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# soldering small surface mount discretes

J

#### John Larkin

Jan 1, 1970
0
Do you know of some good 20uF or so at 75V? They seem to be just above
what's available at Digikey etc. (especially the 75V requirement). I
can put lots in parallel, of course, but it starts to get silly.

Sorry, no. That 22 uF part is rated at 6.3 volts! Sounds like a place
for a polymer aluminum maybe; they have very low esr's and stay that
way down to -55C.

John

J

#### John Popelish

Jan 1, 1970
0
John said:
Do you need a very low wideband noise floor? If it's accuracy you
need, oversample and average or lowpass filter. Any real-life sampling
16-bit ADC system will have many LSBs of noise anyhow.

That adc scares me. Some of the nodes are bypasses of active circuits,
and whenever I see strange, unexplained bypassing requirements, I
wonder if the datasheet is hiding ldo-type stability problems, or if
the applications engineer was just being too enthusiastic.

....or scared to death about a poor design, and hoping some
mythological bypass scheme would save his ass.

J

#### John Popelish

Jan 1, 1970
0
John said:
On Sat, 12 May 2007 06:27:49 -0500, Spehro Pefhany
Sorry, no. That 22 uF part is rated at 6.3 volts! Sounds like a place
for a polymer aluminum maybe; they have very low esr's and stay that
way down to -55C.

The highest voltage rated polymer aluminum caps I have seen
is 20 volts.

Digikey does have a Z5U 100V 22 uF ceramic cap with radial
leads for sale, but at a unit price of $27.17. Yikes! http://www.avxcorp.com/docs/Catalogs/sk.pdf J #### John Larkin Jan 1, 1970 0 S #### Spehro Pefhany Jan 1, 1970 0 Sorry, no. That 22 uF part is rated at 6.3 volts! Sounds like a place for a polymer aluminum maybe; they have very low esr's and stay that way down to -55C. John I'd really like to avoid any kind of electrolytic. The ceramics are on the cusp of being practical (the price goes from something like$1 to
something like \$30 as the specs get reasonably close to the 60uF/100V
I'd like to have).

Best regards,
Spehro Pefhany

D

#### DJ Delorie

Jan 1, 1970
0
Michael said:
I have a friend that sells educational electronics kits for hobbyists.
I'm going to try to convince him to make something similar.

He can use my design, but note that the two oscillators tend to lock
together, which defeats the whole point of the circuit.
If you do another run let me know, I'll take a couple off of your
hands.

Ok! Note that I can home-etch PCBs for 0201 and 01005 parts, so if
you just want to try soldering them, buy a couple parts and make a
test board. The lack of a mask doesn't hurt here, the parts are too
small.
Ah - that'll be interesting. So with both pads clean and free of
solder, you place the part and hold it down, then solder both sides?
Yup.

How do you get solder on to it? It seems to me that both of your hands
would be busy. Just put a little on the tip of your iron maybe?

Solder paste. I dab some on the pcb before putting the part on it, so
the paste is between the part and the pad. Heat from the iron just
melts the paste, I don't actually transfer *solder* from the iron to
the part. The iron is usually pretty bare, which also keeps the
solder glob from pulling on the part too.

Even if you pre-solder one of the pads and reheat it, remember that
the heat goes through the part to the other pad too. So, when you do
the second pad, you still need to hold the part down.

D

#### DJ Delorie

Jan 1, 1970
0
mpm said:
Honestly, I stuggle with 0603's. I suspect I don't have the right
equipment and/or technique.

I use a 10 diopter (3.5x) magnifier visor for the smallest parts (5d
2.5x for the rest), 0.020 conical tip, and 0.020 solder (or, more
likely, SYNtech solder paste). Dab the paste on the pcb, place the
part, use the iron to melt the paste.

A flux pen on the pcb helps too.
I just wanted to add (for us Engineers anyway..) that maybe the Eye
Doctors could update their charts. Instead of 20/20 eyesight, we
could have 06/03, or 02/01.?

I have 20/10 vision (laser corrected) but still need magnifiers to
work on PCBs. I find the visor is the best solution for me.

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