T&T nor MIT certainly weren't the first to make EDCF. I'm not sure of
the exact date, but I believe it was done in the 1930s, obviously
nothing to do with printed circuits. However, it was a batch process on
large polished stainless steel sheets, not a continuous drum cathode,
which was developed in the early 1950s to meet the demand for a more
rational process. If I remember correctly, the sheets were 3 x 4 feet,
but about 6" all round was scrapped as only the centre part was of
uniform thickness. The rough (very!) side of the copper was sprayed with
an adhesive. The laminate made from it was made by the Formica company
on a phenolic paper substrate (later designated as XP, nothing to do
with Microsoft, as Bill Gates wasn't even born then!). The adhesion was
considerably better than with the brushed rolled copper tried before,
but I think the T&T advance was that, with their continuous process,
they were able to treat the copper by chemically oxidising it. Gould
later improved on the treating by depositing a thin layer of zinc, which
formed a brass by diffusion during the press cycle, providing a better
bond to the epoxy.

I'll let you have another try.

Brian

PS Sorry for having hi-jacked the thread by going off-topic.
Mary Jane Chism wrote:

> Group,
>
> Is it mentioned anywhere in any of the IPC standards a visual acuity for
> solder inspection?  Thanks.
>
> Mary Jane Chism
>
>
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