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April 27, 2017

Reflow oven profilers

How important is reflow oven profiling to producing quality circuit boards?

I have been attempting to buy a 'profiler' for some time now, but I run into the "we've done ok without one till now" excuse. Why do we need one? 

Currently we do what I call "profiling by gut." Almost all of the literature describing the importance of profiling comes from someone with a vested interest in selling profiling equipment.



B.W.

Experts Comments

Your move to buy a profiler is probably a smart one. 

Up to this point your company has probably been running the same size board with the same oven settings and getting good results. And if that continues, then "they" are right--who needs a profiler?

BUT, products change. Components change. Technologies change. And all of these changes can't be implemented by art - they need science.

Large BGA's for example can act like huge heat sinks and some balls can reflow while others might not. A thermocouple under the BGA will tell you definitively what is going on there in terms of temperature and allow you to ensure good first pass yields.

The advent of the lead free process changes most of your parameters. Peak temperature increases, dwell times change, liquidous times are different. IN tin-lead soldering, the process window is very forgiving and gut profiling can work as the range of acceptable temperatures can be as high as 30 degrees. But that process window shrinks dramatically in lead free and can be as low as 10-15 degrees depending on the paste and flux. You need a thermocouple on that board to know for sure what the paste and flux are seeing. The temperature excursion for the paste/ flux system is critical to good intermetallics and grain structure formation.

Another way to look at it is to use the cooking analogy. If you were cooking a turkey and didn't have that little pop up thermocouple in there how would you really know it was done? Take it out and take a bite? Put it back in? Take another bite? Maybe, but after a little salmonella might have a problem.

And with PCB's you can't just pop them back in and cook some more. (And you have trouble making money in this business with low first pass yields.)

So if the product and process isn't changing--no profiler is needed. (But your company probably won't be in business in a year or two if it isn't changing and adapting to the new technologies)

Otherwise, a profiler is a good investment that will pay for itself rather quickly.

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Marc Peo
President
Heller Industries Inc.
Mr. Peo has been with Heller Industries for over 20 years and has been President for the past 8 years. Marc has authored several industry articles on Soldering, Flux collection, nitrogen use and Lead Free conversion.

How important is reflow oven profiling to producing quality circuit boards?

There are several reasons for why thermal profiling is important.

1. To ensure quality a product must be produced in spec. The reflow oven is a black box that by itself will not identify whether the production is running in spec. To achieve this, the process window needs to be identified (the intersection between solder paste spec, component, and substrate tolerances), and the part profile needs to be measured in that context. This is only possible with the use of a part profiler or trailing wire profiling.

2. The thermal process is inherently dynamic in that it changes from moment to moment. In addition, over time the thermal properties of the reflow oven also change as a result of oven preventive maintenance, flux build up, wear and tear etc. Oven recipes that produced an acceptable process some time ago may therefore not yield an in spec process today. The profiler will verify this, and it's process optimization software will help adjust the oven recipe to the appropriate settings.

3. Documentation. Customers, QA managers, ISO 9000, or other may require documentation of the process that the PCBs experience, (as opposed to the machine settings).

4. Lead-free electronics have a very narrow process window as a result of the higher melting temperature of solder while the component and substrate tolerances remain the same. Previous acceptable qualities for standard leaded applications do not guarantee acceptable lead-free quality without the use of thermal profiling.

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Doug Dixon
Global Marketing Director
Henkel Electronics
Mr. Dixon has been in the electronics field for over twenty years and is the Global Marketing Director with the electronics group of Henkel. Prior to joining Henkel, he worked for Raytheon, Camalot Systems, and Universal Instruments.

This is a common question. Running reflow ovens without a profiler is not recommend. You can not correct what you do not measure. A profile device is a measurement tool to verify the critical profile sections such as peak temperature, TAL, and soak time.

Precise oven profiling is even more critical today then ever with the introduction of lead free solder paste. The higher temperatures required to reflow the lead free materials are much closer to temperature tolerance of some of the components. You run the risk of damaging components if you do not understand the exact temperature cycle they are experiencing in your reflow oven.

Also the use of miniature components such as 0201's and 01005's require very precise profiles since the flux in the very small volume of solder paste printed for these components will dissipate quickly causing the metal to oxidize and not completely reflow without a very precise profile.

Some users have enough experience to run an oven without running profiles but you will never know if your within the tolerance of the board, material, and components in order to deliver a quality product. I would NEVER trust a product that has been processed on an oven without profile verification nor ever do business with a company that would build my product without measuring the oven performance.

