Allowable BGA vibration

[chassisdeeziner]

Anyone have a rule of thumb for allowable BGA vibration in shock (before failure of solder joints?). We're hoping to find something more recent than the 30 year old Steinberg criteria. Any help?

 

[VonMises]

Hello,

I am also debating these Steinberg formulas. One main concern is that these formulas are good only for one certain type of boundary conditions, i.e. clamped edges.
What happens for a bolt restrained PCB with the same type of components on it? Since we want to control the deflections (or the slope) of the PCB under the critical components we tend to use Steinberg's formula for all cases... I do also wonder if there is any real test data
to correlate the theoretical formulas (for shock or random vibration). I personally think that we over-design using these formulas. But I have no data to do otherwise...
Please let me know if you find anything new!
Thanks,
VonMises

 

[VonMises]

I have a problem and I do not know how to tackle it.
One lead of a large component broke in vibration when it should have not.
Now, the formula I used is the one in the Steinberg
book for random vibration, that predicts
the maximum 3xSigma allowable displacement for 20 million cycles under random environment.

My questions, since the book is not very clear about it on this point, are:
Are the number of cycles, of 20 million, the total ones, including 1xSigma, 2xSigma and 3xSigma random events ?

Is the predicted (allowable) 3xSigma deflection valid only
for the 4.7% of the 20 million cycles?

To make things more confusing, exactly the same, formula is used to calculate the allowable displacement for 10 million cycles under a sine environment. (here we have only one amplitude).

Say that my equivalent random vibration number of cycles is 80,000, ( number of positive crosings)and the 3xSigma deflection predicted is 0.025 inch.
Using the Steinberg formula I calculate the allowable 0.013 inch, for ....how many cycles ? How do I compare the two values now ? What is my Margin of Safety ?

I am all confused. Can you please help me. Do you have any background into this ?
Or how can I get in touch with Mr. Dave Steinberg ? I can not find any phone number, or e-mail, or address of his.

In any case, thank you very much for reading this far, and thank you even more if you have some answers . I wonder what other people in the industry are using ?

VonMises

 

[chassisdeeziner]

VonMises...how about:

Electronic Packaging and Design: "Designing electronics for high vibration and shock" by Howard Markstein.

If you're daring enough to post a Fax# I'll send you a copy of the article. It wades through some example applications of the formulas.

 

[VonMises]

It sounds very good ! Thank you.

Here is the fax number:
In Canada, Montreal:
514-425-3016

Thanks again.
VM

 

[chassisdeeziner]

VM,

Check your fax machine....the article should be there.

 

[VonMises]

I got it !
Thank you very much.

I will let you know if anything new comes along.

VM

 

[esector]

As was asked earlier,
How do you account for different clamping conditions when calculating maximum allowable PCB displacement using Steinberg formulas?
Regards,
Alex