First, you want a eutetic solder, ie. a solder where the phase transition between liquid an solid state is practically immediate. For a non-eutetic solder this takes place over a temperature interval and thus takes some time to happen. During this transition phase the joint is very sensitive to vibrations which may cause a cold joint. The ordinary 63SN/37Pb solder is eutetic with an almost immediate transition at 183 deg. C, while the 60Sn/40Pb is not eutetic, having a phase transition starting already at 190 deg C and ending at 183 deg C. There are also some lead free solders that are eutetic. Here is a table of temperatures for some alloys, although most of these seem not intended for electronics:
http://www.lucasmilhaupt.com/htmdocs/brazing_products/brazing_filler_metals/solders.html
One example of a lead free eutetic alloy for electronics with a reasonably low melting temperature is 96.5Sn/3.8Ag/0.7Cu which melts at 217 deg C.
http://www.lucasmilhaupt.com/htmdocs/brazing_products/brazing_filler_metals/solders.html
One example of a lead free eutetic alloy for electronics with a reasonably low melting temperature is 96.5Sn/3.8Ag/0.7Cu which melts at 217 deg C.
... an addiction to die for...Christer said:
All correct (says me with a degree in metallurgy) but the 60%Tin 40% Lead mix isn't too bad for electronics, it's the 60% Lead 40% Tin alloy that should never be used. That has a very wide "mud" range, it's made for plumbing where a joint between two lead pipes (or lead pipe to copper) can be wiped to a neat shape while still a liquid + solid sludge. A near-forgotten art.
Apart from that, the multicore version contains an aggressive flux not suitable for electronics.
john curl said:
Okay... been there done that Rather than "leaving the proof as an exercise for the reader/student"...
Why not tell (or point) us mere mortals to info about eutectic vs non-eutectic alloys, the ability to quickly and thoroughly "wet" the joint... the more efficient utilization of flux, less "cold joint" problems...etc.
For example:
http://www.logwell.com/tech/servtips/solder.html
lets try for exchange of ideas...as opposed to the "not suffer fools" syndrome of the apparently almighty..
auplater
Geeze! ... I reversed the Sn & Pb in my post... dumb****!
1) 63/37 flows better... and because it flows better, it is easier to know that you have made a good wetted joint.
2) If you are working with low-leakage/high-voltage circuitry, you may be working with water-based flux for easy flux removal. You may do this for environmental reasons as well. These fluxes are not as aggressive or as penetrating as rosin type fluxes; the enhanced solder flow assists the dispersion of flux... particularly in through-hole soldering and gives better wetting on the back side of a joint.
60/40's stronghold is in craftwork, stained-glass work etc... This is where to want solder to "hang" where you put it and stay there.
1) 63/37 flows better... and because it flows better, it is easier to know that you have made a good wetted joint.
2) If you are working with low-leakage/high-voltage circuitry, you may be working with water-based flux for easy flux removal. You may do this for environmental reasons as well. These fluxes are not as aggressive or as penetrating as rosin type fluxes; the enhanced solder flow assists the dispersion of flux... particularly in through-hole soldering and gives better wetting on the back side of a joint.
60/40's stronghold is in craftwork, stained-glass work etc... This is where to want solder to "hang" where you put it and stay there.
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