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July 25, 2014
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Delamination Causing Scrap
We have been experiencing delamination on our printed board assemblies causing scrap. Is there a way to definitively determine that the delamination is being caused by moisture vs. some other type of defect? Is it possible to repair delamination in printed board assemblies?
D.H.

Experts Comments
The #1 cause of delamination is moisture. And by-far. While other failure modes exist (e.g., inadequate bonding layer cure) they do not appear in the Book of Usual Suspects. The repair of delaminated PCBs cannot be recommended. The IPC-1601 PRINTED BOARD HANDLING AND STORAGE GUIDELINES can be recommended.
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Bob Lazzara
VP, Marketing & Tech Support
Circuit Connect, Inc.
Bob has been in PCB design and fabrication since 1976. He has held elected positions with the SMTA, is a member of the MSD Council, has served as a committee member for various IPC standards and is a Certified IPC Trainer.
The easiest way to determine if moisture is the problem is to bake your bare PCBs immediately prior to assembly and reflow. I would recommend 2-4 hours at 250 F and then process IMMEDIATELY!! Don't let them sit so that they can reabsorb moisture. If  the problem goes away, you have your culprit.  

Delamination caused by thermal excursion would not be re-workable in my opinion. Really the only possible rework would require re-pressing (which I do NOT recommend). Since the delamination is occurring after assembly, I assume that you also have components on it.  You cannot re-press a board with components on it. 
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Mark Finstad
Senior Applications Engineer
Flexible Circuit Technologies
Mark Finstad has over 30 years in the flex circuit industry in both design and manufacturing. He is a regular speaker at IPC APEX (Professional development courses) and PCB West (flex circuit design courses). He is also vice chair of IPC-2223 and active member of IPC-6013. Finstad has extensive experience with both domestic and off-shore manufacturing.
Really, here are some broad suggestions to address your problems: (a) determine delamination caused by moisture vs. others - by isolating the causes of delamination, appropriate sensors could be built into the pcb. Example, a capacitive inner layer sensor for change in moisture content. Is this a viable option economically? If not, determine and list the types of environments to which the pcb exposed, rank the causes and work your way down. You will have to start all the way back from the pcb fabrication.. (b) repair of delaminated pcb may not be possible, collateral damage (thermal, mechanical) on components and other features will be huge. Prevention is better than cure!
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Bhanu Sood
Laboratory Director
CALCE, University of Maryland
Bhanu Sood is the Laboratory Director at the Center for Advanced Life Cycle Engineering (CALCE) and actively assists companies and organizations in all aspects of electronics reliability. Sood's key focus area is in design reviews, custom tests, and failure analysis services. He has authored several articles on board and component level reliability and unique failure mechanisms in electronics.
Delamination has been a concern since the beginning printed circuit boards and increased with the introduction of multilayer boards. The most common cause is moisture in the board and baking the boards prior to the wave soldering process will reduce if not eliminate delamination due to moisture. The bake cycle should be overnight at 225C and don't solder the boards while they are hot as this will impact the fluxer process, wait until they reach room temperature.

Among other things to watch for is the plating in the holes, focusing on the thickness of the plating and the integrity of the barrel. Many times if the barrels have voids, blow holes in the solder joints will be evident and delamination around plated through holes will result.

Check for oxidizing layer on the inner layers of multilayer boards to make sure it is applied correctly as this is the surface where the attachment is made between the layers. If this is not done correctly during the board fabrication process delamination will be prevalent.

Is it possible to repair delamination? This all depends upon the extent of the delamination and the technologies of the board - i.e., how many layers are in the structure and where in the structure, i.e., what layer is the delamination located.

I would focus on the cause, conduct a first piece inspection run and if delamination is evident on that circuit, then I would bake all the boards from that lot. Additionally check the storage where the boards are kept making sure they are stored in a dry box if they are going to be stored for long periods of time.

There are many more things involved, but these cover the basic elements and if more is needed please get in touch with me and we can discuss it further.
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Leo Lambert
Vice President, Technical Director
EPTAC Corporation
At EPTAC Corporation, Mr. Lambert oversees content of course offerings, IPC Certification programs and provides customers with expert consultation in electronics manufacturing, including RoHS/WEEE and lead free issues. Leo is also the IPC General Chairman for the Assembly/Joining Process Committee.
As I've mentioned in my answer regarding the bake before rework question, the delamination is commonly caused by moisture ingression in the PCB structure.

The board manufacturer has to be able to provide you the handling guidelines for your PCBs depending on the materials used and the  potential (high or low) for moisture to get in between the board internal layers. If you do not follow those guidelines, then you expose the PCBs to risk.

For the other part of the question, the delamination will usually result in scrap. I am not aware of a fix for such issue. However, check the IPC standards (610 and 600) to determine the acceptability of the exhibited problem.
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Georgian Simion
Operations Manager - A&E, AWS
Projects Unlimited, Inc.
Georgian is Operations Manager for Projects Unlimited in Dayton, Ohio. His background is in Electronics Engineering and has experience in electronic assemblies for over 15 years.
Reader Comment

While moisture is a contributor to delamination we find that there are other factors that also can contribute. Things like board design which includes grid size, hole size, aspect ratio over all thickness may contribute to delamination. The most important factor to preventing delamination is material robustness. All of these factors play a role in delamination. As grid sizes get tighter, holes get smaller and boards get thicker there is a tendency to have more delamination. The number one factor has got to be material robustness. Robust materials are required particularly in lead free applications.

What we find is that delamination that is visible is in the outer layers of a HDI boards. The typical delamination is in the central zone of the board and is hard to find. Baking the board may reduce the amount of delamination that is visible but it rarely gets rid of delamination. An aggressive bake can make delamination worse particularly if it is confused with cohesive type of material failure.

What we do is test for delamination using a representative interconnect stress test (IST) coupon. The majority of IST coupons have is built in DELAM circuits on ground plane layers. The ground planes are flooded with copper and make good planes between which one can measure capacitance. What we do is measure capacitance of the coupon as received then after an assembly and reflow simulation then at the end of a thermal cycle test. A 4% drop in capacitance means material damage. So out of 6 coupons we may have material damage in three. We microsection those three coupons and then understand the type of delamination.

What we find with this capacitance measurement technique is four types of material damage that we categorize as adhesive delamination, cohesive failure, crazing and material decomposition. The two most common types of delamination are adhesive delamination and cohesive failure. The adhesive type of delamination is what you get from moisture that is vaporizing. Adhesive type of delamination happens along planes that have been laminated. Adhesive delamination occurs in the interface between b-stage and c-stage, b stage to copper or along glass bundles. The delamination looks like a blister on cross sectioning that propagates along laminated surfaces.

Most often the type of material failure is a cohesive failure. This is a failure of the epoxy system itself. This appears to be more often cause by a chemical breakdown of the epoxy system rather than out-gassing of moisture or other volatiles. This sort of material damage may cross the b-stage and c-stage boundaries and go thru glass bundles. Cohesive type of material damage, when viewed with a microsection, goes off at angles, may contain branches and is not limited laminated interfaces.

Here is the thing. Baking to get rid of delamination is a good idea but it seldom works. If you bake too aggressively you can make the condition worse. I would limit baking to 4 hours at 105C more aggressive bake than that can exacerbate the material damage. I would do everything in my power to reduce the temperature during assembly. I would make sure not to have boards that have reflowed or fused finishes particularly lead free. I would make sure the boards are fabricated with robust materials.

Paul Reid
PWBIntercennect Solutions

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