[volt-nuts] volt-nuts Digest, Vol 7, Issue 9

[Alan Scrimgeour]

One of the things I like about slow setting epoxy is that heat not only 
speeds up the cure but improves the bond too. I'm so conditioned to expect 
every gain to come at a price that this really surprised me when I first 
heard about it.

Alan


----- Original Message ----- 
From: "J. Forster" <jfor at quik.com>
To: "Discussion of precise voltage measurement" <volt-nuts at febo.com>
Sent: Wednesday, March 17, 2010 8:19 PM
Subject: Re: [volt-nuts] volt-nuts Digest, Vol 7, Issue 9


> The epoxy I use for repais on circuit boards is completely clear two-part
> without any fillers from HySol. Do not use the 5 minute setting stuff
> either. You want something that takes several hours to set up. That's much
> better stuff.
>
> -John
>
> ==============
>
>
>
> [snip] I wouldn't be sure
>> that using the automotive epoxy would be a good idea...
>>
>> Dick Moore
>>
>>
>> On Mar 17, 2010, at 5:00 AM, volt-nuts-request at febo.com wrote:
>>
>>>
>>> Message: 6
>>> Date: Wed, 17 Mar 2010 11:20:37 -0000
>>> From: "Alan Scrimgeour" <scrimgap at blueyonder.co.uk>
>>> Subject: Re: [volt-nuts] Keithley 2001 Multimeter Fault - Update
>>> To: <jfor at quik.com>, "Discussion of precise voltage measurement"
>>> <volt-nuts at febo.com>
>>> Message-ID: <AE27F40615CE4CA08494C3AD153F4414 at AlanPC>
>>> Content-Type: text/plain; format=flowed; charset="iso-8859-1";
>>> reply-type=original
>>>
>>> Perhaps only the copper was 'etched', but I can imagine even epoxy being
>>> attacked by hot electrolysis taking place right next to it. Electrolysis
>>> could produce some very active compounds, depending on the electrolyte
>>> (and,
>>> I'm not sure, but in such close proximity to the electrodes there may
>>> also
>>> be some extremely reactive short lived species, or is that just
>>> Sci-Fi?).
>>> But by some mechanism the upper layer of glass fiber in the board was
>>> visible before I started digging it away.
>>>
>>> The excavation is progressing with care. In the centre the damage has
>>> gone
>>> right through the board to virtually the other side. Presumably air
>>> cooling
>>> stopped or slowed the progress of the damage actually through the very
>>> last
>>> layers of the board.  It appears that once the hot electrolysis had
>>> begun to
>>> damage the pcb it carbonised and in that conductive state, drew current
>>> and
>>> generated yet more heat leading to a chain reaction in the form of a
>>> growing
>>> carbonised region.
>>>
>>> I've just had to cut a wide buried copper track in order to be able to
>>> remove the carbonised pcb beneath it, which is disconcerting, but it
>>> will
>>> just need soldering, or replacing with a piece of wire. I'm more worried
>>> about what to use as a 'filling' in this cavity. I said I'd use epoxy
>>> resin,
>>> but the usual stuff is damaged by soldering temperatures. I have some
>>> 'Auto
>>> Weld' which says it's resistant to a constant 300C and should do. Once I
>>> fill that hole back I'll never get it out again, so I'd better fix it
>>> properly!
>>> I'd like to add that I'm feeling pretty angry about those electrolytic
>>> capacitors. They are sheer vandalism! Time for some companies heads to
>>> bow
>>> down and appologise! Those unstable low dropout regulators are another
>>> annoying self destruct mechanism too!!!
>>>
>>> Alan
>>
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