近年由於人工智慧發展需求的增加，對晶片效能的要求也日益提升，然而，微縮電路線寬增加晶片效能所需的成本難以負擔，且微縮趨勢逼近物理極限，因此產業發展的主流趨勢轉往先進封裝以降低開發成本並提升晶片效能。先進封裝藉由縮減焊點的體積與焊點間距使集成密度及能源效率表現提升，然而當焊點尺寸縮小時，介金屬化合物（intermetallic compounds, IMCs）在焊點中所佔比例會進一步提升，甚至使焊點轉變為全IMC結構。因此IMC性質也成為封裝領域重要的研究。本研究透過暫態液相接合(transient liquid phase bonding)在Ni/Sn-3.5Ag/Cu進行回流焊接模擬小尺寸焊點中IMC生長，並改變不同凸塊高度（bump height）及不同回流焊接時間(reflow time)觀察Cu6Sn5與Cu3Sn之微結構變化，發現在凸塊高度5 µm、回流焊接300s的條件下焊點轉變為全IMC結構，並對此參數進行不同時間時效處理(aging test)，以image j軟體進行Cu3Sn厚度定量分析以推算生長動力學機制，輔以EBSD進行晶粒尺寸分析、EPMA進行元素定量以驗證其動力學機制。
在時效處理前期(時效處理時間24 - 120小時)，Cu3Sn形貌為層狀結構且生長機制為反應控制，起因於晚生成的Cu3Sn晶粒較小且厚度較薄，擴散快，銅原子供應充足，限制系統生成Cu3Sn主要因素為反應速率，故為反應控制。而在時效處理後期(時效處理時間120 - 840小時)，Cu3Sn形貌轉變為網狀結構且生長機制為擴散控制，藉由EBSD進行晶粒尺寸分析發現經過長時間的時效處理後原本的Cu3Sn層變厚，且Cu3Sn晶粒粗化，使整體擴散係數降低，故轉為擴散控制，而當銅原子擴散至上方時，部分銅原子沿晶界擴散並與晶界周圍Cu6Sn5反應，產生網狀Cu3Sn。
平坦狀及網狀Cu3Sn之生長動力學將在本研究中深入討論，並期望藉由此研究對先進封裝微焊點可靠度做出貢獻。

In recent years, due to the increasing demand for artificial intelligence development, the requirements for chip performance have also been rising. However, the cost of improving chip performance by reducing circuit linewidth has become increasingly unaffordable, and the miniaturization trend is approaching physical limits. As a result, the industry has shifted its focus to advanced packaging to reduce development costs and enhance chip performance.
Advanced packaging improves integration density and energy efficiency by reducing the size and pitch of solder joints. However, as the solder joint size decreases, the proportion of intermetallic compounds (IMCs) in the joint increases, potentially transforming the solder joint into a fully IMC structure. Consequently, the research of the IMCs’ property has become crucial in the packaging field.
In this study, transient liquid phase bonding (TLP-Bonding) was used to simulate IMC growth in small solder joints by conducting reflow soldering in Ni/Sn-3.5Ag/Cu system. By varying the bump height and reflow time, the microstructural evolution of Cu6Sn5 and Cu3Sn was investigated. It was found that under the condition of a 5 µm bump height and 300 seconds of reflow time, the solder joint transformed into a full-IMC structure. Aging tests with different durations were then conducted under this condition. The Cu3Sn thickness was quantitatively analyzed using Image J software to evaluate the IMC growth kinetics. Additionally, electron backscatter diffraction (EBSD) was used for grain size analysis, and electron probe microanalysis (EPMA) was conducted for elemental quantification to validate the kinetic mechanism.
In early stage of aging treatment (aging 24-120 hours), Cu3Sn exhibits a layered-structure, and its growth mechanism is reaction control. This is because newly formed Cu3Sn grains are small and thin, allowing fast diffusion with sufficient copper supply. The primary limiting factor in Cu3Sn formation is the reaction rate, leading the growth mechanism become reaction control. In late stage of aging treatment (aging 120-840 hours), Cu3Sn transforms into a network-like structure, and the growth mechanism shifts to diffusion control. EBSD analysis revealed that prolonged aging cause the original Cu3Sn layer become thicker and coarsens Cu3Sn grains, reducing the overall diffusion coefficient and shifting the mechanism to diffusion controll. When copper atoms diffuse upward, some diffuse along grain boundaries and react with surrounding Cu6Sn5, forming a network-structured Cu3Sn structure.
This study discusses the growth kinetics of layered and network-structured Cu3Sn and aims to contribute to the reliability of micro-solder joints in advanced packaging.