2348 超硬磨料砂輪杯形修整器的設計,磨料,砂輪,修整,設計 STUDIES OF SURFACE GRINDING TEMPERATURE AFFECTED BY DIFFERENT GRINDING WAYS OF SILICON WAFERAbstract: The surface g grinding temperature o f the silicon wafer ground by diamond w heels is studied. Rudimentally, the properties o f the surface grinding temperature generated by two grinding methods, ground by straight and cup wheels respectively , are analyzed. In addition, considering the effects o f grain size and grinding depth on surface grinding temperature during these two grinding processes, significantresults and conclusions are obtained from experimental research.Keywords: surface grinding temperature, straight wheel, cup wheel, silicon waferThe machining technique of silicon wafers has gradually become one o f the progressive projects in recent years. With the successful production of large size silicon wafers, researchers all over the world have paid more at tention to the machining techniques of silicon wafersAccording to the ductile grinding principle of brittle materials, remarkable developments have been achieved to make the precision machining of large size silicon wafers become true by adopting the cup wheel surface grinding technique, which is a high efficiency precision machining way and has wide application in hard-brittle material machining fields. To prevent the silicon wafer from burning , the research work of surface grinding temperature should not be ignored. Most of the former research works of surface grinding temperature focused on the straight wheel grinding process mainly . In the difference between these two machining principles, there are some distinct ions in surface grinding temperature, so it is necessary to understand the difference of surface grinding temperature between the cup wheel grinding and the straight wheel grinding processes. At the same time, the relevant researchwork is meaningful to the application of the cup wheel grinding technique.1.Comparison of Surface Grinding Techniques between Cup Wheel and Straight WheelFig. 1 shows the surface grinding method with a straight wheel. The contact length between the w heel and the workpiece, which is closely related to grinding directions and grinding depth, is variable with grinding parameters and has significant influence on grinding heat . The intensity of the heat source will change with the contact length.Fig. 1　Shape of grinding zone with straight wheelFig. 2 show s the surface grinding process with a cup wheel. The contact length between the wheel and the workpiece has little relation with grinding directions and grinding depth. For a given wheel , the contact length keeps constant within a certain rang e of grinding depths. As the cause of the moving heat source is regarded as a linear source based on the traditional grinding heat theory , hence, this theory does not suit the cup wheel grinding process for its grinding zone is an arc instead o f rectangle. Therefore, the grinding heat model for the cup wheel should be set up to meet the needs of this technology.Fig. 2　Shape of grinding area with cup wheel2.Experimental Method, Apparatus and Conditions2. 