From: jeh@cmkrnl.com
Newsgroups: sci.electronics
Subject: Re: Vector wire pencils (and wire-wrap, and ScotchFlex)
Date: 5 Jan 93 11:56:17 GMT
Organization: Kernel Mode Consulting, San Diego, CA

In article <1993Jan3.004714.27542@softwords.bc.ca>, jmacphai@cue.bc.ca 
(James MacPhail) writes:
>>>Are these useful?  They are the "pencils" which wrap a wire around a post
>>>and you then solder it.  I'm trying to determine what system to use for

I've used the Vector "wiring pencil".  It works fine for prototyping.  Key
points:  (1) This relies on "solder-thru" enameled insulation on the wire. You
need a soldering iron that reliably hits 800 deg. F -- preferably a
temp-controlled one.  (2) Vector claims that you can wire directly to the leads
of other-than-ICs with this.  If the component in question can "wiggle" at all,
I don't recommend it.  This is No. 36 wire we're talking about -- it will
tolerate very little tension.  This means that discrete R's, C's, etc., need to
be soldered to a DIP header or to WW posts or something so that the flimsy wire
can be soldered to a non-moveable pin.  Similarly, connections to off-the-board
parts (controls, switches, etc.) need to be done by connecting the solder-wrap
to a board-mounted pin, and on the other side of the board, run a conventional
wire (one that won't break if you breathe on it) from the pin to the off-board
part.  (3) Under no circumstances use this for anything that you give to a 
customer under any circumstances -- it's just too flimsy mechanically.  

>>I dont like the look of wire wrapping ... it doesnt look to reliable to me
>>but then again, there are many companies that use it .... I wont though!

Wire-wrapping and the "wiring pencil" (just described) are two different
things.  WW, when done properly, is production-line-quality stuff.  LOTS of
companies used it for backplanes and the like before other methods became
cheaper.  I've happily used a Vector power wrap tool with the "slit-and-wrap"
bit (eliminates the need for stripping) for many large projects.  One of those
is still in weekly use *ten years later*, and its owner hasn't treated it
gently. 

(At the time I bought my Vector slit-and-wrap power tool, it consisted of one
of their manual tools chucked in a standard electric eraser handle.  I went to
an art supply store and bought a box of electric eraser refills, and Presto!
two handy tools for the price of one.  I never could justify an electric eraser
by itself...) 

imho, using a PCB for a one-of-a-kind project is a complete waste of time,
especially since many modern high-density components have pinouts that make for
easy PCB layouts only if you can do multi- (not just double-) layer... which is
pretty much out of the question for hobbyists, and probably for most one-of-a-
kind contract work too, unless you (or your client) are rolling in spare money.
A WW version can be up and running long before the PCB is ready for drilling. 

Ordinary PCBs ("ordinary" meaning "not surface mount") can't touch the
component densities you can achieve with wire-wrap, either.  

> You guys are aware of ScotchFlex, right? If not, check it out. It is made
> by 3M (and thus tends to be considered over-priced by some).
> 
> It is composed of IDC forks that go through the perf-board from the
> wire side, and DIP sockets that plug on from the component side. The 
> forks stand out about 0.1" and will take 2-3 layers of wire. Wiring,
> unwiring, and changes are VERY fast. No stripping, just push the wire
> into the fork with the wiring tool and cut off the excess.

I think ScotchFlex is *great* for prototyping and debug.  It is FAR more
convenient than WW for debug -- because it's a lot easier to change.  Of course
I'd never ship a product, not even a one-of-a-kind, that used it -- but that's
not what it's for. 

Yes, the cost is relatively high on a per-DIP-socket basis, but everything
except the wire is easily re-usable.  ie you can pull the wires off the back of
a ScotchFlex board MUCH more easily than you could pull wire-wrapped wires off
of wrap posts.  

> I don't know why 3M doesn't market this better. I used to consider it
> a "trade-secret" but if more people used it, the price might come down
> and 3M might expand the line. (Currently there is no support for PGA
> parts etc. just DIPs)

The company I used to work for did 0.1" PGAs by using the ScotchFlex SIP parts,
just lining a bunch of them up together.  

> No, I don't work for 3M.
> 
> James MacPhail  jmacphai@cue.bc.ca  james@mirg2.phy.queensu.ca

Me either, but sometimes I wish I did... from everything I've read it's a great
place to work.  Any company that can be looking for one thing, invent the 
exact opposite, and have the insight and what-the-hell attitude necessary to
turn the latter into a winning product, is doing a lot of things right.  (I'm
talking about the Post-It adhesive... they were looking for a near-permanent 
adhesive at the time!)

	--- Jamie Hanrahan, Kernel Mode Consulting, San Diego CA
Internet:  jeh@cmkrnl.com, hanrahan@eisner.decus.org, or jeh@crash.cts.com
Uucp:  ...{crash,eisner,uunet}!cmkrnl!jeh
Newsgroups: sci.electronics