Allowable permanant PCB deflection.
Allowable permanant PCB deflection.
(OP)
HI
I am designing an enclosure to hold a circuit board supported on pillars from below and pressed onto them from above. My design must always deform the PCB in the same direction to avoid stressing some solder joints. The problem is when I do a tolerance analysis the maximum deflection could be quite high (1mm) over quite a short distance (27.5mm - defined by the support spacing). This gives a radius of curvature of less than 400mm which sounds small.
My question: is there any guidlines on a minimum radius of curvature for a SMT PCB that I can use as a starting point in my design.
When I ask electronics/PCB designers they always say 'as flat as possible' or 'test it'. The trouble is that with my current design 400mm is as flat as possible and my timescales don't allow me to start testing from scratch!
I am designing an enclosure to hold a circuit board supported on pillars from below and pressed onto them from above. My design must always deform the PCB in the same direction to avoid stressing some solder joints. The problem is when I do a tolerance analysis the maximum deflection could be quite high (1mm) over quite a short distance (27.5mm - defined by the support spacing). This gives a radius of curvature of less than 400mm which sounds small.
My question: is there any guidlines on a minimum radius of curvature for a SMT PCB that I can use as a starting point in my design.
When I ask electronics/PCB designers they always say 'as flat as possible' or 'test it'. The trouble is that with my current design 400mm is as flat as possible and my timescales don't allow me to start testing from scratch!
Matt Jackson
Product Design Engineer






RE: Allowable permanant PCB deflection.
> Tighten them?
> Use washers to compensate individual assemblies
> Use elastomeric supports to eliminate hard contact
TTFN
RE: Allowable permanant PCB deflection.
The tolerances are cast base ±0.1 + moulded cover ±0.05 and also a PCB ±0.15 + connector ±0.2 (both of which I have no control over).
I am obviously trying to design out the tolerance problem but I would still need a PCB deflection figure.
Elastomeric supports are an option though - I'm already using some elsewhere. Thanks.
Matt Jackson
Product Design Engineer
RE: Allowable permanant PCB deflection.
Alternatively, you could add a spring, a piece of poron foam, to the stack to absorb the tolerance yet still deliver a load to hold the PCB in place.
-b
RE: Allowable permanant PCB deflection.
Best Regards,
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Sr. Mechanical Engineer
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RE: Allowable permanant PCB deflection.
Use a bracket that you can control to set the deflection the way you want and then float the assembly in the enclosure.
TTFN
RE: Allowable permanant PCB deflection.
I have to admit that I like IRstuff's solution.
Ali
RE: Allowable permanant PCB deflection.
I really appreciate all the suggestions on a workaround but I have considered most of these things - it's really the allowable PCB deflection dims I'm after. However this seems to be somewhat elusive.
Matt Jackson
Product Design Engineer
RE: Allowable permanant PCB deflection.
Tunalover
RE: Allowable permanant PCB deflection.
Ali
RE: Allowable permanant PCB deflection.
RE: Allowable permanant PCB deflection.
I don't currently own Steinbergs book (but I'll order it ASAP!) can anyone that does have a flick through to see if this dimension is available?
Matt Jackson
Product Design Engineer
RE: Allowable permanant PCB deflection.
Tunalover