I would suggest that you be concerned not with the reliability of the
connection to the pad that exhibits breakout, but more the resulting SPACING
between the plated through via hole and the nearest circuit conductor. If
your designers are "normal" they will lay down a circuit at the nominal
minimum spacing between edge of pad to edge of conductor. They ASSUME that
the hole will be contained in the diameter of the copper pad and NOT exhibit
breakout. With respect to long term reliability, minimum dielectric spacings
< 0.005 is generally not accepted in North American telecommunications'
products.

Breakout and it's reliability may be secondary to the proximity of adjascent
circuits and it's effect on long term circuit integrity.

I'd be interested in your findings...

Dave Rooke
Circo Craft - Montreal Canada
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_________  reply separator ____________


>     We are an Australian manufacturer of electronic Telecommunications and 
>     Automated Fare Collection equipment. We use PCBs manufactured both 
>     within Australia and overseas, specifying in all cases manufacture to 
>     IPC-RB-276 standard.
>     
>     We have recently discovered among our incoming goods widespread 
>     incidence of annular ring breakout on the via holes of numerous 
>     multi-layer boards. It appears to be the result of incorrect 
>     registration during manufacture. The attached file contains an image 
>     (in Windows Paintbrush Bitmap format) of a typical example on a 
>     finished product.
>     
>     We are not overly concerned about the 90deg. and 180deg. hole breakout 
>     cases, but greatly worried by the conductor/annular ring junction 
>     cases. The functional tests of our finished products using these 
>     boards show no malfunctions, but we are very suspicious about the 
>     long-term reliability aspects. This is particularly so with those 
>     finished boards whose design service environment is 60degC (140degF) 
>     and >80% humidity.
>     
>     We would be very grateful for opinions and/or assistance from people 
>     with past experience of such a problem and first-hand knowledge of the 
>     long-term reliability implications.
>     
>     
>     Thanks in advance for your help.
>     
>     Eugenio Bini
>     Mechanical Components Engineer
>     
>     ERG Telecommunications Ltd.
>     247 Balcatta Rd.
>     Balcatta WA 6021
>     Australia
>     Tel.: +61-9-2731174
>     Fax.: +61-9-2731173
>     Email: [log in to unmask]
>
D. Rooke
([log in to unmask])