Abstract
The effects of interfacial reaction on the joint strength has been investigated for QFP joints with Sn-l0Pb or Au/Pd/Ni plated Cu lead using lead-free solders such as Sn-3.5Ag, Sn-3.5Ag-0.7Cu, Sn-3Ag-5Bi and Sn-3.5Ag-2.5Bi-2.5In. High temperature exposure test and thermal cycle test were carried out. The joint strength depended on the thickness of the interfacial reaction layers consisting of Cu6Sn5 and/or Cu3Sn. In the case of the joints using Sn-3Ag-5Bi solder with Sn-10Pb plated Cu lead, significant degradation of the joint strength occurred in the high temperature exposure test and the thermal cycle test. This is due to the rapid growth of the reaction layer, which is caused by the melting of Bi and Pb rich phase ahead of the reaction layer. All joints, except for those using Sn-3Ag-5Bi solder with Sn-l0Pb plated Cu lead, showed strength and reliability comparable to the Sn-37Pb eutectic solder joint.