1　Experimental methodT he surface grinding temperature is measured with a thermocouple. Two pieces o f thin thermocouple slices of 0. 1mm thickness, made of standard thermocouple wires, are clamped between two parts of the workpiece and are insulated from the workpiece. When the wheel grinds the surface of the workpiece, the two slices， end points on the workpiece surface can be welded together as a node. Due to the small volume of this node, heat capacity is small enough. If the amplifying and recording instrument s react quickly enough, the response time is extremely short . The real grinding temperature can be measured accurately without furtherdeductive computing .2. 2　Apparatus　　Fig. 3 shows the experiment system. The thermocouple wires out of the workpiece are connected with a DC amplifier which enlarges the thermic signals 100 to 1 000 times. The signals are analyzed by a digital real-time oscilloscope, and recorded by a computer. The minute grinding depth is performed in 0. 1 um per step by a micro-feed system which is manufactured by our own laboratory. T he feed principle is shown in Fig . 3.The computer pro vides accurate digital signals to the amplifier. The amplified signal is transmit ted into a piezoquartz to perform micro-feed.Fig. 3　Principle of measurement system2. 3　Experimental conditionsT ab. 1 show s the experimental conditions by a straight wheel, while Tab. 2 by a cup wheel .Tab. 1 Equipment and parameters of surface grinding with a straight wheelGrinding machine HZ-63 horizontal surface grinderGrinding w heel resin bonded diamond shape: straightΦ300 mm×25 mm　240# , W10Workpiece single crystal silicon 25 mm×10 mm×5 mmGrinding fluid noTab. 2　Equipment and parameters of surface grinding with a cup wheelGrinding machine CG6125A latheGrinding w heel resin bonded diamondshape: cupouter diameter: Φ100 mminternal diameter : Φ90 mmabrasive size: 120# ,W28, W10Workpiece single crystal silicon 25 mm×10 mm×5 mmGrinding fluid water-based coolant3　Experimental Results3. 1 　Comparison of surf ace grinding temperature generated by straight wheel and cup wheelFig . 4 shows the real-recorded thermic voltage signal waveshape of the silicon wafer ground by a straight wheel (W10) . The grinding parameters are, grinding depth 3 um, table-speed 20 m/ min, plunge and dry grinding. The lasting time of the grinding thermic voltage wave varying from rapid ascending to desending gradually only lasts 0. 02 to 0.03s. This result indicates that the range of the high grinding temperature only last s a very short time on any point of the silicon wafer ground surface. T he rapid table-speed during the straight wheel grinding processes makes the grinding zone moving fast through the surface o f the workpiece. Little burn can be found on the workpiece surface.Fig. 4　Signal waveshape ground by a straight wheelFig. 