Peter,

Comumn is an old hi reliability, Class III term, synonomous with column when
wrong key depressed while typing, eating, drinking (probably this one mostly
as Bud), and reading at same time.

Wasn't it 275, can't find my copy now, that had the famous three comumns as
preferred, standard, and reduced producibility. Anyway, I still use the
three as guidlines today but having evolved from reduced to preferred over
the very long time I've been designing and building these type boards.

At any rate 5:1 works fine. I still stick with my previous views concerning
non-functional pad removal as being totally acceptable. My previous comments
brought up the old requirements for two plies of prepreg per dielectric
thickness minimum meaning resin rich material was always present in high
layer count (over 8) MLB's. Because it was so rich, it "pushed" and "pulled"
its way into and out of hole walls effecting separation and such. Now, in
the single ply world, this is not as much a factor or concern, as the resin
to glass ratios are nearly balanced so much less movement is apparent.

Also, I belive 2221 talks to Class III plating thickness requirements as 25
um minimum. What is that table?

MoonMan

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