Indium Blog

Alternate Lead-Free Tabbing Alloys for Solar Module Assembly

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  • Today I received an interesting email that could be useful for my readers. Here goes:


    “Dear Jim,


    I saw your recent blog. I am in the process of prototyping a photovoltaic application. I am aware that Indium Corporation has a lead-free alternative for tabbing and bus wire. Can you comment on why the photovoltaic industry, specifically in the US, has not adopted this standard as a better non-toxic solution and what Indium Corporation has done to promote this alternative? I look forward to hearing your point of view!


    Best Regards,”


    That’s definitely an important question, what an ice breaker! This was my response:


    “First of all, thank you for reading the blog and thank you for the thoughtful question.


    What many people do not realize, is that there are actually a few different types of lead-free alternatives for cell tabbing. The 3 most common alloys for tabbing ribbon are :

    • 96.5Sn/3.5Ag
    • 57Bi/42Sn/1Ag
    • 58Bi/42Sn
    In addition, some customers are using indium-based alloys for specialty modules. I’d say that most of our customers operate under the principle of “if it isn’t broke, don’t fix it”. Sn/Pb based alloys have not been completely restricted yet, so many customers feel they have time to delay their company’s research of alternative lead-free alloys until they are forced to react. This was exactly what we witnessed in the SMT industry.


    Here are the main reasons that people stick with Sn/Pb based tabbing ribbon coatings:


    • Sn/Pb and Sn/Pb/Ag have been extensively proven with many different module designs  
    • Indium (the metal) based alloys are quite expensive compared to Sn/Pb based alloys
    • Sn/Ag melts at a higher temperature range, causing greater expansion of the base copper (and therefore greater coefficient of thermal expansion mismatches).
    • Some people fear the melting point of Bi/Sn and Bi/Sn/Ag may be too low for their subsequent processes (such as lamination)


    The key point I’d like to note is that there are companies currently using each one of these alternative, and finding them feasible in regards to cost and reliability. We promote the use of these alloys - I would personally like to see the 57Bi/42Sn/1Ag alloy take over the market. I like to see my customers making good modules and feeling good about the materials they use too!


    All the best,



    Later on in the day we discussed the technical aspects of using lead-free alloys and settled on Bi/Sn/Ag and GS-5454 as the go-to materials. It was great to have this conversation with someone focused on conscious material selection and eager to learn more about lead-free options.

    What are your thoughts?


    Authored by previous Indium Application Manager Jim Hisert