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|December 9, 2013
Circulation Over 51,000
|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?|
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.
VP, Marketing & Tech Support
Circuit Connect, Inc.
Bob has been in PCB design and fabrication since 1976. He has held elected positions in the SMTA and served as a committee member for various IPC Standards. Bob has been the VP of Technology at Circuit Connect since 1995.
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.
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.
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
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
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.
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.
Vice President, Technical Director
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.
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 105°C 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.
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