Electrochemical Migration Study on Sn-58Bi Lead-Free Solder Alloy Under Dust Contamination

Area of Science:

• Materials Science
• Electrochemistry
• Reliability Engineering

Background:

• Electronic packaging miniaturization increases susceptibility to electrochemical migration (ECM) due to high-density electric fields, moisture, and contaminants.
• Air pollution introduces dust, a significant factor in ECM, containing soluble salts like NaCl and Na2SO4.
• Understanding ECM failure mechanisms in solder joints under dust-induced contamination is crucial for reliable electronic devices.

Purpose of the Study:

• To investigate the electrochemical migration failure mechanism of Sn-58Bi solder joints exposed to NaCl and Na2SO4 solutions, simulating soluble salts in dust.
• To compare the ECM resistance of Sn-58Bi solder in NaCl versus Na2SO4 solutions.
• To analyze the composition of dendrites formed during ECM and evaluate the solder's corrosion resistance.

Main Methods:

• Utilized a water-droplet experimental method to analyze ECM failure in Sn-58Bi solder joints.
• Simulated soluble salt contaminants using 0.2 mM/L NaCl and Na2SO4 solutions.
• Employed X-ray Photoelectron Spectroscopy (XPS) to analyze dendrite composition and polarization tests to determine corrosion potential.

Main Results:

• Sn-58Bi solder exhibited a longer mean failure time in NaCl (53 s) compared to Na2SO4 (32 s).
• XPS analysis identified dendrites composed mainly of Sn, SnO, and SnO2, with Sn(OH)2 and Na2SO4 precipitates.
• Polarization tests showed a higher corrosion potential in NaCl (-0.351 V) than in Na2SO4 (-0.360 V), indicating better corrosion resistance in NaCl.

Conclusions:

• Sn-58Bi solder demonstrates superior resistance to electrochemical migration in NaCl solutions compared to Na2SO4 solutions.
• The difference in anodic dissolution characteristics between NaCl and Na2SO4 significantly impacts ECM failure times.
• Soluble salts in dust pose a considerable risk to the reliability of electronic packaging, with varying impacts depending on the salt composition.