Understanding Reflow for Metal Core PCBs



Understanding Reflow for Metal Core PCBs
How does the reflow process for a metal core PCB differ from an FR4 laminate PCB? We've never processed a metal core before.
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 Board Talk. This is Jim Hall and Phil Zarrow, the Assembly Brothers, pick and place. We're here today to answer for free your process questions and dilemmas and problems. Let's see, what do we have today?

Jim
This comes from P.B. "How does the reflow process for a metal core PCB differ from an FR4 laminate PCB? We've never processed a metal core before, and I would be grateful for any useful advice."

Your profiling procedures are going to become more difficult, and more complex. It would be wonderful to be able to solder the components on the surface without conducting a lot of heat into the metal core, but that's generally impossible because most boards that use metal core are designed to use the solder joints to help conduct the heat from the active components down into the metal core.

Regardless of what technique you use, a lot of heat is going to be conducted down into that metal core, therefore your profile is going to be longer.

You're going to have to heat slower. You may have to add a soak section before liquidus to allow the heat to penetrate into that metal core so that you can safely reflow all the components on the surface without too great a Delta T.

That means achieving full liquidus temperature on all the solder joints without overheating any of the components and materials. It's been used extensively, but you have to anticipate longer profiles, slower ramp rates, and perhaps soak sections or longer soak sections.

Phil
Now this is probably going to bring a smile to certain people we know in Colorado and Minnesota, but wouldn't this probably be a good candidate for a vapor phase, Jim?

Jim
Absolutely. Metal core boards were one of the first assemblies we started processing in vapor phase and continued to process in the early 1980's when vapor phase was the principle reflow technique.

Phil
I remember in the early days of convection IR when we would see an application like this we would go, "Oh, just use vapor phase." But, again, if you don't have a vapor phase oven, hopefully you have a good convection oven with lots of zones.

Jim
Slow it down. Remember, you don't want to heat too rapidly because if you heat too rapidly, you can warp and delaminate these boards.

We want to compliment our questioners. The fact that you've recognized that a metal core board is going to be different is a kudo for you. To some people, a board is a board and they just try to profile it normally and they get into trouble, so you were right, intelligent and astute to question us.

Phil
Remember, whatever you do, don't solder like my brother.

Jim
And keep the kids away from the flux pot.


Comments

Thanks for this timely discussion. I was having this same conversation with a potential customer and your broadcast helped him better understand his issues.
Ed Zamborsky, Metcal, USA

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