From my own experience,the main problem of missregistration is,first of
all,reliability of interconnection,when the drilled hole cuts the line.If
the line is,say,4 mills wide,this is the whole section area that keep the
via barrel connected to the line.taking into consideration z-expansion of
the board,it is not so reliable.The whole idea of internal annular ring is
to assure proper connection between via and internal lines.The next problem
of missregistration will be caused by violating of clereance to power (
lands) inside the board causing shorts.
Edward
Edward Szpruch
Eltek , Manager of Process Engineering
P.O.Box 159 ; 49101 Petah Tikva Israel
Tel ++972 3 9395050 , Fax ++972 3 9309581
e-mail [log in to unmask]
> -----Original Message-----
> From: Gfranck [SMTP:[log in to unmask]]
> Sent: ב אוקטובר 18 1999 22:25
> To: [log in to unmask]
> Subject: Re: [TN] Annular ring requirement by IPC
>
> Ken,
> A few years ago, I became aware of a report covering the reliability of
> innerlayer
> interconnect which attached to a PTH without annular rings, due to
> misregistration done
> on purpose. The results indicated two things. 1) That the annular ring
> interconnect
> was better than the non-annular ring interconnect. and 2) both
> interconnects met all
> the requirements of the stiffest reliability criteria for boards,
> something like 300
> thermal cycles from -10 to +60 C. I believe the annular rings sampled
> lasted 600
> cycles, and not non-annular ring sample lasted 450 cycles. The
> round-robin (?) study
> was sponcered (?) by IPC, and the results were leaked at an IPC meeting I
> attended. No
> one particularly liked the results, as it contradicts years of tradition.
> Perhaps
> someone more informed than I remembers this. I think the IPC meeting was
> in Arlington
> Va.
>
> To answer your question, Designers route traces as close as possible to
> the innerlayer
> pads. If the drilled hole is outside the pad, you decrease the electrical
> spacing
> between the drilled hole and any innerlayer trace that happens to be run
> near the
> hole. This may not be a short today, however one may well develop if
> conditions are
> favorable. So why 1 mil? The cross section is probably not reflective of
> the worse
> case condition. If your design is going to allow the drill to wander
> outside the
> innerlayer pads, you need to increase the innerlayer pad to trace spacing
> to allow for
> this, preventing the minimum spacing from being violated. This is not
> something
> designers want to do.
>
> In simple terms, you can think of those pads as innerlayer keepout areas,
> defining the
> area that the drill may appear. By requiring a 1 mil annular, you require
> to drill to
> fall inside the pad, and greatly reduce the chance of a short due to a
> hole to trace
> spacing violation.
>
> My view is probably not one held by the majority, so take it with more
> than the
> normally required amount of salt.
>
> George Franck
> "my Opinions are Just that".
>
> Ken Patel wrote:
>
> > I have the basic question:
> > Why do we need annular ring on inner layers? If the answer is no then
> why
> > IPC is asking for 1 mil annular ring on Class 3 products. The problem
> arisen
> > due to microBGA application.
> >
> > re,
> > ken patel
> > ______________________________________________________
> > Ken Patel Phone: (408) 490-6804
> > 1708 McCarthy Blvd. Fax: (408) 490-6859
> > Milpitas, CA 95035 Beeper: (888) 769-1808
> >
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