Interfacial Reaction Between Electroless NiPdAu Surface Finish And SnAgCu Solder And BGA Solder Joint Reliability

The rapid growing demand for handheld electronic devices pushes technologyto produce smaller, faster, and more functional devices. The high packagingdensity together with complexity of use condition had made solder jointreliability increasingly vital in the performance of IC packages. Meanwhile,the lead free transition had aroused new challenges in substrate surface finishtechnology. Surface finish must be not only compatible with the lead-freesolder bust also form robust bonds with lead-free solder. The interfacialreactions between lead-free solder and substrate surface finish are the keyelements which affect the solder joint reliability. Recently, the electrolessnickel, electroless palladium, and immersion gold (ENEPIG) is introduced asa promising candidate for the IC package substrate surface finish. However, itis necessary to verify the solder joint reliability between ENEPIG and leadfree solder alloy in use. In this paper, cold ball pull test and board level drop test are applied to evaluate the reliability of bond between SnAgCu solder andENEPIG surface finish. Multiple reflows and aging were subjected to BGAchips and interfacial reactions were investigated. It is proved that theperformance of ENEPIG surface finish is sensitive with different solder alloys.The three types of ENEPIG with different processing technics show differentperformance in both high speed cold ball pull and board level drop test. Thusthe electroless plating process should be strictly controlled to reach a goodbond. It can be concluded that the ENEPIG will form a bond with satisfyingsolder joint reliability as long as proper solder is chosen and strict control ofprocess. The interfacial reaction between ENEPIG and lead free solder afteraging and multiple reflows in investigated. The intermetallic compound layerson ENEPIG were found to be thinner than that of OSP and NiAu. It can beassumed that the diffusion rate is effectively inhibited. In a word, ENEPIGsurface finish exhibits fine solder joint reliability with lead free solder.Considering its cost advantage and better performance over conventionalsurface finish technology, ENEPIG is sure to be a promising surface finishtechnology with wide applications.