Sn-xAg-0.5Cu合金與Au/Ni/Cu基材之界面反應與接合強度研究

Abstract

本研究主要為探討Ag含量對於Sn-xAg-0.5Cu合金(x=1, 3, 4wt%)於熱性能、機械性能、顯微組織以及與Au/Ni/Cu基材在球格狀陣列構裝後的界面反應及銲點強度，此外，探討Co元素添加對於Sn-1Ag-0.5Cu合金之界面反應和銲點強度的影響。 顯微組織研究結果顯示，Sn-xAg-Cu合金中之Ag元素含量的減少將降低Ag3Sn介金屬化合物的占有比例。此外，由機械強度測試結果顯示， Ag3Sn介金屬化合物具有散佈強化的效果，因此，當減少合金中之Ag含量時，而合金之拉伸強度亦隨之降低。 Sn-xAg-0.5Cu合金與Au/Ni/Cu基材於迴焊後之界面反應層均為(Cu,Ni)6Sn5介金屬化合物。Sn-1Ag-0.5Cu合金銲點之界面反應層於150℃高溫儲存試驗的時間延長至1500小時後仍為(Cu,Ni)6Sn5介金屬化合物，無觀察到(Ni,Cu)3Sn4的存在，然而，Sn-3Ag-0.5Cu及Sn-4Ag-0.5Cu合金則分別於500小時及100小時後，在界面反應層中即可觀察到(Ni,Cu)3Sn4的存在。由銲點拉球強度試驗結果顯示，界面(Ni,Cu)3Sn4反應層的形成將導致銲點之拉球強度快速下降，並使破斷型態由銲錫破壞模式轉變為界面破壞模式。此外，比較Sn-xAg-0.5Cu合金之銲點強度則可以發現， Sn-1Ag-0.5Cu合金對於抵抗高溫長時間儲存後，銲點強度衰減的能力優於Sn-3Ag-0.5Cu及Sn-4Ag-0.5Cu合金。 Co元素添加對界面反應與接合強度之影響研究結果顯示，在Sn-1Ag-0.5Cu合金中添加微量Co元素後，其界面反應層中均含有Co元素存在，其界面反應層以能量散佈光譜儀(energy-dispersive x-ray spectrometer, EDX)分析後，顯示為(Cu,Ni,Co)6Sn5及(Ni,Cu,Co)3Sn4介金屬化合物，與Sn-1Ag-0.5Cu合金之分析結果明顯不同。此外，比較多次迴焊試驗後之界面反應層生長結果可以發現，在合金中添加微量Co元素(0.05wt%)將抑制銲錫合金中之Cu元素向界面反應層中擴散。

The microstructure, mechanical property, thermal properties and interfacial reaction of the Sn-xAg-0.5Cu (x=1, 3, and 4 wt%) lead-free solders were investigated. Additionally, in order to clarify the effect of the addition of Co to SAC105 solder, the reaction between solder and Au/Ni surface finish has been investigated, and the joint strength was also evaluated by a ball shear test. The microstructure of Sn-xAg-0.5Cu reveal that the amount of the Ag3Sn intermetallic compounds (IMCs) decreases as the Ag content is reduced. Additionally, the amount of Ag3Sn IMCs in the solder matrix influences the mechanical property. This result causes the tensile strength decrease as the Ag content is reduced. The interfacial IMCs layer in the as-reflowed specimens was only (Cu,Ni)6Sn5 for Sn-xAg-0.5Cu solders. The (Ni,Cu)3Sn4 IMCs layer formed when Sn-4Ag-0.5Cu and Sn-3Ag-0.5Cu solders were used as aging time increased. However, only (Cu,Ni)6Sn5 IMCs formed in Sn-1Ag-0.5Cu solders, when the aging time was extended beyond 1500 hr. Two factors are expected to influence bond strength and fracture modes. One of the factors is that the interfacial (Ni,Cu)3Sn4 IMCs formed at the interface and the fact that fracture occurs along the interface. The other factor is Ag3Sn IMCs coarsening in the solder matrix, and fracture reveals the ductility of the solder balls. The above analysis indicates that during aging, the formation of interfacial (Ni,Cu)3Sn4 IMCs layers strongly influences the pull strength and the fracture behavior of a solder joint. This fact demonstrates that interfacial layers are key to understanding the changes in bonding strength. Additionally, comparison of the bond strength with various Sn-Ag-Cu lead-free solders for various Ag contents, show that the Sn-1Ag-0.5Cu solder joint is not sensitive to extended aging time. After soldering, the interfacial reaction layer in the SAC105-Co solder contained Co, and the chemical composition of IMCs were identified as (Cu,Ni,Co)6Sn5 and (Ni,Cu,Co)3Sn4 by energy-dispersive x-ray spectrometer (EDX), which significantly differed from that of SAC105 solder. After multiple reflows, the formation rate of the (Cu,Ni,Co)6Sn5 IMC for the Co-added solder slow compared with that of (Cu,Ni)6Sn5 IMC for SAC105 solder. Experimental results clearly indicate that adding small amounts (0.05wt.%) of Co to SAC105 solder strongly affected the formation of the IMC at the interface. Furthermore, ball shear test results demonstrate that the SAC105 and SAC105-Co solder joints have good joint reliability.