Blech effect in Pb-free flip chip solder joint

The Blech effect in electromigration is studied in flip-chip-like Pb-free solder joint structures. The results from two different studies indicate that the Blech limit (J×L) c (current density times solder length) is close to 30 A/cm in Sn1.8 Ag solders, where the dominating degradation mechanism is Sn self-diffusion. For Sn0.7 Cu solders, where the failure is driven by interstitial diffusion, the Blech effect is not observed. When Blech product is approaching the Blech limit, a steady increase in resistance is replaced by a near-zero resistance change. This saturation in resistance shift significantly extends the electromigration lifetime in SnAg solders. © 2009 American Institute of Physics.