**6. SEM fractography**

SEM micrographs are generally used to give information about the type of fracture. Here, since tensile tests have not been done, SEM has been used to identify Sn whiskers. There have been some studies showing Sn whiskers in the SEM micrographs of SnCu alloys.

The abovementioned SEM micrographs are of two samples of slightly varying chemical composition. **Figures 18** and **19** show the absence of tin whiskers in both

**Figure 18.** *Sample 1.*

**Figure 19.** *Sample 2.*

the alloys. The presence of tin whiskers results in deterioration of electrical properties. Chuang and Lin [24] showed that 0.5% Zn addition into SnAgCu solder refined the microstructure and suppressed whisker growth.

Sn**▬**Zn alloys have been used as a substitute for Pb**▬**Sn alloys. However, Sn**▬**Zn alloys are susceptible to oxidation and ZnO forms easily (**Figures 20** and **21**) [25–27].

SEM micrographs are for two different compositions of Sn**▬**Zn**▬**La leadfree solders (composition as mentioned in the Hardness **Tables 4** and **5**). Some

**Figure 20.** *SEM micrographs of Sn▬Zn▬La alloys.*

**21**

*Role of Intermetallics in Lead-Free Alloys DOI: http://dx.doi.org/10.5772/intechopen.85515*

precipitates are seen, which may have an effect on the hardness and tensile strength of the solders. However, in this case, it was found that hardness for both alloys is around 18 HV. Hence, the effect of precipitates seems to be marginal for this leadfree alloy. These SEM micrographs have been taken from unpublished work done by

There is not much difference between the EDAX of the two samples. There do not seem to be intermetallics present in this alloy. Hardness values also corroborate

This chapter starts with the importance of intermetallic systems in lead-free solders. The effect of some rare earths like lanthanum and indium on intermetallic formation in lead-free alloys has been explained. Tin-zinc-lanthanum and tin-zincaluminium-indium have been chosen for detailed analysis. Microhardness surveys have been done along two perpendicular diagonals of a square-shaped specimen, and the results of the microhardness surveys have been analysed. Microstructures in both these systems have been discussed with respect to the phases present and their distribution. Based upon both the microhardness and microstructure of the two alloys chosen, the presence of intermetallics and the types of intermetallics has been discussed. Growth kinetics of intermetallics has been briefly analysed. SEM fractographs have been taken to show the type of fracture. EDAX has been employed to

the author as part of undergraduate project work.

*EDAX of Sn▬Zn▬La of slightly different composition.*

EDAX Studies of two samples (**Figures 22** and **23**).

EDAX Studies.

this statement.

**Figure 22.**

**Figure 23.**

*EDAX of Sn▬Zn▬La sample.*

**7. Conclusion**

show the distribution of phases.

**Figure 21.** *SEM micrographs of Sn▬Zn▬La alloys.*

**Figure 22.** *EDAX of Sn▬Zn▬La sample.*

#### **Figure 23.**

*Lead Free Solders*

[25–27].

**Figure 19.** *Sample 2.*

**Figure 20.**

*SEM micrographs of Sn▬Zn▬La alloys.*

*SEM micrographs of Sn▬Zn▬La alloys.*

the alloys. The presence of tin whiskers results in deterioration of electrical properties. Chuang and Lin [24] showed that 0.5% Zn addition into SnAgCu solder refined

Sn**▬**Zn alloys have been used as a substitute for Pb**▬**Sn alloys. However, Sn**▬**Zn

alloys are susceptible to oxidation and ZnO forms easily (**Figures 20** and **21**)

SEM micrographs are for two different compositions of Sn**▬**Zn**▬**La leadfree solders (composition as mentioned in the Hardness **Tables 4** and **5**). Some

the microstructure and suppressed whisker growth.

**20**

**Figure 21.**

*EDAX of Sn▬Zn▬La of slightly different composition.*

precipitates are seen, which may have an effect on the hardness and tensile strength of the solders. However, in this case, it was found that hardness for both alloys is around 18 HV. Hence, the effect of precipitates seems to be marginal for this leadfree alloy. These SEM micrographs have been taken from unpublished work done by the author as part of undergraduate project work.

EDAX Studies.

EDAX Studies of two samples (**Figures 22** and **23**).

There is not much difference between the EDAX of the two samples. There do not seem to be intermetallics present in this alloy. Hardness values also corroborate this statement.
