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lead free soldering

R

R.Lewis

Jan 1, 1970
0
What do I need to change to lead free hand soldering pcb's (about 15 seats)?

Any advice gratefully received.
 
R

R.Lewis

Jan 1, 1970
0
Baphomet said:
I'm not sure why you would want to. Lead free will probably raise the
melting point and to compensate, you would either have to use lighter guage
or flatten it with a hammer before soldering. Since it doesn't sound like
you have much soldering to do, I wouldn't worry about it unless you are lead
allergic.
Click to expand...

For 15 seats read 15 people hand soldering components into pcb's (Yes we
also use flow soldering ).
We need to change from SnPb solders because of customer demand at this time,
and because by July 2006 we will have no choice.
..
 
B

Baphomet

Jan 1, 1970
0
R.Lewis said:
What do I need to change to lead free hand soldering pcb's (about 15 seats)?

Any advice gratefully received.
Click to expand...

I'm not sure why you would want to. Lead free will probably raise the
melting point and to compensate, you would either have to use lighter guage
or flatten it with a hammer before soldering. Since it doesn't sound like
you have much soldering to do, I wouldn't worry about it unless you are lead
allergic.
 
G

Glen Walpert

Jan 1, 1970
0
On Thu, 30 Oct 2003 19:13:19 -0000, "R.Lewis" <h.lewis-not this
What do I need to change to lead free hand soldering pcb's (about 15 seats)?

Any advice gratefully received.
Click to expand...

Almost all of what I have seen published on lead-free soldering has
been for automated soldering only (reflow and wave primarily).
Likewise, most of the new lead free alloys seem to be availible in
paste or bar only. It is not just the solder that is important but
also the flux, and most of the lead free fluxes for automated
soldering are synthetic rather than rosin based (no-clean or water
clean) and are not well suited to manual soldering.

My only suggestion would be to contact Kester and other solder
manufacturers for recommendations and give them a try. Sn/Ag,
Sn/Ag/Cu or Sn/Ag/Bi/Cu solders may prove most suitable based on what
is most commonly used in automated processes. Avoid anything with
Antimony.

I have manually soldered a few boards with Sn97/Ag3 rosin core solder,
and found that melting temp differences compared to tin lead are
insignificant, the grainy appearance looking a bit like a cold
tin-lead joint is easy to adjust to, and soldering clean parts &
boards with a freshly cleaned tip is as easy as with tin-lead. The
main problem is that the lead-free solders oxidise on the iron *much*
faster than tin-lead; while I might solder 20 or 30 leads between tip
cleanings with tin-lead I found myself cleaning the tip every 2 or 3
joints with lead-free. Furthermore the lead-free dissolves the iron
coating on soldering iron tips much faster than tin-lead, so you will
probably get significantly shortened tip life. I am hoping that as
lead-free becomes more common better fluxes and tip coatings will
alleviate these problems, but AFIK this has not happened yet. Spray
or other liquid fluxes pre-applied to the boards can help make the
soldering easier at the cost of more difficult cleaning.

BTW "no-clean" fluxes are NOT no-clean when used with manual
soldering; these fluxes depend on a precise heating profile to
completely deactivate them during soldering which cannot be insured
with any form of manual process; they can be used for manual soldering
but must be cleaned.

I would love to hear how you make out with your conversion.

Regards,
Glen
 
D

ddwyer

Jan 1, 1970
0
R.Lewis <h.lewis- said:
For 15 seats read 15 people hand soldering components into pcb's (Yes we
also use flow soldering ).
We need to change from SnPb solders because of customer demand at this time,
and because by July 2006 we will have no choice.
Click to expand...

A US defence contractor has informed suppliers that lead free
soldering will be unacceptable .
They are particularly concerned about the possibility of tin whiskers
forming. Any knowledge out there.
 
G

Glen Walpert

Jan 1, 1970
0
J

John Woodgate

Jan 1, 1970
0
I read in sci.electronics.design that Glen Walpert <[email protected]>
wrote (in said:
Both of these articles discuss tin whisker growth from now obsolete
matte tin plating, not from lead free solders which are of course
considerably different and most of which are not known to be subject
to tin whisker growth. They would seem to be completely irrevelant to
the subject of lead free soldering!
Click to expand...
For defence and automotive applications, the behaviour of the solders at
temperatures below about -20 C need to be investigated. At -23 C, pure
tin undergoes a phase-change, to an at best semi-metallic form. The
alloying elements no doubt affect this, possibly quite a lot, but one
needs to know!
 
B

Baphomet

Jan 1, 1970
0
Glen Walpert said:
Both of these articles discuss tin whisker growth from now obsolete
matte tin plating, not from lead free solders which are of course
considerably different and most of which are not known to be subject
to tin whisker growth. They would seem to be completely irrevelant to
the subject of lead free soldering!

