Introduction to lead-free Carbon Solder alloy

A view from the technological perspective of Carbon Solder

With the use of a scanning probe microscope with energy analyzing functions, we discovered that adding carbon to the lead-free solder inhibits the crystalline growth of Ag3Sn that precipitate inside the crystals. As the result, it is seen as an improvement in the pulling strength and hardness of the solder.

1. Results from the observation of solder structure

1. Results from the observation of solder structure

The images above display the structure of the alloy before and after adding carbon. The results of the EDX shows that the most of the objects precipitated on any alloys are βSn while the other one is Ag3SN, an intermetallic compound of Sn and Ag. We discovered that adding carbon to the alloy miniaturizes the particle size of Ag3Sn.

はんだ組織観察の結果

Distribution of Ag3Sn grains in the Sn-3.5Ag with (a) and without (b) carbon solders

The size and distribution of the Ag3Sn grains statistically obtained from the SEM results are shown on the graph above. The solder added with carbon are more neatly distributed as its Ag3SN grains became smaller. The average size of the Ag3Sn was approximately 16μm prior to the addition of carbon to the solder. However, when carbon was added to the solder, the average size of the Ag3Sn grain shrank to 6μm.

2. Carbon analysis results via EDX

Carbon analysis results via EDX

Distribution of carbon at Ag3Sn grains

The carbon is present in Ag3Sn and is widely distributed among the solder matrix.

3. Clear results from Carbon Solder via fracture cross section photos

We achieved a success in adding carbon to other non-iron metals (solder, etc.) that was impossible before. In cases of adding carbon to solder, it was discovered the grains (crystals) shrink and improvements have been made to the strength, hardness and elasticity of the solder by adding carbon to it.


Clear results from Carbon Solder via fracture cross section photos


If you look at the fracture cross section of the solder on the electron microscope images above, you can confirm that the appearance of the fracture cross section of the Carbon Solder smoothly stretches like a candy.