中文摘要

因為鉛對地球環境與人類健康有潛在的威脅，因此無鉛銲錫的開發研究已經成為電子構裝產業中最重要的課題之一。近年來錫鋅系無鉛銲錫被認為擁有相當的潛力能夠取代傳統鉛錫合金，最主要是因為錫鋅合金之共晶溫度為二元銲錫系統中與鉛錫合金最為接近的系統，且在已研發的無鉛銲錫中，錫鋅合金的價格是最低廉的；但錫鋅銲錫合金的最大缺點則是抗氧化性太差，以及與一般電子構裝中常用基材間之潤濕性不佳。因此本研究主要目的就是於錫鋅系列銲錫合金中添加鋁元素與銀元素，希望藉由第三、四元素的添加來改善錫鋅銲錫合金之抗氧化性與潤濕性。
顯微結構分析結果顯示，Sn-8.55Zn-0.45Al銲錫合金中添加銀(0wt%~3wt%)，會於合金中形成AgZn3與Ag5Zn8化合物，且造成原本銲錫基地之富鋅相漸漸減少，因此銲錫合金基地組織從原本錫鋅共晶組織偏離成錫鋅亞共晶組織。熱差分析(Differential Scanning Calorimetry, DSC)結果顯示，Sn-8.55Zn-0.45Al三元合金有一共晶熔點，約197ºC；但當銀加入Sn-8.55Zn-0.45Al合金後，所生成之銀鋅化合物，約在300ºC左右才會完全熔融。在機械性質方面，添加銀會稍微增加Sn-8.55Zn-0.45Al-XAg(X=0.5wt%~3wt%)合金之抗拉強度與硬度，但卻使合金之伸長率大幅下降；當銀的添加量到達3wt%時，銲錫合金之伸長率從原本的47.1%下降至20%。
熱重分析(Thermal Gravimetric Analyzer, TGA)結果顯示，銲錫合金在250°C、純氧的環境下，重量增加量之大小順序為Sn-9Zn＞Sn-8.55Zn-0.45Al-XAg＞Sn-8.55Zn-0.45Al。此結果顯示添加鋁可以增進錫鋅合金之抗氧化性，但添加銀反而會使銲錫合金之抗氧化性變差。從歐傑縱深分析(Auger Electron Spectroscopy, AES)得知，銲錫合金表面會生成ㄧ層氧化層；錫鋅合金表面為鋅之氧化物，而含鋁銲錫合金表面則為鋁之氧化物。在潤濕實驗中發現，Sn-8.55Zn-0.45Al- XAg合金與基材之潤濕性隨著銀含量(0.5wt%~ 3wt%)增加而下降，不過低銀含量(0.5wt%)銲錫合金與基材間之潤濕性質，仍優於共晶錫鋅合金。此外亦同時發現，錫鋅系無鉛銲錫合金與銅基材之潤濕性，似乎優於其與銅/鎳-磷/金基材。
錫鋅合金與銅基材間反應生成Cu5Zn8與CuZn5兩種化合物，含鋁之銲錫合金則生成Al4.2Cu3.2Zn0.7三元化合物。經高溫時效後，錫鋅合金與銅基材界面會生成Cu6Sn5化合物，而含鋁之銲錫合金與銅基材界面則生成Cu5Zn8。在與銅/鎳-磷/金基材界面上，錫鋅合金會生成AuZn3化合物，含鋁之銲錫合金則是生成Al2(Au,Zn)化合物，且經高溫時效後，銲錫合金與銅/鎳-磷/金基材界面上之化合物幾乎不會成長。另外，當銀加入Sn-8.55Zn-0.45Al銲錫合金時，其界面會生成AgZn3化合物。
本研究亦探討經多次重流與高溫時效後，Sn-8.55Zn-0.45Al-XAg銲錫合金之可靠度。結果顯示，錫鋅系銲錫合金與銅基材和銅/鎳-磷/金基材接合經多次重流後，其剪力強度並不會下降；但經高溫時效後則發現，錫鋅系銲錫合金與銅基材接合之剪力強度隨時效時間增加而下降，可是與銅/鎳-磷/金基材接合之剪力強度則不受時效時間影響；結果顯示，錫鋅系銲錫合金於銅/鎳-磷/金基材接合之可靠度明顯優於與銅基材接合。

