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August 2011

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Subject:
From:
Bob METCALF <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Bob METCALF <[log in to unmask]>
Date:
Mon, 8 Aug 2011 08:51:36 -0700
Content-Type:
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text/plain (172 lines)
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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