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Effect of ENEPIG Surface Finish on the Vibration Reliability of Solder Interconnects
Keywords: Lead Free Electronics, Solder Interconnects Reliability, ENEPIG
Surface finishes are used to protect exposed copper metallization in printed wiring boards preserving and promoting solderability during component assembly. Though typically the solder used in the assembly process dictates the reliability of the solder interconnect, the surface finish used on the board is known to influence the reliability of the solder interconnect as a result of the formation of intermetallics. The effect on solder interconnect reliability can be particularly strong under high strain rate loading condition. Among the numerous surface finishes available in the industry today, electroless nickel– electroless paladium-immersion gold (ENEPIG) is gaining popularity due to the elimination of the immersion gold process on nickel avoiding corrosion of nickel leading to black pad” a along with its electroless process which makes it conducive for increased miniaturization. In this study, the vibration durability of solder interconnects formed between BGAs and electroless nickel, electroless palladium, immersion gold (ENEPIG) finished pads assembled using SnPb and SAC305 solders is evaluated. Two thicknesses of palladium were examined. Test specimens were preconditioned at 100°C for 24 hrs and 500 hrs in order to evaluate the impact of isothermal aging on the durability of the soldered interconnects. For comparison, tests specimens created with immersion silver (ImAg) finished printed wiring boards were also included. The failure data obtained found the durability of interconnects formed with ENEPIG finish was comparable or better durability than the durability of interconnects formed with ImAg finish irrespective of the solder. The tests also indicate that the use of a thicker palladium layer reduced the degradation in durability which occurred from isothermal aging.
Sandeep Menon, Graduate Research Assistant
CALCE, University of Maryland
College Park, MD
USA


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