Solder mixture - 60/40 67/37

[tkamiya]

Although I've been in electronics for over 40 years, I never gave much thought to solders.  Now I'm wondering about something I'm sure many of you know....

Common lead-tin solder comes in 60/40 and 63/37 mixture.  What is the difference between the two.  Sure, melting point is a bit different by 5 degrees, but that's not much to make two different products.  There got to be more to it.

I've been using them interchangeably.  Can anyone share the secret?

[sleemanj]

63/37 is eutectic, it melts and solidifies at a fairly precise temperature, in other words the transition from melted to solid happens much more quickly,  "melty...solid"  instead of 60/40 which is more "melty...a bit less melty... a little bit solid... getting pretty solid... ok we're done"

[Simon_RL]

63/37 is eutectic, it melts and solidifies at a fairly precise temperature, in other words the transition from melted to solid happens much more quickly,  "melty...solid"  instead of 60/40 which is more "melty...a bit less melty... a little bit solid... getting pretty solid... ok we're done"

So for noobs 60/40 is definitely the better option as it is more forgiving.

[Moshly]

63/37 is eutectic, it melts and solidifies at a fairly precise temperature, in other words the transition from melted to solid happens much more quickly,  "melty...solid"  instead of 60/40 which is more "melty...a bit less melty... a little bit solid... getting pretty solid... ok we're done"

So for noobs 60/40 is definitely the better option as it is more forgiving.

Technically no, 60/40 has a longer time in the plastic (melty) state as its cooling down so the joint has to remain still for longer as you will get a dry joint if moved. For hobbyist it does not matter as you normally hold the part and watch the solder solidify before continuing.

[tooki]

63/37 is eutectic, it melts and solidifies at a fairly precise temperature, in other words the transition from melted to solid happens much more quickly,  "melty...solid"  instead of 60/40 which is more "melty...a bit less melty... a little bit solid... getting pretty solid... ok we're done"

So for noobs 60/40 is definitely the better option as it is more forgiving.

No, the exact opposite: 60/40’s plastic phase is a wider window of time during which the joint can be disturbed. This makes it LESS forgiving of movement during cooling.

60/40 is used because it is/was slightly cheaper, which mattered for mass production. But nowadays they usually cost the same, and IMHO there is no reason whatsoever to choose it over 63/37.

[tooki]

IMHO, a modern hobbyist should have these three solders on hand, especially if they do repairs too:

1. 63/37 leaded, for most uses.
2. SAC305 lead-free, for when working on boards already made with lead-free.
3. 62/36/2 silver-bearing leaded, for when you don’t want lead-free, but are working on silver contacts, like the silvered contacts of old ceramic hybrids and many modern SMD components.

Under no circumstances should the lead-free be used on old boards originally made with leaded, since the boards may be damaged by the higher temperatures. Using leaded on originally lead-free boards doesn’t risk damage, but one should avoid blending the two kinds within one joint, since that results in a random alloy with unknown properties, meaning sucking off all the old solder before installing the new. (So IMHO it’s often just easier to stick with lead-free on such boards.)

[tkamiya]

Thanks everybody.  I'll stay with 63/37.