Comparative electromigration performance of Pb Free flip chip joints with varying board surface condition

For the past several years, the semiconductor industry has been responding to the RoHS directive to eliminate certain hazardous substances from electronic components. One of the areas where work is still ongoing to comply is in the area of flip chip interconnects. Currently, leaded flip chip interconnects are allowed under an exemption in the RoHS directive due to a perceived lack of a technically viable solution. Recently, a number of Pb-Free flip chip interconnects have been introduced to the industry and have been in high volume production for a few years. Electromigration is an area which has received quite a bit of attention over the years. There is a large body of data in the area of High-Pb and Sn/Pb eutectic flip chip interconnect systems, but there is still a relatively small database with regard to Pb-Free flip chip interconnects. This paper addresses relative electromigration performance on different base surface finishes of organic laminates, which is one of the key aspects where additional knowledge is needed to understand the proper implementation direction for Pb-Free flip chip interconnects. The impact of ENIG, ENEPIG, and bare Cu on Sn/Ag bump electromigration including FA results is presented.