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August 2011

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Subject:
From:
Jack Olson <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Jack Olson <[log in to unmask]>
Date:
Tue, 9 Aug 2011 09:03:53 -0500
Content-Type:
text/plain
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text/plain (88 lines)
Thanks everyone, for taking the time to respond.
That was a new one for me.
(its interesting what I take for granted until something goes wrong!)

one more question: 
Is there a difference between soldermask material and silkscreen material?
Aren't they both just colored epoxies?
(ok, two questions!)

Jack

.
On Mon, 8 Aug 2011 08:51:36 -0700, Bob METCALF <[log in to unmask]> wrote:

>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
>
>-----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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