Wire wrap

[Dave Boland]

Can anyone point me to a good document(s) on wire wrap? I'm looking for
a discussion on equipment, technique, performance, and reliability. The
reason for this is that pre-prototype printed cards seem to be a waist
of money because of all of the changes to the cards as soon as they
arrive (most due to the "hey, while your at it" syndrome).

The only downside is the use of surface mount devices, but we can likely
use adapters at that development stage.

Failing any documentation that would impress management, can anyone
answer these questions?

1. If a card is going to be WW, are pads and PTH's really needed? The
reason for the question is that there is no ground plane anyway, and
soldering to the socket lead seems like it is as good as soldering to a
pad. Components soldered are bypass capacitors as close to the device
as possible.

2. What is the number of connections that make power WW equipment
justifiable? I like to see development done (early stages) modularly,
so each card may have between 125 to 250 connections. A typical project
is only a few cards (modules). Once the design is stable we go for PC
cards anyway.

Any useful help would be appreciated.

Thanks,
Dave

 

[Paul Burke]

Can anyone point me to a good document(s) on wire wrap? I'm looking for
a discussion on equipment, technique, performance, and reliability. The
reason for this is that pre-prototype printed cards seem to be a waist
of money because of all of the changes to the cards as soon as they
arrive (most due to the "hey, while your at it" syndrome).

DON'T wire wrap except for trivial circuitry. It takes an age to do,
it's difficult to check, it's bulky and uncomfortable when someone
leaves one on your seat, you need adaptors for everything except DIL and
leaded passives, modifications tend to snowball in complexity. I used to
use it a lot, until low- cost PCB prototypes like PCB Pool came along.

Changes are an advantage, you are actually creating debugged production
tools as you carry out modifications.

No, if you value your time and sanity, use PCBs.

If you want rapid and flexible prototyping, create some of your PCB
prototypes so that they can be used as sub- modules in future projects,
on wire-wrap or matrix, but that's as far as I'd go now.

1. If a card is going to be WW, are pads and PTH's really needed?

They stop the pins from flopping about. It's already a cat's cradle.

Paul Burke

 

[Tam/WB2TT]

Dave,
We gave up on wirewrap about 15 years ago. You could sometimes spend a week
looking for broken wires, or wires that had shorted to a pin that it went
around. Not useful at high frequencies, especially analog. SM requires a
cluge, and at the time, SM only used .050 spacing.

For a while we used Multiwire for digital boards, but that is harder to make
channges on than a PC board.

Tam

 

[Ruediger Kluge]

Hi,
if you have a lot of DIL I Cs you can wire wrap. For wire wrap you need
sockets with pins with the right shape (rectangular) and length(number
of turns).
http://www.tecratools.com/pages/tecalert/wirewrap_guide.html
And you need a grid or 0.1".
So my proposal is nearly the same as from Paul.
I use electro mechanical interface modules (S-sub, smb, modular jacks,
BNC, power connectors...) which are in 0.1" grid, which can be wire
wrapped, soldered or plugged into standard sockets. Or they can even
plugged in breadboards. From here I make the connections to more complex
and special PCB modules.
regards
Rüdiger

 

[John Larkin]

Can anyone point me to a good document(s) on wire wrap? I'm looking for
a discussion on equipment, technique, performance, and reliability. The
reason for this is that pre-prototype printed cards seem to be a waist
of money because of all of the changes to the cards as soon as they
arrive (most due to the "hey, while your at it" syndrome).

If you make them pay for multilayer boards, and pay for revisions,
they'll be a little more willing to do preliminary design reviews, and
stick with the results.

The only downside is the use of surface mount devices, but we can likely
use adapters at that development stage.

The big downside is the huge amount of labor involved, and the rotten
high-speed performance. 5-day multilayer boards are dirt cheap these
days. Think about it, design it carefully, make a board, and sell it.
Design-by-breadboard is a progressive, destructive addiction.

John

 

[Norm Dresner]

Can anyone point me to a good document(s) on wire wrap? I'm looking for
a discussion on equipment, technique, performance, and reliability. The
reason for this is that pre-prototype printed cards seem to be a waist
of money because of all of the changes to the cards as soon as they
arrive (most due to the "hey, while your at it" syndrome).

The only downside is the use of surface mount devices, but we can likely
use adapters at that development stage.

Failing any documentation that would impress management, can anyone
answer these questions?

1. If a card is going to be WW, are pads and PTH's really needed? The
reason for the question is that there is no ground plane anyway, and
soldering to the socket lead seems like it is as good as soldering to a
pad. Components soldered are bypass capacitors as close to the device
as possible.

