A failure analysis of thermomechanical fatigued small outline J (SOJ) lead/Sn-X (X = AgCu and Pb) solder joints over different printed circuit board surface finishes underwent pull test has been conducted. Experimental results showed that the dimple-fracture feature was due to the occurrence of fracture in the solder matrix and the intergranular-fracture feature was due to the occurrence of fracture in the IMC layer. The growth rate of the IMC layer at the SOJ/SnAgCu interfaces is much faster than that of the IMC layer at the SOJ/SnPb interfaces. The increase in the thickness of IMC (Cu6Sn5) and the fatigue of the SnPb solder matrix upon thermal cycling resulted in the decline of the strength of the SOJ/SnAgCu/(Ni/Au) and SOJ/SnPb/(Ni/Au) solder joints, respectively. After a pull test, the existence of different phases and the coverage variation of these phases on the fracture surface disclosed not only the distribution of stress but also the thermal fatigue properties of bulk solder alloy and IMC between the SOJ lead and solder. (C) 2004 Elsevier B.V. All rights reserved.