> I've made thousands myself. Never tinned them, never will.
 Yeah, but let's look at the real issues here:

1. tarnished/oxidized copper may get ugly, but eventually, the Copper Oxide
layer will block the oxidation of the copper beneath the ugly surface.
Tinning and otherwise plating of etched copper boards originally was done to
preserve solderability. Boards that would sit in storage for any significant
time after fab would have to be lightly etched or heavily fluxed before
subsequent soldering. Strong fluxing became the method of choice, but since
it was difficult to remove residual flux from these boards, more serious
corrosion of joints sometimes occurred later on. I think it was US mil spec
454 that first required plating to prevent this. Since virtually every board
house wanted their process lines to comply, it became standard procedure. It
made no sense to skip such an inexpensive process for commercial boards.

2. If a board has been well-cleaned of flux residue and the solder joints
are solid, there's not too much harm that can come from an oxidized surface
layer, other than reduced cosmetic appeal.

3. The level of humidity and contamination in the local environment is
directly proportional to the time it will take for the board to become fully
ugly.

4. PCB Plating is a process that is notorious for being poorly controlled.
Sometimes, a *fresh* copper board will solder better than a week-old plated
board, so judgment is sometimes required.

5. Many fab-houses use only solder-tinning for prototype quantities. While
this may not be a good long term prevention of all oxidation, boards done
this way seem to solder easily for months afterward, even in very humid
conditions.

So, unless boards are going to be stored for a while between fab and
assembly, plating or tinning is not as important as it may seem. If however
you want your boards to shine and reflect all the effort you put into the
design, plate or tin them. The best analogy I can come up with is this: Some
people never wash and wax their cars. Some do. After considering the
practical side of this issue, this is all that's left.......I think.....

Personally, when I etch my own, I use a cold-plating chemical called ITP,
from Kepro, which stands for 'Immersion Tin Plating'. CuTech makes this as
ST225. It's cheap, re-useable, forgiving, and works great. It leaves a real
tin plating about .2 mils thick.

With board houses out there like Advanced Circuits, Inc. who do excellent
proto's tinned, masked, and silked for $33, I just cant often justify
rolling my own very often anymore....The last two jobs I sent them were back
in 3 days, and were perfect.

Chris

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