Dear Camille,

your question is interesting, let me try and comment on the base of the
limited experience that has been collected to far.

If comparing a solder alloy, it should be mentioned what are the others it
is compared with?

When your source says "lower temperature", or "less dross", then it would be
nice to know what to compare with, otherwise there may be improper
preconsumptions.

Temperature:
SN100C (SnCu0.7Ni0.05, Tm ca. 227degC) has a higher melting temperature then
let's say SAC (SnAg3.8Cu0.7, Tm ca. 217degC), but a lower melting
temperature than PbSn8 (Tm ca. 300deg C). It would be bold to suggest that
in wave soldering, SN100C can be used at lower temperature than SAC. The
minimum wave solder temperature is 245degC for SAC, and 255deg C for SN100C;
a few degrees less, and your PCB plays titanic with solder ice bergs. Add
five to ten degrees, to be on the safe side for hole fill - but then you
lose warranty on immersed active devices, which are qualified for wave
soldering temperatures at the most at 260degC (+5, but that is needed for
temperature control in the wave solder pot) , see JEDEC standard JESD22A111
from May 2004. So take a critical look at vertical fill, use heat traps
("heat relief" design) for top side and inner copper layer connections, as
suggested in IPC-2221 design guidelines. And if you solder SMD on the wave
side, make sure they are qualified to withstand your soldering heat.

Dross:
With many companies converting to lead-free soldering, it has turned out
that in wave soldering there is a need for nitrogen atmosphere at least
enclosing the solder pot. Certainly, by this move, the amount of dross is
reduced significantly. But it is the change to nitrogen, which leads to the
dross reduction, not the move towards lead-free solder alloy.

Less bridging:
From a series of wave soldered testboards under investigation with AOI, we
have no indication that either lead-free alloy shows less bridging than the
usual tin-lead.

Copper leaching (dissolution, eating away the copper):
There is an effect of phase formation between Cu, Sn and Ni with definitely
reduces leaching on copper surfaces by applcation of SN100C. Instead, a
thicker intermetallic phase layer is formed, which however does not seem to
affect solder joint strength. We are currently waiting for thermal fatigue
results on the different lead free alloys to see which effect turns out.

Machine Corrosion:
With all lead-free alloys there is a stronger corrosion of even high alloyed
stainless steel in comparison with tin-lead alloy. SN100C seems to perform
somewhat better here, but field experience is only 3-4 years by now.
Recently I heard at a technology meeting that first corrosion effects also
appeared with SN100C. So by all means, have your solder pot and as many
movable parts as possible protected by a ceramic/enamel layer or equivalent.

Schön' Gruß

Thomas Ahrens, Boostedt

----- Original Message -----
From: "Camille Good" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Thursday, June 02, 2005 10:23 PM
Subject: [LF] Sn100C revisited?


> Dear Colleagues:
>
> I recently saw some literature about using Sn100C for
> wave solder operations, from a company that sells
> Sn100C.  There seemed to be a lot of pluses (lower
> temperature, less dross, less bridging, doesn't eat as
> much copper off the PCBs), but I didn't see any
> drawbacks mentioned??
>
> I looked through the lead-free archives of the last
> year or two for discussion of Sn100C.  The biggest
> concerns seemed to be tin pest (where the discussion
> was that Nihon has been running some long-term tests
> and hasn't seen any problems), use of Sn100C for an
> HAL finish, and one company that couldn't use Sn100C
> because it contained nickel.
>
> Has anyone on the list had any negative experiences
> with Sn100C?  Are there any particular problems a
> manufacturer should be watchful for if they use Sn100C
> for wave solder?
>
> Many thanks in advance,
> Camille Good
> Portland, Oregon
>
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