Regards,
Glen
Click to expand...

Apparently not if the government defense industry is currently proposing
banning lead free soldering because of tin whiskers. I really don't know
first hand because I have been out of the military industrial complex since
about '77. Back then, lead free wasn't even a consideration in the mind's
eye of the most politically correct ideologue.
 
J

Jim Adney

Jan 1, 1970
0
Almost all of what I have seen published on lead-free soldering has
been for automated soldering only (reflow and wave primarily).
Likewise, most of the new lead free alloys seem to be availible in
paste or bar only.
Click to expand...

We're now using a lead free alloy from Kester in our lab where all the
soldering is by hand. It's in wire form on rolls that look just like
the stuff we're all used to for the past 70 years.

It seems to work well enough, but I remain skeptical....

-
 
G

Glen Walpert

Jan 1, 1970
0
Apparently not if the government defense industry is currently proposing
banning lead free soldering because of tin whiskers. I really don't know
first hand because I have been out of the military industrial complex since
about '77. Back then, lead free wasn't even a consideration in the mind's
eye of the most politically correct ideologue.
Click to expand...

Where did you hear about this supposed ban on lead-free solder? Any
reference for either the ban or evidence of tin whiskere from any
current lead-free solder? I for one have not seen either, and I read
all articles on lead-free in the major trade rags.

A ban due to evidence of tin-whiskers would be big news these days,
news I probably would have heard. Quite different would be waiting to
approve lead-free for reliability-critical applications until there
were enough years of trouble-free use in other applications, which is
rather more likely, entirely reasonable, and not in any way indicative
of known problems with lead-free.

Regards,
Glen
 
A

Aubrey McIntosh

Jan 1, 1970
0
I don't understand why you think the melting point would rise.
 
A

Aubrey McIntosh

Jan 1, 1970
0
A few years ago, there was a lot of information on the "Indium
Corporation of America" web site on lead free solders. These often
employ tin, indium, gallium(?) and bismuth. They also make "pre
forms" that have just the right amount of solder in just the right
places, in case you are making a lot of some board.

I have worked with Indium / Gallium / Bismuth at different times. The
Indium+Gallium eutectic is liquid at room temperature, and has an
appearance very similar to mercury. It has the suprising property
that it (appears to) dissolve aluminum, which ultimately deposits as a
soot-black powder on the surface. I speculate that this is finely
dispersed sapphire, but haven't run any analysis. Indium alloys also
"wet" glass.

I do have an alloy from the hobby shop that melts in warm water, but I
am pretty sure that it contains antimony, cadmium, or both. I thought
that it would be interesting on a project to electroplate an alloy
that will melt in boiling water, and then use steam on an open stove
to "wave solder" the board. I believe that there is a "green patent"
in that idea.

I am not aware of health concerns with Indium or Gallium. Bismuth is
very inert, and possibly the least toxic of the metals. This is
suprising with respect to its location in the periodic table, but I
believe that this is a soluability issue. It precipitates from
aqueous solutions that are more basic than about pH of 1.5 or 2 and is
probably cubic in hydroxide concentration, so there may be a 10^15
concentration differential from pH 2 to 7. One of the patents in the
last 5 years mention that several bismuth salts kill harmful bacteris
(e. choli I think) in seconds in simulated gastric juice, but are
essentially not harmful to them at neutral pH.

Copper is only sparingly soluble in bismuth. I would anticipate that
a solder intended for hand soldering would be compounded so that it is
saturated with copper, but that is pure speculation from me. I
haven't seen the phase diagrams for copper+indium or copper+gallium.

Bismuth does not tarnish quickly in air at office temperatures. Some
of my ingots are several years old, and still have a "shiny"
appearance. I don't have any tin side by side with the same storage
history, but my gut feeling is that bismuth tarnishes more slowly than
tin. However, in sulfur containing environments I expect bismuth to
form a black sulfide very quickly.

Bismuth has the property that it expands on freezing, so that the
crystals float on the melt. It is possible to compound alloys that
don't appreciably change volume on freezing. These materials are
useful for high detail metal castings.

Bismuth also "flows" pretty much as a liquid under high pressure (high
shear?). I made some pellets of different thickness in a 13mm IR
press (20 ton press) and the bismuth flows up the space between the
piston and cylinder. This is especially suprising because of its
brittleness at ambient conditions. It also takes excellent detail
from the surface, and I am going to try to press holograms into it
whenever I get around to making a master.

Pure indium is very malleable. A person can leave a thumb print in an
ingot of pure indium. I don't know the behavior under pressure, but
it seems worth investigating whether it would stand up to vibration,
or whether mechanical engineering practices could exploite its
softness to make self-healing joints.
 
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