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Wire wrap

Discussion in 'Electronic Design' started by Dave Boland, Jun 24, 2004.

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  1. Dave Boland

    Dave Boland Guest

    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
     
  2. Paul Burke

    Paul Burke Guest

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

    Paul Burke
     
  3. Tam/WB2TT

    Tam/WB2TT Guest

    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
     
  4. 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
     
  5. John Larkin

    John Larkin Guest

    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
     
  6. Norm Dresner

    Norm Dresner Guest

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

    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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  8. Dave Boland

    Dave Boland Guest

    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,
     
  9. **** Post for FREE via your newsreader at post.usenet.com ****
    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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  10. John Larkin

    John Larkin Guest


    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.
    Multilayer protos are cheap now. See the ads in the backs of EE Times
    or EDN.
    Why does a concept need a card?

    John
     
  11. Joerg

    Joerg Guest

    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
     
  12. 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.
     
  13. Nico Coesel

    Nico Coesel Guest

    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.
     
  14. Nico Coesel

    Nico Coesel Guest

    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).
     
  15. 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
     
  16. Joerg

    Joerg Guest

    Hi Nico,
    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
     
  17. JeffM

    JeffM Guest

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

    Joerg Guest

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

    Joerg Guest

    Hi Nico,
    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
     
  20. Greg Neff

    Greg Neff Guest

    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.
    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.
     
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