Fig.1 shows the corrosion morphologies of Cu-90(Sn-58Bi) and Cu-70(Sn-58Bi) in detail. At the joint of Cu-90(Sn-58Bi), Sn inside the joint reacted with the salt spray to transform into Sn3O(OH)2Cl2, and the Bi between the Sn phases failed to maintain the joint. In case of the corrosion morphology of Cu-70(Sn-58Bi), Sn3O(OH)2Cl2and CuCI were coexisted as corrosion products after the salt spray test. The corrosion part was hardly generated due to the high corrosion potential of Cu3Sn compared to Sn. Thus, the cross-sectional micrographs were maintained almost similar to those in the as-bonded state. Only when the salt spray test time increased, local corrosion products(CuCl and Sn3O(OH)2Cl2) were slightly observed inside the joint .
Fig.1. Corrosion morphologies of the Cu-90(Sn-58Bi) and Cu-70(Sn-58Bi) TLPS joint.
As shown in Fig.2, at Cu-50(Sn-58Bi), the joint comprised residual Cu particles, CusSn, and Bi phase. The Cu-50(Sn-58Bi) composition was almost similar to that of Cu-70(Sn-58Bi). However, the corrosion behavior of Cu-50(Sn-58Bi) was higher than that of Cu-70(Sn-58Bi) because the probability of the salt spray penetration inside the joint through the largely formed voids was greater than that in Cu-70(Sn-58Bi).Thus, CuCI and Sn3O(OH)2Cl2 were observed at the cross-sectional micrograph .
Fig.2.Cross-sectional micrographs of the TLPS joints after the salt spray test.
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