Lead Free Temperature Profiling‐ How to do it!

Bob Willis

Electronics Academy Webinar Presenter

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Welcome to the Vision EngineeringElectronics Academy Webinar whichwill start at 2.30pm UK Time

FREE Electronics Academy Webinar Series 

The Electronics Academy Webinar Series takes an in‐depth look at the issuesaffecting PCB/SMT assembly and the challenges of achieving Zero DefectManufacture. Understand the common causes of solder joint failure and learn howto identify and rectify process defects – improving quality and reducing costs withBob Willis and the VE Team

Learn expert tips to identify quality issuesUnderstand the common causes of process failuresA convenient and quick way to update your skills

In the future have access to a video library of online training sessions

Bob Willis

Bob Willis has been involved with the introduction and implementation of lead-free process technology for the last seven years. He receivedA SOLDERTEC/Tin Technology Global Lead-Free Award for his contribution to the industry, helping implementation of the technology. Bobhas been a monthly contributor to Global SMT magazine for the last six years. He was responsible for co-ordination and introduction of theFirst series of hands-on lead-free training workshops in Europe for Cookson Electronics during 1999-2001. These events were run in France,Italy and the UK and involved lead-free theory, hands-on paste printing, reflow, wave and hand soldering exercises. Each non commercialevent provided the first opportunity for engineers to get first hand experience in the use of lead-free production processes and money raisedfrom the events was presented to local charity. More recently he co-ordinated the SMART Group Lead-Free Hands On Experience atNepcon Electronics 2003. This gave the opportunity for over 150 engineers to process four different PCB solder finishes, with two differentlead-free pastes through convection and vapour phase reflow. He also organised Lead-Free Experience 2, 3 + 4 in 2004-2006.

He has also run training workshops with research groups like ITTF, SINTEF, NPL & IVF in Europe. Bob has organised and run three lead-free production lines at international exhibitions Productronica, Hanover Fair and Nepcon Electronics in Germany and England to provide aninsight to the practical use of lead-free soldering on BGA Ball Grid Array, CSP Chip Scale Package, 0210 chip and through hole intrusivereflow connectors. This resulted in many technical papers being published in Germany, USA and the United Kingdom. Bob also defined theprocess and assisted with the set-up and running of the first Simultaneous Double Sided Lead-Free Reflow process using tin/silver/copperfor reflow of through hole and surface mount products.Bob also had the pleasure of contributing a small section to the first Lead-Free Soldering text book “Environment - Friendly Electronics:Lead-Free Technology” written by Jennie Hwang in 2001. The section provided examples of the type of lead-free defects companies mayexperience in production. Further illustrations of lead-free joints have been featured in here most recent publication “Implementing Lead-FreeElectronics” 2005. He has helped produce booklets on x-ray inspection and lead-free defects with DAGE Industries, Balver Zinn and SMARTGroup

Mr Willis led the SMART Group Lead-Free Mission to Japan and with this team produced a report and organised several conferencepresentations on their findings. The mission was supported by the DTI and visited many companies in Japan as well as presenting a seminarin Tokyo at the British Embassy to over 60 technologists and senior managers of many of Japans leading producers. Bob was responsiblefor the Lead-Free Assembly & Soldering "CookBook" CD-ROM concept in 1999, the world’s first interactive training resource. Heimplemented the concept and produced the interactive CD in partnership with the National Physical Laboratory (NPL), drawing on the manyresources available in the industry including valuable work from NPL and the DTI. This incorporated many interviews with leading engineersinvolved with lead-free research and process introduction; the CD-ROM is now in its 3rd edition.

Find out more at:Bobwillis.co.uk

Bob Willis currently operates a training and consultancy business based in England. Bob is a member of the SMART Technical Committee.Although a specialist for companies implementing Surface Mount Technology Mr Willis provides training and consultancy in most areas ofelectronic manufacture. He has worked with the GEC Technical Directorate as Surface Mount Co-Coordinator for both the Marconi and GECgroup of companies and prior to that he was Senior Process Control Engineer with Marconi Communication Systems, where he had workedsince his apprenticeship. Following his time with GEC he became Technical Director of an electronics contract manufacturing companywhere he formed a successful training and consultancy division.

As a process engineer, he was involved in all aspects of electronic production and assembly involved in setting up production processes andevaluating materials; this also involved obtaining company approval on a wide range of Marconi's processes and products including printedcircuit board manufacture. During the period with Marconi, experience was gained in methods and equipment for environmental testing ofcomponents, printed boards and assemblies with an interest developed in many areas of defect analysis. Over the last 15 years he hasbeen involved in all aspects of surface mounted assembly, both at production and quality level and during that time has been involved intraining staff and other engineers in many aspects of modern production.

