中文摘要
銲錫合金在電子構裝中，接合電子元件與基板，因此接合強度是非常重要的性質，而銲錫合金與基材之間的強度，主要是因為銲錫合金與基材間原子的反應生成介金屬化合物，使其產生潤濕的效果，但是若生成過多的介金屬化合物，會使得去潤濕的現象發生，因此必須控制適當的反應溫度、銲錫成份和助熔劑選擇來達成較好的潤濕性，且因為環保議題日趨重要，加速了無鉛銲錫合金的開發。
本研究採用Sn-8.5Zn-xAg-0.01Al-0.1Ga，x=0、0.1、0.3、0.5、1.0、1.5銲錫合金，探討合金的熱性質，以及利用潤濕天平和接觸角測量儀測量合金與銅基材在不同溫度和配合不同助熔劑的潤濕效果， 並觀察界面經過高溫時效後發生的反應。
熱差分析儀測量及電子顯微鏡分析結果顯示，添加銀元素，會使得合金組成偏離共晶成份，擴大兩相區範圍，針棒狀富鋅相的錫鋅共晶組織會逐漸減少，且AgZn3介金屬化合物也會逐漸增多。隨著銀含量的增加，在230˚C和240˚C時，潤濕性會逐漸變差，活化能與接觸角逐漸增大；掃描式電子顯微鏡觀察顯示界面組織為層狀Cu5Zn8，增加銀含量，扇貝狀AgZn3介金屬化合物也會增加，抑制銅元素的擴散與反應，降低潤濕性。
高溫時效反應，會增厚銲錫合金與銅基材間的Cu5Zn8介金屬化合物，但增加銀含量，會降低Cu5Zn8的成長速度，且在120小時之後，層狀Cu5Zn8會逐漸破裂，在Cu5Zn8和銅的界面處會有一層鎵元素析出，到達400小時後，錫元素擴散至銅基材以生成Cu6Sn5，到達900小時後，因為銲錫中的鋅元素漸漸被耗盡，Cu5Zn8的成長會趨於緩慢，但破裂的狀況會更加嚴重，而原本在界面析出的鎵元素，再度固溶回錫基地

Abstract
Solder alloys are used to bond electronics devices. As the size of the solder joints becomes smaller and smaller, the mechanical properties and reliability of the solder alloys become extremely important. This bonding is the results in the diffusion and reaction of atoms from solder and substrate side forming intermetallic compound (IMC). Soldering process could be explained starting from when the molten solder fully covered a substrate surface. Too much IMC formed at the interface will make the molten solder difficult to wet the substrate. Hence the soldering process should be controlled so that only limited IMC would form. The better soldering process with different solder alloys will be required at different soldering time and flux. The trend of lead-free issue for environmental protection accelerates the rate of development of lead-free solders.
The solder alloys used in the study were Sn-8.5Zn-xAg-0.01Al-0.1Ga where “x” indicates silver content in the alloys, x = 0.01, 0.1, 0.3, 0.5, 1 and 1.5. The alloys were initially investigated using Differential Scanning Calorimetry (DSC) to measure their melting temperature. Then the solder alloys were also tested for their solderability using wetting balance and contact angle methods. The microstructure at the interface were observed by SEM and EPMA after the isothermal annealing at 150˚C for 120h, 400h and 900h.
It was found that the two phase region widen with the addition of silver content because DSC analysis showed that the composition of solder diverges from the eutectic composition. SEM analysis showed the quantity of AgZn3 increased after the silver content increased. This increasing amount of AgZn3 might explain why the viscosity of the studied solder increased with the increasing content of silver.
The wetting balance test indicated that the wettability between the Cu and solder alloys is reduced by the addition of silver element with the DMAHCL flux at the 230˚C and 240˚C. The activation energy and the contact angle were also found to increase with the increasing silver content. The reason for poor wettability with the higher silver content is that Ag and Cu atoms are competing to react with Zn atom to form AgZn3 and Cu5Zn8 layer IMC. Furthermore, the wettability is depended on the reaction between Cu atom from the substrate and Zn atom from the solder matrix. If more AgZn3 is formed at the interface, it will retard the diffusion rate of Cu and the reaction between Cu and Zn. In this study, the flux DMAHCL demonstrated better performance compared to the flux SZ555 flux.
The thickness of Cu5Zn8 grows with the aging time at 150˚C but the addition of silver element will slow down the growth of the Cu5Zn8 layer. The Cu5Zn8 IMC layer was broken and a very thin Ga layer segregates at the interface between Cu and Cu5Zn8 IMC after thermal treatment at 120 hours. After 400 hours, the Cu6Sn5 IMC was formed with the Sn diffusing to the Cu substrate. Then the Cu5Zn8 IMC grows slowly due to the depletion of Zn element in the solder matrix but the cracks become obvious. The thin Ga layer which is formed initially disappeared due to the Sn atoms penetrated to the Cu side and then Ga dissolved into Sn matrix after the 900 hours thermal aging.

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