zaft_at_azstarnet.com

From: Richard Erlacher <edick_at_idcomm.com>
Date: Mon Oct 22 17:21:50 2001

Since I've been in the business of proof-of-concept prototyping for the past 25
years, I thought I'd wait until everyone else weighs in on this matter. I have
found very few wirewrap cards capable of distributing power properly, so I have
made my own wherever practical. The boards I make have a continuous ground
plane on the wiring side of the board and a continuous Vcc plane on the
component side, with a ground strip around the exposed edges of the board, away
from the backplane connector. In cases where no backplane is involved, the
ground strip on both sides is available at each edge. This facilitates ground
reference attachment for 'scope and logic analyzer.

The holes are plated through and the board is coated with a dry-film solder
mask, thereby facilitating the use of bare-wire analog circuit construction
where it's needed. I've run fairly large synchronous circuits on a board of
this type, with as many as 250 bipolar flipflops toggling at more or less the
same time, i.e. from the same, albeit separately buffered, clock edge, without
harmful effects, all the while monitoring the power<=>ground noise to be <100mv.

The trick, of course, is that the attachment to the ground and power plane is
normally accomplished by means of a soldered-on capacitor of relatively small
value, typically 0.01 microfarad. Since one lead of a bypass capacitor is
attached to the power pin of each IC, the other can be attached very near the
capacitor by soldering it directly to the ground plane. So long as one keeps
the leads shorter than about 1mm, the maximal benefit from bypass will be
obtained.

I still use boards of this type, albeit seldom with the solder mask, since I buy
the big "colander" panels at RadioShack.com and cut them to fit. I still
isolate the outer edges of the continuous power plane on the top of the board by
relieving it from the main plane by means of a dremel too with a saw blade, and
then connect the edges to ground with a solder bridge wherever it's convenient.
That way I can still attach probe grounds wherever I need.

There are few ways, short of having them made up, which is what I did, to get
decent wire-wrap boards that will accomodate the connectors and IC packages
you'll need. The RS.com store located here in Denver has large panels of this
ground and power plane equipped perf board with plated-through holes, for about
$100, which is plenty, but the boards are big enough to warrant it.

regards,

Dick

----- Original Message -----
From: "Gordon Zaft" <zaft_at_azstarnet.com>
To: <classiccmp_at_classiccmp.org>
Sent: Monday, October 22, 2001 3:21 PM
Subject: Re: OT: power & ground for wirewrap boards


>
> Thanks for all the feedback! I'll let y'all know how it turns out..
>
> Gordon
>
>
Received on Mon Oct 22 2001 - 17:21:50 BST