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January 15, 2018

Delamination Dilemma

We have been experiencing delamination on a small percentage of circuit board assemblies during the reflow process. We believe we have properly addressed the issues regarding proper handling and storage of the bare board prior to assembly.

Can you point to any other potential causes of delamination or any other steps we should take to prevent it?

R. M.

Experts Comments

To find procedures for the proper stocking and moisture protection of electronic components, you can refer to IPC standards. (IPC/JEDEC J-Std-033C) If you are looking for guidance to handle printed circuit boards the more recently published IPC 1601provides some level of standards for stocking and moisture protection for printed boards, including caution against baking.

Even if you are paying attention to handling and floor time, the packaging quality of PCBs as received from the manufacturers can have a significant effect. Often a simple foil bag or an ESD bag is used instead of a well spec'd Moisture Barrier Bag (MBB) with desiccant and HIC (Humidity Indicator Card).

With such packing, boards are likely to arrive having already absorbed moisture, and stored like this they will be useless after a short time. Desorption process desiccant drying cabinets, such as those pioneered by Totech (http://www.superdry.info/) can be used for their careful drying.

The procedure is simple and cost-effective. The previously absorbed moisture is removed from the printed board without temperature stress and with a controlled, revertive drying process in an atmosphere of less than 0.5 g/m 3 vapor content (in effect, a moisture vacuum).

In addition, oxidation is stopped by the removal of the electrolytic water molecules. Because these storage systems work at room temperature, (or accelerated with mild heat), boards need not be removed until ready for processing.

Dried and stored in this way even oxidation sensitive OSP coated printed boards (which 1601 states should never be baked) are protected and can be used over long periods of time without the risk of delamination and with consistent wetability characteristics.
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Richard Heimsch
Director
Protean Marketing
Now a director at Protean Marketing, Mr. Heimsch has worked in the electronics industry 25+ years in a wide variety of international sales, marketing and operations roles. Rich spearheads Protean's international business development, specializing in Brand Management and Strategic Communications.

I'd be very suspicious of defects in either the adhesive or the surface it's being laminated to. The adhesive defects can be due to insufficient adhesive laydown or the existence of gels in the adhesive.

It is also possible that the adhesive composition is non-uniform, which might allow delamination zones to occur. Also, surface contamination on the substrate will result in insufficient wetting between the adhesive and the surface, resulting in delamination. I assume that the lamination pressure was uniform when adhesive was laminated to substrate?

The smallest speck of dust can also cause a focal point for delamination to occur. There are some analytical means available to troubleshoot these ideas, but you need access to a good chemical/analytical lab to do some thermal analysis, and some FTIR spectroscopic analysis.

In this case, before I can get more definitive, I absolutely will want to see samples to do comparisons between "good" and "bad" in the lab.

Jim Williams
Chairman
Polyonics, Inc.
Jim Willimas is a PhD Chemist in Polymers and Materials Science. He specialize in printing, cleaning, inks, and coatings used in electronics manufacturng operations. Williams has more than 30 years experience.

Please review your bake out time and temperature for your bare boards. Rule of thumb is 105C for 6 hours and the only caveat is to make sure we do not overtsack the pcb in the bake out chamber.

The pcb should be separated into small stacks to insure the boards reach temperature for atleast 4 hours to insure moisture is driven out of the laminate.

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Mark McMeen
VP Engineering Services
STI Electronics Inc.
Mark T. McMeen is STI Electronics Inc.ʼs Vice President of Engineering Services. He oversees the daily operations of the Engineering Services division of STI. He has over 18 years experience in the manufacturing and engineering of PCBs.

You should verify the temperature profiles of your pcb assy during the reflow process. If they are confirmed within tolerance, show them to the pcb supplier(s), together with the delaminated boards. It should then be the pcb laminates problem.

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EH Lim
Managing Director, Asia Pacific
ECD
EH Lim has been in the PCB Assy industry since 1985, starting at Thomson/Singapore for 5 years before moving to Electrovert Asia Pacifc. Lim was Sales Director for Vitronics Soltec prior to joining ECD in 2007 as Managing Director for Asia Pacific.

Delamination is generally a result of moisture content, PCB lamination controll problems with Epoxy system and/or inherent stress that is evident in the PCB.

Because the lamination system is suspect, first place to start would be your humidity and moisture control systems.

From here, I would also check your preheating system and ensure you are not surpassing your PCB laminate system temperatures.

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Rodney Miller
Capital Equipment Operations Manager
Specialty Coating Systems
Rodney is currently Operations manager at SCS coatings, Global Leader in Parylene and Liquid Coating equipment. Rodney applies his BS in Computer Integrated Manufacturing from Purdue University, along with 20+ years of Electronic manufacturing and Equipment Assembly, to direct the Equipment business at SCS Coatings. "We provide unique, value added coating equipment solutions for our customers". Including conformal, spin and Parylene coating expertise.

Delamination, unfortunately, is a fairly common problem for modern circuit boards, especially high-density, multi-layer boards or those composed of advanced materials such as PTFE (which is inherently difficult to bond to other layers.) Your boards are probably delaminating because, during processing, they are thermally and/or mechanically stressed beyond their limits of adhesion.

One way to reduce or eliminate this problem would be to increase the bonding strength between all the layers of the board, so that they don't delaminate. This can be accomplished using a suitable plasma treatment on the layers of the board before they are bonded together. For example, increased adhesion (and decreased delamination) can be achieved by treating the individual layers of the board using an Argon-based plasma in a chamber in a low-vacuum environment, prior to the layers being bonded together to form the final board.

