In a message dated 96-10-25 18:06:59 EDT, you write:

>What is the minimum acceptable tin/lead etch resist thickness useable in
>practice?  We have people using anything from 5 to 15 microns and obviously
>need>to get people to use a minimum thickness to minimise waste and
treatment
>costs as>well as environmental impact.

10 microns = 2.5 mils is about the minimum standard in the US, but the
practical minimum is determined on a shop by shop basis, and is a function of
plating speed, which in reality determines throwing power, (thus slower
plating=more uniform deposit=lower minimum plating required) and uniformity
of current density over the boards being plated.

>How practical are lead free/or reduced lead alternatives e.g. pure tin?
>
Very practical, and in the US, pure Tin is now the prevalent etch resist.

>What options are there for tin/lead stripping solutions that might be
capable
>of>recycling the dissolved metals?

Anything is possible, if the financial incentives are present (which they
are, at least currently), and the government bureaucrats are not.

However, given the state of the PCB fabrications industry (Which, summarized,
can be described as "If you don't like the way things are being done now,
wait 3 months, they will change), a business person would be better off
putting money into roulette than investing in a major metals recycling plant,
which depended on spent Tin, or Tin/Lead stripper as a raw material.

Rudy Sedlak
RD Chemical Company

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