5 show s the thermic voltage wave of the silicon wafer ground by a cup w heel (W28) . The grinding parameters are as follows: grinding depth is 10 um, tablespeed is 12 mm/ min, and coolant is engaged. Compared with Fig . 4, the thermic voltage signal wave lasts about 12. 5 s from ascending to descending. Obviously ,the lasting time of the high temperature in the cup wheel grinding process is as long as several hundred times compared with the straight wheel grinding process.The longer time the high temperature lasts, the more influence the workpiece qualities will suffer by heat . A complementary test , in which the conditions are similar to Fig. 4 but the coolant , presents further evidence to above opinions. Serious result s appeared: extreme high temperature, cracks o n the workpiece surface, and the scorch of the adhesive between the workpiece and its supporter . These experimental results suggest that the coolant is essential to the cup wheel grinding process, and some suitable methods, such as decreasing the width of the cup wheel, choosing a proper coolant and dressing w heel in time, shouldbe adopted to reduce the generation of grinding heat .Fig. 5　Signal waveshape ground by a cup wheel3. 2 　Experimental phenomena and analysis during straight wheel grinding processThe surface grinding temperature of spark-out grinding was tested to observe the laws of surface grinding temperature during the elastic recovery process of the grinding system in which the actual grinding depth decreases gradually to zero . During this grinding process, the material removal mechanism might change and there will have some influence on the surface grinding temperature.Fig . 6 shows the relation between the surface grinding temperature and spark-out times. With the increase of spark-out times, surface grinding temperatures degrade step by step, finally to steady state.From the experiment result s, we have the following discussions.Fig. 6　Relation of surf ace grinding temperature and spark-out timesFirst , at the sixth spark-out grinding time, the surface grinding temperature increases abnormally. Similar test s w ere repeated three times to avoid possible errors. The tests present similar abnormal resultsat the same time. There may exist sever al factor s causing the results, such as the abnormal contact of thermocouple node, etc. We attribute the results to the change of material removal mechanism. When the actualgrinding depth decreases with the spark-out grinding times, the material removal mechanism turns to ductile-mode from brittle-mode. In this process, the grinding force and temperature will have significant changes. The results also ex press that the ductile-mode grinding has not close relationship with grain-size. Proper conditions provided, a coarse grain size wheel can realize ductile-mode grinding , too . Because of the less number of grains around the coarse grain wheel periohery , the surface roughness ground by a coarse grain wheel is larger than that g round by a fine grain wheel .Second, according to Fig . 