|Ask the Experts|
May 28, 2014
What Is Acceptable Bending For Assembled PCBs?
How much bend is acceptable when fitting a PCBA into a box build. We have a PCBA that attaches to a front panel, this then goes into a unit and attaches to a back panel. The problem is that the front panel has a tolerance on the flaps that attach to the back of PCBA and thus this could cause the PCBA to bend when being attached. I've searched for similar issues, but all I can find relates to unpopulated PCBs.
|Expert Panel Responses|
The limits of acceptable bending depend strongly onthe type and size of components mounted. BGAs in particular are sensitive tobending stresses, and the larger the part, the smaller the allowable bendingstress. Given the strong design-dependence of the situation, I'm very reluctantto throw out any numbers, and I would encourage you to talk to someone who canreview the design, model the bending, and give you an opinion.
It's better practice to avoid any bending on theassembled PCB for two reasons. There has to be some room for coefficient ofthermal expansion in use and secondly to avoid creep loading of solder joints.creep loading i.e relatively small stress on tin-lead solder joints leading tofractured joints over a period of time. this has been a silent killer in manyinstances.
Astra Microwave Products, Hyderabad, AP India
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