Electronics Assembly Knowledge, Vision & Wisdom
Proper Exhaust Pressure for Reflow Ovens?
Proper Exhaust Pressure for Reflow Ovens?
What is the proper exhaust pressure for a reflow over? Where should we measure the pressure? How should we measure pressure?
Board Talk
Board Talk is presented by ITM Consulting

Phil Zarrow
Phil Zarrow, ITM Consulting
With over 35 years experience in PCB assembly, Phil is one of the leading experts in SMT process failure analysis. He has vast experience in SMT equipment, materials and processes.

Jim Hall
Jim Hall, ITM Consulting
A Lean Six-Sigma Master Blackbelt, Jim has a wealth of knowledge in soldering, thermal technology, equipment and process basics. He is a pioneer in the science of reflow.

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Welcome to Board Talk. This is Jim Hall and Phil Zarrow, the Assembly Brothers, pick and place or place and pick. We're here to answer your process questions regarding SMT and the associated realm. What's today's question.

This question comes from E.R. You had mentioned about proper exhausting of the reflow oven. At what exhaust pressure normally should the oven be measured at?

Well, certainly measuring pressure in an exhaust system is one way to quantify it. You've got to have the right exhaust and it's important. The real critical parameter that most ovens will specify is a flow rate in cubic feet per minute or cubic meters per hour or some other volumetric flow rate.

Then the static pressure, if it's outside the oven, to create that flow rate is going to depend upon the geometry and dynamics of your exhaust piping. Some ovens may give you a pressure tap inside the oven within their known piping. But the bottom line is you go to the manufacturer.

If they give you a flow rate, then you go to your piping and make the conversion using standard duct flow procedures.

What instrument would E.R. be using to performs these tests?

For measuring static pressures, it's just any kind of a pressure gauge or manometer. Often you see these little red mercury or alcohol manometers that they use in duct work. The key is pressure is only an indication of flow rate.  And what you're really concerned about is getting the proper volumetric flow rate and that it's stable. That it doesn't vary over time such as when the people down at the end of the exhaust duct turn on the spray booth or something and the static pressure, and therefore the flow rate, changes and your oven thermal process is upset.

The only thing I want to add is when you do your ducting, make sure that the ducting you're using to connect from the oven to the rest of your exhausting system is rated for the proper temperature for the reflow oven.

Depends upon the way the oven is ducted internally and so forth. But yes, high tempered and cleanable, you know, all the manufactures do their best to put filters for flux-capture inside, but always anticipate the possibility of some flux getting into the duct and condensing somewhere. Make sure that you put in provisions to take the duct apart and clean it.

I hope we answered E.R.'s question. The only thing I could add to that is no matter how you're exhausting your reflow oven ...

Don't solder like my brother.

Don't solder like my brother.

Yes, settings are very machine specific as the internal design of the exhaust will dictate settings.

General rule of thumb however is evacuation & containment. IE keep fumes from escaping into workspace but not so much as to be sucking heat or inert atmosphere out of the machine. I have often seen relocated ovens never perform the same as in their original location as the exhaust characterization was never duplicated
Ray Chartrand, Chartrain Consulting
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