2. What is the number of connections that make power WW equipment
justifiable? I like to see development done (early stages) modularly,
so each card may have between 125 to 250 connections. A typical project
is only a few cards (modules). Once the design is stable we go for PC
cards anyway.

Any useful help would be appreciated.

Thanks,
Dave

I have a substantial investment in W/W equipment but my own rules are:
1. I'll wire-wrap (almost) all one-off [and sometimes two's as well]
circuits that aren't "too large"
2. I won't wire-wrap any circuit that I can't test easily. This means
a) it's a small circuit
b) it's a medium [or even somewhat large] circuit that can be built and
tested *modularly* and I build and test as I go.
c) it's not either RF or too high in frequency for logic. I'm very shy
going above 10-15 MHz this way
d) Unless it's a very simple circuit in which I can route wires very
carefully, it won't be an analog circuit either (but 555's are exempt from
this rule).
e) If it's a large circuit and I can't follow rule (b) then I use the
likelihood of changes as a determining factor.
3. There is no [convenient] PCB layout available. Since I use EagleCAD,
this generally forces me forego W/W unless there's substantial uncertainty
about the circuit design.

Norm

 

[Jan Panteltje]

**** Post for FREE via your newsreader at post.usenet.com ****

If you make them pay for multilayer boards, and pay for revisions,
they'll be a little more willing to do preliminary design reviews, and
stick with the results.




The big downside is the huge amount of labor involved, and the rotten
high-speed performance. 5-day multilayer boards are dirt cheap these
days. Think about it, design it carefully, make a board, and sell it.
Design-by-breadboard is a progressive, destructive addiction.

John

Yea, but how good are you?
I have seen these guys soldering little wires, cutting tracks...
Not one but 50 boards, hehe
At least calculate for 2?
JP


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[Dave Boland]

All,

Clearly, everyone seems against use of Wire wrap. I'm not that fond of
it myself, which explains why I don't use it much and have some
questions. Especially when you consider the cost of some of the card
shops today, it seems like wire wrap is not needed.

The problem is the reality of early development. A company pays an
engineer to layout a card with either a PCB program or a CAD program.
Card data is sent and in a few work days the card arrives. Within the
next few days, lands are cut, more holes drilled, a lot of wire wrap
wire used for "engineering changes", until the card is worthless. Let's
not forget that most of the quick turn cards are only two sided, so they
don't have a reference plane to stabilize the trace impedance anyway.

So, after seeing this go on for a while, it seems like there should be a
faster, more flexible way to do early development. One that the design
engineer can do in hours, and change as needed, etc. I thought wire
wrap may be that answer, but perhaps not. Is there a better way to do this?

Keep in mind that these are concept cards, well ahead of any product
prototype, so looks and long term reliability are not an issue. In
fact, I would consider the white board if the contacts were a little
more reliable (I have seen components fall out of the white boards when
moved).

Dave,

 

[Jan Panteltje]

**** Post for FREE via your newsreader at post.usenet.com ****

So, after seeing this go on for a while, it seems like there should be a
faster, more flexible way to do early development. One that the design
engineer can do in hours, and change as needed, etc. I thought wire
wrap may be that answer, but perhaps not. Is there a better way to do this?

Keep in mind that these are concept cards, well ahead of any product
prototype, so looks and long term reliability are not an issue. In
fact, I would consider the white board if the contacts were a little
more reliable (I have seen components fall out of the white boards when
moved).

Dave,

The way I do that is use veroboard with round iles (.2 inch round holes, no
stripes, solder in sockets, use some flatcable, split the wires, and
solder the connections one by one.
Have some Eurocards with uP and say 30 CMOS chips that way, still work after
20 years... You can throw them around.
You need good soldering, good eyesight, check every soldering connection.
Of cause the ones I did that way were all 100% working, so I could have made
the PCB directly hehe.
But nice to add and test things.
These days with FPGA and SMD .. not so useful anymore.
JP

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[John Larkin]

All,

Clearly, everyone seems against use of Wire wrap. I'm not that fond of
it myself, which explains why I don't use it much and have some
questions. Especially when you consider the cost of some of the card
shops today, it seems like wire wrap is not needed.

The problem is the reality of early development. A company pays an
engineer to layout a card with either a PCB program or a CAD program.
Card data is sent and in a few work days the card arrives. Within the
next few days, lands are cut, more holes drilled, a lot of wire wrap
wire used for "engineering changes", until the card is worthless.

Sounds like you should spend more time thinking and less hacking. Most
of our 6 or 8-layer VME boards work the first time. You can do that if
you want to.

