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RoHS Board Delamination

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We are experiencing an issue with RoHS boards delaminating d... - Oct 24, 2006 by markb  

#44668

RoHS Board Delamination | 24 October, 2006

We are experiencing an issue with RoHS boards delaminating during SMT. In tyring to determine root cause, our board mfg house states the issue is with the laminate.

The laminate supplier states that the board house is not taking the proper precuations in preventing moisture absorption prior to processing. They state that due to the higher temperatures of RoHS processing, additional care must be implemented to ensure that there is no residual moisture during storage prior to processing (i.e. environmentally controlled storage required), and that a pre-bake should be performed prior to assembly.

Is this increased sensitivity of RoHS boards to moisture standard? We have not had any issue with the non-RoHS boards, so we are confident that this is isolated to just the RoHS boards.

Any advice would be appreciated.

Thanks.

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aj

#44669

RoHS Board Delamination | 24 October, 2006

Mark,

We have experienced this also.

We sent back the effected batch and they supplied us with new ones which did not have the delam problem. We are currently following this up to see what the cause was.If we ever find out!

aj...

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#44670

RoHS Board Delamination | 24 October, 2006

aj,

Did you have to implement a pre-bake operation prior to SMT? Or did the new batch work just fine with your current process?

Just curious if we should be implementing a pre-bake process, or keep pushing on our supplier...or both.

Thanks, Mark

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JAX

#44671

RoHS Board Delamination | 24 October, 2006

The need to Pre-Bake depends on multiple variables: 1. Packaging from the vendor (dry packs, vacuum sealed, etc...) 2. Storage at your facility (temp, humidity, etc...) 3. Moisture absortion rate of Laminate (FR406BC is one of the highest)

Other reasons involve solderability and have been left off.

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SWAG

#44672

RoHS Board Delamination | 24 October, 2006

We are having the exact same problem! We do about 6 or so ROHS SMT builds. 5 are fine now but we had problems with most initially and 1 is trouble still. All boards are same material, same PCB manufacturer. Initially, when the delam. problem occured, the PCB house changed process and the 5 builds seem to be O.K. now. I do not understand the processes involved to manufacture a PCB but they ended up having to make the resin or epoxy layer between material layers in the PCB's thinner or something like that. (from what I understand, moisture did not seem to be a root problem when they cross-sectioned the boards). This helped a great deal but one build is still trouble. We are working hard to get to the bottom of it and I'll keep you posted. The one board that is still trouble is large (about 3" x 17" and has big areas of ground planes in it so maybe a design thing?). If you don't mind me asking, what material is your PCB made from? What kind of reflow peaks, TAL's, etc. are you subjecting boards to? It would be interesting to see what commonalities we are dealing with. We are thinking about pre-baking some boards once we research the material mfg's recommendations on this and reflow them multiple times. Like you, we have never had moisture problems non-ROHS. I'll let you know what happens.

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#44674

RoHS Board Delamination | 24 October, 2006

SWAG,

The reason that our suppliers are focusing on moisture is that vapor pressue increases exponentially with temperature. So the higher temp processing of RoHS boards causes a significant increase of vapor pressure, which may cause delamination (where this wasn't noted on non-RoHS boards).

Of course, this is just initial info, so we are still digging into our specific issue.

Do you know why your board house thinned the epoxy layer? I'm just curious, and maybe it is something we should be looking at too.

Thanks, Mark

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SWAG

#44675

RoHS Board Delamination | 24 October, 2006

I'm not sure why that was done. They based that decision on what they saw in cross-sectional analysis of the failures.

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aj

#44684

RoHS Board Delamination | 24 October, 2006

Mark,

The pcb manufacturer recommended we bake the boards , so we did. I even weighed a batch before and after and seen slight decrease possibly 0.1g in weight. However we still seen some delam after all this. I am confident our issue has nothing to do with moisture - it has to be their process.

With the new batch they sent us they included (either intentinally or by mistake 10 of the old batch code) one of these delaminated very badly on a fully populated board worth around �500, so the head buck here was not very happy. The rep. is calling in later this week to explain what is going on,so it will be interesting to hear what he says! I will post his feedback when I have it...

Would it be bad of us to name the Board house , maybe its the same one that is having these problems???

aj...

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MFG CAVEMAN

#44742

RoHS Board Delamination | 27 October, 2006

Since I didn't see it mentioned - Are you specifying a laminate that is considered compatible with a RoHS process? I don't mean just a high Tg but a high Td (decomposition) and CTE material such as Isola 410, FR408 etc.

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#44747

RoHS Board Delamination | 27 October, 2006

We use the Isola 410 laminate. They just issued a tech bulletin on the same day (coincidence???) that we found the problem. It mostly talks about handling (i.e. environmental storage) and pre-bake operations to prevent issues like this.

