Interfacialreactionsandeleciromigrationinlead-freesoiderjoints with copper and au-nisurfacefinished coppersubsiratfs

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Date
2009-11
Authors
Ngoc Binh, Duong
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Abstract
Properties of lead free solder alloys (Sn-9Zn, Sn-8Zn-3Bi and Sn-3Ag- 0.5Cu) on Au-Ni surface finished copper and copper substrates were investigated. Results obtained showed good wetting of all three solder alloys on Au-Ni surface finished substrate at appropriate temperatures. Contact angle measurement and wetting force results reaffirmed that good wetting of solder alloys on substrate was achieved. Microstructural analysis of the interface between solder alloys and Au-Ni surface finished copper substrate revealed that the Au layer on the substrate had dissolved completely into solder alloys after 20 seconds. A layer of Au-Zn intermetallic compound (IMC) was formed at the solder substrate interface, i.e. Au5Zn3 in Sn-9Zn and AuZn3 in Sn-8Zn-3Bi. With Sn-3Ag-0.5Cu, AuS114 IMCs were found distributed in the solder alloy and a layer of (Ni,Cu)6Sns IMC was formed at the solder-substrate interface. Electromigration has thickened the IMC layer at the interface of solder joint, which is Cu5Zn8 IMC in Sn-9Zn and Sn-8Zn-3Bi joints whilst it is CU6Sn5 in the Sn-3Ag-0.5Cu joint. The thickening process occured at different rates, faster IMC thickening was observed on the anode of a specimen than on the cathode. Also, the Cu5Zn8 layer which is formed in the Sn-9Zn and Sn-8Zn-3Bi solder joints were found to grow faster than the CU6Sn5 layer in the Sn-3Ag-0.5Cu joint. Electric current was found to have an effect on the growth of CU6Sn5 in Sn-3Ag- 0.5Cu, with elongated Cu6Sn5 phase being formed along with the current direction.
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Deleciromigrationinlead-freesoiderjoints , Au-nisurfacefinished coppersubsiratfs
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