Let's
not forget that most of the quick turn cards are only two sided, so they
don't have a reference plane to stabilize the trace impedance anyway.

Multilayer protos are cheap now. See the ads in the backs of EE Times
or EDN.

So, after seeing this go on for a while, it seems like there should be a
faster, more flexible way to do early development. One that the design
engineer can do in hours, and change as needed, etc. I thought wire
wrap may be that answer, but perhaps not. Is there a better way to do this?

Keep in mind that these are concept cards, well ahead of any product
prototype, so looks and long term reliability are not an issue. In
fact, I would consider the white board if the contacts were a little
more reliable (I have seen components fall out of the white boards when
moved).

Why does a concept need a card?

John

 

[Joerg]

Hi Dave,

While you compare against prototype PCBs keep in mind the incredible
amount of time some poor technician needs for wire wrapping. And the
cost this adds.

Also, even vanilla logic chips are several times faster today than 25
years ago. This adds to the signal integrity problems on a wrapped board.

I have never, ever, allowed any of my designs to be wire wrapped. As a
result my boards were done a lot faster than the wrapped ones. It is no
fun waiting for the others who are still chasing crosstalk, loose wires
and so on. I have seen engineers on the verge of bursting into tears
because their wrapped designs didn't work, the deadline was just hours
away and the boss nervously standing behind them.

My advice is the same that others provided: Don't wire wrap.

Regards, Joerg

 

[Peter Bennett]

Can anyone point me to a good document(s) on wire wrap? I'm looking for
a discussion on equipment, technique, performance, and reliability. The
reason for this is that pre-prototype printed cards seem to be a waist
of money because of all of the changes to the cards as soon as they
arrive (most due to the "hey, while your at it" syndrome).

3M makes (or used to make) a prototyping system that used wire-wrap
wire, and IDC connection points rather than wire wrap posts. I found
it much easier to use (and re-work) than wire-wrap.

However, I haven't used that system for some time - most of my
projects of any complexity have all the logic inside Altera FPGAs,
which are even easier to modify than the IDC system.

 

[Nico Coesel]

All,

Clearly, everyone seems against use of Wire wrap. I'm not that fond of
it myself, which explains why I don't use it much and have some
questions. Especially when you consider the cost of some of the card
shops today, it seems like wire wrap is not needed.

Keep in mind that these are concept cards, well ahead of any product
prototype, so looks and long term reliability are not an issue. In
fact, I would consider the white board if the contacts were a little
more reliable (I have seen components fall out of the white boards when
moved).

I used to use thin insulated wire. Nowadays I use thin wire which is
intended to wind transformers and so on. The main advantage is you
don't need to strip it. Just heat it with the soldering iron, the
insulation will melt and presto: you have a tinned wire. There is also
special wire available for this purpose in different colors.

 

[Nico Coesel]

Hi Dave,

While you compare against prototype PCBs keep in mind the incredible
amount of time some poor technician needs for wire wrapping. And the
cost this adds.

I have never, ever, allowed any of my designs to be wire wrapped. As a
result my boards were done a lot faster than the wrapped ones. It is no
fun waiting for the others who are still chasing crosstalk, loose wires
and so on. I have seen engineers on the verge of bursting into tears
because their wrapped designs didn't work, the deadline was just hours
away and the boss nervously standing behind them.

I've seen large wire-wrapped -production- boards (in a computer
tape-drive). I guess wire wrapping is in a way a true art. If done
well, wire wrapping is more reliable than soldering (say >100 years
versus 30 years).

 

[Rene Tschaggelar]

Can anyone point me to a good document(s) on wire wrap?

[ don't wire wrap ]

Any useful help would be appreciated.

To start with, digital stuff is done with CPLDs and FPGAs.
And for some analog stuff, there are systems on a chip available.
both for in circuit programming.

Rene

 

[Joerg]

Hi Nico,

I used to use thin insulated wire. Nowadays I use thin wire which is
intended to wind transformers and so on. The main advantage is you
don't need to strip it. Just heat it with the soldering iron, the
insulation will melt and presto: you have a tinned wire. There is also
special wire available for this purpose in different colors.

Just make sure you are ventilating the fumes away. I have some of that
stuff as well and the stench that comes off when the lacquer melts is
awful. The usual transformer wire may not be such a good idea as the
temps to melt are higher and the fumes might be toxic. So be careful.

Regards, Joerg

 

[JeffM]

Can anyone point me to a good document(s) on wire wrap?

Dave Boland

The concensus of documents on the web (as in this thread)
is *avoid wirewrap*.

A nice overview page for PCB/PWB is
http://en.wikipedia.org/wiki/Printed_circuit_board

 

[Joerg]

Hi Rene,

To start with, digital stuff is done with CPLDs and FPGAs.

