BOB HAYNES asked:
>>This question is in regard to inspection of internal annual ring. IPC
>6012 Para. 3.4.2 allows breakout. When coupon F and/or X-ray
>techniques are not to be utialized and microsection is only option.
>How do you evaluate breakout?
You mean "annular ring". Well, like the rings of a tree, you won't count
'em exactly if you don't chop it down, or maybe test with Carbon 14 dating.
So you're left with some guesswork. You're out in the woods, you sort of
look at the branches, the overall size, and you say "yep, that oak oughta
be about 50 year old".
Guessing you are referring to multilayers, and in the shop with no tools,
you'd put in on a light table, and check to see if there is light clearance
around the thermal relief pads in all quadrants of the panel. They ought to
be concentric with the clearance rings of power and ground internal layers.
If the internal layers are shifted, you would see lopsided light rings
aroung the thermal relief pads. If the board does not have thermal relief,
I have no suggestions for you.
Of course, breakout _is_ acceptable, and if you are worried about whether
that tree is really 45 or 50, and whether you have zero breakout or minor,
then you will have to use xray or section. I suggest that you also have the
internal pads teardropped on your original designs, or ask the boardshop to
add them.
regards,
Jerry Cupples
Interphase Corporation
Dallas, TX USA
http://www.iphase.com
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