結合微致動器之微電阻焊技術於微組裝之研究

Abstract

本研究特色是提出結合微熱致動器於微電阻焊技術並應用於微元件二維及三維的組裝，內容包含機構與元件設計、製造、與測試。雖然電阻焊技術已在傳統機械領域中廣泛應用，但以往並沒有任何將微致動器運用於微尺寸結構的微電阻焊技術之相關研究。電阻焊的原理是利用兩受壓物件會有高電阻特性，通過電流時可在接觸區域產生高溫，進而形成熔接接合。本研究利用金屬面型微加工技術，結合電熱式微致動器與待焊接元件在同一晶片上，可有效利用加工能量，提供良好接觸壓力控制，避免徒手操作的誤差，對微組裝自動化可有所助益。 本研究第一部份先開發平面式的微組裝技術，來驗證以微熱致動器進行微電阻焊的可行性，並建立相關元件及焊接參數的可行範圍。本研究發現初始接觸電阻會隨著接觸壓力的增加而減少，而較小的初始接觸電阻可以增加焊接強度，也就是較大的接觸壓力 (接觸壓力3.09 MPa時，接觸電阻為2.7 歐姆)能夠增加焊接強度。另外，也發現焊接能量是可靠度之重要參數。在本研究中，輸入超過一定焊接能量時，在此是1焦耳，可以使微電阻焊成功率達100%，確認了應用微熱致動器於微電阻焊之可行性與可靠度。 本研究的第二部分則是進一步開發以微電阻焊技術用於三維微組裝。鎳質微元件透過製程及微絞鍊機構，形成可活動的絞接微結構後，在元件下方放置磁鐵，即可透過改變磁鐵位置，變化磁力來控制其抬昇的角度。微熱致動器在此同樣是用來提供所需的接觸壓力，使微電阻焊可將微元件固定在空間中。研究結果顯示，微元件可固定在14° 到90°間角度範圍，這是其他微組裝技術很難作到的。另外也對相關設計參數的影響進行探討，例如微致動器的尺寸以及焊接樑寬度。結果發現，窄的焊接樑會讓焊接處有高接觸壓力，有利於增加焊接熱量傳遞，但相反地，寬的焊接樑可降低熱應變，減少焊接樑的形變。另外，由於微絞鍊機構在此是由金屬材質構成，具有導電性，可將平面輸入之電源有效傳遞至組裝立起來的立體微元件上，本研究也展示透過三維電阻焊技術所組裝之立體曲臂式微熱致動器，通以0.56瓦的電能可產生27.7 μm的出平面位移，顯示本研究所提出的微電阻焊技術應用於微組裝時，不但可以組立被動式微結構，也可運用於需要電性導通之主動式立體微元件組裝。

Here, micro resistance welding with in situ micro actuators and corresponding two-dimensional (in-plane) and three-dimensional (3D) micro assemblies are proposed, including designs, fabrications, measurements, tests and discussions. Traditionally, resistance welding is a common scheme of assembly in macro scale by pressing two workpieces with current passing through to generate joule heating at contact region due to high contact resistance. There are, however, few studies focused on micro resistance welding with micro actuators in micro world. Under assistance of in situ micro actuators next to welding regions, increasing efficiency of welding energy, providing easy-controlled welding pressure and avoiding manual misoperation can benefit micro resistance welding. The scheme proposed here would be helpful in automation of micro assembly. First, in-plane micro assembly with electroplated nickel micro structure is proposed to verify the practicability of micro resistance welding and understand the feasible ranges of welding parameters. The calibrated initial contact resistance is shown to decrease with the increasing contact pressure. In addition, stronger welding strength is achieved at a smaller initial contact resistance, namely, a larger clamping force would enhance the welding strength as large as 3.09 MPa at contact resistance of 2.7 ohm here. The input welding energy is also found to be a critical factor. In our tests, providing higher welding energy, such as 1 J, yield also increases to be 100%. In this case, the feasibility of the proposed technique is confirmed. After this feasible study, three-dimensional micro assembly of hinged nickel micro devices by magnetic lifting and micro resistance welding is further developed. Lifting the released micro structure to different tilted angles is accomplished by controlling positions of a magnet beneath the device. Micro resistance welding is utilized for immobilizing the tilted structure. As mentioned, the micro actuators also used to provide necessary pressure. The proposed technique is shown to immobilize micro devices at controlled angles ranging from 14° to 90° with respect to the substrate, which is a difficulty to other techniques. Design parameters such as the electro-thermal actuator and welding beam width are also investigated. It is found there is a trade-off in beam width design between large contact pressure and low thermal deformation. Finally, a lifted and immobilized electro-thermal bent-beam actuator is shown to displace upward about 27.7 μm with 0.56 W power input to demonstrate the capability of electrical transmission at welded joints by this proposed technique. With demonstration and characterization of micro resistance welding by in situ electro-thermal micro actuators, not only the passive micro structures but also the active micro structures which need electrical connections can be assembled with this proposed method.