Werner, do you not think that inner layer foil cracks are more probable with
1/2 oz inner copper as compared to 1 oz?

Dave Rooke
Circo Craft - Pointe Claire
A division of Viasystems

= = = =
>Hi George,
>Somewhere along the way, Andy's message got somewhat mixed up. There are
>essentially three possible failure modes for PTH/PTVs. Listed in order of
>decreasing importance, they are (i) barrel fracture, (ii) interconnect
>separation (post separation), and (iii) corner cracking. Some of the steps to
>minimize one failure mode may increse the failure potential in one of the
>other modes.
>
>All of these failure modes are primarily driven by loading during soldering
>processes, in particular manual processes. Thicker PTH plating will reduce
>(i), but increase (iii) and to a lesser degree (ii). Thinner, or no, inner
>layers near the PWB surface will increase (iii) and (ii), because of
>increased land rotation and thus larger bending moments at the attachment
>points of surface and innerlayer lands; there is no significant effect on
>barrel stresses (see Iannuzzelli, DEC). Thinner inner layers increses (ii)
>also because of a reduced attachment area to the PTH barrel/cross-ection of
>the foil.
>Putting all of this in a practical context: by using a high Tg PWB polymer,
>using E3 (HTE) copper foil, avoiding manual soldering operations with high
>maximum temperatures, and having good production quality, you should have no
>real adverse effect by switching to 1/2 oz. foil.
>
>Werner Engelmaier
>Engelmaier Associates, Inc.
>Electronic Packaging, Interconnection and Reliability Consulting
>23 Gunther Street
>Mendham, NJ  07945  USA
>Phone & Fax: 973-543-2747
>E-mail: [log in to unmask]
>
>