超音波打線的音洩監測與品質研究

Abstract

打線機在金屬墊與導線接合過程中，可能會對光電元件造成破壞或失效，打線製程參數的設定與元件接合的良窳息息相關。本論文採用音洩感測技術即時監測接觸面滯滑瞬間釋放的應力波訊號，並以力感測器量測超音波換能器的毛細管對於元件的接觸力。 超音波單點打線所需時間約數至數十毫秒。金屬導線的線徑愈粗，所需之超音波功率愈大，致動的時間也愈長。超音換能器下方之毛細管施予元件金屬墊的正向力愈大，剪切摩擦力就愈大，愈多能量輸至打線銲點，造成導線末端結球或金屬墊之塑性變形及音洩能量。短時傅立葉轉換頻譜顯示換能器輸出能量過高會釋出高頻的音洩訊號，然而以聚焦離子束電子顯微鏡切片卻未能發現裂紋，有待進一步確認音洩監測的有效性。實驗分析顯示若音洩訊號能量佔輸出能量的10%，且達到6-12 (mV)2sec時，接合成功的機率最高，可以作為音洩監測打線接合品質的指標。

The ultrasonic wire bonding process probably causes fracture and failure of the optoelectronic and microelectronic devices. The wire bonding quality of the device depends on bonding parameters. In this thesis, acoustic emission technology was used to real-time monitor the stress wave signals suddenly released from stick and slip of the capillary tool on the contact surfaces. The contact force induced by the tool on the bond pad was measured by piezoelectric force sensor. The weld time takes several to tens milliseconds during the ultrasonic welding process. The bonding wire of greater diameter requires higher power output and longer duration. The larger normal contact force on the bond pad due to application of the capillary tool, the greater friction will be yielded. More energy is essentially transferred into welding energy for wire bond, plastic deformation of the free air ball and bond pad, as well as acoustic emission energy. High-frequency acoustic emission signals have been found in some specimens in accordance with the spectra carried out by short time Fourier transform. Unfortunately, no defects were observed in the small amount of specimens by using focused ion beam technique and scanning electronic microscope. Further specimens are needed to assure validity of acoustic emission monitoring. Experimental evidence indicates that acoustic emission energy could be a notable index for quality assessment. Successful wire bonds usually appear in case that the acoustic emission energy is in the range of 6 to 12 (mV)2sec and occupies 10% energy delivered by the transducer.