A fracture mechanics approach is used to investigate how the fatigue life of a solder grid array (SGA) may be increased or decreased by the application of an axial force to individual solder interconnects, such as may be induced by use of an underfill, by warping of a printed wiring board, or by some other mechanical constraint. The predominant loading on the SGA is assumed to be the shear resulting from a difference in thermal expansion between the package and the printed wiring board in the presence of cyclic temperature variations. A fatigue crack growth model, akin to the Paris law, is proposed for the cycles to failure of an individual cracked interconnect which undergoes a cyclic mode-II shear loading in conjunction with either a constant crack opening force (mode-I) or a constant crack closing force. For typical SGA packages in use today, the model predicts that forces on the order of only one newton can significantly impede or accelerate the propagation of a fatigue crack.

Issue Section:
Technical Papers
Keywords:
fracture mechanics, soldering, printed circuit manufacture, fatigue cracks, packaging
Topics:
Compression, Die cutting, Fatigue cracks, Fatigue life, Fracture (Materials), Printed circuit boards, Shear (Mechanics), Shearing (Deformation), Solders, Stress, Temperature, Tension, Cycles, Thermal expansion, Fracture mechanics, Electronic packages, Failure
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