On Sun, 31 Jul 2016 21:36:09 -0700, you wrote:
>Harvey,
>
>The name HASL is appropriate because it is a hassle. It requires special
>equipment. The boards are first solder dipped, and then passed between
>hot air knives, where the air is hot enough to reflow the solder. The
>excess solder is blown off, leaving a thin coating of solder on the
>board. I suppose that this could be approximated by a hot plate and a
>heat gun with a flat funnel type adapter on the front. Might work. This
>could leave slivers of solder bridging some of the traces.
This might not be a problem when the slivers are near enough the pads
to melt when soldering components. However, I like the idea of wiping
off the melted solder with a pad (or perhaps brass sponge).
I'd be worried about the process overheating the board myself,
especially if the boards do not have plated through holes (and mine
won't).
>
>I my early days in the Aerospace Industry, we would solder coat the
>boards by solder plating them, and then reflowing the plated solder by
>floating the boards on hot peanut oil. A rather sloppy process.
I can only imagine. Not sure how they were done where I used to work,
but from what I remember, they did a resist over the areas to be
etched, then plated the copper on the board, then tin plated the
board. Removing the resist was next, then the boards were etched in
ammonium persulphate which apparently didn't attack the tin plating.
There was no solder mask on these boards, but there could have been
silk screen (don't really remember much if they did or not)
These were mil-spec boards, so there was eventually a conformal
coating, I think. (nasty stuff to deal with).
the other (other) Harvey
>
>The other Harvey
>
>
>On 7/31/2016 9:06 PM, Harvey White madyn@...
>[Homebrew_PCBs] wrote:
>>
>> 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.
>> >>
>> >>
>> >>
>> >>
>> >>
>>
>>