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January 2001

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Subject:
From:
"Barmuta, Mike" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Fri, 5 Jan 2001 13:48:52 -0800
Content-Type:
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text/plain (240 lines)
Lisa:
1. Why not apply the a UV curable nomenclature ink to directly the tin final
finish after processing. Cure it with a conveyorized UV oven and eliminate
the high temp/time bake.

2. If you can not use a UV ink there are two component epoxy based
nomenclature inks that will cure at room temperature or slightly elevated
temperatures.

3. I don't know what you are using for an ink or what your surface prep
process is but there are inks available, again two component epoxies that
should bond well to copper if prepped right. I could recommend a supplier
off line.

4. Do you really need to put it directly onto the metal? Can a continuos web
of soldermask be placed underneath it to aid the adhesion?


Michael Barmuta

Staff Engineer

Fluke Corp.

Everett WA

425-356-6076

-----Original Message-----
From: Lisa Angle [mailto:[log in to unmask]]
Sent: Friday, January 05, 2001 11:56 AM
To: [log in to unmask]
Subject: Re: [TN] Nomenclature with Immersion Tin/Silver


I agree with you on the point of putting nomenclature and mask on before
the tin process.  I have seen temperature's detrimental affects on tin
intermetallics and therefore the solderbaility of the deposit, and do not
want to go down this path of disaster.  However, I am still faced with the
issue of nomenclature peel off of metal surfaces after the immersion tin
process.  At first glance, the problem seemed to be undercut of the copper
surface under the nomenclature.  However, I ran some tests where I
increased my nomenclature font to very large mil thickness and still
experienced the problem, that is what has lead me down the chemical bond
attack theory.  Have you successfully applied nomenclature to metal
surfaces and immersion tinned the boards and seen no peel?  Does anyone put
nomenclature on metal surfaces and immersion tin them with success?  I have
no problem with the nomenclature on mask areas.  These spots do not
experience any type of peeling.

Thanks in advance.
Lisa





Don Vischulis <[log in to unmask]>@IPC.ORG> on 01/05/2001 02:37:48 PM

Please respond to [log in to unmask]

Sent by:  TechNet <[log in to unmask]>


To:   [log in to unmask]
cc:

Subject:  Re: [TN] Nomenclature with Immersion Tin/Silver


Tony and Lisa:

I suggest that you speak to your chemistry supplier about this.  Immersion
silver
finishes contain an organic additive to preserve solderability.  I don't
know
enough about the tin finishes to be certain, but I believe that they use
similar
organics.  Elevated temperatures (used to cure mask and nomenclature)
degrade
the final finish resulting in diminished shelf life and possibly reduced
solderability.


IMO the best practice is to apply mask and nomenclature before the final
finish.
 The fewer thermal excursions that the finish is exposed to, the longer the
shelf life of the board.

Don Vischulis


>Lisa,
>Being in the pcb manufacturing, we have installed immersion tin as a final

>finish surface.
>As I suspect, with any immersion process such as tin, silver, gold,
>soldermask and nomenclature
>adhesion sometimes become bigger problems than the actual process itself.
We

>experienced
>the same problems. Through many agonizing weeks of evaluation we have come

>up with using
>a predip prior to the application of LPI or legend, which consists of a
>diluted version of
>an oxide replacement bath. This chemistry contains adhesion promoters for
>which gave us the
>the ability to withstand IPC tape test.
>
>
>Tony Steinke
>Circuit Technologies Inc.
>----- Original Message -----
>From: Lisa Angle <[log in to unmask]>
>To: <[log in to unmask]>
>Sent: Thursday, December 21, 2000 3:45 PM
>Subject: [TN] Nomenclature with Immersion Tin/Silver
>
>
>> All,
>> I was wondering how you go about putting nomenclature on copper surfaces

>> and subsequently processing thru immersion tin or immersion silver
without

>> experiencing nomenclature peel?  I have of course thought of the
>> alternative which is to process the boards thru immersion processes and
>> subsequently nomenclature them, however, our current inks require a long

>> cure time and very high temperature which artificially ages the
finishes.

>> Thanks.
>> Lisa Angle
>> Alternative Surface Finish Engineer
>> Teradyne
>>
>>
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