Vibration fatigue

[SunderBob]

Hello,

I'm new to vibration fatigue, so I would really appreciate all the input from more knowledgeable and experienced colleagues.

I want to do a fatigue analysis of simple PCB with one CSP soldered with four solders. The solders are my main interest here.

Now, I have Steinberg's book on vibration/fatigue analysis, and there are a couple of things that aren't too clear to me.

Specifically, I'm talking about critical and max displacement which are required to determine number of cycles to failure.

The thing that puzzles me is where are solder properties, or number of solders in those equations. I've seen a couple of equations that use stresses instead of displacement, but can you tell me what is the difference between the two?

Also, does someone know where I can find S-N curves for SAC solders. Or is there a way of generating them?

Basic questions I know, but like I said, I'm new to fatigue

All your help is greatly appreciated.

 

[izax1]

I know Steinberg is focusing on displacements, but that is often not the main failure criterion. In my experience it is the curvature of the PCB. The curvature is of course related to displacements, but depending on the distribution of components on the PCB and connection points, you can have small displacements and still large curvature depending on frequency and vibration mode order. It is the bending stresses from curvature in the PCB that will cause solder joint fatigue. I have had the opportunity of discussing this with Steinberg some years back, and although we did not quite agree on the matter, we had an interesting discussion anyway.

So besides checking the displacements, you should also check the curvature.

 

[SunderBob]

Thanks for the tip.

But the thing is, I can not do anything without S-N curve for SAC solders (Steinberg has some for SnPb).

I have the stresses in the PCB, but I don't know how many cycles will it last.

I've been looking for days now, but I haven't found anything useful. And since I can't do an experiment, there is no way I can generate them.

Do you know where S-N curves for SAC can be found?