Journal of SMT Article


Author: Kiyoshi Hasegawa
Company: Hitachi Chemical Co.
Date Published: 1/1/2001   Volume: 14-1

Abstract: The use of PBGA (plastic ball grid array) is increasing with the spread of semiconductor package mounted on high-density printed circuit board. The solder joint reliability of PBGA has unresolved problems when compared with TSOP (thin small outline package) and QFP (quad flat package). The solder joint reliability under dropping impact of PBGA used in PDA (personal device apparatus) is under discussion nowadays. Though the relationship between solder joint reliability and surface finishes has been reported by many companies, there is no clear and noticeable trend.

Therefore, we developed a high-speed shear test that simulates the drop-impact conditions. We also developed an electroless Ni-P/Pd/Au plating of good reliability for solder joint. Solder joint reliability is evaluated by the ball shear test. The shear strength and the fracture mode are influenced by shear speed. When low-speed shear test was conducted, the effect of surface finish on the solder joint reliability was not apparent. But, when the high-speed shear test was used, the solder joint reliability to different surface finishes became clear. The high-speed shear test revealed that immersion Au lowered solder joint reliability during the electroless Ni-P/Au plating process. The cross-section of the electroless Ni-P/ immersion Au layers was observed by FIB/SIM (focused ion beam/scanning ion-beam microscopy). From FIB/SIM observation, we found that the corrosion on the surface of the electroless Ni-P with immersion Au had reduced the solder joint reliability. Some different methods to prevent the corrosion on the surface of the electroless Ni-P were studied and we found out that electroless Pd plating over electroless Ni-P was very effective. To conclude, the solder joint reliability of PBGA with electroless Ni-P/Pd/Au is equal to that of OSP (Organic Solder Preservation) and electrolytic Ni/Au.

Keyword: CSP, BGA, solder ball joint, shear speed, electroless Ni-P/Pd/Au.

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