Re: breadboarding fast, tiny stuff

On Sat, 01 Mar 2008 19:30:21 GMT, Joerg
<notthisjoergsch@xxxxxxxxxxxxxxxxxxxxx> wrote:

John Larkin wrote:
On Sat, 01 Mar 2008 18:58:28 GMT, JosephKK <quiettechblue@xxxxxxxxx>
wrote:

John Larkin wrote:
We got some samples of an NEC hj fet and were wondering what its
time-domain response might be like. The part is only 2x2 mm and the
leads are 1.2 mm pitch, and I hadn't previously had a lot of luck
breadboarding stuff like this.

We found two tricks:

Get a piece of copperclad, epoxy-glass or preferably teflon; the
teflon is easier to cut. Cut out "pads" with a very sharp xacto knife,
under a Mantis magnifier. This will make horrible burrs and shorts, so
the first trick is to scrub it really hard with a Scotchbrite pad
between cuts. This cleans it up beautifully.

The second trick is to use small patches of kapton tape as insulators.
like where parts join or whatever. Soldering doesn't bother it at all.

ftp://66.117.156.8/FetTest.zip

Here, the fet is in a first-pass test circuit, just to see how fast we
can turn it on and off. The TDR pulse from the sampling head is the
gate drive, 0 (Idss) to -0.5 (pretty much off) at 50 ohms source z.

The drain is pulled up through a 47 ohm resistor, and the 150 ohm
resistor off to the side is an "attenuator" into the other scope
channel. The turnon fall is very clean, no nasty ringing or whatever,
with a 190 ps fall time. Turnoff is similar; these things don't store
charge! The TDR of the gate (lower trace) indicates that the gate
capacitance is loading the drive, so we need a bigger gate swing, from
a lower source impedance, to make this thing switch really fast. That
will be next.

John

Hell, you have a webpage to work with post gif's not zip's.


I'm offering free data and advice, and you're whining about the price.

And it's not a web page, it's an FTP site.

And my camera makes jpeg's, not gif's.


Did I leave anything out?


Yes, one item: It works :-)

(Both the web site and the circuit)

I'm right now doing the next version, a new board, with (I hope)
improved copper-hacking technique [1]. It will include an MC10EL gate
driver, SO-8, to really wail the thing. I'd post more pics, if I
didn't think I was boring people.

John


[1] Score two parallel lines in the copper with an x-acto, and cut the
ends, to make, say, a long, skinny rectangle, like a 50 ohm CPW gap
for example. Tin the strip, or dab it with liquid flux. Now place a
soldering iron near one end, and lift the trace; this is the tricky
part, getting started. Once the end is free, pull it up gently with
tweezers and run the iron along the trace, peeling up behind the tip.
The heat softens the epoxy and the copper comes off like a zipper.
Very clean cutouts of, say, 30 mil width or bigger can be done.

Do they make really tiny Dremel router bits? That could be
interesting.





.

Relevant Pages

  • Re: breadboarding fast, tiny stuff
    ... The drain is pulled up through a 47 ohm resistor, ... The TDR of the gate (lower trace) indicates that the gate ... Very clean cutouts of, say, 30 mil width or bigger can be done. ...
    (sci.electronics.design)
  • Re: breadboarding fast, tiny stuff
    ... The drain is pulled up through a 47 ohm resistor, ... The TDR of the gate (lower trace) indicates that the gate ... Very clean cutouts of, say, 30 mil width or bigger can be done. ...
    (sci.electronics.design)
  • Re: Brazing or welding thick copper?
    ... >for the gate frame and the infill of the gate will mostly be .5" x .5" ... >square copper rod. ... >and .1875" round bar and I've been very pleased with how the Thermal ... reduce the heat loss enough to get a good puddle going. ...
    (rec.crafts.metalworking)
  • Re: breadboarding fast, tiny stuff
    ... leads are 1.2 mm pitch, and I hadn't previously had a lot of luck ... The drain is pulled up through a 47 ohm resistor, ... The TDR of the gate indicates that the gate ...
    (sci.electronics.design)
  • Re: PCB Design
    ... Even with regards to trace width it depends on your allowable trace ... of plated copper compared to your total external trace ... calculator that is no longer offered by the company. ... What is the standard for track thickness for different currents? ...
    (sci.electronics.cad)