Over the past few years Mr. Willis has travelled in the United States, Japan, China, New Zealand, Australia and the Far East looking atareas of electronics and lecturing on electronic assembly. Mr. Willis was presented with the Paul Eisler award by the IMF (Institute of MetalFinishing) for the best technical paper during their technical programmes. He has conducted SMT Training programs for Texas Instrumentsand is currently course leader for Reflow and Wave Soldering Workshops in the United Kingdom. Mr Willis is an IEE Registered Trainer andhas been responsible for training courses run by the PCIF originally one of Europe's largest printed circuit associations. Bob has conductedworkshops with all the major organisations and exhibition organisers World Wide and is known for being an entertaining presenter and theonly presenter to use unique process video clips during his workshops to demonstrate each point made. Bob has written two book which arefree to download on line, Design & Assembly with Pin In Hole Intrusive Reflow & Package On Package Design, Assembly andInspection

Mr. Willis was Chairman of the SMART Group, European Surface Mount Trade Association from 1990-94 and has been elected HonoraryLife President and currently holds the position of SMART Group Technical Director, he also works on BSI Standards Working Parties. He isa Fellow of the Institute Circuit Technology, an NVQ Assessor, Member of the Institute of Quality Assurance and Society of EnvironmentalTest Engineers. Bob Willis currently writes regular features for AMT Ireland, Asian Electronics Engineer and Circuits Assembly the USmagazine. He also is responsible for writing each of the SMART Group Charity Technology reports, which are sold in Europe and Americaby the SMTA to raise money for worthy causes. Bob ran the SMART Group PPM Monitoring Project in the United Kingdom supported by theDepartment of Trade and Industry. He was coordinator of the LEADOUT Project for SMART Group. LEADOUT was one of the largest EUfunded projects, currently he is coordinating European projects TestPEP, uBGA and ChipCheck

In September 2015 Bob voted the Best Speaker at SMTA International Conference in Chicago

Find out more at:Bobwillis.co.uk

What component type causes you most problems?

Fine pitch QFP20%

QFN/LGA18%

Chip components

16%

Through hole19%

BGA27%

Bob Willis webinar 2017 survey

Which process contributes most to your defect levels?

Paste printing21%

Placement15%

Reflow soldering

35%

Selective soldering

18%

Wave soldering

11%

Bob Willis webinar 2017 survey

Reflow Soldering

100oC

140-160oC

Reflow Soldering

180-185oC

225oC

235-240oC

Reflow Soldering

Solderable Plating

Base Material Component LeadCopperBrass AlloySteelAlloy 42

Copper

OSP, Tin, Nickel/Gold, Silver, Lead-Free Solder

Intermetalic layer

Lead-Free Reflow Soldering

J Lead Reflow video

Gull Wing Lead video

Lead-Free Ball Grid Array Reflow

BGA Reflow video Sn/Ag/Cu

LGA/QFN Reflow Simulations

Video shows reflow of LGA devices using a video simulator. The system cansimulate a profile of convection reflow system and allow engineers to monitorthe process directly on a printed board assembly

Pin In Hole/Intrusive Reflow Simulation

The board is assembled then placed in the x-ray system with reflow simulatorwhich allows engineers to reflow and examine the complete process

TMV Package on Package Assembly

The ball terminations sit directly on the exposed solder balls on the bottom package with eitherpaste of flux from the dipping process. After reflow the connections will look like a column ofsolder, however head in pillow has been found by the author.

Download Bob’s Guide to Package On Package Assembly at www.packageonpackagebook.com

Process of Reflow Soldering

Solvent EvaporationFlux ActivationTemperature StabilisationSolder ReflowJoint FormationCooling Phase

BW Reflow Deluxe 7

Reflow Soldering System

Reflow Solder Profile

Zone Number: 1 2 3 4 5 6 7 8

Top Set points: 110 120 120 120 145 190 245 260

Bottom Set points: 110 120 120 120 145 190 245 260

Conveyor Speed 75

Statistics Values: TC-1 TC-2 TC-3 TC-4 TC-5 TC-6 TC-7

Max Rising Slope 1.7 1.5 1.9 1.7 1.5 1.5 1.6

Soak Time 100-120C 68.7 68.3 65.5 71 69.8 68.8 66.1

Reflow Time /179C 57.9 60.6 61.2 57.6 53.8 60.3 56.3

Peak Temp 209.7 210.6 218.7 212.9 208.6 215.2 213.2

Temperature Profiling Examples

Temperature Profiling Examples

BGA361

Temperature Profiling Probe Position

Temperature Profiling for Reflow

BGA361

Vapour Phase Reflow SolderingVPS Fluid Options:

