Letter 12089

Difference between SnPb 90/10 and SnPb 60/40 

I'm working for the connector industry and someone was asking the difference between plated SnPb 90/10 and SnPb 60/40 soldertails.

Is there a difference in melting point, solderability, application or whatever? Can someone help me?

Thanks in advance.

Frank van Meijl
- Hertogenbosch, The Netherlands

60/40 solder is what is known as eutectic composition. Although it is an alloy of two metals, it solidifies at one temperature as though it was one metal (strictly speaking, the eutectic is at 61.9 percent Sn, but 60 percent is the usual industry standard). Solidification temperature is 183 degrees C.

90/10 is well away from the eutectic. It begins to solidify at 300 degrees C, and the first metal to solidify has composition 97Sn 3Pb. Solidification then is progressive as the temperature is allowed to fall, with the last bit of metal to solidify being 65Sn 35Pb at 250 degrees C.

60/40 is the usual electrical solder. Can't help you with application for 90/10.

Bill Reynolds
- Melbourne, Victoria, Australia

I don't know about the solderability, but the melting poing of the 90/10 alloy will be higher than 60/40. The eutectic point for tin/lead is 63/37.

James Totter, CEF - Tallahassee, FL

Both are industry standards and the terminology simply means that there is 60% by weight tin & 40% by weight lead in 60/40. As said above, 60/40 will solder - melt, as in when soldering - at a lower temperature than 90/10. This may be important in assemblies where higher temperatures will damage some components and will also have energy saving implications. The 90/10 alloy is often called out to get that little bit of lead in the deposit. The lead is believed to halt or slow the formation of tin whiskers.

Megan Pellenz
- Syracuse, NY

90/10 is used in some electronics for its higher melting temperature than eutectic solder. Using 90/10 inside a component will allow the component to then be soldered into its next higher assembly (such as onto a PWB) without the worry of solder joints inside the component reflowing and creating a defect. Sometimes the reflowing of solder inside a component may be a worry, other times it is not.

Dave Laidig
- Chandler, AZ, USA

Thanks Dave. Couldn't think of why anyone would deliberately make a soldering job more difficult by using 90/10 instead of 60/40, but your explanation makes one smack one's forehead and mutter about things that should have been obvious!

Bill Reynolds
- Melbourne, Victoria, Australia

Thanks a lot guys for your response on my question. It helped me to understand the difference between 90/10 and 60/40 solder alloy.

Best regards,

Frank van Meijl
- The Netherlands

90/10 Sn/Pb solder balls are typically used in high-speed applications such as BGA packages, pc-board type stuff. I don't know if that aspect has come out already, but I hoped it might be helpful.

Have a great day.

Ralph Raiola
Electronic Products magazine - Garden City, NY, USA

can i simply replace an 80/20 finish with a 90/10 finish. my concern is that the 80/20 finish is too soft and tend to be scraped during trim and form. since 90/10 is a bi harder, it might be able to address the scraping issue.

manny ramos
- Philippines

The basic difference you face in 60/40 and 90/10 is the composition of Sn and Pb by weight. The lowest melting point in the eutectic is reached at a composition of 63/37. Addition of Sn increases the hardness of the alloy and so as the melting point.

I have read a paper stating the preference of 90/10 over 60/40 is the formation of dentrite during aging. When maintained at high humidity conditions or with some potential difference the dentrite formation (needle like growth) is more prevalent in 90/10 then 60/40. These dentrites can grown to extent of short circuiting and causing failure.

60-40 has the advantages of melting at lower temperature so in reflow soldering (SMT Components) the whole board along with the components is brought to the melting point of the solder. Some manufacturer prefer that the temperature not be raised above 200 ' c,in this case 60/40 is preferable while manufactures who doesn't mind about high temperatures prefer 90/10 who's melting point is 220-225 'c. If your requirements can match these criteria you can change from 60-40 to 90-10 or 80-20. Those who don't want to go to 90/10 range but prefer a low temp soldering stick with 80/20.

Good luck...

Karthik
- Singapore

I see in the letter above where the 90/10 SN/PB melting range is higher than the 60/40 but can anyone give me the melting range of 80/20?

Regina J Huff
Electronics - St. Petersburg, Florida, USA

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