Study Of Composition Design Optimization And Soldering Reliability Of The Pb-Sn-Sb-Ag Solder Used For Hybrid Integrated Circuit

Most of the devices in the hybrid integrated circuit are welded with Sn62Pb36Ag2 solder.Although this solder has good physical properties and excellent welding performance,the melting point is low from 179?to 183?.During the long time high temperature vacuum baking and the subsequent severe temperature cycle test,the metal compound between the solder and the pad is in the excessive growth.This is esay to cause deterioration of mechanical properties.It is difficult to meet the high reliability of the product.So it is emergency to develop a kind of high reliability solder used in the hybrid integrated circuit.In this issue,the melting temperature and wetting property and reliability of the solders were investigated by differential thermal analyzer,reflow oven,optical microscopy?OM?,X-ray diffraction?XRD?,energy dispersive spectroscopy?EDS?,scanning electron microcopy?SEM?,for designing and optimizing the composition of the solder alloy.Meanwhile the wetting property,the microstructures of solder joints for Pb-x Sn-x Sb-xAg and the growth of intermetallic compound layer during thermal fatigue were investigated and evaluated.Pb-Sn-Sb-Ag was chosen as the design of alloy composition on the base of the study for the melting temperature,wetting property and reliability,of Sn62Pb36Ag2/Sn63Pb37,Sn-3.5Ag-3Pb,Pb-5Sn-10Sb,Pb-40In,Pb-15Sn-8Sb.Pb-10.5Sn-xSb-x Ag and Pb-xSn-xSb-x Ag were designed initially combining with phase diagram design.Pb-x Sn-xSb-xAg was developed finally as the new solder used in hybird integrated circuit after the above research and analysis.The wetting property on the copper of Pb-x Sn-xSb-xAg solder was studied and found the wettability is better than Pb-Sn-Sb.After wetting and spreading,the surface of solder point was smooth,and no obvious massive residue.The microstructure of the solder joints contain primary phase Pb,Sb₂Sn₃ on the matrix of Pb,the fine Sb₂Sn₃,the dispersed Ag₃Sn and the intermetallic compounds Cu₃Sn.The joints have uniform thickness and uniform distribution in the solder joints straight.Evenly the large area of the dendrite distributed inside.There is a very thin and uneven distribution of Cu₃Sn intermetallic compound layer between the solder and base metal.The average thickness of the intermetallic layer was measured about1.8?m.The average thickness of the Cu₃Sn intermetallic compound layer at the interface of the solder joint was gradually increasing with the thermal cycling test.During the 200 weeks and 600 weeks,the average thickness of Cu₃Sn intermetallic compound layer was the most obvious,and the average thickness of Cu₃Sn intermetallic compound layer increased slowly during the period of 600 weeks to 1000 weeks.The growth of intermetallic compound layer in Pb-xSn-xSb-x Ag solder joints was studied under the welding state,high temperature baking and thermal fatigue test in 1000 weeks.In these three states,the intermetallic layer thickness of Pb-xSn-xSb-x Ag solder are about 1.8?m,about 5?m,about 8.8?m.The growth rate of intermetallic layer is slower than the Sn62Pb36Ag2 solder.The shear strength of the Pb-xSn-xSb-x Ag solder joint is higher than that of the Sn62Pb36Ag2 solder joint after the thermal cycling test.Therefore,the thermal fatigue reliability of this solder is stronger than Sn62Pb36Ag2 solder.