Solder mixture - 60/40  67/37 - Page 1
Forum section: electronics / beginners

author: tkamiya
author_rank: Super Contributor
timestamp: January 18, 2020, 11:30:41 pm
content: 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?

author: sleemanj
author_rank: Super Contributor
timestamp: January 18, 2020, 11:43:10 pm
content: 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"

author: Simon_RL
author_rank: Regular Contributor
timestamp: January 19, 2020, 02:52:43 am
content: Quote from: sleemanj on January 18, 2020, 11:43:10 pmSo for noobs 60/40 is definitely the better option as it is more forgiving.

author: Moshly
author_rank: Regular Contributor
timestamp: January 19, 2020, 07:20:29 am
content: Quote from: Simon_RL on January 19, 2020, 02:52:43 amTechnically 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.

author: tooki
author_rank: Super Contributor
timestamp: January 19, 2020, 02:47:14 pm
content: Quote from: Simon_RL on January 19, 2020, 02:52:43 amNo, 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.

author: tooki
author_rank: Super Contributor
timestamp: January 19, 2020, 02:55:27 pm
content: 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.)

author: tkamiya
author_rank: Super Contributor
timestamp: January 20, 2020, 11:22:57 pm
content: Thanks everybody. I'll stay with 63/37.