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SWAG

#44770

RoHS Board Delamination | 30 October, 2006

We are performing a pre-bake + reflow experiment on this same material today per mfg's recommendations. I'll let you know what happens.

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SWAG

#44781

RoHS Board Delamination | 30 October, 2006

We are done with our experiment - approx. 25% of the boards we sent through this test showed delamination.

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#44789

RoHS Board Delamination | 31 October, 2006

SWAG - Was your experiment on the board with the large ground plane? The board we are seeing issues with also has a large ground plane (approx 50% of PCB), and 90% of the delamination occurs in that area. The delamination is about the size of a silver dollar.

We are currently running some life testing on the boards to see how they affect fucntionality.

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SWAG

#44791

RoHS Board Delamination | 31 October, 2006

Yes, this board is approx. 3" x 17" x .062"T with large areas of ground planes. However, the delam. does not seem to be confined to the plane. We also see it around component pads and fiducials. Generally speaking, it could be said that the first delam. occurs in non-populated areas where there is ground plane. One thing we noticed is that you must inspect the boards very quickly after reflow as some of the delam. will actually flatten out in time and become difficult to see. It will sometimes disappear after a second reflow pass as well.

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#45102

RoHS Board Delamination | 16 November, 2006

Does anyone have new info on their ROHS PCB delam. problems? We ran two profiles (different from ours) per supplier recommendations with no improvement on this problem. These profiles included a plateau or soak at 190 deg. C for 20 seconds and a slow ramp (<0.5 deg. C/sec.). Some PCB's did just fine inside of 6 passes and other delam'd after the first pass during this experiment. We received new PCB's made from entirely different material and had no problems with this small sample. So, we really don't have any answers outside of the possibility that new material might work for this build.

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#45107

RoHS Board Delamination | 16 November, 2006

I still think the best bet is probably an SMT pre-bake operation to ensure that there is no moisture in the board. Vapor pressure is usually the leading cause for delamination, so removing the source should significantly help out.

Unfortuantely, pre-bake did not turn out to be economical in our situation, so we are trying an alternate chemistry during copper oxidation (prior to prepreg lamination) which creates more "texture" to the copper plane. Thus, giving more adhesion surface area, increasing the peel strength. All of our delamination was between the copper ground plane and the prepreg. In addition, we are adding some wash steps after oxidation to ensure a VERY CLEAN surface for the prepreg to adhere to.

In assembly, we ran regular RoHS profiles (targeted for 240C peak), and it appears to work OK. We are about to put it in production, and we'll see how reliable it is for the long term.

Does that help any?

Mark

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#45124

RoHS Board Delamination | 16 November, 2006

Yes - Thanks, Mark. I'll keep you posted on anything we find out on our stuff.

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#45145

RoHS Board Delamination | 16 November, 2006

#45205

RoHS Board Delamination | 17 November, 2006

SWAG - I also forgot to mention a few things. Our delmaination was always between the large copper plane and the laminate. It is a multi-layered board, so even when the delamination appeared around components (through visual inspection), cross-sections showed that the delamination actually occurred between the large copper plane and the lamination.

One other thought was to cross-hatch the copper plane. However, due to EMI requirements of our board, this was not an option. It may, however, be an option for your design. Laminate should not delaminate from other laminate layers, so a cross-hatch pattern should help.

Just a thought.

Hope you find a solution.

Rgds, Mark

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SWAG

#45298

RoHS Board Delamination | 20 November, 2006

Thanks Mark and Dave. It sounds like our board design and problem areas are similar to yours, Mark. We talked with our customer about the grid pattern but I'm not sure where we are at with that. In reference to the Tg/Td thread, the material is a widely used material common for ROHS application that has higher values of Tg/Td. It seems to me that it's looking more like an isolated problem that occured during the mfg. of the PCB's. I can get sample lots of arrays to pass through the oven up to 6x with no trouble at all while one array in the sample will show massive delamination. It's just too random to be a profile or design issue in my opinion.

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SWAG

#46299

RoHS Board Delamination | 20 December, 2006

We ended up switching PCB suppliers and PCB material altogether. We built 400+ units with the new material and got zero delamination. It's still unclear what the real solution is as we introduced two changes at once. This new supplier is going to send us a sample lot of the original material so we can narrow it down.

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SWAG

#48831

RoHS Board Delamination | 2 April, 2007

I hate to drag this one out again but we are done with this. We tried an oven profile on the bare panels that was quite different from our original. This profile was recommended by the mfg. of the laminate. We experienced random delamination. Some panels delamed all over the place on the first pass while others made it through multiple cycles. The supplier has taken these boards back, credited us and it appears to be a manufacturing defect or material problem.

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