Removing Warpage from PCBAs

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Removing Warpage from PCBAs

We have populated boards with components on both sides that are warped. Components are varied height. What methods can we use to flatten them? Phil Zarrow and Jim Hall, The Assembly Brothers, discuss their recommendations.
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
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
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
And welcome to Board Talk with Jim Hall and Phil Zarrow of ITM Consulting, also known as the Assembly Brothers. Place and pick. In our never-ending quest to help people solve their assembly processes, situations and hopefully not to confuse them.

Today we have a question from E.J. E.J. says from a large lot, we have 20 populated boards with components on both sides that are warped. Components are varied height. What methods can we use to flatten them?

Jim
Syntax issues here, Phil. Is he saying the components are warped or the boards are warped? If it was components, it would probably have to big things like BGAs.

Frankly they would each have to be dealt with individually and I don't know any way to flatten components that have been warped. I suspect that for some reason 20 of the PCBs during the double- sided assembly process, the boards have become warped.

The first question it begs, as we put on our FA hats, is 20 populated boards in the process, what changed? What happened here? Was it the way the boards were stored or handled? Was it your reflow oven? Did something change there? Somebody lacking on support? That is one thing.

I don't know if there is a way with some fixturing that we can iron out these boards.

Jim
Going back to the causes, typically you think about warpage coming from inadequate board support, improper reflow profiles causing warpage during the process. But 20 boards, the thought I had Phil was one package of boards that wasn't packaged properly and came in with warpage, the bare PCB coming in.

I'm thinking 20, maybe that is the size of a package of boards that are coming in from your vendor, from your PCB fab. Maybe one package was damaged, got moisture in it or something else so that you got 20 raw boards coming in that either had warpage or had some variation in them such as moisture absorption which caused them then to warp during the assembly process.

Phil
Yeah. There is a lot of things we don't know. We aren't even sure if he is talking about boards or components that are warped either. But running on that assumption.

Jim
You have to accept the fact that it may be impossible to flatten out. If 20 of these PCBs are warped, it may be impossible to flatten them out and still maintain the reliability of your product.

To straighten them out, as Phil said, you can envision some sort of fixture much like a board support fixture that you would use to prevent warpage with pins that would contact the board in between, the components that are mounted on both sides, with fixtures that could put pressure on them to flatten out the board and leave them for some time, hoping that would flatten out or reduce the warpage. That may be possible.

In any case, if you try to do that you have to be conscious that you have solidified solder joints in that warped configuration. It may be the reality that if you try to straighten you are going to crack some of those solder joints.

It may not be possible to salvage these boards if you require a certain flatness in the final assembly.

Phil
I wouldn't be surprised if some of our listeners chime in with some methodologies, homeopathic or otherwise that they have used to de-warp boards. It will be interesting to see on this one. It is a tough one. I just wish we had more information.

Jim
That is a great lead in, Phil. All of you faithful followers of Board Talk, when we do this initially and these are presented on Circuitnet it is just us, our ideas good or bad. But over time people send in comments. We have a lot of very conscientious listeners who share their experiences.

This is a good case where someone may have had this problem, might have come up with a really good solution that doesn't come to our minds right at the moment.

E.J., or other people with similar problems, wait a week or a couple weeks and go back online and pull up this session on the archives and see if anyone has posted a suggestion.

There have been in the past many good suggestions. Corrections, for mistakes we made and so forth by our listeners. We thank you all for your active participation.

Phil
And on that note, you have been listening to Board Talk with Phil and Jim, the Assembly Brothers. As you go forth, no matter how warped you might be, please don't solder like my warped brother.

Jim
And don't solder like my brother.

Comments

If you clarify your requirements on the drawing, and if you design the board to allow a tolerance for acceptability (example: 90% Acceptability). Warping is going to happen, considering you are working with various layers with different thermal properties. As we go smaller and smaller with our technology, so do our materials. These two technologies are not always parallel in terms of advancement so of course we may have to work with less-than-ideal materials. Just because we have micro components, doesn’t mean our board materials are ideal for the smaller working parameters. Re-working should be not an inline process, only for MRB/NCR purposes.

Edward Rogers, Medtronic

There are many factors can make PCBA warpage. The provided info is not enough e.g. laminate type, Tg, copper density across PCB is uniform? Thick or Thin PCB? e.g. Laminate with less Tg or with not uniform Cu across the Fab -> can have warpage easily, Plus if have component with some dense area than the rest can be one factor, or some dense solder joints/leads in one area more than the rest etc. Also at what process the bd warp -> SMT or Wave Soldering or Reworking? These 20 bds passed any additional process than the rest?

***If at SMT reflow -> do not use any fixture to constraint the PCBA during reflow -> it will create another defects if the bd cannot freely expand in the reflow oven. It will not have any total solutions if we don't know what mentioned above.

***If the PCBA already warp -> do not use any fixture to bend them -> it will crack solder joint.

Pongtip P, Celestica Thailand Ltd.

As the Assembly Brothers mentioned, there is no info given as to the size of the board, the extent of the warpage, or its location on the board. However, that being said, you may consider adding a stiffener. Provided there is sufficient clearance to do so, you would need to drill holes through the board in order to anchor the stiffener, which may pose a problem, and you may also need to use insulating washers or stand-offs, but with proper care and planning, this may be a viable solution to your problem.

Don Flint, Phoenix Test Systems LLC