TECHNET Archives

February 2013

TechNet@IPC.ORG

Options: Use Monospaced Font
Show Text Part by Default
Show All Mail Headers

Message: [<< First] [< Prev] [Next >] [Last >>]
Topic: [<< First] [< Prev] [Next >] [Last >>]
Author: [<< First] [< Prev] [Next >] [Last >>]

Print Reply
Subject:
From:
Inge Hernefjord <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Inge Hernefjord <[log in to unmask]>
Date:
Wed, 6 Feb 2013 08:39:39 +0100
Content-Type:
text/plain
Parts/Attachments:
text/plain (80 lines)
I think Merlin Thayer's method is the fastest. However, we used plasma for
removal of silver sulphide. You mix Argon and Hydrogen about 10/90. The
disadvantage : slow!  Can take up to 2 hs, depending on the
target-to-source distance and angle, thickness of corrosion layers,
possible presence of grease. We used plasma because we did not want the
objects to suck up water . I don't remember the RF frequency, but it's
probably around 20 MHz. Likewise, I've forgotten the gas pressure ( our
machine had a current indicator. You increased the gas with a needle valve
until ignition, then continued increase gas until certain level of RF
milliamps, the later obtained by a lot of experimenting). My opinion about
plasma cleaning is: you must know what you are doing and...you don't get
much help from the manufacturer. Remarkable things happen e.g. you clean
several identical objects until suddenly there is one that won't be cleaned
at all, without finding any reason.

Inge



On 6 February 2013 00:30, Wayne Thayer <[log in to unmask]> wrote:

> Hi Rich-
>
> Mildly oxidized ImAg usually solders fine, even if it doesn't look good.
>  So try a bit.  If you really need to do something, then I don't think a
> plasma will help.  There is only a very tiny amount of silver on the
> surface, so if you remove the ugly stuff, you'll most likely expose a bunch
> of copper.
>
> So IF anything is needed, then the common approach is to REDUCE the silver
> oxides and sulfides back to elemental silver.  This is done the same way as
> advertised frequently on late night TV (only they use snake oil and do
> voodoo dances):
>
> Heat some water up to 70C and add 1TBS/quart of baking soda.  Dissolve the
> baking soda.  Then take some new shiny aluminum foil and crumple it up,
> then iron it back out.  Put this in the hot water bath with the circuit
> board.  It doesn't have to actually make contact with the circuit board,
> and you really don't need a whole lot of aluminum foil.  Within about 2
> minutes, the freshly exposed aluminum will pull the oxygen and sulfur away
> from the silver and you will be back close to the original finish.
>
> Rinse THOROUGHLY in DI water, then dry the board in an oven until it is
> completely baked out.
>
> Wayne Thayer
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Richard Kraszewski
> Sent: Tuesday, February 05, 2013 5:54 PM
> To: [log in to unmask]
> Subject: [TN] Silver Sulfide & Plasma
>
> Any of you ever have luck cleaning silver sulphide off of a PCB enough to
> make it solderable with NC flux, by using plasma?
>
> If so , can you please provide me with the gas mix you used?
>
> Thanks
>
> Rich  Kraszewski
> PLEXUS
>
>
> ______________________________________________________________________
> This email has been scanned by the Symantec Email Security.cloud service.
> For more information please contact helpdesk at x2960 or [log in to unmask]
>
> ______________________________________________________________________
> This email has been scanned by the Symantec Email Security.cloud service.
> For more information please contact helpdesk at x2960 or [log in to unmask]
> ______________________________________________________________________
>


______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
For more information please contact helpdesk at x2960 or [log in to unmask] 
______________________________________________________________________

ATOM RSS1 RSS2