6, surface grinding temperatures tend to have a steady value after the sixth spark-out grinding process. That is to say, maybe there is not any material being removed from the workpiece， s surface. Thus there exist s a limit time of silicon wafer spark-out grinding .It is useless beyond the limit .Finally, after the sixth spar k-out grinding process, surface temperature also can be tested even if it is meaningless in fact . The tested temperatures keep constant on the whole even after the sixtieth spark-outgrinding . The grinding thermic voltage curve measured is shown in Fig.7.Fig. 7　Signal waveshape after the sixth spark-out grindingIn contrast with Fig. 4, it is obvious that these two kinds of thermic voltage curve differ entirely . The fact that the thermic voltage curves change from one peak to multi-peaks ex presses that the grinding heat isgenerated by individual grains. Though, there is no actual grinding depth and no material removal, the wheel and workpiece contact anyway in the form of ploughing or scratching . There is still some energy transformedinto grinding heat . In order to verify the assumption that each peak in the multi-peak curve results from the sing le grain grinding intercourse, the relationship between the number of peaks and workpiece tables-peed is observed, as shown in Fig. 8.Fig. 8　Relation between grain number and table speedT he faster the tables-peed is , the fewer the peak number is. This is because the contact time between the w heel and the workpiece becomes shorter with the increase of table-speed, so , the number of grain engagedinto grinding process decreases. The effective grain number can be measured through this method during the spark-out grinding process.3. 3　Effect of grain size and grinding depth on surface grinding temperature3. 3. 1　Surface grinding temperature caused by straight wheelFig . 9 shows the experimental relations between the surface grinding temperature of the silicon wafer and straight w heel grinding parameters that include grain size, grinding depth, up grinding and down grinding. The grinding wheel speed and the table-speed are kept constant , where the grinding wheel speed is 22. 8m/ s, table-speed is 8m/ min. From Fig . 9, we know that, at the same grinding depth, the surface grinding temperature ground by a fine g rain wheel is higherthan that by a coarse g rain wheel, in which a similar relation in grinding force was observed by other scholars . Though the surface grinding temperature increases with the grinding depth increasing, the increasingrates are different with grain size. When the grinding depth is smaller than 0. 02 mm for a 240# wheel, the surface grinding temperature increases slowly. When the grinding depth is over 0. 03 mm, the surfacegrinding temperature increases abruptly and causes burn of the workpiece. As to a wheel o f grain sizeW10, the surface grinding temperature grows quickly at a grinding depth of 0. 005 mm, but , when the grinding depth is higher than 0. 