Steve,
You bring up a topic I spent many years of my life working on. I was the
former product manager for Dynachem/Morton/Shipley in charge of solder mask
products (I am no longer employed by them). I was part of the development
team that developed and commercialized the Dynamask Dry Film Solder Mask
Products. You didn't mention which version of Dynamask you had or how thick
the product is. There are two versions of the product; Dynamask KM and
Dynamask 5000. Dynamask KM is available in two thickness; 3 mil and 4 mil.
Dynamask 5000 is available in (I believe this is still true) 2 mil, 3 mil
and 4 mil.
Let me give you a little background on why you are seeing less chemical
resistance. When the original version of this product was designed there
were no true class III (under IPC SM 840 B) dry film solder masks. The main
problem was related to thermal cycling. The current dry film product
offerings (this was back in the late 80's) could not make it to 100 cycles
required under SM 840 B. If you were to examine the products that were on
the market after thermal stress (multiple soldering operations; surface
mount and through hole) you would find micro cracking. This cracking became
worse with each thermal excursion. This was a problem for both board
manufactures and end users as technically, the available dry film products
at the time could not be used in high reliability environments. At the time
dry film solder masks were the predominant photoimageable solder masks as
liquid photoimageable masks were just gaining market acceptance and were
still expensive.
Decisions had to be made in which path we were going to pursue in order to
gain class III approval with the next generation dry film product (Dynamask
KM). It was decided to go with a more flexible material that would be more
compatible with the laminate expansion during thermal stress. The trade off
was less chemical resistance. Several studies were conducted to determine if
this would be a major issue in the environment the product was expected to
perform in. We found common cleaners available on the market would be
compatible with the product AS LONG AS YOU FOLLOWED CONCENTRATION,
TEMPERATURE AND DWELL TIMES recommended by the various manufactures. With
N0-Clean fluxes becoming the standard at the time this appeared to be a
reasonable trade off.
Yes the product from Dupont was more robust in some processes. The Dynamask
product outperformed the Dupont product in some processes as well. The
problem was when there was failure with Dynamask, it usually was something
like you described. The other competitive product's failures were often more
subtle.
Dynamask 5000 was developed to give more chemical resistance while
maintaining the class III capabilities. The product did show measurable
improvements in cleaning systems that used to give us problems. However, the
product could still fail if pushed to it's limits of chemical resistance.
Now to your current problem. The Zyzen product was one that I used to get a
lot of phone calls about. Usually we could correct the problem by checking
the concentration, temp and dwell time. And yes, most of the time we had
failures it was in a batch system. Temperature is more inconsistent is many
batch cleaning systems that are out there. You can re-mask as someone else
suggested. My experience is most current available liquid photoimageable
soldermasks are compatible with Dynamask. I have used Shipley liquid
photoimageable soldermask many times but have found Taiyo and Enthone to
work well also. Keep in mind there are many different versions of "Taiyo"
and "Enthone" and you will need to run your own compatibility testing.
Also check with your board supplier to insure they are properly curing
Dynamask. Both KM and 5000 need a significant UV cure in addition to a final
thermal bake. UV energy in the range of 3000-5000mj cm is required. Thermal
curing is 300 F for 60 min. Have your vendor check their UV curing unit out.
Bulbs with more that 1000 hours use put our more IR than UV but will still
look OK on many radiometers. Old bulbs have caused many failures over the
years. Also the reflectors need to be cleaned when the bulbs are changed.
Also have them check out their thermal curing ovens. Most use batch ovens
that can have major temperature fluctuations. A thermal profile should tell
them if the boards are seeing proper cure temp in all parts of the oven.
Sorry for the long response but I felt a little background info my help.
Regards,
Bob Metcalf
949-709-2544
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Stephen Gregory
Sent: Tuesday, May 17, 2005 9:28 AM
To: [log in to unmask]
Subject: [TN] Bubbly, flaking, soldermask...
Hi All...
Boy, I hope your day is going better than mine...
One of my inspectors called me to to look at an assembly she had. I
came to her station and started looking at the assembly, and just about
cried (not really). I observed something that I've seen before...
The solder mask is losing adhesion from all copper features, traces, vias,
everything copper. This starts occuring after about 2-3 wash cycles in our
batch cleaner. Take a look at; "Mask Bubble, Mask Bubble 2, 3, and 4", at:
http://www.stevezeva.homestead.com
I've seen this before and thought we had the problem taken care of. It's
caused
by the chemistry we use to clean RMA flux residues, not being compatible
with
certain dryfilm solder masks. We use Kyzen Aquanox 4512P in the
manufacturers
recommended concentration, and we see this problem everytime a Dynachem
Dynamask (now Shipley) dry film is used. We used to use Aquanox XJN and had
the same problem.
On our PO's we have a note that when dry film solder mask is called out on
the fab
drawing, use Dupont Vacrel series dry films, as we know that we have
absolutely no
problem with Vacrel.
The last time I had this problem and posted about it, there were a few
responses that
I shouldn't be having these problems, that the Dynachem Dynamask dry films
are very
robust. But I swear, everytime I see the mask bubbling and flaking like you
see in the
images I've posted, it turns out that a Dynachem dry film was used.
Can I be the only one that has these probelms?
Kind regards,
-Steve Gregory-
Senior Process Engineer
LaBarge Incorporated
Tulsa, Oklahoma
(918) 459-2285
(918) 459-2350 FAX
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