Dear Edward:

A dilute sufuric solution (10%) following peroxy/sulfuric or persulfate
microetching is generally considered an optional step, but is frequently
employed to assure cupric sulfate and/or persulfate residues are
completely removed from the copper surface.  Generally, I believe it is
cupric sulfate precipitation and adhesion to the copper surface which is
the primary problem.  Because the microetch bath is generally heated,
cupric sulfate solubility is higher than at room temperature.  Thus, if
the bath is operated prior to reaching working temperature, or the bath
is near the end of its life (hence high copper concentration), the etch
solution remaining on the board may precipitate cupric sulfate while it
is being transported from the microetch to the rinse station.  These
cupric sulfate crystals may adhere to the copper surface of the board.
Additionally, they are often too small to see without magnification, and
thus overlooked.

While cupric sulfate is very soluble in water, its rate of dissolution
is very slow UNLESS the solution is HEATED or ACIDIFIED.  Hence a 10% by
volume sulfuric dip is common to assure cupric sulfate precipitate on
the copper surface is completely removed.  If it is necessary to
eliminate the sulfuric step, pay close attention to the post rinse
quality, and consider reducing the upper copper concentration allowed in
the microetch.

Regards,
Ted Stern

Eltek Ltd. - Process Engineering wrote:
>
> Hi !
> We are considering some changes in our vertical ( racks ) PTH line based on
> thin copper electroless . Today microetch section consists of :
> 1 ) microetch at following steady state operating conditions :sodium
> persulfate ( 40g/l) , sulfuric acid ( 60-80 gr/l) , dissolved copper ( 12 g/l )
> 2 ) flowing rinse
> 3 ) sulfuric acid post-dip ( 100 to 200 g/l )
> 4 ) flowing rinse
> 5 ) static catalyst pre-dip
> Due to lack of space in the line for some expansion I am considering
> cancelation of sulfuric acid post dip and the following rinse , since
> microetch solution allready has enough sulfuric acid .
> All opinions ( pro , contra ) will be very appreciated.
> Regards
> Edward Szpruch
> Eltek Ltd - Israel
> Tel  972 3 9395050
> Fax 972 3 9309581
> E-mail :  [log in to unmask]
>
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