超音波輔助錫銲應用於矽基材太陽能電池導線可靠度之研究

隨著環境保護需求，發展綠色能源已成為全球共識，由於太陽能具豐富、乾淨且低汙染等優點，為現今主要發展之綠色能源。太陽能電池中矽基材電池具較高效率且周邊相關設施發展完整，為現今太陽能電池之主要型式，但矽基材太陽能電池因易脆性質，其電力輸送導帶之製作過程中無使用傳統之錫銲，而以超音波輔助錫銲製程克服矽基材太陽能電池與電力輸送導帶之銲接，然而太陽能電池隨設置地點之差異，受熱過程不同，均對超音波錫銲製程應用於電力導帶與太陽能電池銲合之可靠度造成影響，故本研究擬以超音波錫銲製程進行矽基材太陽能電池之製作，評估錫銲道於矽基材太陽能電池之可靠度。本研究採用矽基材表面鍍著鋁膜作為太陽能電池之基材，以市售Sn-Zn-Sb銲線為錫銲材，以120℃之矽基材預熱溫度與超音波輔助振幅4.7μm進行超音波輔助錫銲實驗。，根據IEC 61646 可靠度測試規範之相關要求，將銲合完成之試片進行濕熱測試、濕冷測試、熱循環測試以及高溫儲存測試來探討其可靠度與失效機制。實驗結果顯示經過壽命試驗之銲道其剪力強度均有明顯下降之趨勢。濕熱測試之剪力強度主要由錫銲料主導，錫銲道之晶粒隨可靠度測試時間曾長，晶粒粗大化，其剪力強度隨著濕熱測試之時間延長而下降；經濕冷測試之錫銲道，隨著測試時間越長，其界面會析出Sb，進而破壞界面強度，使銲道產生缺陷，降低剪力強度；銲道在經過熱循環測試後，其界面會因為錫銲料與矽基材之間之熱膨脹係數不同而導致界面產生裂痕與孔洞，故使剪力強度有明顯下降之情形；經高溫儲存測試後，錫銲料之晶粒有粗大化之趨勢，故其剪力強度隨著測試時間越長而逐漸下降。

The solar cell has become a major source for green energy due to environmental friendly, cost-effective process and the high conversion efficiency. However, a fracture or micro-cracks would be formed for crystalline-silicon solar cell subjected to an excessive bonding load or ultrasonic power using the conventional bonding process. The ultrasound assisted soldering provides a great solderability between the solder and the aluminum comparing with the conventional soldering. An assisted ultrasonic power can be transmitted to the molten pool of solder, and the oxide layer on the aluminum was then removed by the assisted ultrasound to enhance the wettability of the solder and the aluminum, finally the solder well joined on the aluminum layer to be the interconnect on the solar cell. In this study, the commercially available Sn-Zn-Sb solder wire was selected to be the solder material, a continuous solder bead was welded on the aluminum layer over the silicon substrate for the silicon substrate was preheated to 120ºC and ultrasonic-assisted amplitude of 4.7 μm was employed. The reliability tests of the damp heat, humidity-freeze test, temperature cycling test, and a high temperature storage on the continuous solder bead were performed according with the IEC 61646 reliability test specifications to verify the reliability of ultrasound assisted soldering process. The experimental results displays that shear strengths of solder paths decreases with increasing the test durations of various reliability tests. For the specimen subjected to damp heat test, the fracture occurs at solder path after shear test and the grain growth of the solder path was found., indicating the joining strength of the solder onto silicon substrates was higher than those of the solder and the grain growth results in shear strength decreased. Similarity, the phenomena also can be found on the solder path for specimens subjected to the high temperature storage test at various test durations. Neither cracks nor delaminations are observed at joining interface between the solder path and the silicon substrates. A sound joining can be obtained after high temperature storage test. For specimens subjected to humidity-freeze and temperature cycling tests, the cracks can be observed at solder path and joining interface. The fracture exists joining interface between the solder path and silicon substrates after shear test, implying the joining strength was decreased with increasing the test durations when specimens subjected to humidity-freeze and temperature cycling tests. A thermal stress would be raisin due to the thermal coefficient mismatch between the solder and silicon substrate at test durations, the cracks was then formed, finally the shear strength decreased significantly with extending the test durations.