隨電子產品微型化之趨勢，電子構裝技術除了追求高封裝密度以外，更要求高功能性。新型三維封裝（3D packages）被視為延續莫爾定律（Moore’s law）之重要技術。其中，導通電路之微銲點與現今業界常用的覆晶封裝 (flip-chip technology) 之銲接點，在體積上有頗大的差異。這些銲點主要由界面介金屬化合物（intermetallic compounds）以達成晶片與電路板穩固接合及電路導通，其性質如形貌、生成相性質與相穩定性皆會影響銲接點可靠度。許多研究由改變銲料合金與凸塊金屬，影響介金屬化合物之性質，以提升整體封裝之可靠度。

本研究延用業界常用之鎳及銅金屬基材至微銲點中，藉由不同接合順序，以探討此二元素在極小錫銲料中之交互反應。分別為先接合無電鍍鎳金 (ENIG) 基板，再接銅基板; 以及先接合有機保銲銅 (OSP-Cu) 基板，再接鎳基板。此外，在微銲點中，由於錫銲料體積微型化，在銲點中生成之介金屬化合物體積比例劇增，因此介金屬化合物之性質將會是影響封裝可靠度ㄉ重要因子。

在 ENIG/Sn-3.5Ag/Cu 三明治微銲點結構中，利用不同回銲時間以觀察介金屬化合物生成演變機制。僅僅10 之微小錫銲點中，生成複雜之五層相結構。在經過30秒回銲時，只有在ENIG端有兩相介面的形成，分別為 (Ni,Cu)3Sn4 與高鎳含量之 H-(Cu,Ni)6Sn5 組成。再5分鐘回銲後，發現兩相介面形成於ENIG端及Cu端，ENIG端一樣為 (Ni,Cu)3Sn4 及 H-(Cu,Ni)6Sn5 ，而Cu端則由高鎳含量之 H-(Cu,Ni)6Sn5及低鎳含量之 L-(Cu,Ni)6Sn5 組成。錫料中大量L-(Cu,Ni)6Sn5 攜出，形成一個五層相堆疊之結構。由於兩相介面易於裂痕擴展，此系統之相結構相信會降低微銲點之機械性質，進而劣化電子夠裝之可靠度。

相反的，在OSP-Cu/Sn-3.5Ag/Ni對照組中，經長時間回銲後，只有低鎳含量之 L-(Cu,Ni)6Sn5 生成，並無任何的兩相介面。在微銲點中，經由金屬基材之接合順序，即能使生成之介金屬化合物差異慎大。綜合上述，本研究將利用熱力學相關理論，配合墊子顯微鏡之觀察及背向散射繞射儀之結果，對介金屬化合物生成機制做深入探討，並提供業界有關於製成順序對元素反應之影響，將因微型化趨勢逐漸放大。

With the highly demand for the miniaturization of large-scale-integration of circuits on Si chips, the electronic packaging technology has been evolved from conventional flip-chip bumps to small micro-bumps. Dramatically reduction of soldering volume results in a great concern of packaging reliability. Furthermore, in micro-bumps, not only the characteristics of interfacial reaction will be a main concern but also more limitation in fabrication process. As a result, architecture control through process modification to alter the microstructure of micro-bumps was demonstrated to affect the interfacial reaction in micro-bumps. Meanwhile, the understanding of interfacial reaction in micro-bumps is a potential way to solve the critical issues in this small solder volume system. In this study, two steps of boing process were investigated. One with ENIG substrate bonded ahead of the Cu substrate, the other with OSP-Cu substrate bonded ahead of the Ni substrate.

