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March 2004

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Subject:
From:
Graham Naisbitt <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Tue, 23 Mar 2004 13:52:38 +0000
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David

Your comment is grossly misleading.

You cast aspersions on the intelligence of the users of this product the
vast majority of whom have carried out thorough and rigorous testing on
their end product under extreme conditions - with highly satisfactory
results.

As to Lum Wee Mei's question, I suggest that you might be observing bubbles
where the solvent has expanded within the drying/dried coating. Brushing
will probably result in a very thick coating. IPC-CC-830 recommends that the
coating thickness should be 2mils ±1mil (50 micron ±25 micron) on a flat
surface. Do you know the thickness of the coating in this area?

As to the CTE issue, with tin-lead solder at ~16ppm/DegC and a coating at
something >250ppm/DegC, there is bound to be some effect especially when you
exchange temperatures from -65DegC to +125DegC which are the extremes to
which this coating has been independently tested and QUALIFIED.

I hope this helps rather than hinder?

-- 
Regards Graham Naisbitt

[log in to unmask]

Cell: 079 6858 2121
Office: +44 (0)1252 813706

Concoat Limited - Engineering Reliability in Electronics

NEW Additional Web address: www.conformalcoating.com

www.concoat.co.uk     www.concoatsystems.com



> Wee,
> 
> Why are you using 1B31, with a Tg of 15 degrees C??
> 
> If this product is staying in an "office" environment then it may work.
> For anything else it is very problematic!!
> 
> At room temperature, about 25 degrees C, there will be problems with
> cold flow so the CTE doesn't matter (it's too soft!).
> 
> David A. Douthit
> Manager
> LoCan LLC
> 
> Lum Wee Mei wrote:
> 
>> Hello,
>> 
>> My colleague coated several test boards using 1B31 through brushing that
>> have BGAs moutned on them. When he took some X-rays on them, he found
>> many balls are deformed with what he termed as "cauliflowers" like
>> patterns on the balls. He attributed the casue to the CTE difference of
>> the acrylic coating. Is that possible?
>> 
>> I will try to get the X-rays from him and post it to steve so that you
>> experts out there can provide a second opinion on this "cute"
>> observation. Meanwhile, hope some of you can share your experience with
>> BGAs and 1B31 coating.
>> 
>> Thanks and regards,
>> Wee Mei
>> 
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