PROCEEDINGS OF THE IV INTERNATIONAL CONFERENCE/HIGH TEMPERATURE CAPILLARITY JOURNAL OF MATERIALS SCIENCE 40 (2 0 0 5 ) 2547 – 2551 Application of push-off shear test for evaluation of wetting-interface structure-bonding relationship of solder joints N. SOBCZAK ∗ , J. SOBCZAK, R. NOWAK, A. KUDYBA, P. DARLAK Foundry Research Institute, 73 Zakopianska Street, 30-418 Cracow, Poland E-mail: natalie@iod.krakow.pl B. MIKULOWSKI AGH University of Science and Technology, 30 Mickiewicza Ave., 30-059 Cracow, Poland A. WOJCIECHOWSKI Motor Transport Institute, 80 Jagiellonska Street, 03-391 Warsaw, Poland The relationship between wetting behavior, interface structure and mechanical properties of solder/substrate couples has been studied on example of Sn-alloys and Cu substrates. The sessile drop method was used to investigate the solder wetting and spreading on polished Cu substrates in vacuum at a temperature of 503 K. The sessile drop samples after solidification were bisected perpendicularly to the substrate at the mid-plane of the contact circle. The first half of each sample was used for structural characterization of interfaces and evaluation of their mechanical properties by improved push-off shear test. The second half was used for investigation of the effect of thermocycling on structural stability and corresponding mechanical behavior of model solder/Cu joints. A comparison with the results obtained on standard solder joints has shown the usefulness of the improved push-off shear test performed directly on solidified sessile drop samples as an express test for evaluation of technological and mechanical compatibility of solder/substrate couples, particularly at the first stage of solder candidate selection. C  2005 Springer Science + Business Media, Inc. 1. Introduction Since lead and lead-containing compounds are among the most toxic substances, a global economic forces the development of new generation solders to replace widely used lead-containing ones. However, none of the known lead-free solder alloys meets all require- ments in terms of specific combination of melting temperature, solderability, thermal and electrical con- ductivity, thermal-expansion coefficient compatibility, corrosion and thermal-fatigue resistance, adaptivity to existing joining procedure, flexibility in designing joints. Because lead replacement problem is compli- cated by enormous number of interacting parameters that must be considered, a number of expensive and time-consuming tests should to be done for proper se- lection of the solder alloy and corresponding process- ing parameters. Therefore, the development of cost- effective research procedure for the selection of new generation solders is of practical importance. The aim of this paper was to check the adaptivity of the procedure recently proposed in [1] for evalu- ation of wetting-interface structure-bonding interrela- tionship of metal/ceramic couples as express test for ∗ Author to whom all correspondence should be addressed. solder selection. In this procedure the sessile drop specimens produced in wettability test under repeat- able and well-controlled conditions are used as model metal/substrate joints, which mechanical properties can be estimated by the proposed improved push-off shear test. Such procedure was selected, based upon prior ex- perience on ceramic joining of several metal/ceramic systems (Al/AlN [2], Al/Al 2 O 3 [1, 3–4], Al/Si 3 N 4 [5], Al/TiO 2 [6], Ni/Al 2 O 3 [7] and Cu/Al 2 O 3 [8]) and im- portance of shear properties because the strain in solder joints of electronic interconnects is mostly shear due to CTE mismatch between the solder and the substrate [9]. For the reasons that solder joints are the weakest link in the hierarchy of the electronic interconnects and ther- momechanical fatigue is the major cause of their failure [9] the effect of thermal cycling on shear properties of model solder/Cu joints has been studied. 2. Experimental procedure The materials used were Cu substrates and several Sn-alloys, the chemical composition and properties of which are given in Table I. 0022–2461 C  2005 Springer Science + Business Media, Inc. 2547