White mask historically has performed different than it's green
counterpart. Depending on the pigment used to make it white, it can have
an affect on cure, but also the initial exposure step that created the
image (I'm assuming we are talking about a liquid photoimagable solder
mask). If the UV light does not cross link the mask enough in the initial
exposure step the developer will "attack" the mask more in the development
stage and diminish performance during the assemble process.
In addition to insuring the proper curing steps are observed, which could
include a UV cure, I would make sure they are tack drying and exposing the
white mask to the manufactures recommendations. If the fabricator is
simply using the same steps used to process green mask, this could be
creating your problem.
Regards,
Bob Metcalf
Western Regional Manager
Atotech USA Inc
1750 Overview Drive
Rock Hill, South Carolina 29730 USA
Mobile: 714-334-7667
e-mail: [log in to unmask]
Internet: www.atotech.com
Managing Director: Kuldip Johal
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From: Frank Kimmey <[log in to unmask]>
To: <[log in to unmask]>
Date: 08/08/2011 08:03 AM
Subject: Re: [TN] White SolderMask
Sent by: TechNet <[log in to unmask]>
Jack,
Looks like could be caused by incomplete curing of soldermask.
Baking would complete curing process.
Delamination of Soldermask seems to be commonly caused by poor cure and
then to high a thermal excursion (i.e. soldering).
I would start with the PCB fabricator and look at their soldermask curing
process and times.
It is possible the white mask needs a bit more time then the conventional
green type.
I would definitely talk to the PCB supplier about the failure as I would
think the assembly just caused a fab failure mode to appear.
Just some thoughts,
FNK
Frank N Kimmey CID+
Manager - PCB Design
Powerwave Technologies Inc
Mobile - 916-670-0645
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Jack Olson
Sent: Monday, August 08, 2011 7:47 AM
To: [log in to unmask]
Subject: [TN] White SolderMask
Greetings,
Have any of you experienced mask problems like the ones shown in these
pictures?
http://frontdoor.biz/PCBportal/WhiteMask.jpg
The bottom picture shows exposed copper, and I believe there is a copper
plane on the top layer.
(this has happened to different boards, different lot codes, but MIGHT be
the same batch of mask)
What I'm wondering is, is it more likely that the problem is related to
the
fact that the mask is WHITE, or that it is some other problem?
If the properties of white mask are different, maybe it doesn't adhere as
well to the surface? I remember back in the olden days they used to ask us
to break up solid copper planes so the mask would stick better to the
laminate, but I haven't heard of anyone having problems with that for a
long
time.
The supplier said they baked some bare boards and ran them through the
oven,
and the problem went away, but we are reluctant to just blindly add a
permanent baking step if there are other considerations.
Jack
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