Ah, but that depends.....

Graham ☺


On 3 Jun 2008, at 21:47, Douglas O. Pauls wrote:

> 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]>
>
>
> To
> [log in to unmask]
> cc
>
> 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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