I can't rememver all I forgot on the subject. Before BGA days, in the middle
to late 80's, I did some work addressing leaded and chip device voiding.
I'll ask Steve to post a few images showing solder joint voiding in
x-section. I had some from x-ray as well but the images have dissapeared.
Anyway, some of us used the same rule (20%) for maximum voiding allowable
after determining, in small quantities on a few boards, failures occured
after very few mechanical and thermal cycles when the requirement was exceeded.

It should be noted some of the solder thickness, between leads and solder
termination areas, measurments exceeded the 1.5 times requirement then used.
I don't know if this rule still applies but probably is.

I'll get the pictures up for you if interested. They simply will complement
your stuff.

Earl

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