鉍偏析於錫鉍微銲接點之研究;Study of Bi segregation at the Sn-Bi micro-joint interface

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Title:	鉍偏析於錫鉍微銲接點之研究;Study of Bi segregation at the Sn-Bi micro-joint interface
Authors:	胡毓晉;Hu,Yu-Jin
Contributors:	化學工程與材料工程學系
Keywords:	微電子封裝;錫鉍共晶銲料;三維整合;鉍偏析;冷熱衝擊測試;IC packaging;Sn-Bi eutectic solder;3D itegration;Bismuth segregation;thermal shock test
Date:	2016-08-16
Issue Date:	2016-10-13 12:46:26 (UTC+8)
Publisher:	國立中央大學
Abstract:	隨著微電子構裝技術快速的發展，微銲接點的尺寸不斷縮小，以提供高密度的I/O (input/output) 數目於IC 晶片上。同時，三維積體電路製造技術的出現，不僅僅使得摩爾定律得以延續下去，更重要的是能於單位體積中容納更多的電晶體數目以及降低功率耗損，因此，三維積體電路製造技術將會是電子構裝技術的主流。然而，隨著微銲接點的尺寸縮小，直徑大小不到20微米的微接點將會取代以往數百微米尺寸的接點，微銲接點之可靠度將受到極大的挑戰。由於接點尺寸的大幅縮小，傳統以錫為主的銲料將會在極短的迴焊時間內反應完全形成介金屬化合物充滿在微銲接點鐘，因此介金屬化合物存在於接點之微結構組織以及強度便成為影響電子構裝可靠度的重要議題。本研究以極具發展淺力之低熔點錫鉍共晶銲料，在不經外壓應力下進行接合。首先，我們建構了錫鉍銲料組成與基板表面之粗糙度對微接點之微結構組織的影響，藉由提高錫含量以及基板表面之粗糙度，我們可以使得脆弱的鉍相不連續的偏析於微接點之介面，這種不連續偏析於介面且無孔洞生成的微結構使得脆弱的鉍相被相對高機械性質的介金屬化合物給保護住。最後，於晶片強度以及冷熱衝擊的測試中，我們得知此微結構具有良好的可靠度。在第二部分的討論中，我們以介金屬化合物成長動力學的探討來了解液態錫鉍銲料的偏析機制於迴焊過程中如何發生。我們發現到在迴焊過程中，當生成之扇貝狀介金屬化合物於介面與基材非常接近時，便能夠能夠阻止因鉍相析出而造成大量孔洞的生成。另外，因為此介金屬化合物於接觸到基材後的於平行晶片方向的持續成長，將液態錫鉍銲料排擠至晶界上造成液態錫鉍銲料不連續的偏析於微接點之介面，隨著鉍含量於液態錫鉍銲料隨著反應而增加，最後鉍相將不連續的偏析於微接點之介面。另外，介金屬化合物的成長速率將會受到液態錫鉍中鉍含量的影響，使得鉍偏析的驅動力大幅下降，造成孔洞於接面生成。;In recent years, the size of interconnections in the electronic devices are continuously shrinkage as the rapidly development of the electronic packaging industry. It can provide much higher I/O (input/output) ratio for the requirement of faster, thinner, and reliable electronic devices. Meanwhile, the three-dimensional integration technique has great potential for the coming decades. The most important issue for the reduction size of the interconnections would be the structural defects in the micro-joints. According to the solder would be consumed in a short reflow time, the mechanical properties of the intermetallic compounds at the micro-joint interface should be concerned. In the first part of this thesis, we observed that microstructure of the Sn-Bi solders that reflowed on the substrates would be affected by the composition of the solder and the roughness on the surface of the substrate. We could obtain a void-free micro-joint interface when we increase the Sn content in the Sn-Bi solder and the roughness on the substrate surface. Also, the discontinuously segregated Bi phases at the interface would provide good mechanical properties for micro-joint. Second, we figured out the segregated Bi phase at the micro-joint interface would related to the growth kinetic of the intermetallic compounds at the interface. As the scallop-like IMC grains grow at the interface and approached to the substrate enough, it would prevent the voids formed at the interface. Also, the discontinuously segregated Bi phases at the interface were attributed to the growth of the IMC grains. The growth of the IMC grains would expel the molten Sn-Bi solder away from the IMC grains at the interface. And the driving force that for expelling the molten solder would be inhibited with the increasing Bi content in the Sn-Bi solder.
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