**3.4 Analysis of Cu-SnAg3.5Ti4(Ce,Ga) joint**

**Figures 20** and **21** show the interface of Cu-SnAg3.5Ti4(Ce,Ga) joint. A continuous layer of reaction elements is formed in the interface of solder and copper. Primary effect upon bond formation is exerted by Sn. Cu is dissolved in Sn matrix

**39**

**Figure 20.**

**Figure 18.**

**Figure 19.**

*Soldering by the Active Lead-Free Tin and Bismuth-Based Solders*

*Microstructure of interface of Al2O3-SnAg3.5Ti4(Ce,Ga) joint (SM).*

and forms the Cu3Sn and Cu6Sn5 phases which grow in the direction from the phase interface to solder matrix. Similarly to the case of soldering Al2O3, rapid dilution on the side of parent materials has not occurred. Sn matrix prevails in the solder, while

the darker zones are formed by binary alloys of Sn with Ti and/or Ag.

*Microstructure of interface of Cu-SnAg3.5Ti4(Ce,Ga) joint (a) (SEM) and (b) (SE).*

*Interface of Al2O3-SnAg3.5Ti4(Ce,Ga) joint (SEM) + concentration profiles of elements.*

*DOI: http://dx.doi.org/10.5772/intechopen.81169*

*Soldering by the Active Lead-Free Tin and Bismuth-Based Solders DOI: http://dx.doi.org/10.5772/intechopen.81169*

#### **Figure 18.**

*Lead Free Solders*

**Figure 17.**

crack formation in the bond plane.

**3.2 Analysis of Cu-BiIn25Sn18 joint**

**3.3 Analysis of Al2O3-SnAg3.5Ti4(Ce,Ga) joint**

**3.4 Analysis of Cu-SnAg3.5Ti4(Ce,Ga) joint**

was not observed (**Figure 19**).

Based on the performed SEM and EDX analyses, it can be supposed that In primarily contributes to bond formation by creating indium oxide—In2O3. Besides In, Bi also partially contributes to bond formation. The presence of Sn is indifferent, and it does not exert any effect on the bond formation. Its presence was revealed in the grey phase. The interface contains exclusively a pale matrix composed of Bi and In. The formed reaction products are brittle with poor toughness that caused the

*Interface of Cu-BiIn25Sn18 joint (SEM) + concentration profiles of elements.*

**Figure 17** shows the interface of BiIn25Sn18-Cu joint. In the interface of BiIn25Sn18 solder and copper, a noticeable increase in the proportion of the darker phase, formed mostly of Sn, may be seen. A continuous transition zone of reaction elements is formed in the solder interface. Based on the study of binary diagrams and performed analyses, formation of the following phases is supposed: Cu3Sn, Cu6Sn5 and Cu9In4. A thinner, non-wettable phase rich in Cu (Cu3Sn), which is followed with Cu6Sn5 phase, is formed in the joint interface. From the map of quantitative proportion of chemical elements, it is obvious that in the copper-solder interface mainly, the presence of In and Sn is exerted. However, Bi does not play any significant role in bond formation and does not create any phases with copper.

**Figure 18** shows the interface of Al2O3-SnAg3.5Ti4(Ce,Ga) joint. A continuous reaction layer containing Ti was observed in the interface of Al2O3-

SnAg3.5Ti4(Ce,Ga) joint. This reaction layer allows the wetting of ceramic material and the tin-silver matrix of solder guarantees the desired strength and sufficient plastic properties of soldered joint to compensate the strains and stresses formed during cooling down. Slightly increased concentration of cerium was also observed in the joint interface. The presence of gallium and/or its effect upon bond formation

**Figures 20** and **21** show the interface of Cu-SnAg3.5Ti4(Ce,Ga) joint. A continuous layer of reaction elements is formed in the interface of solder and copper. Primary effect upon bond formation is exerted by Sn. Cu is dissolved in Sn matrix

**38**

*Microstructure of interface of Al2O3-SnAg3.5Ti4(Ce,Ga) joint (SM).*

#### **Figure 19.**

*Interface of Al2O3-SnAg3.5Ti4(Ce,Ga) joint (SEM) + concentration profiles of elements.*

#### **Figure 20.**

*Microstructure of interface of Cu-SnAg3.5Ti4(Ce,Ga) joint (a) (SEM) and (b) (SE).*

and forms the Cu3Sn and Cu6Sn5 phases which grow in the direction from the phase interface to solder matrix. Similarly to the case of soldering Al2O3, rapid dilution on the side of parent materials has not occurred. Sn matrix prevails in the solder, while the darker zones are formed by binary alloys of Sn with Ti and/or Ag.

**Figure 21.** *Interface of Cu-SnAg3.5Ti4(Ce,Ga) joint (SEM) + concentration profiles of elements.*

It was found out that Ti does not contribute at all in bond formation and its effect upon bond formation was unobservable. Ag element did not exert any significant interaction with the parent material; however, its presence in the interface was observed. The Ce and Ga elements occurred in the boundary in such low amounts that they could not be identified at all.
