隨半導體製程技術發展日益成熟，晶片單位面積之接點數大幅上升，面積陣列式覆晶接合技術已逐漸取代傳統熱音波銲線製程。本研究將發展成熟之熱音波鍵合技術應用於金凸塊與氧化鋁基板之覆晶製程，先以熱音波銲線製程將金凸塊接著於矽晶片上銅銲墊，陶瓷基板之銅電極鍍著鈦膜擴散阻絕層與銀膜接著層，再以熱音波覆晶接合機將銲著金凸塊之矽晶片接合於陶瓷基板，完成晶片上板(COB)製程。本研究除探討製程參數對覆晶接合之接著率與接合強度影響外，並驗證覆晶接合後之高溫儲存可靠度。由實驗結果得知於適當參數範圍，矽晶片與鍍著鈦擴散阻絕層及銀接著層陶瓷基板之銲著率達100％，且由推力測試得知，接合強度遠高於業界規範之要求。製程參數對接合強度之探討包含下壓力、超音波功率與銲合時間，下壓力與接合強度成正比，提高下壓力有助於金凸塊與陶瓷基板之緊密接合，但該下壓力超過995(gf)，接合強度趨於穩定值；提高超音波功率可有效提高金凸塊與陶瓷基板之銲著強度，因超音波功率可有效提高接面之接合溫度，促進金、銀原子之交互擴散，進而提高接合強度；銲著時間則為0.5秒為最佳，時間太短無法提供接合所需之足夠能量，時間太長造成部分金凸塊由矽晶片側剝離，進而降低整體之接合強度；經高溫儲存測試得知，矽晶片與陶瓷基板之接合強度不隨持溫時間增加而降低，且接合介面無孔洞或裂縫等缺陷，推論金凸塊與銀接著層之熱音波覆晶接合製程應無高溫儲存可靠度之疑慮，故此一製程深具應用於發光二極體(LED)或低接點數(Low pin counts)晶片封裝之潛力。
As semiconductor device are reducing in scale, the flip chip assembly becomes an attractive scheme for use in high performance and miniaturized microelectronic packaging. In this study, thermosonic bonding was applied to a chip with gold bumps flip bonding to an alumina substrate with a copper conductor. The gold bumps were first thermosonic boned on the chip based on the conventional wire bonding process, and a chip with gold bumps was then flip onto an alumina substrate using thermosonic bonding. A silver bonding layer and a diffusion barrier layer of titanium were deposited on the surface of copper conductor to improve the bondability and bonding strength. One hundred percent can be achieved for a chip with gold bumps onto a substrate using appropriate bonding parameters. The bonding strength is much greater than that stated in JEDEC standards. The effects of three bonding parameters on the bonding strength were investigated, including bonding force, ultrasonic power and bonding time. The reliability of the high temperature storage test also was verified in this study. The experimental results indicted that bonding strength increases with increase bonding force form 300 to 995gf, and then bonding strength maintains a steady value after bonding force higher than 995gf. A high ultrasonic power results in greater bonding strength since more thermal energy could promote the inter-diffusion between the silver bonding layer and gold bumps. The bonding strength did not degrade after prolonged storage at elevated temperature after HTS test. Thus, the reliability of HTS for gold bumps onto the silver bonding layer is not a serious concern. According to experimental results in this work, the chip with gold bump s flip bonding to the silver bonding layer not only provide an excellent bonding strength and bondability, but also has a greater reliability for the HTS test. This technology has a potential to be applied to the electronic packaging or LED packaging.
