Vitaliy wrote:
>> ... "only problem is, it takes too frickin' long!"
> =

> Exactly! :) Plus, what's the fun in that?

Exactly!
("Accrint'n Stanley, who're they?" -- "Exac-lee!")

> It can also be more cost effective, as long as you don't have four people =

> just standing there watching the fishtank for 15 minutes. ;)))

Let's see... 15 minutes times four people is an hour... still only =A310 =

($15 or so) assuming that's their hourly rate (probably a bit low, but =

still not worth worrying about).

Now, all those rubbernecking staff walking past.... them's the folk you =

need to be watchin' out for :)

>> Hm. Is that ammonium persulphate etchant? Not a fan of ferric chloride
>> then, I guess?
> =

> Used probably more than a bathtubful of that nasty brown stuff back in th=
e =

> day.. Ammonium persulphate is so much nicer: you can see the PCB, it does=
n't =

> stain hands, clothes, or furniture, doesn't require the use of CLR after =
you =

> dump it in the sink..

You probably shouldn't dump it in the sink....

I was always told the best way to dispose of FeCl3 was to mix it with =

sodium carbonate (or alternatively sodium bicarbonate / baking soda or =

sodium hydroxide PCB developer), then keep adding Na2CO3 until the pH =

passes neutral and starts to go alkaline. Run it through a sheet of =

filter paper -- the liquid is water with dissolved sodium salts, the =

sludge is a mix of iron and copper and should go to a hazchem dump.

Needless to say, don't do this in your FeCl storage bottle.

Apparently the easiest etchant to work with is cupric chloride -- to =

start it off, you use a mix of hydrogen peroxide and hydrochloric acid, =

then etch a ton of copper with it. Dump a load of scrap copper in the =

tank and bubble air through it. After a while your HCl+H2O2 etchant =

becomes CuCl etchant. There's a chapter on this in "Electronic Prototype =

Construction" by Steve Kasten (Blacksburg / Sams, published some time in =

the late 70s). I think someone's typed in said chapter and published it =

online...

>> Nice board. Did you immersion-tin it as well, or is that just the way
>> the light's reflecting off the copper?
> =

> That's the green resist. The mfr said you can leave it on and solder thro=
ugh =

> it, so we did.

I tried that with some of mine -- they made a really nasty fishy smell =

while I was soldering them, so I got a bottle of acetone and gave it a =

dip. Followed that with a fairly liberal spray-coating of Electrolube =

SMFL solder flux.

>> Which is why you go SMD. "Holes, what holes? For components? Why would I
>> need those?"
> =

> :)
> =


On a more serious note, I'm doing a PCB design for a piece of fairly =

low-volume DAQ hardware. >95% of the holes in the board are vias, and =

almost all of said vias are there either for thermal relief or to keep =

the impedance of the power planes down. The SMPSU stuff uses big, meaty =

power and ground planes -- GND on the bottom of the board. To pull GND =

to the top, I create a second, smaller GND plane on the top layer and =

link it with a few vias arranged in a grid.

Well, it's what TI suggested in the reference design... "To keep ground =

plane impedance and EMI at manageable levels, and to improve thermal =

performance, use multiple vias to link to the ground plane."

I don't know if this is bullcrap, but it doesn't really do any harm. =

Plus the six thermal vias underneath the QFN power management chip might =

make the thermal pad a bit easier to solder... unless they draw all the =

heat from my hot-air station down onto the ground plane (which would be =

a Bad Thing).

-- =

Phil.
piclist@philpem.me.uk
http://www.philpem.me.uk/

-- =

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