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The Influence of Nickel/Gold Surface Finish on the Assembly Quality and Long Term Reliability of Thermally Enhanced BGA Packages

01 January 1999

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There is an increasing number of chip carrier package such as ball grid arrays (BGA) and chip scale packages (CSP) that use electroless nickel/immersion gold (ENi/IAu) as a surface finish. The principal advantage of electroless processes is that they can be used to meet requirements for increased routing density at design, when there is insufficient space to allow bussing for the more common electrolytic Ni/Au plating. However, the results of several studies attribute brittle failure of solder balls to the presence of the ENi/ IAu surface finish. Brittle fractures have occurred in service and have been generated under a variety of testing conditions including thermal cycling (infant mortality failures), bending, shear, or vibrational stress, and thermal or mechanical shock. The typical failure mode in all these cases is brittle fracture at the interface between the Ni plating and the intermetallic compound formed during soldering.