Disagree on the the coating... although the coating may be softer initially,
the acrylic coating can be hardened during the life of the product, may be
interfere the venting mechanism. Agree with your customer, it should not be
coated (see attached).
my 1.6 cents.
jk
"In the operation of a wet electrolytic capacitor a certain amount of gas is
generated from the electrolysis of the electrolyte and unless means is
provided for the purpose quite high pressures may be built up inside the
container. For this reason it has been found necessary to provide the covers
with some form of vent. In practically all instances this vent takes the
form of a thin sheet of gum rubber which is perforated by a very small hole.
The thickness of the rubber and the size of the perforation determine the
pressures at which venting action will occur. In practice it is desirable to
obtain venting action at the lowest pressure which will prevent actual
leakage or escape of electrolyte through the perforation. "
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Brian Ellis
Sent: Monday, October 11, 2004 2:32 AM
To: [log in to unmask]
Subject: Re: [TN] Aluminum electrolytic Cap's
I see no reason why hermetically sealed elcos cannot be conformally
coated. If an elco generates pressure, it is because it is already in a
fault condition and should therefore be changed, anyway.
Brian
Lum Wee Mei wrote:
> Hello,
>
> Since we are on electrolytic cap, how about conformal coating (acrylic) on
them?
> We have been coating them since day one as no one has instructed that
> electroltic cap cannot be coated.
>
> Recently, there have been opinion that we cannot coat them as there will
be no
> gap for the pressure to escape - similar to the below issue?
>
> What are your opinions?
>
> Regards,
> Wee Mei
>
>
> Quoting Brian Ellis <[log in to unmask]>:
>
>
>>It depends on what cleaning medium you are using. If you are using a
>>halogenated solvent and just a microgram penetrates inside the casing,
>>you will see customers complaining of failures after 6 months to 2
>>years. This is well-known and was publicised by Sprague in the 1960s.
>>This company recommended using only hermetically sealed elcos if
>>cleaning in halogenated solvents. They also tested aqueous cleaning and
>>determined zero effect by aqueous cleaning, including with saponifiers
>>which could cause superficial corrosion of the outer case. However,
>>IMHO, it always makes sense with aqueous cleaning to have each stage
>>slightly warmer (say 5 deg C) than the previous one, so that you always
>>have positive pressure inside the cans while they are wet, to prevent
>>the ingress of contaminated water.
>>
>>Brian
>>
>>Scott Lefebvre wrote:
>>
>>
>>>We have a problem with the plastic disk coming off after being process
>>
>>through our In-Line PCB washer. What concerns if any should I have.
>>
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