01 mm, the grinding process is unsteady , the surface grinding temperature increases abruptly, and the workpiece burn is found.Fig. 9　Surface grinding temperature ground by straight wheel3. 3. 2　Sur face grinding temperature caused by cup wheel　　T he cup w heel speed and the workpiece feed speed are constant . Experimental conditions are listed in T ab. 2. The rotation speed of the cup wheel is 1 500r / min, the feed r ate of the workpiece is 12 mm/ minand the grinding depth ranges from 0. 001 mm to 0. 01mm. The experimental result s are show n in Fig . 10. In the same straight w heel grinding process, the surface grinding temperature ground by a fine grain w heel is obviously higher than that by a coarse grain w heel .Moreover , the coolant has critical influence on the cup wheel grinding process. Without a coolant , the grinding heat will remain and accumulate in the workpiece, and finally, cause the unstability of the grinding process and workpiece burn.Fig. 10　Surface grinding temperature ground by cup wheel4.Conclusions1) Ground by a cup w heel, the high temperature period lasts longer than that ground by a straight wheel. The coolant takes very important effect s to reduce the lasting time of high temperature.2) For both straight wheel and cup w heel, the surface grinding temperature ground by fine grains is higher than that by coarse grains.3) T he effective spark-out grinding times have a limit with a straight wheel . After the effective sparkout grinding times, there is some energy converted into grinding heat . T his process can last for a long time.4) T he experimental setups and methods can reflect the effective numbers of g rains during the sparkout grinding process with a straight wheel.References[ 1] Jaeger J C. Moving sources of heat and the temperature at sliding contacts [ J ] . Proc Roy Soc of New South Wales ,1982, 76: 203.[ 2] Kenichiro Imai, Hiroshi Hashimoto. Some fundamental findings in ductile grinding various brittle materials[ C] . Proceedings of the ICPE， 96 & 6th SJS SUT , 61～63.[ 3] Pang N, Zhou ZX, Zheng H W. T he study of plastic ultrasonic grinding machining process in silicon wafer [ C ] . Proceedings of the IC PE， 96 & 6th SJ SSUT , 83～86.[ 4] Zhan g C H, L in B. T he experiment al analysis of ELID grinding force in super -precision mirror finishing[ J] . Aviation Precision Manufacturing Technology , 1998, 34: 8～11.磨削方式對單晶硅表面磨削溫度的影響摘　要: 研究金剛石砂輪磨削單晶硅片時的表面磨削溫度. 針對平形砂輪和杯形砂輪兩種不同平面磨削方式所產生的表面磨削溫度特點進行了比較分析. 對砂輪粒度和磨削深度對這兩種平面磨削方式的表面磨削溫度的影響進行了試驗研究, 得到了一些有意義的試驗結果和結論.關鍵詞: 表面磨削溫度, 平形砂輪, 杯形砂輪, 單晶硅在硅晶片加工技術已逐漸成為近幾年來大力發(fā)展的項目之一的今天，隨著大尺寸硅片生產成功，世界各地的研究者們在對硅片的加工技術發(fā)展?jié)摿Φ难芯糠矫娓冻隽烁嗟木Ω鶕g性和脆性材料磨削的原則，在大尺寸硅片精密加工已經取得了顯著的發(fā)展并獲得成功，方法就是通過采用杯形砂輪表面研磨技術，這是一個高效率的精密加工方法，并已廣泛應用于對脆性材料加工領域。為防止硅片燒毀，表面磨削溫度的研究工作就顯得不可忽略。前人對表面磨削溫度研究的大部分主要是集中在圓盤砂輪加工工藝方面。對于這兩個不同的加工原則，有一些表面磨削溫度的區(qū)別，因此有必要了解杯形砂輪和圓盤砂輪磨削加工工藝不同的表面磨削溫度。與此同時，有關的研究工作對于杯形砂輪磨削技術的應用是很有意義的。1、杯形砂輪和圓盤砂輪表面磨削技術的比較圖 1顯示了圓盤砂輪表面磨削技術。車輪和工件之間的接觸長度是與磨削深度、磨削方向和多變的研磨參數密切相關,而且對磨削熱有著十分重要的影響。熱源強度會隨著接觸長度的變化而變化。圖 2顯示了杯形砂輪表面磨削技術。車輪和工件之間的接觸長度與磨削方向和磨削深度很少有關系。對于一個給定的砂輪, 在某一磨削深度范圍，接觸長度保持常值。