I have a product that will be subjected to reliability testing (random vibration and thermal shock) and I need to design a footprint for an SMT power inductor that will give the best mechanical strength to resist damage during vibration testing. I've looked through the IPC 7351 standard but I cant find anything that talks about how different pad size (resulting in different fillet shape) will affect the mechanical strength of the solder joint. The part I am working with is Murata LQH3NPN1R0MMEL. It has a mass of approximately 0.05 grams.
Does anyone have a method for calculating a land pattern for optimal mechanical strength?
Best Answer
If you're serious about this, you must take into account the mounting geometry of the pcb, the material stiffness, and the location of the inductor. You'll need to do a FEA vibration analysis to identify nodes on the board and coupling of vibrational energy into the inductor footprint.
If you don't have the in-house expertise for that, and don't have access to an outside expert you can hire, you're best off making a blank pcb with just the inductor and shaking/shocking the hell out of it until it fails.
EDIT Sometimes the physical straightforward approach can save a lot of time over careful analysis. There's a story about Edison. Supposedly he assigned a task to a new engineer - determine the capacity of a an oddly-shaped glass bulb. The engineer spent a day taking careful measurements of the bulb and calculating precisely how much volume this entailed, after making due allowances for the (measured, of course, at several places) thickness of the bulb. Edison, it is said, took the bulb, walked over to a water tap, and filled the bulb, then poured the water into a graduated cylinder.