低危害性銅銲線與銅銲墊超音波銲合製程與銲點之可靠度研究

Study on the low hazardous process and reliability of copper wire bond to copper pad using the ultrasonic bonding

温智穎(Chih-Ying Wen)

指導教授 ： 莊正利

中山醫學大學/健康管理學院/職業安全衛生學系/碩士(2021年)

https://doi.org/10.6834/csmu202100032

摘要

本研究選用導電性優異與價格低廉之銅銲線與銅銲墊，進行超音波銲線接合，作為電動汽車鋰電池之串接導線。首先進行超音波銲頭與線徑之選用，依銲著率結果選定適用銅銲線之線徑與超音波銲頭尺寸，並由改變超音波接合參數，以剪力試驗量測銅銲點之接合強度；以拉勾試驗量測銅銲點之拉力值；以光學顯微鏡與掃描式電子顯微鏡，觀察銅銲點之破斷表面型態與接合界面之完整性；將熱電偶放置於銅銲墊下方，於超音波接合時量測於不同超音波參數下溫度之變化，綜整相關實驗與分析結果，進而優化超音波銲線接合品質，並評估該製程作為鋰電池電力導線接合製程之可行性。隨後以適銲超音波參數進行接合之銅銲點，依JEDEC標準進行可靠度試驗，分別為高壓蒸煮試驗與高溫儲存試驗，評估超音波銲線製程之可靠度。由實驗結果顯示隨著超音波輸出功率與超音波接合時間之增加，於接合過程中輸入之能量越高，可有效提高銅銲線與銅銲墊接合界面之溫度，促使接合界面產生原子間之交互擴散，進而提高銅銲點之接合強度，但於過大之輸出功率(45 W)下因提供過多之能量，導致銅銲點過度變形，造成溢料導致銅銲點減薄化，拉勾試驗於薄化銲點根部處破斷，造成較低之拉勾值；而於過高之超音波接合負荷(167 MPa)下，會抑制超音波功率之輸出能量，並限制界面間之相對運動，使接合界面之溫度降低，造成較差之接合品質，本研究之適銲參數為超音波輸出功率28 W、超音波接合時間0.3 s與超音波接合負荷67 MPa。超音波接合銅銲點經前述兩種可靠度測試用以驗證其可靠度，實驗結果顯示銅銲點經不同時間之高溫儲存與高壓蒸煮測試後，銅銲點皆無從銲合處破壞，仍維持一定之接合強度，顯示銲點之可靠度未隨測試時間之增長，而出現大幅衰退之現象，故超音波銲線製程技術具取代電阻銲接與雷射銲接等熔融接合製程之潛力，可應用於鋰電池芯模組化之相互連接，以較低溫之製程溫度，提高接合銲點之安全性與可靠度。

關鍵字

銅銲線超音波銲線製程 ； 銅銲點 ； 鋰電池芯

並列摘要

Copper has an excellent conductivity and a low cost, thus, the copper wire and copper pad were selected to be an electrical loop of the lithium-ion battery using ultrasonic bonding in this study. To examine the effects of bonding parameters on the bondability and bonding strength, the bonding parameters are varied using design of experiments (DOE). For copper wire bonded on the copper pad, the shear test and wire-pull test are employed to determine the bonding strength and wire-pull force. The SEM and OM are conducted to observe the microstructure at bonding interface and to identify the fracture mode after the shear test and wire-pull test. The bonding mechanism of the copper wire bonded to copper pads using ultrasonic bonding is proposed in according with the experimental results on shear test, wire-pull test and analytical results. The reliability of high storage temperature (HTS) and pressure cooker test (PCT) were employed to check the reliability of copper wire bonded on copper pad in accordance with JEDEC standards. Combination of the bonding experimental result and reliability test are used to evaluate the feasibility of this bonding process applied to join the electrical loop of the lithium-ion battery. The experimental result shows the copper wires can be well bonded on the copper pads at room temperature and 100% bondability can be achieved using the adequate bonding parameters. For a high ultrasonic power or extended bonding duration, an elevated temperature was detected when a high bonding energy was provided during the copper wire bonding to copper pads, and the elevated temperature resulted in increasing atomic interdiffusion between copper wire and copper pads, finally a sound copper bond with sufficient bonding strength is obtained. However, a severely plastic deformation on copper bond is found when an excessive bonding power was supplied, and then the fracture occurred at thin heel of copper bond during the wire-pull test resulted in a low wire-pull force. Similarity, when the bonding load is exceeded high, the ultrasonic power would be suppresses and the atomic interdiffusion is insufficient, the unbonded zone formed at bonding interface between copper wire and the copper pads, the shear strength is thus degraded. The adequate bonding parameters for copper wire ultrasonic bonding to copper pads are 0.3 s in bonding duration, 28 W in bonding power and 67 MPa in bonding load. For copper bonds subjected to reliability of PCT and HTS tests, no significantly change on the bonding strength, indicating the copper bonds keep good reliability. A coarse grain can be found at heel of copper bond for copper bonds subjected to HTS at 1000 h, implying the grain growthed when higher thermal energy was provided and then the wire-pull force and hardness are decreased. A copper wire can be well bonded onto copper pads with a sound of bonding strength at room temperature and no significantly decreases in the bonding strength of copper bonds. This bonding process has great potential to be used in bonding of the electrical loop of the lithium-ion battery.

並列關鍵字

copper wire ultrasonic wire bonding ； copper bond ； lithium-ion battery cell

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