on Tue, 28 Mar 2006 at 04:36, aggie_672000 wrote:
>It is my understanding you tin plate the pcb after etching to
>protect the new copper trace from corrosion. TINNIT is the name of
>the material used to tin plate.
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[Please _do_ trim your quotes]
Your understanding is correct and that is one such product,
which applies a tin coating by purely chemical means..
However, if you had been attendiing to this thread you might
have understood that it is about applying a tin plating as an
etch-resist _before_ etching. This is done through a developed
photo-resist or similar while the copper foil is still intact, so
there is no need to use an electroless plating solution.
After etching, the tin layer may then be chemically stripped.
To go some way towards answering the OPs question...
On Mon, 27 Mar 2006 at17:50 +0200, matt clement wrote:
>...fab house...used a negative photo resist...then tin coated...board.
>...Then the board was chemically etched... the tin protects the copper.
>Would we...be able to come up with a similar system... printing a
>negative image and then tin plating before etching?
As Stefan says, yes but why bother? Extra work, more
messy chemicals, another hazardous waste problem...
>The toner...probably melt when...tin the board with an iron,
>but maybe a chemical plating process?
If you are already using an electroless tinning process
to protect the finished board you could use that, but
since the copper foil is still intact electroplating is feasible.
>Does anyone know for sure if tin etches away with FeCl?
A visit to Electrochemical Series (Corrosion Reactions) for Common Metals
http://www.efunda.com/materials/corrosion/electrochem_list.cfm?sort=com
suggests that it would - even the high level of copper ions could, but
the picture might be complicated by the low solubility of some tin salts,
by bath additives which exploit this or, if it were a tin/lead coating, by
passivation effects (really another way of saying the same thing).
The commercial process described here implies it does:
http://www.pcbfab.com/outreth2.html
"Etching Outerlayer Printed Circuit Boards"
>The use of Tin or Tin/Lead as an etch resist essentially mandates
>the use of ammoniacal etchant, because this is the only commonly
>used etchant chemistry that will not attack the Tin or Tin/Lead.
Regards, LenW
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