臺灣博碩士論文加值系統

本論文利用四點彎矩法研究基板的應變對於無鉛錫銅介金屬層形成所造成的影響，試件分別從四吋拋光矽晶圓及400 μm厚的銅片切割成27 mm × 5 mm之長條形，由於矽晶圓不導電因此先使用濺鍍機鍍上一層非常薄的黏結層，在黏結層和銅片上鍍上10 μm厚的銅金屬層，再分別鍍上35 μm厚的霧錫及亮錫於銅金屬層上，將試件模組放置於200 ℃的烘箱，給予試件拉、壓及無應變(±1.54 x 10-4, ±2.3 x 10-4 and ±3.46 x 10-4)並於不同的老化時間下觀察對IMC層之影響，經由SEM可以很清楚觀測各層之厚度，實驗結果顯示當霧錫受壓其IMC厚度增加，受拉則減少，另一方面，亮錫於受壓跟受拉狀態下IMC層皆增加，並發現於相同應變下亮錫的IMC厚度成長率高於霧錫，而且，對於不同的錫給予外加應變其IMC微結構也非常的不同。衍伸之以外加應變實驗量測對運用標準製程產生之的無鉛銲錫薄膜成型與擴散之影響，此研究測試之數據，能清楚對照微封裝製程使用的銲接薄膜材料，於應用過程中產生之材料受機械應力產生之行為及使用的相關性，對目前研究之各種不同配方之無鉛銲錫薄膜材料可靠性和各項實驗機械應力影響作分析。數據將可提供微製造時選用之無鉛銲錫薄膜材料的之參考，也對產品元件使用之可靠度分析提供一極有價值之研究。

This thesis presents the results from four point bending tests conducted to investigate the strained substrates effect on interfacial Cu-Sn inter-metallic compound (IMC) formation layer growth. The test specimens were cut into strips 27 mm in length and 5 mm in width from 4 inch double polished silicon wafers or 400 μm Cu substrate. A very thin adhesion layer was deposited onto the substrate using sputtering. A 10 μm thick copper layer was deposited on top of the adhesion layer using the electroplating method. Two types of tin samples (Matte and Bright) were tested. A 35 μm tin layer (Matte or Bright) was then deposited on top of the copper film. During the experiment a set of samples were placed into a furnace at 200 ℃. In-plane bending strain was applied to the samples under tension, compression and without strain. The IMC formation results affected by different substrate strain (1.54 x 10-4, 2.3 x 10-4 and 3.46 x 10-4) and different aging time is presented. The thickness of each phase (Cu3Sn) and (Cu6Sn5) could be observed clearly and separately in scanning electron microscope images. The IMC layer thickness was increased when the sample was under both compression strain and tension strain. The enhanced effect caused by the compressive substrate strain was more severe than that due to the tensile substrate strain. We hypothesize that the observed increase in IMC thickness is related to strain enhanced out-diffusion of Cu towards the solder and strain in the underlying lattice at the diffusion interface.
The results on intermetallic formation affected by different strain levels and aging time were presented. Both of tension and compression strain would affect the Cu/Sn IMC formation. The thickness of IMC was increased when Matte tin sample under compressive strain and decreased when Matte tin sample under tensile strain. On the other hand, the thickness of IMC was increased when Bright tin sample under both compression and tensile strain. We also observed the growth rate of IMC was faster in Bright tin under strain than in Matte tin. Moreover, the IMC micrograph structures from different tin sources present very differently under external strain during formation

Table of Contents
摘要 iii
Abstract iv
Chapter 1 Introduction 1
1.1.Background 1
1.2.Goal of the study 7
Chapter 2 Literature Review 10
2.1. Previous studies on the mechanical behavior of lead free solder 10
2.2 Literature Review on four point bending study 12
Chapter 3 Experimental Procedure 16
3.1 Sample Design and Fabrication 16
3.2 Four point bending test 19
3.3 Energy-dispersive spectrometry (EDS) test 23
3.4 Nanoindention test 23
Chapter 4 Results and Discussion 25
Chapter 5 Conclusions and Future work 45
References 46