215oC230oC235oC240oC

Heater Coils

Cooling Coils

Lead-Free Reflow Soldering Profiles

Convection Profile

VPS Profile

To run the profiles download PowerPoint player http://www.globfx.com/downloads/swfpoint/

Original Vapour Phase Systems

One of my old batch systems used in GEC and Texas Instruments in 1990s

Solder Voids In Reflow Solder Joints

Reflow solder joints are being viewed in x-ray allowing us to see the voids as they move in thebulk of the solder joint. The void is air or gas trapped in the solder, depending on the time thesolder is in a liquid state may allow this to escape. In the case of via in pad or underfill the voidsmay not escape at all. Videos from Cores Japan

Void Reduction with Vacuum

Voids under QFN Packages

There are many reasons why you may see voids under these types of component. The boards were solderedin vapour phase with and without vacuum. The sample on the left soldered without vacuum shows a higherlevel of voids, on the right virtually no voids

It is not to say that the example with voids is unacceptable but it’s a good example of void reduction.Regardless of paste, profile and good stencil design and no vias its not always possible to eliminate all voidsunder large terminations

Component Lifting During Reflow

Main factors for lifting:Speed of wettingDesign rules usedVolume of pasteNitrogen level

Non Paste Coalescence/Grapping

0201 chip component with lead-free solder paste that has not fully reflowed in air. This is a common fault on small paste deposits whenpeople return to a traditional soak profile. Some solder pastes are far more tolerant that others; the resulting solder joint is sound but the ballshave not fully reflowed into the bulk of the solder joint.

This type of issue has been seen during 2003, 2004 on 0201 chip terminations and on 01005 chips in convection reflow but never in vapourphase soldering due to the inert atmosphere during the soldering stages of the process. Basically the small solder paste deposit is exposed toa long period at elevated temperature during a lead-free profile which reduces the performance of the flux in the paste. It is seen more withprofiles that have a long pre-heat like a traditional profile. A profile which does not have long dwell prior to reflow is less affected. Many pastesuppliers have recommended the straight ramp profile but in the real world many users have not been able to achieve this with lead-free onexisting ovens. In most cases the actual joint is satisfactory and only the outer surface shows this effect; however, most people would notaccept this type of process defect

Reflow Temperature Profiles

Example reflow profiles from different convection ovens

BGA & Solder Paste Reflow

Example of BGA reflow with lead-free paste in air. The video shows evidence of head in pillowformation with open joints. These connections could be intermittent if not detected in manufacture,the video was specifically created by us for a solder material supplier conference in the US

X-Ray Inspection of POP

Open circuit joints on packages produced with dip paste. Assembly trials conducted in the UK by the author and x-ray inspection conducted at ITRI with DAGE x-ray system

What is a Thermocouple?

Two different materials are welded together to form a junction/bead. The two wire are insulated from each other to stop intermittent contact and false readings. The two wires are then covered with an outer cover. 1-60 micro volts can be produced between the wires which is converted to a temperature reading.

Example Thermocouple

Temperature Profiling Probes

Soldered Probes

Aluminium Foil

Kapton Tape

Epoxy Adhesive

Contact Probes

Visit NPL Defect Database Live http://defectsdatabase.npl.co.uk

Temperature Profiling Standard

IPC-7530A Guidelines for Temperature Profiling for Mass Soldering Processes Reflow and Wave

Temperature Profiling for Reflow & Rework

Flexi Rigid Board Design

Multilayer Design

Temperature Profiling Probes

Care need to be taken that the thermocouple bead is in the solderjoint and not on the surface. If the wires are twisted and touching thiswill also give false random readings during measurement

Temperature Profiling ProbesWhen printed boards are to beassembled in a pallet the pallet mayhave a significant effect on thetemperature profile. Make sure thedesign of the pallet is optimised andthe position of the thermocouple beadsis taken into consideration on the pallet

Temperature Profiling Flexible

Assembly Pallet for Flexible Circuit

Thermal relief areas on the base ofpallet to improve delta T duringreflow. Also consider drain holesunder the flex if using vapour phasefor lead-free reflow

Lead-Free Reflow Inspection

Sn/Ag/Cu Alloy

Intrusive Reflow Bottom Intrusive Reflow Top

Lead-Free Reflow Inspection

Intrusive Reflow BottomIntrusive Reflow Top

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Process Defect Guidesproduced for SMART Group