- 學位論文
銀合金線在金銲墊接合及其LED封裝可靠度研究
Ag-alloy Wires Bonded on Au Pads and their Reliability Tests for LED Packages
摘要
本研究分為兩部分，第一部分研究銀合金線於LED晶片的金銲墊打線接合後的界面反應機制與可靠度，同時比較其與銀合金線與鋁銲墊界面反應的差異，結果顯示在As bond後驗證了銀合金線與金銲墊無IMC的生成，其界面反應機制為擴散固溶，在高溫200℃熱老化168小時後，發現添加Pd於銀合金線中可提升線材機械性質，且銀合金線與金銲墊的鍵合強度有提升的趨勢，推測此因隨著熱老化的時間增加, 銀合金與金有足夠的時間進行擴散固溶反應所造成, 亦可從推力測試後, 金屬球在金銲墊的殘留面積變化論證，且銀合金線添加Pd比Au更有助於As bond時的BST強度提升，而添加Au的三元銀合金線則較Pd有助於鍵合強度的熱穩定性。此外，透過測試關鍵品質管控的Cpk參數, 提出了銀合金線使用於LED封裝產品在打線接合後製程檢測規範的建議。 第二部分則是將摻雜不同比例的Pd與Au元素的二元與三元銀合金線材封裝於白光LED後，進行各項可靠度測試的討論，如硫化、冷熱衝擊、低溫儲存、高溫儲存、高溫操作與高溫高濕操作老化，主要探討各種線材在白光LED成品的初始光通量及可靠度測試後的光通量維持率表現。在發光效率部分，純銀線封裝的LED成品有最佳的亮度表現，整體而言銀合金線封裝成品亮度皆較金線佳，銀合金線封裝的白光LED在高溫高濕老化的光維持率雖然稍差於金線，但尚屬可接受範圍，考慮整體應用需求，包含光通量與各項可靠度表現，金屬導線的較佳選擇，在二元銀合金線部分為Ag-4Pd銀鈀合金線，三元銀合金線則為Ag-3Pd-20Au銀合金線,且可適用於照明應用的中功率白光LED。
並列摘要
There are two parts in this study. In the first part, we investigated the mechanism of interfacial reaction of Ag-alloy wires in the gold bond pad of an LED die after a wire bonding process, and their reliability. The results showed that in the as-bonded condition, no IMC formed between the Ag-alloy wire and the gold bond pad and that the interfacial reaction mechanism was diffusional solid solution reaction. After 168 hours of thermal aging at 200°C, it was found that adding Pd to the Ag-alloy wire could improve the mechanical properties of the wire, and the bonding strength between the Ag-alloy wires and gold bond pad showed an increasing trend. It was speculated that increasing the thermal aging period allowed sufficient time for the diffusion reaction between the silver alloy and gold bond pad. The gold ball residual area difference indicated that adding Pd to Ag-alloy wire was more helpful than adding Au for boosting BST strength in the as-bonded condition, while adding Au to ternary Ag-alloy wire helped the bonding strength in terms of thermal stability. Process specifications are suggested for Ag-alloy wire joints in LED packaging products based on tests of the critical quality parameters of Cpk. In the second part, mainly investigate the binary and ternary Ag-alloy wires which are doped with various Pd and Au concentration, and each wire was encapsulated in the LED package, then proceed in various reliability tests, including the sulfur test、thermal shock、low temperature storage life、high temperature storage life、wet high temperature storage life、high temperature operating life and wet high temperature operating life test. It mainly investigated the performance of the initial luminous flux and lumen maintenance after reliability testing. In terms of luminous efficiency, pure Ag wire fabricated in LED package has the best luminous efficiency performance, and all the Ag-alloy wires package was better than Au wire package. The lumen maintenance performance of Ag-alloy wires LED packages were slightly weak than Au wire LED package at wet high temperature operating life test, but that were within the acceptable limits. Considering the overall demand for LEDs, including luminous flux and variable reliability, the binary Ag-4pd alloy wire and ternary Ag-3Pd-20Au alloy wire appears to be suitable for mid-power white light LEDs of the lighting applications.