MoonMan
Please allow me to add
10) Quality of glass cloth: much of the cloth we are seeing today has
been woven unevenly, often with the warp and weft locally not even at
90° to each other. This is rolled up under stress and goes straight into
the treater. Result: when the prepreg is pressed and the resin melts,
some of the resultant strain is relieved, but is partially dissipated in
the adjacent layers, which also become stressed (if they aren't
already). Just waiting for a passage above Tg for stress relief!
Brian
Earl Moon wrote:
>
> Wes,
>
> I just finished a consulting assignment in Connecticut concerning the very
> same thing. I have done many of these contracts recently as everyone seems
> to be having the same problems.
>
> As I told Tom Gervascio (another Siemens person), first read my article on
> the SMTnet (their newsletter) in the September 1999 edition. It speaks
> clearly, though technically, to this and other issues concerning MLB
> technology. I am assuming boards, on the panel, are this type even though
> double sided types also may perform this way.
>
> 1) The MLB construction, beyond balanced copper planes, as material
> selections. Also, material availability becoming more of a problem due to
> glass fiber shortages (much being diverted to fiber optics industry - what a
> surprise!)
>
> 2) The lamination process not effectively managed as press cycle from ramp
> through pressure, time, and temperatures used.
>
> 3) Lamination press issues as non parallel press plattens, thermal problems
> as uniform heat transfer or heater elements not working, etc.
>
> 4) Number of books in each press opening along with thermal lag material,
> etc.
>
> 5) Total cure not effected during lamination
>
> 6) Variations in your assembly process as reflow profiles, including cool
> down.
>
> 7) The type scoring used and how well the process managed
>
> 8) A thin panel that is too large (how large are the panels?) especially
> when not effectively supported during reflow.
>
> 9) Other variables not so common
>
> Earl Moon, Proof Of Design
>
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