By bonding the ENIG substrate ahead of the Cu substrate, the microstructure evolution of ENIG/Sn-3.5Ag/Cu micro-bumps after reflow was studied. Due to the short diffusion path between two opposite substrates, the effects of substrate dissolution by two-steps reflowing process in ENIG/Sn-3.5Ag/Cu micro-bumps revealed a complex 5 layered structure. After 30 sec of reflow, only ENIG side has a dual phase structure composed of H-(Cu,Ni)6Sn5 and (Ni,Cu)3Sn4. After longer reflow time, it is interesting to note that dual phase structure appeared at both Cu and ENIG sides. H-(Cu,Ni)6Sn5 and L-(Cu,Ni)6Sn5 showed up at the Cu side, meanwhile, H-(Cu,Ni)6Sn5 and (Ni,Cu)3Sn4 were at the ENIG side after reflow for 5 min. The dual phase structures are believed to be vulnerable to cracks and lead to degradation of micro-bumps’ reliabilities.

In contrast, by bonding the OSP-Cu substrate ahead of the Ni substrate, the microstructure evolution of OSP-Cu/Sn-3.5Ag/Ni micro-bumps after reflow was also studied. It is noted that the microstructure of IMCs on both interface of the substrates showed a significant difference as only one phase was found, which was L-(Cu,Ni)6Sn5. Also, the deteriorative dual phase structures found in ENIG/Sn-3.5Ag/Cu micro-bumps were no longer shown in OSP Cu/Sn-3.5Ag/Ni micro-bumps. With the aid of the field emission electron probe micro-analyzer (FE-EPMA), the mechanisms of the microstructural evolution are probed in detail by the phase diagram and the diffusion related migration of the constituents. It is expected that the results derived in this study can provide useful information for the industry of microelectronic packaging.

Contents I
Lists of Table IV
Figures Caption V
Abstract IX
Chapter 1 Introduction 1
1.1 Background 1
1.2 Motivation and Goals in This Study 2
Chapter 2 Literature Review 5
2.1 Electronic Packaging and Flip Chip Technology 5
2.2 Solder Bump 6
2.2.1 Sn-Pb Solder 7
2.2.2 Lead-Free Solder 8
2.3 Under Bump Metallization 9
2.3.1 Cu based UBM 9
2.3.2 Ni based UBM 10
2.4 Interfacial Reactions in Pb-free Solder Joints 11
2.4.1 Interfacial Reactions between Pb-free Solder and Cu based UBM 12
2.4.2 Interfacial Reactions between Pb-free Solder and Ni based UBM 13
2.4.3 Cross-interaction of Cu/Solder/Ni Sandwich Structure 14
2.4.4 Dual Phase IMC Structures 15
2.5 Novel Electronic Packaging System 16
2.5.1 System on Chip (SoC) 16
2.5.2 System in Package (SiP) 17
2.5.3 Three-dimensional Integrated Circuit (3D-IC) 17
2.6 Reliability Issues in Micro-bumps 19
Chapter 3 Experimental Procedure 48
3.1 Micro-bumps Fabrication 48
3.1.1 The Fabrication of ENIG/Sn-3.5Ag/Cu Micro-bumps 48
3.1.1 The Fabrication of OSP Cu/Sn-3.5Ag/Ni Micro-bumps 49
3.2 Sample Preparation for Characterization 49
3.3 Characterization and Analysis 50
3.3.1 Microstructure Evolution 50
3.3.2 Composition Analysis 50
Chapter 4 Results and Discussion 54
4.1 Microstructure and Formation Mechanism of Complex 5 Layered IMCs in ENIG/Sn-3.5Ag/Cu Micro-bumps by first reflow ENIG UBM 54
4.1.1 Formation of IMCs and Elemental Distributions 54
4.1.2 Mechanisms of phases formation at the ENIG side 58
4.1.3 Mechanisms of phases formation at the Cu side 59
4.2 Microstructure and Formation Mechanism of IMCs in OSP-Cu/Sn-3.5Ag/Ni Micro-bumps by first reflow OSP-Cu UBM 67
4.2.1 Formation of IMCs and Elemental Distributions 67
4.2.2 Mechanisms of phases formation at the OSP-Cu side 70
4.2.3 Mechanisms of phases formation at the Ni side 70
Chapter 5 Conclusions 80
References 82

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