Abstract

The development of lead-free solders has become an important issue in the electronics packaging industry because of environmental and health concerns. Recently, Sn-Zn based solders have been considered to be a potential candidate for lead-free solder because its melting temperature is relatively close to that of eutectic Sn-Pb solder. Sn-Zn solders also have lower cost than other lead-free solders. However, Sn-Zn solders exhibit unsatisfactory oxidation resistance and poor wettability on commonly used substrates. The purpose of this research is to investigate the incorporation of Al and Ag in Sn-Zn solder in order to enhance its wettability and oxidation resistance. The microstructure, mechanical property, wettability, oxidation behavior, interfacial reaction and reliability of the Sn-8.55Zn-0.45Al-(0~3wt%)Ag solders were investigated in this study.
The microstructure of Sn-Zn based solders shows that the AgZn3 and Ag5Zn8 compounds are formed at the addition of (0.5wt%~3wt%)Ag to Sn-8.55Zn-0.45Al solders. The formation of Ag-Zn compounds (AgZn3 and Ag5Zn8) results in the variation of matrix from eutectic to hypoeutectic structure. The results of DSC (Differential Scanning Calorimetry) reveal that the Sn-8.55Zn-0.45Al solder has eutectic temperature at 197°C, but Ag-Zn compounds (AgZn3 and Ag5Zn8) melt above 300°C as Ag is added to the Sn-8.55Zn-0.45Al solder. An increase in Ag content results in little change in UTS (Ultimate Tensile Stress) and microhardness, but the elongation is prominently decreased. The elongation of the solders drops from 47.1% to 20% when Ag content increases from 0 to 3%.
The results of TGA (Thermal Gravimetric Analysis) show that the weight gains at 250°C under O2 atmosphere descend in the order of Sn-9Zn>Sn-8.55Zn-0.45Al-(0.5wt%~3wt%)Ag>Sn-8.55Zn-0.45Al. This means that the incorporation of 0.45wt%Al enhances the oxidation resistance of Sn-Zn solder, while the weight gains of the Sn-8.55Zn-0.45Al-XAg solders increase as Ag was added into the Sn-8.55Zn-0.45Al solder. Auger depth profile shows that Zn and Al form an oxide film on the surface of Sn-9Zn and the Al-containing solders. The wetting results indicate that the wettability of Sn-8.55Zn-0.45Al-XAg solders decreases with increasing Ag content of solders. The Sn-Zn-Al-XAg solders containing low Ag content (0.5wt%) exhibit better wettability than the eutectic Sn-9Zn solder. Furthermore, it was also found that the wettability of Sn-Zn based solders on Cu substrate is better than that on Cu/Ni-P/Au substrate.
The results of interfacial reaction indicate that Cu substrate forms Cu5Zn8 and CuZn5 with Sn-9Zn solder, and Al4.2Cu3.2Zn0.7 compound with Al-containing solders. However, it was detected that Cu6Sn5 forms at the Sn-9Zn/Cu interface and Cu5Zn8 forms at the Al-containing solders/Cu interface after aging for 1000 hours. In contacting with the Cu/Ni-P/Au substrate, Sn-9Zn solder forms AuZn3 compound, and the Al-containing solders forms Al2(Au,Zn) compound at the interface. After long time aging, the intermetallic compounds existing between solders and the Cu/Ni-P/Au metallization layers almost do not grow. It was found that the inter-diffusion between solders and Cu/Ni-P/Au is slower than that with Cu under aging. Furthermore, the additions of Ag to Sn-8.55Zn-0.45Al solder result in the formation of AgZn3 particles at the interface.
This present work also investigated the reliability of the Sn-8.55Zn- 0.45Al-XAg solders under multiple reflow and thermal aging test. The results show that Sn-Zn based solder balls on Cu and Cu/Ni-P/Au substrates retain the shear strength under multiple reflow. Under thermal aging test, it was found that the shear strength of Sn-Zn based solder balls on Cu substrate decreases with increasing of aging time. However, the shear strength of Sn-Zn based solder balls on Cu/Ni-P/Au almost dose not change under thermal aging test. Thus, it was known that the Sn-Zn based solder balls on Cu/Ni-P/Au substrate exhibit better reliability than that on Cu substrate.

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