移動熱源的原因被認為是一種線性源基于傳統(tǒng)磨削熱理論,因而, 在其圓弧代替激光束的矩形磨削區(qū)域，這一理論不適合與杯形砂輪磨削加工。因此,杯形砂輪的磨削熱模型也應建立起來以迎合這項新技術需要。2.實驗方法、儀器和條件2.1實驗方法表面磨削溫度通過使用熱電偶測量。熱電偶由兩片薄 0.1毫米厚度的標準熱電偶絲制成，并被夾在兩個工件中間，且與工件絕緣。當砂輪研磨工件表面，兩片熱電偶在工件表面的終點可焊接在一起作為一個節(jié)點。由于這個節(jié)點體積小，熱容量足夠小。如果放大和記錄儀器的反應速度足夠快，那么響應時間極短。真正的磨削溫度可以精確地測量計算不通過進一步的演繹計算。2.2儀器圖 3顯示了實驗系統(tǒng)。工件的熱電偶導線連接直流放大器，使信號放大 100--1 000倍。這些信號由一個數字實時示波器進行分析，并由計算機記錄。那一刻執(zhí)行的磨削深度通過微進給系統(tǒng)保持在每步 1微米，微進給系統(tǒng)是由我們自己的實驗室制造的。進給原理如圖 3所示計算機提供精確的數字信號放大器。被放大的信號傳輸到一個壓電晶體進行微進給。2.3實驗條件標簽 1顯示了圓盤砂輪的實驗條件，而標簽 2杯形砂輪。標簽 1設備及圓盤砂輪表面磨削參數研磨機 赫茲- 63 水平平面磨床砂輪 樹脂結合劑金剛石外形：直板Φ300 毫米×25 毫米 240＃，W10工件單 晶硅 25毫米×10 毫米×5 毫米磨削液 無標簽 2設備及杯形砂輪表面磨削參數車床 磨床 CG6125A砂輪 樹脂結合劑金剛石形狀：杯形外徑 Φ100 毫米內部直徑 Φ90 毫米磨料尺寸 120＃，W28，W10工件 單晶硅 25毫米×10 毫米×5 毫米磨削液 水基冷卻液3實驗結果3.1比較圓盤砂輪和杯型砂輪產生的表面磨削溫度圖 4顯示了實時記錄圓盤砂輪硅片電熱電壓信號的波形直輪（W10）。磨削參數，磨削深度 3微米，工作臺速度 20米/分，翻孔和干磨。該磨削電熱電壓脈沖，持續(xù)時間從快速上升到后來逐漸變?yōu)槌掷m(xù) 0.02至 0.03秒，這一結果表明，高磨削溫度變動對任何硅片只持續(xù)相當短的時間?？焖俚墓ぷ髋_使得圓盤磨削砂輪表面快速通過磨削工藝磨削區(qū)。細微的燒傷可在工件表面發(fā)現。圖 5顯示了硅晶片的電熱電壓信號波形是根據杯形砂輪確定的（W28）。磨削參數如下：磨削深度為 10微米，工作臺進給速度為 12毫米/分鐘，冷卻液占線。相較于圖 4，電熱電壓信號波形持續(xù)約 12.5由上升至下降。顯然，在磨削過程中杯形砂輪高溫持續(xù)時間是一樣長的圓盤砂輪的數百倍較.較長時間的持續(xù)高溫，更會影響工件的質量。一個互補實驗，其中條件類似圖 4，除了冷卻液，從而進一步來證明上述結論。嚴重的結果出現了：極端高溫，工件表面的裂縫，和工件與支撐之間的膠粘劑燒焦。這些實驗結果表明，冷卻液是必不可少在杯形砂輪磨削過程中，應采取一些適當的方法，如降低杯子的輪寬，選擇一個合適的冷卻液和砂輪修整的時間，以減少磨削熱的產生。3.2圓盤砂輪在磨削過程中的實驗現象和分析 表面磨削火花磨削溫度進行了測試，觀察期間的粉磨系統(tǒng)中的實際磨削深度逐漸減小到零彈性恢復過程中表面磨削溫度的法律。在此研磨過程中，材料去除機理可能會有變化，有一些表面上的磨削溫度的影響。圖 6顯示了磨削溫度，引發(fā)出次表面的關系。隨著出火花次數的增加，表面磨削溫度一步一步分解，最后到穩(wěn)定狀態(tài)。從實驗結果，我們有下面的討論。首先，在第六次出火花的研磨時間，表面磨削溫度升高異常。類似的測試重復3次，以避免可能的錯誤。目前的測試顯示在同一時間出現相近異常的結果。這可能由于一些因素，如熱電偶節(jié)點異常接觸造成的結果等等，我們將結果歸結于材料去除機理的變化。當實際的火花磨削深度隨著磨削次數減小，材料去除機理由韌性模式轉向脆性模式。在這個過程中，磨削力和溫度將有重大變化。研究結果還表示，該韌性模式已經與磨粒度沒有密切關系。另外提供適當的條件，粗晶粒尺寸砂輪也可以實現韌性模式研磨。由于粗磨輪周圍的磨粒比較少，所以使得粗磨輪表面的粗糙度比細磨粒的粗糙度大。其次，根據圖 6，表面磨削溫度往往在第六個火花磨削加工后出現穩(wěn)定值。這就是說，也許沒有任何從工件表面被刪除的材料。因此，存在一個時間限制火花硅片出磨。它是超過極限的，是無用的。最后，在第六次出火花的磨削工藝中，表面溫度也可以進行測試，即使它實際上是毫無意義的。經測試溫度保持不變，甚至對整個第六十次出火花磨削。研磨電熱電壓曲線測量圖如圖 7所示。與圖 4的對比，顯然，電熱電壓曲線這兩種完全不同的。這一事實從一個放熱峰的電壓變化曲線為多峰表示，該磨削熱是由單個顆粒產生。雖然，沒有實際磨削深度，沒有材料去除，砂輪和工件接觸正在刨傷或刮傷的形式。還有磨削熱轉化成一定的能量。為了驗證中的每個從單一的磨性多峰曲線結果高峰期，高峰之間的數量關系和工件工作臺進給速度觀察的假設，如圖 8所示。進給速度越快，則波峰數目越少。這是因為砂輪與工件之間的接觸時間會隨著進給速度增加而減少，所以，磨粒數導致研磨過程變短。有效磨粒數可以通過此方法可在火花磨削工藝中進行測量。3．3 磨削粒度和磨削深度對表面磨削溫度的影響3.3.1表面磨削溫度由圓盤砂輪造成圖 9顯示了表面磨削溫度的硅晶片和磨削參數，包括晶粒尺寸，磨削深度，降低了磨磨直輪實驗的關系。砂輪速度和進給速度依然能保持恒定，那里的砂輪速度為 22.8米/秒，進給速度是 8m/分鐘。從圖 9在相同的磨削深度，表面研磨輪由細晶溫度高于地面是由粗磨輪，其中在磨削力的相似關系是由其他學者觀察。雖然磨床磨削深度增加溫度升高面，提高率與顆粒大小不同。當磨削深度小于 0.02毫米為 240＃砂輪，磨削表面溫度上升緩慢。當磨削深度超過 0.03毫米，表面磨削溫度急劇增加，導致燒傷的工件。作為一個磨（W10）輪，表面磨削溫度迅速增長在磨削深度為 0.005毫米，但是，當磨削深度為大于 0.01毫米，研磨過程是不穩(wěn)定的，表面磨削溫度急劇增加，和工件燒傷被發(fā)現。3.3.2由杯形砂輪引起的表面磨削溫度杯形砂輪速度和工件進給速度是恒定的。實驗條件列于標簽 2。杯形砂輪的轉速為 1500r/ min時，工件進給速度為 12毫米/分鐘，磨削深度變動范圍為從0.001毫米為 0.01毫米。實驗結果顯示在圖 10中。在同樣的圓盤砂輪磨削工藝過程中，磨削表面由細粒組成磨輪的溫度明顯高于由粗磨粒組成的磨輪。此外，冷卻液對杯形砂輪在磨削過程中有著至關重要的影響。沒有冷卻液，磨削熱將依然存在，并且在工件上積累，最后導致磨削過程的不穩(wěn)定性和工件燒傷。4.結論1）由杯形砂輪磨削高溫持續(xù)時間比圓盤砂輪磨削更長。冷卻液在減少高溫持續(xù)時間方面具有非常重要的作用。2）無論圓盤砂輪還是杯形砂輪，磨削面細顆粒溫度比磨削面粗顆粒高。3）有效的火花研磨次數對于圓盤砂輪有一定限制。在有效的火花研磨次數之后，有一定的能量轉換成磨削熱，這個過程可以持續(xù)很長時間。4）這個實驗裝置和方法可以反映在與圓盤砂輪火花磨削過程中的有效的磨粒數量。