Abstract
The effects of substrate surface roughness, joint thickness, time above liquidus, and testing temperature on the chevron notch fracture toughness of Cu/96.5Sn-3.5Ag solder joints are investigated. Of these four variables,only the surface roughness of the copper surfaces to be soldered has a significant effect. A minimum fracture toughness is obtained when the average surface roughness, Ra, is between 0.2 and 1.0 μm. This encompasses the surface roughnesses produced by many cold forming operations. Decreasing the roughness to 0.04 μm increases the fracture toughness from 4.7 to 11.0 MPa√m, an improvement of 135%. Increasing the roughness to 2.0 μm increases the fracture toughness to 8.8 MPa√m, an improvement of 80%. We attribute these effects to the increased growth stresses that develop in the brittle intermetallic layer when the size scale of individual intermetallic particles is comparable to the size of the roughness features of the substrate. Two models that describe how these growth stresses might develop are provided.
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Stromswold, E.I., Pratt, R.E. & Quesnel, D.J. The effect of substrate surface roughness on the fracture toughness of Cu/96.5Sn-3.5Ag solder joints. J. Electron. Mater. 23, 1047–1053 (1994). https://doi.org/10.1007/BF02650374
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DOI: https://doi.org/10.1007/BF02650374