On the other hand, adding more solvent to the mix can result in more 
stress resulting in the coating, which may then crack in extreme thermal 
cycle conditions.

Doug Pauls




Graham Naisbitt <[log in to unmask]> 
Sent by: TechNet <[log in to unmask]>
06/03/2008 11:03 AM
Please respond to
TechNet E-Mail Forum <[log in to unmask]>; Please respond to
Graham Naisbitt <[log in to unmask]>


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Subject
Re: [TN] Tiny Bubbles






Hi Kenny

What I think is happening is that you are trapping solvent in the 
coating because it is drying too fast.

Try to add more solvent when you spray and keep the RH between 40% and 
60% in the coating area.

You mention this is a polyurethane - if it HumiSeal 1A33, just try a 
Material 1part to Solvent 2 parts and then reduce the solvent content 
until you have the desired result.

If it another urethane that might be moisture curing, then you have a 
different problem to overcome.

I would still like to see the IPC-CC-830 changed to show 3 conditions:

1                Tack-Free
2                Dry
3                Fully Cured

I think you have arrived at stage 2 too fast.

Graham Naisbitt

Gen3 Systems Limited
www.gen3systems.com

[log in to unmask]


On 2 Jun 2008, at 17:58, Ken Bloomquist wrote:

> Woops, I forgot to mention that we spray coat these boards. The 
> bubbles are
> most prevalent along thick edges but pretty much everywhere. I'll 
> see if I
> can get Steve to post a picture.
>
> Thanks,
>
> KennyB
>
> -----Original Message-----
> From: Kathy Kuhlow [mailto:[log in to unmask]]
> Sent: Monday, June 02, 2008 9:53 AM
> To: 'TechNet E-Mail Forum'; Ken Bloomquist
> Subject: RE: [TN] Tiny Bubbles
>
> Are the air bubbles along component edges or open areas? It might be 
> that
> you are moving the board in/out of the material too fast.  I know 
> from a
> past project we needed to allow extra time during the dip prior to 
> removal
> for the air bubble to release on SOT package devices.
>
> Kat
>
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