鑽石厚膜與薄膜硬焊強度及量測方法之研究

Abstract

鑽石厚膜與薄膜硬焊強度及量測方法之研究學生：鄭晏熙 指導教授：郭正次 教授國立交通大學材料科學暨工程研究所摘 要本研 究以商業用鑽石厚膜(約1.2mm厚)和以N-type Si(100)基材採用微波電漿 氣相沉積之鑽石薄膜，探討Ag-Cu-Ti系列(CB1、CB2、CB4、CB5)及Ni-Cr 硬焊合金之硬焊接合特性，並設計適當的測試夾具以期能直接量測其硬焊 強度。利用Raman及XRD來鑑定鑽石之品質，及利用DTA及ICP-AES分析來了 解硬焊合金的熱特性及合金成分。實驗中利用SEM、EPMA、XRD來研究鑽石 膜與硬焊合金的界面反應情形。硬焊實驗之主要參數包括焊接溫度、持溫 時間、環境氣氛與真空度。結果可分為以下三方面:(1) 硬焊強度量測方 法本研究成功地設計剪斷及拉伸強度測試夾具可以直接量測鑽石膜之硬焊 強度，這是其它量測方法所無法做到的。而且由鑽石厚膜與Ag-Cu-Ti系列 硬焊合金接合所得之剪斷強度結果，可以比較出硬焊製程參數(焊接溫度 、持溫時間、環境氣氛及真空度)對於剪斷強度之影響。其趨勢跟學理依 據及文獻相當一致，顯示所得剪斷強度結果具有相當的可信度。至於拉伸 強度測試而言，則視硬焊強度和鑽石對基材之附著強度的大小，可以量測 較弱一方的強度。(2) 硬焊參數的影響本研究顯示所用之Ag-Cu-Ti系列合 金，其硬焊溫度在某一溫度範圍(約900℃)，可得最佳之剪斷強度。溫度 太低，流動性則不佳，所以潤濕性較差而無法得到較高的剪斷強度。反之 ，若溫度太高，由於Ti和C原子擴散速度的差異，可能易造成Kirkendal- Frekel效應。且高溫使得鑽石轉換成石墨的機率增大，因而降低硬焊合金 潤濕性。以上兩種效應，皆會造成溫度太高時剪斷強度下降。至於持溫時 間跟硬焊溫度有如一體兩面，溫度高時則持溫時間較短。硬焊氣氛與真空 度之影響，主要是保持硬焊合金不受氧化及降低鑽石之石墨化速率。實驗 結果看出，在氬氣保護下硬焊接合所得之剪斷強度皆比在低真空(10-3 torr)下所得者為高。而在高真空(10-6torr)下以Ni-Cr系列硬焊合金(焊 接溫度1050℃，持溫時間10min)與鑽石厚膜接合所得剪斷強度(41.70MPa) 又比在氬氣保護下所得者(4.48MPa)為高。因此可知較乾燥的氣氛及較高 的真空度皆有助於提高硬焊強度。以本研究所用氣氛來比較，Ar氣氛優 於10-3torr真空度，10-6torr真空度又優於Ar氣氛。(3) 硬焊合金成分的 影響就硬焊合金成分之影響而言，依各焊料與鑽石厚膜硬焊接合所得之剪 斷強度來比較，其優劣依序為CB1>CB5>CB4>CB2>Ni-Cr。就Ag-Cu-Ti系列 硬焊合金作比較，其中以CB1硬焊合金所得剪斷強度結果(128.18MPa)為最 佳。這是由於其焊料之Ag-Cu組成接近Ag-Cu合金之共晶組成(Ag-28.1%Cu) ，所以流動性較好，而能夠充分潤濕鑽石厚膜並提高剪斷強度。至於Ni- Cr硬焊合金，由於其熔點高易跟鑽石膜反應，而且容易氧化並造成流動性 下降，所以剪斷強度不佳。也許減少持溫時間可以改善此種現象。 Study on Brazing Strength and Its Measuring Techniques for Diamond Thick and Thin Films Student: Yen-Hsi-Jen Advisor: Dr.Cheng-Tzu KuoInstitute of Materials Science and EngineeringNational Chiao Tung UniversityAbstract Commercial Diamond thick films and CVD diamond thin films onSi substrate were used to study the brazing behaviors using various brazing alloys including Ag-Cu-Ti series(CB1,CB2,CB4,CB5)and Ni-Cr alloys. Two testing fixtures were also designed for direct measurements of shear and tensile brazing strength. Raman spectroscopy and XRD were used to evaluate diamond quality.The thermal behavior and composition were analyzed by DTA and ICP- AES. The interface structure and the possible interactions among diamond, Si substrate and brazing alloy were characterized by SEM, EPMA and XRD. The primary brazing parameters include brazing temperature, holding time and reaction atmosphere. From the experimental results, the following conclusions can be divided into three parts. (a) Brazing strength measurement Both the designed fixtures were successfully used to directly measure the shear and tensile brazing strengths. The testing methods are superior to other conventional indirect methods, which can only be used for qualitative comparison of the brazing strength. The results of shear strength testing could successfully differentiate the brazing behaviors under different brazing conditions, and the tendency of the behaviors is in agreement with the theoretical prediction and literature results. Therefore, this may indicate that the new shear testing method is a high reliable method for brazing strength determinations. As to the new tensile testing method, it can be used to measure either the brazing strength of diamond film or the adhesion strength of the film on the substrate, depending on which one is weaker. (b) Effect of brazing parameters The results indicate that there is an optimum brazing temperature range for the best brazing strength. A lower brazing temperature will result in a lower fluidity of the brazing alloy, and so a poorer wettability and brazing strength. On the other hand, a higher temperature gives rise to a high tendency to observe the Kirkendal－Frekel effect due to the high difference in diffusivity between C and Ti. Furthermore, a higher brazing temperature can also cause more diamond-graphite transformation, and so decease the wettability of brazing alloy on diamond film. Both effects may result in a poorer brazing strength at higher temperature. As to effect of holding time on brazing behaviors, it is known that both temperature and time are actually interrelated. A higher temperature will require a much less time to reach the same effect. Effect of brazing atmosphere on brazing behaviors is essentially to protect the brazing alloy from oxidization and to decrease the speed of diamond to graphite transformation. In the present experiment conditions, the brazing strength under different atmospheres seem to be in order of 10-6torr vacuum > Ar > 10-3torr vacuum. In the words, a dryer atmosphere or a higher vacuum will favor a higher brazing strength.(c) Effect of brazing alloy compositions Using different brazing alloys, the results show that the order of the best brazing strength is CB1 > CB5 > CB4 > CB2 > Ni-Cr alloy. As to Ag-Cu-Ti alloys, the shear strength of CB1 brazing alloy can reach to 128.18MPa, which is the best one among these brazing alloys. This is due to the fact that Ag/Cu ratio in CB1 alloy is close to the eutectic composition(Ag-28.1%Cu) of Ag-Cu binary alloy. Therefore, the fluidity and wettability will be much better, and so the brazing strength will be higher. In other words, the alloy with Ag/Cu ratio more to close to Ag-Cu eutectic composition will result in a greater brazing strength. As to Ni-Cr alloy, it has a much higher melting temperature. Therefore, it subjects to a highly susceptible to oxidation and so a lower fluidity and brazing strength. A decrease in holding time may improve the brazing strength.