本研究之目的為探討在Sn-3Ag-2Sb無鉛銲料中添加微量的稀土元素鑭(La, 0.05, 0.1, 0.5, 1.0 wt.%)對其潤濕性、微結構、銲點剪切強度與破壞模式之影響；同時亦透過150、200℃高溫儲存至400小時，測試評估La添加量與銲點抗熱性之關係與影響。
研究結果顯示Sn-3Ag-2Sb-xLa銲料在La元素之添加達0.05wt.%時其潤濕效果最佳，超過0.05wt.%La添加量時，其潤濕效果並沒有跟著提升；微結構方面，Sn-3Ag-2Sb-xLa主要是由β-Sn、Ag3Sn與微量LaSb化合物所構成，而隨著La添加量增加至0.5 wt.%時，基地中有LaSb化合物出現。未熱儲存下，以SAS-0.05La之微結構表現最為緻密。經150、200℃熱儲存400小時後，Sn-3.5Ag粗大化之情況最為嚴重，SAS-0.05La依保持著部份Ag3Sn散佈強化效果存在。IMC層經高溫熱儲存後之觀察結果發現，有添加La之界面IMC層，經400小時高溫熱儲存皆有抑制且較薄的現象。剪切強度方面，as-soldered情況下發現Sn-3Ag-2Sb添加La後剪切強度與延性下降，SAS-1.0La強度明顯下降最多。其主要原因在於大量LaSb化合物存在於基地使其接合性較差，於剪切試驗時裂紋易由這些應力不連續處形成，而此裂紋為造成強度與延性下降之主因。熱儲存後，斜口韌窩相較於as-soldered條件呈現較大且延展較廣，其主要是由於銲料內部軟化所致。銲料經熱儲存後其破斷模式由銲料模式轉變為混合模式，甚至在SAS-1.0La中有發現IMC破斷模式。La的添加明顯可以抑制界面層的成長，但添加至0.5wt.%La以上時， LaSb化合物之存在所造成的負面影響大於其抑制效果。因此Sn-3Ag-2Sb-xLa中， La不適合過量添加，就目前研究結果0.05 wt.%La添加量有較佳的表現。

This study investigates the effects of trace amounts of rare earth element La addition on the wettability 、microstructure、shear strength and fracture behavior of Sn-3Ag-2Sb based solder joints. Sn-3Ag-2Sb-xLa quaternary alloy solder joints are prepared by adding 0~1.0wt% La to Sn-3Ag-2Sb alloy and then using the resulting solders to join two pure Cu rods. Those solder joints are stored isothermally at 150、200°C for up to 400 h, and the relation between the amount of La additions and the thermal resistance were also investigated.
Experimental results show that the wettability has weak correlation with the increasing La, only the 0.05wt.% La addition shows the best wettability. In as-soldered state, the microstructure of SAS-0.05La presents the finest. After aged at 150℃ and 200℃ for 400h, the SA structure showed the most coarsened among the test samples, SAS-0.05La however, remains partial of its strength due to the existing of Ag3Sn dispersion hardening. With La addition, the growth of interfacial IMC layer of solder joints was apparently retarded. great restrained in contrast with those without La addition by isothermal aging for 400h. Shear test fracture observation of the 0.5, 1.0La samples showed the appearance of LaSb IMCs partial dispersed in the bottom of fractured dimples which lowered the shear strength and ductility, also excess of La addition lead to the formation of LaSb compound more easily, so that it contradicted the solid-solution strengthening effect of Sb. Base on experimental results, the 0.05wt.% La addition is recommend in Sn-3Ag-2Sb solder.

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