Yisrael Leshman asked:

>the IPC standard calls for 0.003% arsenic in a 63/37 solder.

Huh? I think you may be referring to _antimony_ formerly required per QQ-S-571.
On PWB's it should be Sn60, Sn62, or Sn63 per J-STD-006. Antimony was
formerly specified to prevent allotropic transformation of tin at very low
temperatures. This is a phenomenon first reported on arctic expeditions
where the pure tin coating on cans turned powdery and fell off, ruining the
cans. Admiral Byrd had lots of pull with the MIL-STD folks, and that meant
we got antimony added per MIL-STD here in the US (that part may be
mythology).

Some people believe antimony additions are still advisable, IMO, for
tin-lead solders in electronic applications, they actually retard wetting
and are of no real benefit (allotropic transformation of tin-lead alloys is
not known to be a problem).

I recommend you stay with eutectic tin-lead at the highest practical purity.

>does anyone knows if possible to get solder bars with  0.001% arsenic ?
>could you recomend a source ?

No, not in the free world. If you get any, check for terrorist suppliers.

Quoting Howard Manko:

"There seems to be no solid solubility of arsenic in either tin or lead.
Two intermetallic compounds, SnAs2 and SnAs, appear as long needles in the
microstructure...The amountof arsenic in the raw material should be closely
controlled, as it is detrimental to many soldering applications."

_Solders and Soldering_, 3rd ed. 1992 ISBN 0-07-039970-0


Shalom,

Jerry Cupples
Interphase Corporation
Dallas, TX USA
http://www.iphase.com

Jerry Cupples - [log in to unmask]
Interphase Corporation
13800 Senlac Dr.
Dallas TX 75234
(214) 654-5150
(214) 654-5500 FAX


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