Thank you all for your answers. That confirms a lot of speculations. Only
one
question remains: Can this affect the reliability of the coating and have
long
terms effects? Since it seems that moisture vapor is condensed into the
coating,
I guess that yes, but for those who faced this situation before, were you
able to
use the boards in this condition without problems?
Thanks again!
Jean-François Bissonnette
> -----Original Message-----
> From: Alan Brewin [mailto:[log in to unmask]]
> Sent: Tuesday, June 19, 2001 4:28 AM
> To: TechNet E-Mail Forum.; Bissonnette, Jean-Francois
> Subject: Re: [TN] Conformal coating: white haze
>
>
> Jean Francois,
>
> Blushing is generally caused by high humidity. It is usually
> worst in spray
> applications, but can become an issue in dipping/brushing
> applications as
> well.
>
> Essentially, as the solvent starts to flash-off, the
> evaporation causes
> cooling (cf. acetone on your hand!), which then causes some
> of the saturated
> moisture vapour to be condensed onto and into the coating.
> Atomisation
> causes more cooling and hence greater problems with blushing.
>
> You could try adding a retarder solvent, but a much better
> solution would be
> to try and reduce your humidity. You could try using a portable
> de-humidifier and held-held probe to try and maintain a max
> RH of about 60%,
> but aim for 40%.
>
> Hope this helps,
>
> Best Regards,
>
> Phil Kinner
> (Masquerading as Alan Brewin!)
>
> ----- Original Message -----
> From: Bissonnette, Jean-Francois
> To: [log in to unmask]
> Sent: 18 June 2001 16:35
> Subject: [TN] Conformal coating: white haze
>
>
> This is a question for all the conformal coating specialists of this
> world.
>
> We're experiencing some problems with the application of
> conformal coating
> in high humidity
> conditions. Just after the application is finished, some
> kind of white haze
> appears in the coating.
> It disappears a little be during curing but some of it stays.
> The finish of
> the coating is then a little
> less smooth and shinny than normal.
>
> In order to avoid excess of humidity, the boards are
> pre-heated for 24h.
> The coating used is
> acrylic.
>
> Anyone knows what causes this?
>
>
> Jean-François Bissonnette
> Contrôle de la Qualité, Électronique
> Quality Control, Electronics
> Vapor Canada Inc.
> 10655 Henri-Bourassa O.
> St-Laurent, Qc
> H4S 1A1
> (514) 335-4200 Ext: 2021
>
>
>
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