Luck?
Graham
On 12 Aug 2008, at 09:02, Hernefjord Ingemar wrote:
> ???????? Don't understand. We perform refurbishment of military
> equipment from the field, often covered by powderlike sand and dust.
> Only way to remove it is with water. We add some tenside to the tap
> water and brush the boards gently, followed by rinsing in DI and
> finally drying with dry nitrogen pistol. The coating used is 1B31,
> and we never saw any lifted or defect coating. How is that?
> Inge
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Phil Nutting
> Sent: den 11 augusti 2008 18:46
> To: [log in to unmask]
> Subject: Re: [TN] Washing of conformally coated boards
>
> Ioan,
>
> I agree with Graham... from personal experience. We use an acrylic
> conformal coat and even a very short (30 seconds) wash at 100° F
> will loosen the coating. I'd vote for the full strip if the board
> bust be reworked and washed. From what I've read, doing anything
> else will compromise your long term reliability.
>
> Phil
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Graham Naisbitt
> Sent: Monday, August 11, 2008 11:11 AM
> To: [log in to unmask]
> Subject: Re: [TN] Washing of conformally coated boards
>
> Ioan
>
> If its acrylic, don't do it.
>
> You would be better off stripping the coating, carrying out the re-
> work and re-coating.
>
> Your cleaning the coated assembly will, almost certainly, compromise
> the protection it is there to provide.
>
> The UV tracer is in the coating for inspection at the coating stage.
> It is not a long-term aid and prolonged exposure to sunlight will
> cause it to deteriorate over time.
>
> You say you have to use a WS flux, so it's acid content is high and
> it must not therefore be left on the circuit. To make sure it is
> gone you will have to employ a pretty effective wash process that
> the coating was not designed to withstand.
>
> Stripping the coating is pretty simple as it will dissolve, but
> check with the manufacturer the most suitable solvent for the job.
> Leaving it to soak for around 20 minutes at say 40C to 60C or higher
> should do the trick.
>
> Hope this helps
>
> Graham Naisbitt
>
>
> On 11 Aug 2008, at 15:39, Ioan Tempea wrote:
>
>> Thanks Brian!
>>
>> It is acrylic I'm talking about. Will 140F be OK?
>>
>> Also, what the should worry be: any damage to the protetcive layer
>> that cannot be seen under UV light or moisture entrapment?
>>
>> Should I consider a low temp (how low) post-wash bake?
>>
>> Thank you,
>>
>> Ioan
>>
>> -----Message d'origine-----
>> De : Brian Ellis [mailto:[log in to unmask]] Envoyé : 11 août 2008
>> 10:23 À : TechNet E-Mail Forum; Ioan Tempea Objet : Re: [TN] Washing
>> of conformally coated boards
>>
>> Theoretically no, if it was properly applied in the first place.
>> Provisos:
>> a) tender coatings, such as acrylics, like neither high temps nor
>> aggressive chemicals in your wash water.
>> b) silicone coatings will wash OK but you may have problems with
>> moisture absorption/adsorption in the drying stage.
>> c) urethanes and flexibilised epoxies should normally be OK
>>
>> Brian
>>
>> Ioan Tempea wrote:
>>> Dear Technos,
>>>
>>> A quick one : can I water wash conformally coated boards?
>>>
>>> This means conformally coated boards have been returned for rework,
>>> we will change the components (have to use WS flux) and have to
>>> wash.
>>>
>>> Can regular water wash at 140F do any damage to coating?
>>>
>>> Thanks,
>>>
>>> Ioan
>>
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