This answer supplied by Marc Apell and Joseph Belmonte

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Joe Belmonte
Principal Consultant
ITM Consulting
Mr. Belmonte has been a process engineer and process engineering manager in the electronic manufacturing industry for over 25 years, with experience in all aspects of electronic product assembly operations. He is well-known throughout Asia and SE Asia for both his process work and teaching engagements.

Yes you are correct; much of the information readily available on the importance of thermal profiling comes from the manufacturers of the profiling systems.

I am the Managing Director of SolderStar Ltd in the UK, and yes we are a manufacturer of profiling tools for both reflow & wave solder processes, so I will try to be as objective as possible with my answer.

As with any form of calibration or process control, if you do not measure then ultimately you do not know. It may be the case that your process is near perfect, all paste parameters neatly centred etc., unless your profile regularly you have no way to prove it. So when things do go wrong you have no traceability in place to discover the source of any problems.

Many small/medium size manufacturers are successfully producing good soldering quality on assemblies with no great problems and profiling solutions are seen as a luxury item that cannot be justified.

This is true in many cases when the following applies,

(1) Your assemblies do not widely differ thermally and one profile does all

(2) You are not effected in any way by the industry move to lead free soldering

(3) You don't have to justify the process to anybody but yourself

Luckily for the profiler manufacturers it is difficult for all the above statement to be true and hence the need for our industry.

Profiling of an assembly should be performed at the NPI stage; it is also prudent to perform a verification profile before any new batch of assemblies is processed; this confirms the oven temperatures are stable and as previously intended.

A fully populated assembly should be dedicated & instrumented with thermocouples, on board product profiles can then be established for this product.

It maybe the regular profile that you use on a number of assemblies will suffice, maybe not. Unless you perform these initial process measurement you will never know, the components maybe soldered to the board & the joints may be shiny, but these are not parameters we can easily measure.

Solder paste is a mixture of fluxes, alloy & solvents that all play their role in maximising the soldering quality. The paste manufactures test at great lengths to establish the available profile operating windows, and all for good reason.

A number of parameters and temperatures are specified in their datasheets, your job is to find the best fit for your electronic assembly with this available working window. This will give you the maximum chance of producing quality soldered joints when variables you have less control over take effect on the overall process, i.e. Natural tolerance in heater set-points, conveyor speed, oven load etc.

To summarise, profiling is a task that cannot be skipped, without it you are running blind.

If you produce your own products then you motivation must be to reduce rework cost, and minimisation of early field failures due to poor soldering or component thermal stress.

If you are an EMS provider, contracts where profiling evidence is not a basic requirement will soon be few and far between.

Profiling needn't be expensive; it can be performed by the on-board profiling systems on many machines, even by a low cost external datalogger if you have a modest budget. 

The tools on offer by the profiler manufacturers simply make the whole task a less time consuming exercise, if you are involved in the move to lead free or you profile on a regular basis you will soon see the pay back from you investment in a purpose designed profiling system.

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Mark Stansfield
Founder / Director
SolderStar Ltd
Co-founder and M.D of UK based thermal profiling equipment manufacturer SolderStar Ltd. He has software and electronic design experience specifically in the development of thermal profiling solutions for the electronics industry.

Benchmark yourself. What does ok mean? What is your first-pass yield? What is your DPMO? Is it up to industry expectations?

Reflow processes should have DPMO's of approximately 50 ppm. If you are close, maybe the team is right. However, if you DPMO is 500 ppm or your yields are below 95% for low to moderate complex boards, you've got huge room for improvement.

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Dr. Craig D. Hillman
CEO & Managing Partner
DfR Solutions
Dr. Hillman's specialties include best practices in Design for Reliability, strategies for transitioning to Pb-free, supplier qualification, passive component technology and printed board failure mechanisms.

Well, I am the wave solder guy but I do work with reflow from time to time and I can tell you that to get the best reflow and quality solder joint in reflow you MUST profile. There is just no good way to guess at the temperature from product to product and have a optimized process. Listen to those guys that sell the profilers, I know most of them and they know what they are talking about.

To answer your question from management; "The only way to control the process is to know the process and to know the process you have to measure it.

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Greg Hueste
Senior Applications Engineer
Speedline Technologies
Greg joined Electrovert in February 1984. Based out of the Electrovert applications laboratory in Camdenton Missouri, Greg has been in the process applications support role since 2000. His primary responsibilities include providing process and machine applications support for the wave soldering lines as well as process, machine and operations training. He also provides applications support for the reflow and cleaner lines. Greg is a PBET certified trainer and holds two patents on wave solder nozzle design.