Yes, and that takes away all this prototyping effort to a large extent
because you can "re-wire" things on the PC.

And for some analog stuff, there are systems on a chip available.
both for in circuit programming.

I know this is off topic here but are there any newer ones out that can
do more than a few MHz? What I saw so far doesn't contain much in terms
of speed and quantity but was really expensive.

For analog I'd seriously advise against wire wrap. I have seen people
try it but I have never seen that work in the end. Sometimes the radio
in the lab went quiet when they turned on the power ;-)

Regards, Joerg

 

[Joerg]

Hi Nico,

I've seen large wire-wrapped -production- boards (in a computer
tape-drive). I guess wire wrapping is in a way a true art. If done
well, wire wrapping is more reliable than soldering (say >100 years
versus 30 years).

To be honest I wouldn't buy a product if I knew it had wrap boards in
there. Art? Yes, in one company there were only two techs that could do
it. And I have seen wrapped boards work, at least for a while, but
usually only after they soldered all the posts.

Regards, Joerg

 

[Greg Neff]

Can anyone point me to a good document(s) on wire wrap? I'm looking for
a discussion on equipment, technique, performance, and reliability. The
reason for this is that pre-prototype printed cards seem to be a waist
of money because of all of the changes to the cards as soon as they
arrive (most due to the "hey, while your at it" syndrome).

The only downside is the use of surface mount devices, but we can likely
use adapters at that development stage.

Failing any documentation that would impress management, can anyone
answer these questions?

1. If a card is going to be WW, are pads and PTH's really needed? The
reason for the question is that there is no ground plane anyway, and
soldering to the socket lead seems like it is as good as soldering to a
pad. Components soldered are bypass capacitors as close to the device
as possible.

1) Forget copper clad boards. Use bare 0.62" thick FR4 boards with
0.042" holes on a 0.1" grid.

2) If you have any parts that won't fit through the holes then now is
the time to mark and drill. Don't forget mounting holes.

3) Power distribution is the most important issue. Stake Vector
T46-5-9 terminals (using a proper staking tool) in two rows at a space
of 0.3" Place 0.1uF axial ceramic caps between each pair of posts,
wrap the leads around the posts once (360 degrees) and don't trim the
ends. Lay 14 AWG or even 12 AWG solid copper wire along the outside
of the posts on top of the capacitor leads. Wrap each capacitor lead
up over the copper wire and back on to the post. This ties the copper
wire to the posts. Trim the leads. Oh yeah, add some tantalum caps
along the way, maybe every 10 pairs of posts. Use a heavy soldering
iron or gun to solder this all together. Careful with the heat on the
tantalums. Enjoy a beverage while the contraption cools. Now you
have reasonably low impedance power for low-speed applications, and a
rigid PCB.

4) Place and solder any miscellaneous stuff that isn't going to be
wrapped.

5) When you place the IC sockets beside the bus bars, keep the ground
end of the IC closest to the bus. I liked to glue down my sockets
using epoxy so they wouldn't squirm while wrapping. Mark the
reference numbers on the bottom of the board. Don't forget that the
chips are upside down when you are counting pins. If you want to get
fancy use OK Industries Socket-Wrap I.D. tags.

6) Make your ground connections to the ICs first, then the VCC
connections. Have fun with the rest.

7) For troublesome high speed or sensitive signals you can try running
twisted pairs. For single-ended stuff use a ground wire as the second
wire in the pair.

8) Say goodbye to your family for a couple of weeks, because that's
how long it's going to take you to get the mess to work.

2. What is the number of connections that make power WW equipment
justifiable? I like to see development done (early stages) modularly,
so each card may have between 125 to 250 connections. A typical project
is only a few cards (modules). Once the design is stable we go for PC
cards anyway.

Any useful help would be appreciated.

Thanks,
Dave

The last time I bothered with wire-wrap I was driving an AMC Gremlin.
Never mind why I was driving an AMC Gremlin. It could have been worse,
it could have been a Pacer or a Pinto. Anyway, if done properly
wire-wrap can be reliable. The wire-wrap connections are gas tight if
done correctly. IMHO, the main reliability problem is the quality of
the socket contacts that grab the IC leads. Also, signal integrity is
a nightmare. If you are using plain old slow TTL or CMOS then it can
work. With todays fast logic families I would not hesitate to laugh
out loud at an engineer that would suggest it. These days wire-wrap
is strictly starving-student stuff, and the enclosed pointers are for
their benefit.


================================

Greg Neff
VP Engineering
*Microsym* Computers Inc.
[email protected]