PCB board question

Discussion in 'General Electronics Chat' started by Joe24, Mar 15, 2008.

  1. Joe24

    Thread Starter Active Member

    May 18, 2007
    Hello all,

    Someone recently showed me a PCB board that had several IC chips in DIP form. That person turned the board around and pointed at some pins that were soldered. I was asked " Would it be a problem if the pins that are sticking out are too long?" I answered "no, it's not a problem." But I started thinking about it, and wasn't sure if I answered correctly. Does anyone know the answer to this question?? Thanks
  2. hgmjr

    Retired Moderator

    Jan 28, 2005
    It is good practice to keep the leads trimmed nearly flush to the board. This often avoids the possibility of the leads coming into contact with a conduction surface such as a metal mounting bracket or the metal enclosure into which the PCB is mounted.

  3. helicopterrun

    New Member

    Mar 13, 2008
    It all depends on weather or not the board will be mounted in a place where the pins would come into contact with another conducting surface. For example if the board were to be mounted in a plastic project box the pins do not have to be trimmed; however, if the board is mounted in a steal NEMA box etc. you would need to trim the leads. Another problem with long lead is that it is possible to short leads to each other. Also watch out for solder joint overlap between pins.
  4. Joe24

    Thread Starter Active Member

    May 18, 2007

    Ok sure that makes sense. Now let's say that the board will not be in close contact with any other conducting materials/surface etc... One question that I ask myself ( I don't know if it is a silly one or realistic one ) is that since these pins will have current throught them, and if the pins are not cut nicely short and flush, will it be a problem in terms of magnetic fields being generated by these long pins. I assume this may cause a problem when dealing with high-frequency application PCBs.

  5. John Luciani

    AAC Fanatic!

    Apr 3, 2007
    Unless you are working with frequencies above 100MHz I would not worry
    about the short stubs created by the leads.

    Unless the leads are longer than a hundred mils I would not bother cutting.
    You can save yourself some work (and avoid cutting something you didn't
    want to ;)

    (* jcl *)
  6. DC_Kid

    AAC Fanatic!

    Feb 25, 2008
    i would answer that it depends on the circuitry, what is it doing, etc. in highly sensitive cicuits (even with small DC signals) the pins themselves can pick up unwanted noise, add capacitance component, etc.
  7. 3BwEH

    Active Member

    Feb 25, 2007
    well it depends on the frequency u are using
    try to use the equation λƒ = c
    where λ is the electrical length and f is the frequency
    while c is the speed of light if ur not working in a substrate with a dielectric in this case divide by square root of the dielectric constant

    anyways after using this equation to figure out what λ measure the length of those legs
    if they are compatable ull have problems regarding parasitics