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tolerance of SMT components placement and soldering

sylyra

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What tolerance should I expect in placement of SMT components, that need to interface to a mechanical part?
Example - two pressure sensors on the same PCB with a cylindrical tube interface need to be inserted into matching holes in a manifold. While the holes position in the manifold can be done very accurately, I expect the placement on the PCB will have a larger tolerance which I have to take into account (if tolerance is too large then maybe it will not be possible to have them on the same PCB as it will create mechanical stress when inserted into the matching holes in the manifold).
So what tolerance should I expect (obviously not manual soldering)?
 

KlausST

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Hi,

if I were on your place I'd go the other way round: Instead of asking for tolances I'd decide the tolerances and give them to the PCB manufacturer.
But for this you also need to decide where the toleranced measure relies to.
What I mean:
* drill to drill tolerance is rather tight.
* drill to outline could be relaxed if both (milling and drilling) are done during the same process
* drill to solder pads will maybe be to complicatest

Klaus
 

sylyra

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Hi,

if I were on your place I'd go the other way round: Instead of asking for tolances I'd decide the tolerances and give them to the PCB manufacturer.
But for this you also need to decide where the toleranced measure relies to.
What I mean:
* drill to drill tolerance is rather tight.
* drill to outline could be relaxed if both (milling and drilling) are done during the same process
* drill to solder pads will maybe be to complicatest

Klaus
Thanks,
So, assuming that the best tolerance is achieved between monting holes and components holes, since it is the same process/machine, then a possible solution could be to switch to TH devices and follow the next procedure:

Install sensors on the mechanical part
Mount the PCB to the mechanical part with components holes matching the sensors legs
Manual soldering

Makes sense?
 

marce

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I have done camera sensor boards and similar for automotive using SMD parts, no problem with interface to the mechanical parts. For critical parts the footprint is critical, trim pads to IPC-7351 least to avoid component movement.
 

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