The plasma treatment can clean the layers and remove micro-contamination that interferes with bonding strength (this process is sometimes referred to as "plasma cleaning" the layers prior to bonding). The plasma treatment can also activate the surface of the layers before bonding together to make a finished board, so that each layer adheres more strongly to the other layers around it.

Plasma treatments are particularly useful and effective when trying to bond advanced materials like PTFE or various flexible materials together such as polyimide, in order to prevent delamination and increase board quality. Contact March Plasma Systems if you'd like to try some plasma cleaning solutions for your particular case.

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Scott D. Szymanski
Global Marketing Manager
Nordson MARCH
Mr. Szymanski works to expand strategic alliances, strengthen partnerships with equipment suppliers, and develop future product offerings tailored to the semiconductor market.
NOTE: Mr. Szymanski is no longer working at Nordson MARCH
What we find is material damage can be grouped into four types that include adhesive delamination, cohesive cracks, crazing and material decomposition. The first thing to do is to determine the type of material damage that you are experiencing.   

Material decomposition is obvious in that it produces a blackening of the dielectric material and in extreme cases black balls of carbon on the surface of the PWB usually next to holes. This occurs when one uses low end material in a lead free application and, in reality, it is a rare type of material damage.  

Crazing is a separation between the individual glass fibers and the dielectric material.  This type of material damage is not visible upon macroscopic examination but it is seen as a silver separation running down groups of glass fibers in microsections. The silver sheen is from air gaps between the epoxy and the individual glass fibers. This type of material damage is particularly found when the grids size, the hole to hole spacing is .020" or less. This type of material damage is a concern in conductive anodic filament (CAF) formation.   

The two most common types of material damage include adhesive delamination and cohesive cracks. What we find is that adhesive delamination and cohesive cracks are most often not visible upon macroscopic examination. The material damage occurs in the central zone of the PWB and that there is no visible expression of the material damage. If you can see the delamination after assembly then it is often in the outer layers of the laminate. 

In adhesive delamination this is a separation between two laminated surfaces. It is usually between the B-stage and C-stage, B-stage and copper or between the glass bundles as a group and epoxy. This type of failure looks like a blister on cross section and usually ends in a single point that rarely branches. This is the type of material damage that may respond to baking to drive down the amount of volatiles, like water, that is trapped within the dielectric material. The problem is I have never seen baking get rid of delamination. If you divide material that is prone to delaminate into two groups, bake one group and don't bake a group, I find that the baked boards will often still delaminate. It is rare that baking makes a significant difference in delamination. What I suggest is that you try baking at 105 C for four hours. More baking can cause a breakdown of the material that could increase the material damage.  

The forth type of material damage is cohesive cracks. Cohesive cracks tend to produce cracks that go through the C-stage and B-stage layers and through glass bundles. These cracks tend to go off on any direction and frequently branch into multiple points.  What appears to happen is the material become over cross linked, shrinks, builds up tress and then cracks.  

There are many factors that cause cohesive failure, like problems in lamination or material that is beyond it's shelf life. One of the most common causes is lead/free assembly and rework. Assembly temperatures of 260 C are at the limit of what most modern materials can stand. Of the 24 material we just tested for a consortium we had 15 the showed material damage. What you should do is to consider changing the material to one that is more robust in your assembly environment. Also is would be prudent to limit the temperature that you are using for assembly and the number of rework cycles. This means to profile your assembly temperature to give a good solder joint for the largest and smallest components at the lowest temperature possible.
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Paul Reid
Program Coordinator
PWB Interconnect Solutions
Paul Reid has over 35 years experience in bare board fabrication, quality and reliability. Working for PWB Interconnect Solutions, which does thermal cycle evaluations (IST) of representative coupons, Paul provides failure and root cause analysis of how PWBs fail. His area of expertise includes how circuit board's copper interconnections and material fails in assembly, rework and in the field, as a result of thermal cycling.
In order to solve this problem, more data is needed. The PCBs can have moisture trapped from the supplier or there might be a fabrication issue depending on the materials used. Like the assembly materials, the PCB fabrication materials have shelf lives and going beyond the shelf life on materials like pre-preg can cause issues, one of them being delamination.

Now improper handling in your assembly process can cause an issue like this by itself or in a combination with the PCB fabrication process.  So it would be really inappropriate to point out an issue with missing data. A cross section on few boards would give you more information so I would suggest that you do that before changing a lot of other things.
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Georgian Simion
Engineering and Operations Management
Independent Consultant
Georgian Simion is an independent consultant with 20+ years in electronics manufacturing engineering and operations.
Contact me at georgiansimion@yahoo.com.
Reader Comment
By far, the most common type of delamination is due to moisture uptake.  Since all polymeric materials absorb moisture, eventually they will reach equilibrium with the environment. The typical environment for assembly is in a well controlled operations facility that is typically around 50-60% relative humidity. Unfortunately, this is not a good controlled environment to store boards. It is common practice for assembly houses to open the package and inspect the product before putting it back in the warehouse. Within weeks, the boards will reach an equilibrium and will be susceptible to moisture induced delamination. There are some materials that less sensitive than others, but poor handling and storage can result in delamination.

At IPC/APEX 2015 in San Diego, I spoke to a customer who described this very case. Boards processed fine upon receipt, but after 8 months in the warehouse unsealed, the boards delaminated. The classic pattern was   delamination between layer one and two next to a large copper plane. The user baked the boards and the problem was solved.

Baking can be used if performed properly and solderability is tested as well, but the best solution and least time consuming is maintaining good product packaging to protect boards that are stored for long periods of time.  IPC-1601 is an excellent guideline and provide the necessary information to significantly reduce assembly delamination.
Michael J. Gay, Isola Laminate Systems, USA
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