Homebrew PCBs

Hi Ted,

That IS a lot of parts for a discrete RF design!  I can see how working back
and forth on the schematic and layout would be an ideal way to get good
routes.  Do you already have a parts layout in mind before you do this?  I
got into the habit of laying out wire-wrap projects by inserting WW sockets
into prototype board beforehand to get an idea of the layout.  Discrete
parts as well.  But then I would solder ALL of the sockets down first.  This
"tightly interactive" annotation between schematic and layout is great!

On this board I found that the "flying wires" and parts profiles made it
fairly easy to initially get all of the packages down and roughly
orientated.  Quite a difference from working with a bag of WW sockets!

I won't be using a ground plane, but it's nice to learn how you've done it.
Hopefully I'll be able to MILL isolation traces, but I may also try
Press-n-Peel Blue, just to be able to compare the results.

I have been wondering how much of the board to manually route, and when to
just let the auto-router do it.  Last night I got my first exposure to
routing power traces by hand, and watching the flying wires disappear after
a net was routed (and the rat's nest updated).  CUTE!  I thought I'd run
into a snag when I routed a ground trace from an IC over to a servo ground.
I couldn't delete my added route!  But I found out that if I ripped it up
(back to an air line) that the rat's nest update would then delete the bit I
wanted (I already had the two nodes connected; I didn't want a ground loop).
I also found out how to rip up the entire board, which I needed!

73's,

Alan  KM6VV

> 
> Alan,
> That's right, it isn't very high for digital circuitry.  A 16F877 and
> a few other supporting ICs will run the count up in a hurry.  That's
> why I mentioned that my 215-pin design was discrete components only.
> The design was the IF system in Figure 6.50 of "Experimental Methods
> for RF Design", the one using two pairs of J310 JFETs in cascoded
> arrangement.  There are a lot of components in that design, and I had
> about a 1 square inch open area left on the 3 x 4 Eagle board when I
> was finished.
> 
> I manually routed the board as I went, by the way.  I added the
> components for a functional section to the schematic, for example the
> JFET pairs and associated circuitry for the board signal input from
> the crystal filter, laid them out on the board in a logical position,
> and routed; then I moved on to the next section, etc., following the
> signal flow from the schematic in the figure.
> 
> Doing it that way made it pretty easy to tweak the routing when I had
> all of the components on the board, without having to unsnarl any
> oddball paths created by autorouting.  I found that when I'd rip up a
> few tracks to move components around a bit, I could just hit the
> autoroute icon, and it would redo the routes pretty much as I wanted.
> 
> Originally, I laid the board out with two 12 volt feeds, and some
> jumpers from the on-board regulator for Vcc to various points in the
> cicuit, but as it turned out, I was able to lay down tracks for most
> of the power feeds to the functional sections by the time I was finished.
> 
> I did this board with a ground plane for the component side.  To avoid
> having to mill clearance holes for non-grounded through-hole component
> leads, I exported the board image as a BMP file, and using the layer
> feature in Photoshop (freeware Paint.net will do layers, too), I
> manually added circular clearance holes for the ground plane side.
> After  I printed the bottom layer tracks and ironed, I drilled a few
> holes in through-component lead pads to line up the holes, and then
> aligned the ground plane printout by holding the board up to the
> light.  Then I ironed the ground plane pattern onto the PCB.
> 
> I found that when I reheated the board while ironing on the ground
> plane/component side, some of the bottom layer tracks' toner
> transferred to the pad I was using as a surface for ironing.  Next
> time I do a double-sided board, I think I'll etch the tracks side
> (masking the other side with electrical tape), drill my registration
> holes, and then iron the ground plane side.  It shouldn't be necessary
> to do it that way.  Under my old process of applying the toner to
> Press-n-Peel Blue with a copier, that reverse-transfer wouldn't have
> happened. P-n-P is so tough when it's applied with a copier, you just
> about have to sand it off (or use acetone, as I learned after many
> boards :) ).  Now that I'm using my Brother 2040 laser printer for
> toner transfer, I have real problems in getting the toner to stick to
> the board in the first place, which has been much discussed here in
> this group.
> 
> 73,
> Ted KX4OM
> www.kx4om.com
>