不同金屬墊層結構對錫2.3銀微凸塊經熱循環測試後裂縫形成之研究

Abstract

隨著封裝技術從平面演進到立體的堆疊，其中接點尺寸的微縮將無可避免，許多研究中指出，介金屬化合物的脆性，將不利於三維積體電路封裝的發展，但在越來越小的接點中，介金屬化合物將佔據大部分的體積比例，研究介金屬化合物對於微凸塊接點機械性質的影響，是個很重要的議題。 本研究利用不同的金屬墊層去製備出銲錫高度10 µm與40 µm的微凸塊接點，其結構可分為Cu/Sn2.3Ag/Cu、Ni/Sn2.3Ag/Cu、Ni/Sn2.3Ag/Ni，接著在260oC經過不同的時間迴銲熱處理，最後進行-55oC到125oC的熱循環測試，探討不同熱處理時間、銲錫高度與金屬墊層結構對於微凸塊接點破壞模式的影響。 觀察微凸塊接點在兩端的介金屬化合物接合之前，在介金屬化合物與銲錫的界面產生疲勞裂縫，提高銲錫高度則使得裂縫產生從介面轉移至銲錫內部，改變UBM結構後，發現三元的介金屬化合物能穩定與銲錫的界面，進而抑制裂縫成長，而完全轉變成介金屬化合物的微凸塊接點，擁有良好抗熱循環測試的能力，甚至在經過2000次的熱循環測試後，依舊沒有任何破壞現象產生，可見介金屬化合物並沒有如報導中預期，在熱循環測試後有因材料脆性而發生破壞的現象。

Due to the progress of packaging technology from 2-dimension to 3-dimension (3D) stacking, the decreasing in pitch of microbumps is inevitable. It was reported the intermetallic compounds (IMCs) are brittle and thus not good for 3D integrated circuit (IC) reliability. While the microbumps are getting smaller, the IMCs will occupy a large percentage of joint volume. Therefore, it is important to study the effect of IMC formation in mechanical properties of microbumps. In this study, different kinds of structures, Cu/solder/Cu, Cu/solder/Ni, and Ni/solder/Ni, were used to study the effect of different IMCs on the crack resistance during thermal cycling test (TCT). The solders are Sn2.3Ag, and the heights were 10µm and 40µm. After various reflow time at 260 ℃, the microbumps were tested under TCT. (-55oC to 125oC) We will discuss the effect of reflow times, solder heights, and the IMC compositions on the failure mechanisms of microbumps under TCT. After long period of reflow, the IMC bridging phenomena was observed in most of the low solder height samples. Before IMC bridging, we can observed the crack appeared from the edge of the IMC/solder interface. The length of cracks increased as the solder height. Comparing the Cu/solder/Cu and Cu/solder/Ni system, the ternary IMCs can significantly reduce the cracks between the IMC/solder interface and inhibit the cracks propagation. The IMC-bridged microbumps can endure 2000-cycle TCT and reduce crack propagation. According to these obtained results, the IMC bridging is an advantageous to the TCT in microbumps. The IMC bridging effectively minimize the crack initiation and propagation.