List of Tables
Table I Relationship between designated film stress and substrate thickness 20
Table II The Sn/Cu IMC thickness (Matte tin sample) as a function of annealing time under in-plane compressive, tensile strain and no strain conditions. 31
Table III The Sn/Cu IMC thickness (Bright tin sample) as a function of annealing time under in-plane compressive, tensile strain and no strain conditions. 33

 
List of Figures
Figure 1 The silicon strip in four-point bending 13
Figure 2 Schematic of Cu-Sn sample preparation.(a)on the silicon structure.(b) on the copper structure. 18
Figure 3 Schematic of prepared sample under dead weight load supplied by a fused quartz loading pan next to four strip specimens plus two controls on the carrier boat. Where (a) is before and (b) is after the sample subjected to a tensile, compressive strain and no strain. 21
Figure 4 Schematic view of sample during thermal aging under strain. 22
Figure 5(a) SEM micrographs showing the cross sections of the Sn/Cu interface 25
after thermal aging at 200 ℃ for 72 h, where is the sample without bending 25
Figure 5 (b) SEM micrographs showing the cross sections of the Sn/Cu interface after thermal aging at 200 ℃ for 72 h, where is the sample subjected to a 3.46x10-4 tensile 26
Figure 5 (c) SEM micrographs showing the cross sections of the Sn/Cu interface after thermal aging at 200 ℃ for 72 h, where is the sample subjected to a 3.46x10-4 compressive strain 26
Figure 6 SEM micrographs showing the cross sections of the Sn/Cu interface of (A) Matte tin sample (B) Bright tin sample after thermal aging at 200 ℃ for 120 h, where (a) is the sample without bending and (b) and (c) are the samples subjected to a 1.2 x 10-3 tensile and 1.2 x 10-3 compressive strain, respectively, in bending. 28
Figure 7 Cu3Sn phase and total IMC thickness versus aging times for film strain of ±1.54 x 10-4, ±2.3 x 10-4 and ±3.46 x 10-4, and unloaded control. 29
Figure 8 Increasing IMC film thickness versus film strains as a function of aging time. 30
Figure 9 Total Sn/Cu IMC thickness of Matte tin type sample versus aging times for film strain of±8.15 x 10-4, ±1.2 x 10-3 and ±1.5 x 10-3, and unloaded control 31
Figure 10 Total Sn/Cu IMC thickness of Bright tin type sample versus aging times for film strain of±8.15 x 10-4, ±1.2 x 10-3 and ±1.5 x 10-3, and unloaded control. 32
Figure 11 Total Sn/Cu IMC thickness of Matte tin type sample versus aging times for film strain of±8.15 x 10-4, ±1.2 x 10-3 and ±1.5 x 10-3, and unloaded control. 34
Figure 12 Total Sn/Cu IMC thickness of Bright tin type sample versus aging times for film strain of±8.15 x 10-4, ±1.2 x 10-3 and ±1.5 x 10-3, and unloaded control. 37
Figure 13 The EDS results in the presence of elements in the IMCs from Matte tin (a) and Bright tin (b) samples after thermal aging with 1.2 x 10-3 compression strain. 39
Figure 14 Schematic diagram showing the interfacial IMC between Cu substrate and Sn layer. As indicated by the arrows, higher compressive stress at the Cu substrate promotes out-diffusion of Cu towards the solder. 40
Figure 15 AFM images of interfacial morphology in Cu, Sn and Cu/Sn IMC 40
Figure 16 The load-depth curves 41
Figure 17(a) The hardness versus bending strain in the Cu3Sn at12hrs and 96hrs 42
Figure 17(b) The hardness versus bending strain in the Cu6Sn5 at12hrs and 96hrs 42

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