迴銲後期熱處理對錫銀銅銲接點衝擊可靠度、銲料微結構及錫結構方向性之影響

Effects of Thermal Annealing during the Post-Reflow Process on Microstructure, Tin Crystallography, and Impact Reliability of Sn-Ag-Cu Solder Joints

陳玟琳(Wen-Lin Chen)

指導教授 ： 杜正恭

國立清華大學/工學院/材料科學工程學系/碩士(2014年)

摘要

為了增加銲接點強度，本研究嘗試改變迴銲的條件且利用高速撞擊測試(high-speed impact test)去評估銲接點的可靠度。在迴銲後期固化的過程中，對銲接點進行不同溫度和不同時間長度的熱處理，探討在Sn-Ag-Cu/Cu與Sn-Ag-Cu/Ni銲接點內的微結構、錫(β相)的結晶和銲料硬度的變化。
在固化過程中，對Sn-Ag-Cu/Cu 銲接點施以180度或210度的熱處理，以了解不同熱處理溫度的影響。在熱處理後，靠近界面的局部析出物，從點狀分佈轉變成網狀分佈。此外，透過電子背向散射儀(EBSD)的分析可察知析出物的分佈與錫的結晶息息相關。熱處理後，由於銲料內銅元素的再分佈，讓銲料內錫的結晶結構從多個且交織狀成長成少許大顆的錫晶粒。值得注意的是，以210度熱處理會加速上述微結構的改變，並提升銲接點的強度。
為了探討熱處理對不同的凸塊底層金屬的影響，Sn-Ag-Cu/Cu 與Sn-Ag-Cu/Ni銲接點在固化過程中經過210度的50秒或100秒的熱處理。在對照組以快速冷卻的Sn-Ag-Cu/Cu銲料中，其析出物以網狀分佈且佔據大部份的銲球體積，然而在Sn-Ag-Cu/Ni 銲料中析出物係以點狀結構佔據大部份的體積。隨著熱處理時間增加，析出物逐漸成長，界面的介金屬化合物稍微的增厚，而銲料變的較軟。Sn-Ag-Cu/Cu和Sn-Ag-Cu/Ni在熱處理50秒後，銲接點強度皆有所提升且延展性斷裂的比例也增加。然而，當熱處理達100秒後，在Sn-Ag-Cu/Ni銲接點的界面上，因相對硬脆的介金屬化合物(Cu,Ni)6Sn5增厚，導致銲接點強度下降。Sn-Ag-Cu/Cu和Sn-Ag-Cu/Ni在銲接點強度表現的差異性與銲料的微結構及銲料硬度有關。

關鍵字

電子封裝 ； 無鉛銲料 ； 高速擺錘衝擊測試 ； 硬度 ； 微結構

並列摘要

This study aims to improve the impact performance via modified reflow conditions. A high speed shear tester was used to evaluate the impact reliability of solder joints. During solidification step of reflow process, the solder joints were annealed under various annealing temperature and heating time. The microstructure, β-Sn structure, micro-hardness of Sn-3.0Ag-0.5Cu/Cu (wt. %, SAC/Cu) and Sn-3.0Ag-0.5Cu/Ni (wt. %, SAC/Ni) solder joints were investigated.
To evaluate the effect of annealing temperature on impact performance, the SAC/Cu solder joints were annealed at 180 oC and 210 oC, respectively, during the solidification step. In the annealed solder, the precipitations in the limited region near the joint interface varied from the dot type toward the network type. Additionally, electron backscatter diffraction (EBSD) analysis indicated that the β-Sn grain structure depended on the distribution of precipitations. The β-Sn grain structure was altered from interlaced grains to larger grains due to the redistribution of Cu in the solder. Noteworthily, the annealing at higher temperature (210 oC) can accelerated the variation of above-mentioned microstructure, leading to enhancement of the impact reliability.
The effect of annealing process on various UBMs was investigated. The SAC/Cu and SAC/Ni solder joints were annealed to 210 oC for 50 s and 100 s, respectively. In the rapid-cooled solder joints, the network type precipitations were distributed in all the solder volume of SAC/Cu joint, while the dot type precipitations in the SAC/Ni joint. With increasing annealing time, these precipitations grew larger, the interfacial intermetallic compounds (IMCs) became slightly thicker, and the hardness of solder alloys gradually decreased. After annealing for 50 s, the impact toughness of both SAC/Cu and SAC/Ni solder joints was enhanced, and the fraction of ductile fracture in these solder joints increased. However, the growth of (Cu,Ni)6Sn5 at the SAC/Ni interface degraded the impact toughness as SAC/Ni was annealed for 100 s. The difference of impact toughness in SAC/Cu and SAC/Ni was correlated to the variation of microstructure and hardness in solder joints.

並列關鍵字

electronic package ； lead free solder ； impact reliability ； harndess ； Microstructure

參考文獻

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