Your picture looks very familiar from a past employers shop.
In that instance, the pad lifting was caused by a lack of ductility, which was
identified as Iron (Fe) contamination of the plating bath.  The deposit functions well
in all other respects, except it has an exceptionally High tensile strength, causing
the lifted pads.

Once we dummy plated the Fe levels down to a reasonable level, AND removed the wrench
that a maintenance man had dropped into the tank (and told no one about), the problem
was resolved.

George Franck

Gerry Cooper wrote:

> Alain is right on with his comments about thermal effects, however
> generally for military purposes, you would thermal shock coupons prior to
> sectioning.  It's not common to find lifted pads even with that.  Pads lift
> primarily due to plating thickness being to thick at the corners.  When the
> board swells in the Z axis from heat and then shrinks back during cooling
> it will bring the pad with it unless the plating thickness is strong enough
> to overcome the bond between the copper foil and the laminate.  Typically
> the problem starts to show up when the thickness reaches 0.0022" or greater
> of plating thickness.  I have seen problems where the amount of pad
> actually bonded to the laminate is very small which also contributes to the
> problem, as it's the same area of bond verses thickness of copper problem.
> In rare instances, I suppose the ductility of the deposit could have an
> effect, but I would assume if it was bad enough to cause this, you would be
> seeing other problems as well.
>
> Questions I would think about would be; are all the pads and panel
> thickness' the same, or are you looking at a particular design?  Are these
> thick panels?  (which would expand more)  Is your plating evenly
> distributed or do you have a significant "dog boning" problem?  As Alain
> said are you thermally shocking the board more then normal, like maybe at
> your hot oil reflow dip tanks, because the preheater isn't hot enough?
>
> Let us know how you make out.
>
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