everyone starting a assembly operation, will start with manual soldering. As volumes increase, manual soldering will not cater for the required throughput.Many assemblers move from manual soldering to a method of manual flux application and dipping of the PCB in a solder pot. This will provide for higher throughput, as all the components can be soldered at once, but quality is compromised, as this operation relies on a operator, and factors like flux quantity and time spent in the solder is not controlled.Wave soldering provides a process where important parameters are controlled and high throughput rates can be achieved. Robot soldering and selective soldering are specialized processes, and typically need specialized equipment and fixtures. Though these two technologies are suitable in certain applications, they are not always suitable as a general soldering tool required when assembling a variety of different products. Six basic steps are required to perform the wave soldering operation.Some components leads need to be preformed prior to insertion, and in some cases, lead clinching may be required.Components can be inserted by an operator, or by automatic equipment.Flux is applied to the bottom side of the PCB, typically by a fluxing unit inside the wave solder machine.As the PCB are transported on a conveyor, the PCB is pre-heated from the bottom side by a pre-heater mounted under the conveyor.The molten solder in the solder bath is pumped though channels to form a solder wave. The PCB moves over the wave of molten solder, which solders the leads protruding on the bottom side of the PCB.The PCB cools down after it exits the wave solder machine. The reason component performing was introduced to electronic assembly, was to save cost. By using preformed components, the insertion operator can concentrate on inserting components, without having to perform lead forming first.Preforming saves time, streamlining the assembly operation, resulting in higher production output. Preformed components are uniform, giving a good cosmetic appearance, and it reduces the change of quality problems during the soldering operation.

When the PCB hole is less than 1.5 times the lead thickness, a lead bent to slightly less than 90 degrees will hold well.If the ration is more than 1.5 times, then it may be beneficial to add a dimple, though this will take more time to accomplish.There are times when the component must be raised from the PCB, it may be for heat dissipation, or to allow for effective cleaning. This can normally be accomplished by offsetting the lead by 1 x the lead thickness.

The primary purpose of flux is to prevent oxidation of the PCB pads. Solder attaches very well to copper, but poorly to the various oxides of copper, which form quickly at soldering temperatures. Flux is a substance which becomes a reducing agent at elevated temperatures, preventing the formation of metal oxides.Additionally, flux acts as a wetting agent, allowing solder to flow easily on the working piece rather than forming beads as it would otherwise. The primary purpose of flux is to prevent oxidation of the PCB pads. Solder attaches very well to copper, but poorly to the various oxides of copper, which form quickly at soldering temperatures. Flux is a substance which becomes a reducing agent at elevated temperatures, preventing the formation of metal oxides.Additionally, flux acts as a wetting agent, allowing solder to flow easily on the working piece rather than forming beads as it would otherwise. The foam fluxer consists of a tank of flux into which a plastic cylinder with tiny holes is immersed; this is sometimes called a flux stone or a foam pipe. The flux stone is covered with a metal chimney. Air is passed through this cylinder which causes flux foam to rise up the chimney, forming a head of foam. As the PCB passes over the foam head, flux is applied to the PCB. An air knife is provided to blow off the excess flux, which will return to the flux container.Some spray fluxers consist of a robotic arm which travels from side to side while spraying a fine mist of flux onto the bottom side of the board. Other spray fluxers consist of a stationary bar with a series of nozzles that spray a fine mist. For either flux application method, precise control of flux quantities are required. Too little flux will cause poor joints, while too much flux may cause cosmetic or other problems.The foam fluxer consists of a tank of flux into which a plastic cylinder with tiny holes is immersed; this is sometimes called a flux stone or a foam pipe. The flux stone is covered with a metal chimney. Air is passed through this cylinder which causes flux foam to rise up the chimney, forming a head of foam. As the PCB passes over the foam head, flux is applied to the PCB. An air knife is provided to blow off the excess flux, which will return to the flux container.