I would rate a reflow profiler as a "must-have" for process control of the soldering process (and I have no vested interest in this!).

There are several reasons to have a profiler for your company's reflow operation. For starters, the use of a profiler is critical to gaining process control over the reflow process. Without a profiler, you wouldn't know if the oven was functioning properly, needed to be calibrated, etc.

Additionally, a profiler is critical to verifying that all components on the board and the solder paste are held within the manufacturer's processing guidelines to insure reliability and defect minimization. As an example, some components have a maximum temperature of 240C; without a profiler, how do you know if you have stayed within this recommendation?

Another good reason to have a profiler is for defect reduction and defect analysis. Several soldering defects are directly related to the ramp rate, soak temperature, soak time, time above liquidus, peak temperature and other reflow parameters. Without a profiler, you would have no way to accurately measure any of these critical characteristics to the reflow process.

Finally, as you introduce new boards into your process with higher or lower thermal load, they will require fine-tuning of the reflow parameters (zone settings and conveyor speed) in order to insure compliance with component and solder supplier's recommendations.

If you are a contract manufacturer, you can bet that a customer of yours will eventually audit your operation and ask how you are controlling your reflow process. Without a profiler, the reflow oven completely lacks process controls.

This above represents only a few of the good reasons to have a reflow profiler, but it should be enough to seriously consider buying one.

Regards,

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Brian Smith
General Manager - Electronic Assembly Americas
DEK International
Mr. Smith has been supporting customers in the electronics assembly industry since 1994. His expertise is focused on solder paste printing and reducing soldering defects. He holds a BS in Chemical Engineering and an MBA in Marketing. He has authored several papers in trade magazines and at industry conferences. He is an SMTA Certified Process Engineer.

I don't sell profiling equipment. My experience has been with curing ovens which is a bit different than reflow ovens. Having said that, profilers are a very useful tool in documenting a process and troubleshooting.

I'm a big fan of independent verification. If you have multiple lines and different yields between the lines, using profiler can help you pinpoint differences. If you have a single line and you profile it when things are working well, it is a good way to check if it has changed if you start experiencing yield excursions. For multiple production sites or a CM trying to reproduce results from an OEM, it can be very important. Even if the profiler doesn't find the problem, it can help confirm that temperature profile is not a problem and allow you to focus your efforts on finding the root cause.

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Alan Lewis
Director of Application Engineering
Asymtek
Mr. Lewis worked for The Aerospace Corporation for 6 years before joining Asymtek in 1993. He holds multiple patents in dispensing technology for electronics assembly and packaging. He has a Master's Degree in Mechanical Engineering from University of Missouri-Rolla.
NOTE: Mr. Lewis is no longer working at Asymtek.

You may not want to hear from me because I do have a vested interest in selling profiling equipment. However, here's an interesting fact. Your reflow oven is probably the largest piece of equipment in your facility. And yet you have absolutely no idea what happens to your assemblies once they go into your oven. Many people still do not profile their products or ovens. Although nowadays, it is a rarity. Especially with excellent quality profilers starting at about $3,200.

So can it improve your quality? Well if you are an OEM making the same products day in and day out for the past umpteen years and nothing has changed, probably not. But if you often introduce new products and need to set up new process parameters, it definitely will improve your quality. Todays profilers will automatically look at the capabilities of your oven, analyze the assembly and setup the best possible recipe to meet even the most demanding solder paste specs. Without a doubt, the closer your are to the center of the process window, the better the quality. And at the bare minimum, it will cut the time it takes to set up the oven process in half.

You didn't mention lead-free. So I assume that is not an issue. However, if it ever does become an issue, you will find that you can not set up your process to the very tight parameters of lead-free solder without a profiler.

One last huge benefit to consider is documentation. Virtually every manufacturing process performed today requires it. And the reflow oven is no exception. More and more customers are demanding it. If you ever have failures down the road, a profiler can prove the process was performed correctly. Quality people love data.

Oven manufacturers and solder paste suppliers have no vested interest in profilers. Speak to them and get an unbiased opinion. Otherwise, feel free to contact me off line for any additional help.

Richard Burke
National Sales Manager
Datapaq
Mr Burke currently has eight years of thermal profiling experience in the Electronics Assembly industry including SMT, Wave, Curing, Wafer Bumping, Ceramics and a host of other thermal processes. He is a Graduate of Indiana University of Pennsylvania School of Business.
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