添加稀土元素La對Sn-58Bi無鉛銲錫球格陣列構裝界面反應與錫鬚之影響研究

Abstract

在Sn-58Bi合金成份中，添加重量百分比0.5％的La，會形成平板狀介金屬鑲嵌在銲錫基地中，且因形狀效應抑制含稀土介金屬錫鬚快速生長現象。經過迴銲，Sn-58Bi和Sn-58Bi-0.5La銲錫合金與化鎳金（ENIG）基板生成Ni3Sn4介金屬化合物，與有機保銲膜（OSP）基板生成Cu6Sn5介金屬化合物，且隨著在75℃和100℃時效處理的時間增加，介金屬化合物呈線性成長，且Sn-58Bi-0.5La合金系統界面介金屬相較Sn-58Bi合金系統薄許多。然而，Sn-58Bi-0.5La合金系統，稀土元素La活性大容易氧化，迴銲時氧化物被助銲劑帶出，在銲錫與基板之間產生孔洞，導致接合強度下降，相較於Sn-58Bi合金系統封裝強度為差。此外，Sn-58Bi和Sn-58Bi-0.5La銲錫的慢速（0.4 mm/s）及快速（2000 mm/s）推球試驗，破斷面都呈現脆性破壞。

Adding 0.5 wt.％ La into Sn-58Bi solder alloy forms plate-shaped intermetallic compound in solder matrix. And the fast tin whisker growth is alleviated by the shape effect on rare-earth element containing intermetallic compound. After reflowing, Sn-58Bi and Sn-58Bi-0.5La solder alloys form Ni3Sn4 interfacial intermetallic compound with ENIG pads and form Cu6Sn5 interfacial intermetallic compound with OSP pads. The thickness of interfacial intermetallic compounds linearly grows with aging time at both 75℃ and 100℃. And the thickness of interfacial intermetallic compound in Sn-58Bi-0.5La alloy is much thinner than the one in Sn-58Bi alloy. However, the rare-earth La in Sn-58Bi-0.5La alloy is very active and oxidizes easily which leads the oxidization to be brought out by the flux during reflowing. Then the holes form on the interface between solder and pad and result in lower bonding strength compared with Sn-58Bi alloy system. In addition, the cleavage of both ball shear test (0.4 mm/s) and high speed ball shear test (2000 mm/s) of Sn-58Bi and Sn-58Bi-0.5La solder alloys shows brittle fracture.