Bench Top Reflow or Inline Reflow?



Bench Top Reflow or Inline Reflow?
Assuming that all things are equal, which would be a better option, a conveyor-type reflow oven or a batch-type reflow oven?
Board Talk
Board Talk is presented by Phil Zarrow and Jim Hall of ITM Consulting.
Process Troubleshooting, Failure Analysis, Process Audits, Process Set-up
CEM Selection/Qualification, SMT Training/Seminars, Legal Disputes
Phil Zarrow
Phil Zarrow
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
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.

Transcript


Phil
Welcome to The Board Talk. This is Jim Hall and Phil Zarrow, the assembly brothers, here to attempt to answer your process questions, equipment, materials, components, all kinds of fun stuff. All right, Jim, what have we got today?

Jim
Today's question has to do with reflow. We have been producing small batches of lead-free boards, using a bench-top reflow oven that we want to replace. We have narrowed down the options to either a draw-style batch oven, or a small conveyor-type reflow oven.

Both look like they will get the job done, and have very similar specs and features. Assuming that all things are equal, which would be a better option, a conveyor-type oven or a batch type?

Phil
The operative word here is "look like they'll get the job done."

Being reflow guys, I believe you can use anything to reflow, and I have often said that you could use a GE toaster oven. But let's look at the technical and thermal issues.

Jim
The main way to judge any reflow system is its heating capability. The ability to heat uniformly with repeatability. The only way you're going to know is to run your actual boards with thermal couples and see how uniformly they're heated with the heating profiles you want.

What can this oven produce in terms of different profile shapes? Can it produce a straight ramp? That's the easiest for any heating system to produce. But what if you need a soak for thermal or process reasons? Can it provide an accurately controlled soak? What capability does it have for cooling? That's where you create the actual solder joint structure.

Those are the things that should guide you much more than whether it's a batch type or inline. Batch systems have limitations because of their fundamental inability to change temperatures quickly.

In a multi-zone convection oven, where you have good separation between zones, you can create very sharp slope changes in your profile and create good, accurate profiles. A batch system, with its typically slower response, will have some limitations.

Phil
You should also take into account ease of operation, ease of profiling, and a lot of it is going to depend on the thermal transfer mechanism. A lot of batch ovens, the smaller bench-top type, do not use a lot of convection. They depend on radiant energy. As two guys who hearken back to the days of convection IR and IR ovens, we can tell you, it's not a lot of fun to work with IR.

Jim
The result being lack of uniformity, particularly on complex boards, and lack of repeatability from one board to the next.

Phil
Much trial and error trying to get a solid profile. If it was my money, I would seriously consider a conveyor oven. For lead free, we're probably talking a minimum of six vertical zones to do it right.

Jim
I want to reinforce, what I said was you want good heating capability so you can heat uniformly and repeatably, and that ultimately means good quality higher-volume fans. Some of the systems that we've seen, both inline and batch heating, there have fans, but they don't do a very effective job of moving air through the process chamber such that you get effective and uniform heating.

In our opinion, it's not a place to try to skimp. We've seen people who have skimped, and they've regretted it.

Phil

So we recommend you take your most difficult board, thermal-couple it, take your data recorder, and demo. Try them out. And that will give you the bottom line and help you come to a conclusion.

I would also add to the mix, consider a used conveyor oven - as long as it's fairly relative vintage. See what works best for you and, again, use your most complex board and your data recorder. I think we've said what we had to say about that. Jim?

Jim
We fried that one to death.

Phil
We've fried that one indeed.



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