本研究目的在於探討Ag含量(0~3 Wt.%)對Sn-Ag-Cu無鉛銲料微結構及特性的影響，並探討在不同溫度條件下(25、80、125 ℃)疲勞性質，評估銲料低週疲勞之可靠度表現。
實驗試件利用直徑1.11±0.02 mm之錫球，與Cu基板銲接成單點剪切試件，之後再進行IMC觀察以及疲勞性質評估。實驗結果顯示，當Sn-Cu二元銲料添加Ag元素0.5 Wt.%可以有效的降低固相點，由Sn-0.7Cu的228.8 ℃下降至218.5 ℃，且隨著Ag含量持續添加，固相點不會再產生改變。而在Sn-Ag-Cu三元銲料裡，Ag含量增加固液相區間隨之減小。在微結構方面，Sn-Ag-Cu銲料組成皆為Ag3Sn、Cu6Sn5與β-Sn所組成之網狀共晶組織。當Ag含量越多時，Ag3Sn析出越密集，並有效提升銲料之硬度。而在Sn-0.7Cu二元合金中，Cu6Sn5密集的析出，對合金之硬度提升效果不顯著。
低週疲勞測試中，在±0.025 mm位移量下，銲點剪切強度隨著Ag含量提高而上升。在不同溫度條件下，銲點疲勞壽命大致上隨Ag的添加而增加，因銲接點之塑性位移量隨著Ag的添加而減少，塑性位移愈少造成有較佳的疲勞壽命。而在溫度25 ℃時，Sn-3.0Ag-0.7Cu在疲勞試驗中為混合破壞模式，裂紋會沿著IMC和銲料內部造成銲點失效，並降低其疲勞壽命。在測試溫度80、120 ℃時，所有銲料破壞模式為銲料內部破壞，因為隨著溫度的提升，銲料容易受到潛變的影響，造成銲點本身抗疲勞性質下降，並降低疲勞壽命。
綜合銲料固液區間、微結構、疲勞壽命，研究結果顯示Sn-1.5Ag-0.7Cu 會有較佳之性質。

This research is aimed to investigate the effect of Ag content (0~3 Wt.%) on the pasty range and microstructure of Sn-Ag-Cu lead-free solder. The Low-cycle fatigue properties of the solder joints at diffirent temperature conditions (25, 80, 120℃) were evaluated.
Sn-xAg-0.7Cu solder in form of solder balls with 1.1±0.02 mm in diameter were fabricated. Solder balls were re-flowed with Cu substrate in the form of single lap shear specimen, and then the Low-cycle fatigue test were performed. Experimental results show that when Sn-0.7Cu alloy is added Ag, the solidus point will decrease. However, it will not change when more Ag is added. The gap between solidus and liqiudus temperature (Pasty range) will reduce with more addition of Ag.
The microstructure of Sn-xAg-0.7Cu alloys consists of plate-like Ag3Sn intermetallic compounds, together with the copper present as rod-like Cu6Sn5 within a β-Sn matrix for all alloys. The increase in silver content may enhance the hardness of the solder alloy as a result of an increase in volume fraction of Ag3Sn intermetallics.The matrix of Sn-0.7Cu consists of β-Sn equiaxial grains and small particles of Cu6Sn5 that have not significantly influence on the hardness of solder.
In the condition with constant displacement of 0.025mm, shear strength of the solder joints is increased with higher Ag additions. In the diffirent temperature conditions, Fatigue life of the solder joint approximately increases with greater Ag additions. The reason is the plastic displacement of the solder joint decreases with higher Ag additions, and the lesser plastic displacement the better fatigue life. However, The fracture modes of Sn-3.0Ag-0.7Cu alloy is mixture mode at 25 ℃, and the mixture mode will decrease fatigue life by fracturing in IMC layer and solder. In this research,
III
the fracture mode of all the alloys are solder fracture mode at 80℃ and 120℃. Beacuse the alloys have influnces on creep behavior which decrease the fatigue properties of solder joints.
With compare of pasty range, microstructure and fatigue life of Sn-xAg-0.7Cu solder. The solder contains 1.5 Wt.% Silver has better behaviors.

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