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September 1998

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Subject:
From:
Graham Naisbitt <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Wed, 2 Sep 1998 15:14:18 +0100
Content-Type:
text/plain
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text/plain (109 lines)
Lum,

Now that I know the coating material, I am 99% sure that your problem is
solvent popping from material trapped under the device. My company is a
manufacturing licensee of HumiSeal!

As to a solution, having checked with Mr Conformal Coating himself, John
Waryold, try using IR on the opposing side of the assembly to that on which
the power module is attached for 20 to 30 minutes BEFORE you do your temp
cycling. If you cannot use IR, then follow the following suggestion:

After application, leave to dry at ambient for around 1 hour
Then warm the board to 50 deg C for around 1 to 2 hours or more - I do not
know the size of your assembly and the power module
Do not heat too high too fast, or the problem will return.

This should do the trick but let me/us know

Regards, Graham Naisbitt

[log in to unmask]

Concoat Ltd             Phone: +44 1276 691100
Alasan House          Fax:      +44 1276 691227
Albany Park
CAMBERLEY
GU15 2PL UK

Any opinions expressed are those of this employer.
-----Original Message-----
From: Lum Wee Mei <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Date: 02 September 1998 08:21
Subject: Re: [TN] Bubbles from conformally coated board


>We are using Humiseal 1B31 with Thinner 521. The coated gone thru' 22
cycles of
>static burn-in , temp profile range from -40 to +85 deg. C.
>
>Regards
>
>Richard Haynes wrote:
>
>> What temp cycle and coating and solvent?
>> Richard
>> -----Original Message-----
>> From: Lum Wee Mei <[log in to unmask]>
>> To: [log in to unmask] <[log in to unmask]>
>> Date: Monday, August 31, 1998 10:28 PM
>> Subject: [TN] Bubbles from conformally coated board
>>
>> >The test engineer came back to us to complain that bubbles are found
>> >along the edge of the power modules after going through the temperature
>> >cycling tests. This problems are found on both coated boards. The power
>> >modules are mounted completely flushed onto the board and subject to
>> >conformal coating using the diping method. The coated board undergo QC
>> >to ensure all components are completely coated, inlcuding the edges
>> >around the modules.
>> >
>> >What could be the problem?
>> >
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