Which Solder Paste Melting Point You Use? (Poll)

[Mechatrommer]

i saw variants in solder paste's temperature, this is new to me... but i tend to go with the lowest temp as its easy to reflow, doesnt burn plastic components too hard in oven such as relays etc. but drawback is the product cannot work in higher temperature than 138°C. so whats your regular use? or you think the commonly used? i dont know what temperature my leaded solder wire is? any thought the common one? higher temp solder wire is not big issue to plastic as we use solder iron on the components leads only, will not touch nearby plastic. but this solder paste can be an issue if i try to use higher temperature one, no? cheers.

[JustMeHere]

If I'm doing hot air with a blower, at least 250.  Hotter is better because you end up spending less time in the work area.

[Bucataru]

[Benta]

You solder temparatures are way off base, or you're using something unknown (to me, at least).

[KrudyZ]

138 is Sn42Bi58
158 is an SnAg alloy
183 is Sn63Pb37
217 is SAC305

All of these are the low end of where they start to melt, so you need to be above that in practice.
The ones with lower temps than the tin lead eutectic are both expensive and harder to get, so you would not see them in production unless absolutely needed.
However, they could be a good choice for small volume if you need to be lead free and don't have good temperature control in your (toaster ) oven.

[Mechatrommer]

You solder temparatures are way off base, or you're using something unknown (to me, at least).

what do you mean? i dont understand. those temperatures i got from whats available in market such as see attached...

[ArdWar]

Yes there are a whole bunch of different solder alloys for different applications, with widely different melting points too.

As you can see in your listing screenshot, most of the low melt variants contain bismuth. It is okay to use on its own, albeit a bit more brittle. I also use them albeit only sparingly to "poison" hard to melt solder joint for easier rework.

The tricky part is to make sure bismuth containing solder to NEVER get contaminated with the usual SnPb solder, or the other way around, never contaminate SnPb solder with bismuth containing one. At least if you intend your joint to last. A SnPbBi alloy can easily get their melting point down to ~90C. Surely something you'd like NOT to happen to your board right?

Heck, that 138C SnBi alloy probably isn't something you normally want for long term too.

[tooki]

Mechatrommer, consider editing the title to something containing the phrase “melting point” since it’s clearly already caused confusion to some as to whether you mean what reflow temperature you use.

The melting points are the same for paste and wire solder, of course; the alloy alone determines this. So standard 63/37 leaded is 183C, 60/40 leaded 183-188C (since it doesn’t melt at a single temperature, since it’s not eutectic).

You should also add 227C to the poll, since that is the temperature of most of the newer lead-free alloys.

[Mechatrommer]

Mechatrommer, consider editing the title to something containing the phrase “melting point” since it’s clearly already caused confusion to some as to whether you mean what reflow temperature you use.

thanks, already edited, sorry for my broken english..

You should also add 227C to the poll, since that is the temperature of most of the newer lead-free alloys.

sorry i cannot add poll element anymore, max is 5 elements. so consider it as "others"

btw thanks guys for highlighting it, my focus now on bismuth element the cause of low melting point, maybe selecting PbSn alloy without Bi (bismuth) is wiser for long term use.. but i will need to experiment if higher oven temperature setting will cause issue to plastics components on pcb. fyi i already bought 2 type solder paste, 138°C and 183°C. visibly, the 183°C variant reflowed quite nicely without "orphan blobs" on pcb (i only dab the paste on pcb with flat surface thing just for reflow experiment). cheers.

[tooki]

Just be sure to never mix the bismuth and lead solders, as ArdWar said: when combined the melting point falls, and can go as low as 90C!!