Tolerance Stackup

Discussion in 'General Electronics Chat' started by tindel, Apr 28, 2013.

  1. tindel

    Thread Starter Active Member

    Sep 16, 2012
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    I'm trying to layout a AAx2 battery holder and I'm having trouble with tolerance stackup - I just can't see it logically in my mind.

    Each lead is spec'd at 0.81mm +/- 0.25mm. Assuming my PWB manufacture can drill within 0.25mm, I think that means I need 1.31mm +/- 0.25mm for my layout drill hole and 2.50mm diameter for my pad should be sufficient.

    What I'm really having a hard time with is if drill holes should be made bigger due to tolerance stackup. The distance between the two drill holes is 14.99mm +/- 0.25mm. I think that my drill holes need to increase another 0.125mm to 1.425 +/- 0.25mm. But I'm not sure if this is correct.

    I'm not a mechanical guy - my brain doesn't work this way. :rolleyes:

    Is this right?
     
  2. tindel

    Thread Starter Active Member

    Sep 16, 2012
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    All that said, I believe a 1/16" (1.588mm) drill bit will be adequate with a 1/8" (3.175mm) pad if I space the holes at 14.99mm +/- 0.25mm
     
  3. tubeguy

    Well-Known Member

    Nov 3, 2012
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    What I get is the max pin diameter would be .81 + .25 0r 1.06 mm max.

    The pin spacing seems OK. Do you have any wiggle room as far as bending the pins a bit ?
     
  4. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    I doubt that. First of all, pins are quite bendy so you don´t need to have so big tolerances. Second thing is that the bit is twice the size of the pins, which will lead to unnecessary play in the holes and probably some trouble with soldering them. I´d use something like 1.2 or 1.3mm drill.
     
  5. tubeguy

    Well-Known Member

    Nov 3, 2012
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    Another consideration. Assuming these are plated-through holes does the mfr
    calculate the drill for you based on the finished hole size or are you expected to consider that in your calculations. I haven't ordered PCB's in a long time but I seem to remember being asked to consider the through hole plating dimension when specifying driil size.
     
  6. tindel

    Thread Starter Active Member

    Sep 16, 2012
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    Here is a link - should have put this in my first post! Sorry.: http://www.google.com/url?sa=t&rct=...=NEEIEeNLl7mchAVvmLSOWQ&bvm=bv.45645796,d.aWM

    I have a sample and the leads are pretty rigid - There really isn't much 'bending' in the pins. The pins move a little bit radially, but are not easily bent. I also need the structure to mount sturdily on the PCB because the heat dissipated in the batteries is high, so I need as low thermal resistance as possible (I know most of the heat will go into the copper via the leads).

    I have not identified a manufacture - I'm still prototyping, but trying to think ahead.

    Tube guy - thanks for the tip... I hadn't considered the plating. I would expect the manufacture to take that into account (drilling out more, and plating up to my required hole size.)
     
  7. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    Unfortunately, the general tolerance definitions on the bottom were cut off in your pdf scan.

    Fortunately, there is a mounting detail specified in the top right corner. Just go with that and you should be good to go.
     
  8. tindel

    Thread Starter Active Member

    Sep 16, 2012
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    Ernie -

    The general tolerance is 10mil [0.25mm], That mounting diagram only appears to consider nominal pin diameter, or I would.

    Tinman
     
  9. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    I would believe the general tolerance note (that someone could overlook) is incorrect long before I'd believe the suggested layout (that someone thought about) ignored tolerance.

    Hey, your project so your rules, but for my projects if Simon sez "do this" then I do just that.

    I wonder if you could get a hold of someone to ask.
     
  10. MrChips

    Moderator

    Oct 2, 2009
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    I wouldn't add up the tolerances. You will end up with a hole that is way too big.
    Go with your gut feeling. Take the diameter of the pin, add an amount for the plated through hole, add another 0.20mm. I think about 1.20mm should do it.

    The other way I do it is I find a PCB with a hole that is just right for that the pin and measure that hole with a drill bit. Then add the plated thru amount.

    Find out if the PCB fab wants drill sizes or finished holes.
     
  11. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    The PCB mounting layout is "clearly" posted on the drawing... follow it.. done..
     
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