For either flux application method, precise control of flux quantities are required. Too little flux will cause poor joints, while too much flux may cause cosmetic or other problems.In foam fluxers, the flux density must be controlled by measuring the density with a hydrometer. Density measurements are affected by water content and temperature changes. A temperature decrease of 5 degrees, can fake an increase of 2.5% in solid content.Contamination from dirty PCBs or oil contamination from the compressed air supply, can affect the flux and cause soldering problems.In a foam fluxers, the flux should be completely replaced every 40 hours, depending on the conditions.Some spray fluxers consist of a robotic arm which travels from side to side while spraying a fine mist of flux onto the bottom side of the board. Other spray fluxers consist of a stationary bar with a series of nozzles that spray a fine mist. For either flux application method, precise control of flux quantities are required. Too little flux will cause poor joints, while too much flux may cause cosmetic or other problems.Tips for the successful implementation of VOC-Flux technologyVerify the compatibility of your type(s) of solder-resists with VOC-Free flux technology Work with board vendor(s) to reduce variation of the surface state of the solder resist: o Curing rate o Ionic contamination (Preferably under 0.5 micrograms/cm2 of NaCl-equivalents Reconsider the design of pallets with regard to water entrapmentOld pallets partially may have delaminated. Water entrapment may be an issue! A good spray fluxer must have a nozzle positioned not too far from the board providing o A quantifiable and controlled film thickness o Minimum overspray o Good thru-hole filling Medium wave length Infra Red preheating elements are preferred the 1st preheat zone Forced convection helps to create a good plateau temperature level in proceeding zones For recommended preheat profiles, see the User's Guidelines of the products concerned.When - for one or more of the above reasons, or for any other reason - your process window currently appears too small for full VOC-free water-based fluxes, an excellent drop-in replacement for alcohol-based fluxes may appear to be Low-VOC fluxes!IR Elements provide the most efficient energy absorbance for both alcohol as well as water-based (VOC-Free) fluxes. Therefore IR elements are recommended as the first zone in a preheat section. IR elements are slow in reacting to temperature changes, but when stable temperature is reached, they provide a homogeneous heating of the PCB.Quartz elements are quick reacting in temperature changes, typically used to provide a boost in temperature at the end of a preheat section. Effieciency may decrease with time check at regular intervals.Forced convection heating is very effective in drying the assembly after the application of the wet flux deposit by using thermal energy in conjunction with the physical displacement force of the gas flow. Care should be taken that the active materials in VOC-Free fluxes are not removed by a turbulent gas flow. Forced convection enables heating plateau values providing excellent flux activation times without overheating the components. Very homogeneous heating of the PCB.

IR Elements provide the most efficient energy absorbance for both alcohol as well as water-based (VOC-Free) fluxes. Therefore IR elements are recommended as the first zone in a preheat section. IR elements are slow in reacting to temperature changes, but when stable temperature is reached, they provide a homogeneous heating of the PCB.Quartz elements are quick reacting in temperature changes, typically used to provide a boost in temperature at the end of a preheat section. Effieciency may decrease with time check at regular intervals.Forced convection heating is very effective in drying the assembly after the application of the wet flux deposit by using thermal energy in conjunction with the physical displacement force of the gas flow. Care should be taken that the active materials in VOC-Free fluxes are not removed by a turbulent gas flow. Forced convection enables heating plateau values providing excellent flux activation times without overheating the components. Very homogeneous heating of the PCB.

Wetting is the intermolecular bonding interaction that takes place as a result of the molten solder coming into contact with the solid surfaces on the PCB and components.The solder moving up the barrel of the through holes is called wicking. To generate a fully wickedup solder joint, it is important to consider the T between the bottom and the topside of the barrel.As the PCB exits the wave, the solder drains away from the PCB.


Lead Free Solders all Largely Tin based Silver provides mechanical strength, but has worse ductility than lead. Copper lowers the melting point, improves resistance to thermal cycle fatigue, and improves wetting properties of the molten solder Bismuth significantly lowers the melting point and improves wettability Indium lowers the melting point and improves ductility Zinc lowers the melting point and is low-cost. Antimony is added to increase strength without affecting wettability.


Cobalt Iron Bismuth Silicon Titanium Chrome, Manganese, Nickel, Germanium and Zink4th element modifications of SAC solder alloys, that are intended to improve wetting performance, reduce dross, and increase mechanical strenght.




wave soldering

Documents

flux flow

flux typesalcohol

skipsexcessive flux

flux station

compressed airreplace

flux deposit spcno

wide process window

mmideal flux stone pore