Soldering Iron Temperature for Lead Free Solder (Sn99.3%, Cu0.7%)

Thread Starter

toby159

Joined Apr 29, 2020
4
IMG_20210619_185656.jpg
Recently I bought this lead free solder (Sn99.3%, Cu0.7%), D0.6mm.
I have seen many suggest at least 350°C for soldering iron.

IMG_20210619_185730.jpg
But I tried at around 225°C (between 200°C - 250°C), the solder still melt well.

All shiny surface IMG_20210619_185622.jpg
(All shinny surface) (Some dull some shinny)
Funny thing is, the lead free solder surface should be dull as everyone is saying. For my trial, it gets shinny surface and of course dull surface also. And the solder flow I feel quite ok actually.

Should I depend on lead free solder diameter size to determine temperature of soldering iron?
Or should I follow 350°C as the solder surface sometimes shinny and sometimes dull?
 

Ian0

Joined Aug 7, 2020
2,579
I’m told by my solder supplier that the soldering iron is best operated at 120°C above the melting point of the solder.
I‘m also told that Sn 0.7% Cu doesn’t have enough copper in the alloy to prevent Tin-pest.
 

Thread Starter

toby159

Joined Apr 29, 2020
4
I find that question very hard to answer because I constantly adjust the heat of my iron depending on the work I'm doing.
Will the diameter of solder wire matter? Like smaller diameter requires lower temperature and for bigger diameter requires higher temperature.
 

Ian0

Joined Aug 7, 2020
2,579
You might need more heat on a small iron if you are soldering to a large copper area, but I have also never needed to adjust for diameter of solder. Might need more flux on larger diameter solder.
 

crutschow

Joined Mar 14, 2008
27,392
Why are you using lead-free solder, which requires a higher temperature and is more difficult to use?
There's no known danger that you can get any significant lead ingestion by using leaded solder.
 

Ian0

Joined Aug 7, 2020
2,579
Why are you using lead-free solder, which requires a higher temperature and is more difficult to use?
There's no known danger that you can get any significant lead ingestion by using leaded solder.
That's a very good point. Why would anyone use lead-free solder if the weren't forced to?
And, having chosen to use it, why use the worst type. (TSC alloy is almost passable)
Any why use an alloy that might be prone to Tin-pest?
 

DickCappels

Joined Aug 21, 2008
7,533
I tried lead free solder a few years ago. It was difficult to get satisfactory joints, and finally I realized that my circuits had an insignificant amount of lead in them compared to the world wide production. A lot of pain for nothing! I am back to leaded solder. It stays in my house and is not subject to EU requirements.
 

Ian0

Joined Aug 7, 2020
2,579
You're the lucky one! the RoHS regulations are entirely dubious.
When we make an off-grid power system, we are not allowed a single milligram of lead on the control boards, but by the time the product is shipped out with its batteries, it contains 1.6 tonnes of lead.

Have you ever made up an XLR lead?
No leaded solder allowed to solder to those XLR pins, which are made of easy-machining brass.
Composition according to Neutrik's datasheets:
Contacts: Brass (CuZn39Pb3)
Yes, that's 3% lead, and you may not use more than 0.1% lead to solder to it!
 
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