Electrolytic and electroless Ni/Au are common pad surface finishes on area array (BGA or CSP) packages and printed wiring boards (PWB). The electroless nickel/immersion gold (ENIG) process often is implemented when there is insufficient space to allow bussing for the more common electrolytic Ni/Au plating. The ENIG process continues to be used despite evidence that it may cause catastrophic, brittle, interfacial solder joint fractures. In this investigation a plastic ball grid array (PBGA) test vehicle is used to compare quality and reliability of standard and experimentally modified ENIG surface finishes. The standard electrolytic Ni/Au surface finish is used as the control cell for the experiment. Ball shear tests and optical and scanning electron microscopy are performed on as-received and thermally preconditioned packages to evaluate package quality prior to assembly. Accelerated temperature cycling (0 +100 C and 40 +125 C) is used to evaluate solder joint attachment reliability. Detailed failure mode analysis is used to compare the fracture modes in the ball shear and thermal cycled samples in the electroless and electrolytic packages. The results are discussed in terms of the failure modes and the characteristics of the different Ni/Au surface finishes.

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Electrolytic and electroless Ni/Au are common pad surface finishes on area array (BGA or CSP) packages and printed wiring boards (PWB). The electroless nickel/immersion gold (ENIG) process often is implemented when there is insufficient space to allow bussing for the more common electrolytic Ni/Au plating. The ENIG process continues to be used despite evidence that it may cause or contribute to catastrophic, brittle, interfacial solder joint fractures. In this investigation a plastic ball grid array (PBGA) test vehicle is used to compare quality and reliability of four variations of the ENIG surface finish. The standard electrolytic Ni/Au surface finish is used as the control cell for the experiment. Ball shear tests and optical and scanning electron microscopy are performed on as-received and thermally preconditioned packages to evaluate package quality prior to assembly. Accelerated temperature cycling (0/+100 °C and -40/+125 °C) is used to evaluate solder joint attachment reliability. Detailed failure mode analysis is used to compare the fracture modes in the ball shear and thermal cycled samples in the electroless and electrolytic packages. The results are discussed in terms of the failure modes and the characteristics of the different Ni/Au surface finishes.

In printed circuit boards (PCB), the selection of surface finish is a balance of cost, performance and material compatibility consideration. When the operating frequency is in gigahertz range, the signal loss in interconnects has stronger dependence on the material composition of traces, surface finishes, substrates, and geometry of the traces. Skin effects, frequency dependent dielectric properties and the electrical functioning mechanism are important factors that affect signal integrity. In this work, both measurements and finite element method (FEM) based full wave simulation are used to investigate the effects of hot air solder leveling (HASL) and its alternatives on signal degradation of high-speed interconnect structures. For the microstrip line structure, the loss due to surface finishes is negligible. For the differential mode coupled microstrip lines, the loss increment resulted from surface finish can be up to 50%∼200% at 10 GHz. Surface finish caused signal loss must be carefully considered for differential mode interconnects.

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