Homebrew PCBs

On Mon, 1 Aug 2016 05:45:53 +0200, you wrote:

>RoHS allows 0.1% lead.
>
>I think this Liquid Tin is based on thiourea, something much, much worse
>than lead. Remember to wash your hands and wear a hardhat or something ;-).

I think it is.  It comes with lots of warnings, most of which involve
the word "poison".

I use gloves and tongs, and wash the boards thoroughly. Also, this is
done quite outside the house.

Wonder if I could do something like HASL....


Harvey

>
>ST
>
>On Sun, Jul 31, 2016 at 9:37 PM, Harvey Altstadter hrconsult@...
>[Homebrew_PCBs] <Homebrew_PCBs@yahoogroups.com> wrote:
>
>>
>> This is the problem with the ROHS directive being in absolutes. A mere
>> pinch of lead would do away with the whisker problem in it's entirety.
>>
>> I am not familiar with the Liquid Tin product, but if it leaves any
>> elemental tin (not oxide), then it can be a source of whiskers. I suspect
>> that this is the same thing that the industry calls immersion tin.  That
>> process is a chemical replacement where the liquid is a tin salt, and the
>> reaction exchanges the copper for tin, leaving elemental tin on the
>> surface, with the copper going into solution as a copper salt. Clean copper
>> quickly oxidizes, making soldering to the board difficult to impossible.
>> The purpose of immersion tin is to keep the surface solderable when the
>> board is not immediately used. It is an identified source of whiskers.
>> http://www.epectec.com/articles/pcb-surface-finish-advantages-and-disadvantages.html
>> I hope this answers all your questions.
>>
>> Harvey
>> On 7/31/2016 9:48 AM, alan00463@... [Homebrew_PCBs] wrote:
>>
>>
>>
>> Thanks, Brad.   I watched the NASA video.
>>
>> No, Harvey A., my circuit has no glass diodes, or other components that I
>> know to contain glass.
>>
>> I am glad you mentioned condensation, as I had never thought of
>> it occuring on my circuit board.    Having just defrosted my freezer yester
>> day, I  know it grows quickly on cold surfaces.    Since my circuit con-
>> troller will always be outdoors while in use, I will keep it inside when
>> not in use, so that condensation doesn't happen.    Nonetheless, I will
>> inspect the PCB for condensation when the outdoor temperature drops.   The
>> only "spray" the box might be subjected to is rain, which is distilled
>> water.   The box will be on my screened-in wooden porch.  The porch was
>> built with pressure-treated wood many years ago, but for the past several
>> years moss has been growing on the wood, which should tell you how damp it
>> is. (Another project--re-waterproofing the wooden porch.!   Will probably
>> need another recommendation for treating that wood too, but email me
>> privately for that.)
>>
>> Okay, copper oxidation won't degrade the circuit's performance.
>>
>> What about tin oxide?   Does either Liquid-Tin coating or leaded
>> solder contain tin?   If yes, do you think tin oxide will degrade the
>> circuit's
>> performance ?   Or is too "self-limiting" and of no consequence?
>>
>> I am not sure what you meant by the "Polyurethane wood polish" you
>> recommend.   I am trying to identify a furniture polish containing
>> polyurethane.   So far, I am only finding furniture polishes designed for
>> wood furniture that has a top coat of polyurethane, like the one on your
>> local tavern's wooden bar top.   I'm not sure whether to look for a
>> furniture polish that was designed to be applied to a polyurethane top
>> coat, or that actually contains polyurethane as listed in the
>> ingredients.   Or are they one and the same?    As you can tell, I am
>> pretty much ignorant about this product.   I am guessing its purpose is to
>> fill in surface scratches on a polyurethane top coat.
>>
>> 73 to all.
>>
>>
>>
>> 
>>