Research Summary Lead-Free Solders
Dyna-Powered, five lofts, $130. A return to the classic look, including bore-through hosel. www.wilsongolf.com 800-469-4576.As an improvement over the previous Sn-Ag eutectic solder in lead-free electronic assembly applications, the Sn-Ag-Cu eutectic6 and neareutectic solders offer a reduced melting temperature (about 4C lower) and additional tolerance for variations in cooling rate after reflow.7 Prior calorimetric studies8 revealed the very similar melting behavior of several closely related Sn-Ag-Cu alloys, consistent with the phase diagram studies9 on this system. Compared to other common choices, the copper alloy addition to Sn-Ag is abundant and low cost, is compatible with common noclean paste fluxes", and, unlike bismuth and antimony, is not a by-product of lead mining.The higher magnification and atomic number contrast of the scanning electron microscopy-backscattered electron image (SEM-BEI) micrographs in Figure 2 provide additional information on the as-solidified joint microstructures shown in Figure lc and id, along with joint microstructures made from iron and cobalt modifications of Sn-3.7Ag0.9Cu. In Figure 2a and 2d, for example, it seems that Cu6sub 6^Sn^sub5^, rather than tin, is the primary phase in the solidification of Sn-3.6s-l.OCu and Sn-3.7Ag-0.6Cu0.3Co solders, as confirmed by EDS in the SEM, followed by solidification of an extremely fine ternary eutectic. An interesting difference in the intermetallic at the copper/solder interface is also apparent, where the finely-spaced rounded stubs of Figure 2a and 2c contrast with the partially faceted Cu6Sns fingers of Figure 2b and the finer interfacial Cu6Sn5 intermetallic in Figure 2d, which has a continuous 1-2 gm thick Cu6Sn5 layer on the copper substrate. Actually, the intermetallic interface in Figure 2d is very similar to that in a solder joint made from a Sn3.6Ag-1.OCu-0.45Co solder alloy under equivalent solidification conditions in an earlier study.'7,11Vokey Oil Can, nine lofts, $125. Heated oxide treatment wears to rusted finish. www.titleist.com 800-825-8500.EXPERIMENTAL PROCEDURE Sn-3.SAg (wt.%) solder alloy wire (1.57 mm) came from a commercial vendor. Other wires were fabricated from 99.99% purity Sn, Ag, Cu, Co, and Fe by Ames Laboratory in 100 g chill-cast ingots that were drawn into 1.57 mm wire. The nominal ingot compositions consisted of Sn-3.7Ag0.9Cu (wt.%), Sn-3.7Ag-0.6Cu-0.3Co, Sn-3.7Ag-0.7Cu-0.2Fe, Sn-3.OAg0.SCu, Sn-3.Mg-0.6Cu, and Sn-3.6Ag1.OCu.Merging Steel Histories in the 1990sPELZThe Austrian government reacted quickly, passing new legislation in 1946 nationalizing all of its "German" companies. Yet the first Nationalization act, while protecting the businesses in the zones controlled by the British, French, and Americans—which respected Austria's claim—remained ineffectual in the Soviet zone. The nationalization of the remaining industries and businesses nonetheless gave the Austrian government oversight of the distribution of reconstruction aid provided by the United States in particular. In this way, the government was able to subsidize its nationalized businesses and aid in the reconstruction. Over the next decades, government control proved less than efficient; after a number of crises, the government instituted a series of reforms in the 1960s, leading to the creation of a new public limited company, Osterreichische Industrieverwaltungs AG (later Osterreichische Industrieholding AG, or OIAG), in 1970.RESULTSMIZUNODUNLOP
A summary of the ambient temperature shear test results for all of the alloys studied are shown in Figure 3. The repeatability of the maximum shearstrength values is indicated by the narrow range ( 2.5-5 MPa) of the standard deviation of the measurements, where at least seven specimens were tested for each type of solder joint. The weakest of the solder joints was made from the Sn-3.OAg-0.SCu, while the strongest joints were made from Sn-3.7Ag-0.7Cu0.2Fe. The shear strength of the baseline Sn-3.SAg solder joints fell in the middle of the range of values, stronger than previously reported.7 This apparent strengthening may have resulted from a minor increase in cooling rate over the previous study due to the sensitivity of the Sn-3.SAg solder microstructure to solidification conditions.7,11,11 The difference between the maximum shear strength and the apparent yield strength is an indication of the reasonable ductility exhibited by these samples, although the yield-strength values had an increased standard deviation. The results of elevated-temperature (150'C) testing indicated a drop of at least half of the shear strength of the ambient temperature measurements. 17 Due to the increased standard deviation of the measurements, no significant differences can be reported between the elevated-temperature shear strengths of the solder joints made from any of the alloys tested. The microstructural response to elevated-temperature aging of all of the experimental alloys remains to be characterized in a subsequent report.
Author: Anderson, I E, Cook, B A, Harringa, J L, Terpstra, R L
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