本研究目的在於探討Ag含量(0~3 Wt.%)對Sn-xAg-Cu無鉛銲料與銅片銲接成單點剪切試件後，利用120℃時效(25、100、225小時)前後對銲點界面層厚度及機械性質之影響，並透過低週疲勞試驗及後續斷口形貌分析，以評估銲料低週疲勞之可靠度表現。
剪切試驗中，Sn-0.7Cu銲料微結構方面，是由Cu6Sn5與β-Sn所組成；而Sn-Ag-Cu銲料部分，隨Ag添加上升，Ag3Sn與Cu6Sn5之網狀共晶組織越密集，使銲料強度提升。實驗結果顯示，四種銲料剪切強度隨Ag含量添加而上升，但延性卻隨之下降，因緻密的網狀共晶組織阻止差排滑移所致。
低週疲勞試驗中，Sn-0.7Cu二元合金無Ag3Sn之析出強化，因此斷口分析中，銲料內部強度低於IMC層之強度，使裂紋向銲料內部發展，故疲勞強度及壽命為本實驗中最低的合金成份。而在Sn-Ag-Cu三元合金銲料部分，三種銲料皆屬於混合破壞模式，疲勞強度隨Ag含量添加而上升，起始裂紋會於銲料內部靠近邊界處生成，而Ag含量上升，銲料內部緻密的網狀共晶組織會使裂紋向IMC層處生長，使裂紋提早與IMC和銲料間之裂紋合成，促使裂紋快速發展，因此SAC307銲料之疲勞壽命較SAC207及SAC157銲料低。而經時效後之低週疲勞試驗結果顯示， IMC層產生相變化，六角柱狀之Cu6Sn5轉為單斜晶狀之Cu6Sn5，以柱狀成長進入銲料內部，使IMC層及銲料介面間不連續性上升，導致於IMC層處產生脆性斷裂，降低整體疲勞壽命。
綜合剪切試驗、介面層觀察、低週疲勞試驗及斷口分析，研究結果顯示Sn-1.5Ag-0.7Cu擁有較佳之抵抗疲勞能力。

The effect of different Ag addition (0~3 Wt. %) on the IMC layer thickness and mechanical properties of Sn-xAg-Cu solder joint was studied. Single-lap shear test was carried out where solder joint was performed on performed copper sheets. Meanwhile, microstructure characteristics of solder joints before and after aging at 120℃ for different duration(25, 100, 225 hours) were studied. The behavior and reliability of the solder joint by low cycle fatigue were examined and the fracture morphologywas analyzed and discussed.

Sn-xAg-0.7Cu solder in form of solder balls with 1.10±0.02 mm in diameter were fabricated. Solder Mask with 1.1 mm in diameter was set to be the boundary on Cu substrate. Solder balls were reflowed with Cu substrate in the form of single lap shear specimen, and then the low-cycle fatigue test were performed. Solder alloys SAC157, SAC207 show similar microstructure features whilst SAC307 solder alloy displays a very fine microstructure with intermetallic phases dense within the β-Sn matrix. The increase in silver content enhances the mechanical strength of the solder alloy as a result of an increase in volume fraction of Ag3Sn intermetallics.

The fatigue life test reveals that fatigue life curve of the solder joint is similar between barrel type and hourglass type.To sum up the shear test, boundary layer observation, low cycle fatigue test and fracture analysis, the findings show that the Sn-1.5Ag-0.7Cu has better fatigue resistance.

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