Steve,

If the pad lets go from the laminate, then check the peel strength of the raw
laminate.  If it is over 8 lbs ( I think that is the number..), then you are out of
luck...  you probably need to plot BIGGER SMT pads.

As two 2 layers of copper... yes there are 2 layers.
The bottom layer is the copper foil.
The surface copper was plated on at the same time the Plated Thru holes were plated.
This interface can separate if it is weak enough.  That weakness is usually caused by
contamination on the copper foil (electroless copper also there) surface prior to
plating the top layer of copper.  One typical cause is photoresist residue from a)
marginal developing, or b) a long hold time after develop prior to plating, esp if
stored in the presence of blue light.

For option b) the supplier may have had equipment or chemistry problems with the
plating line.  Often they will create a big mountian of work in front of the plating
line, as if that will make the plating line get better faster.  (It doesn't)

Been there, done that, ... bought the scrap.  (If you keep the developed mountian of
work in the yellow room or in the dark, option b) won't happen as quickly)

George Franck
"My Opinions are just that"



"Stephen R. Gregory" wrote:

> Hi ya'll!
>
> Here's something weird I've never come across, but maybe some of you have. We
> built this Hi-Rel board here that the PCB drawing calls out for 2-ounce
> copper.
>
> The board has this leaded SMT multi-capacitor part (it's like 3 huge ceramic
> capacitors stacked on top of each other) and has 8-leads. After assembly, and
> before we test then conformal coat it, we put the assembly on this vibration
> table to go through some ESS.
>
> There's been a few of these capacitor deals come loose because they're so top
> heavy, but that's a whole 'nuther issue...
>
> What we've been seeing on some of these boards, is that either the pad
> completely lets go from the laminate (it's a polyimide), or sometimes we'll
> see the pad come up in what looks like a layer of copper, yet there's still
> copper down on the PCB...as if the copper has split horizontally in two
> distinct layers? Is this possible? Does 2-ounce copper clad laminate get the
> copper plated an ounce at a time? Is this a defect? I've never seen something
> like this before, and I can take a picture and send it to ya' if you want me
> to....
>
> Thanks!
>
> -Steve Gregory-
>
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