氣溶膠噴射列印技術應用於重新佈線層與打線接合焊墊之可行性研究

Abstract

本研究成功利用氣溶膠噴射列印技術(AJP)取代傳統製程完成多層重新佈線層(Redistribution Layer, RDL)結構封裝體，並證實具有高度技術上可行性。研究中透過溶劑對奈米銀顆粒墨水濃度進行調整，結果顯示比例2:1(Ag:PGME)之銀墨水濃度，具有良好的霧化性與穩定性。再者，藉由適當的鞘氣氣流與霧化氣流參數，可成功列印出品質良好之銀線路，且可依需求將線寬控制於20-30 µm。而銀墨水透過直接溫度燒結法，燒結在180℃以上1小時後，即可具有良好之導電性、傳輸穩定度與附著性，其最小平均電阻率達到2.22×〖10〗^(-6) Ω‧cm，約為塊銀之2倍，而附著性等級則達到5B。此外，亦透過添加高分子墨水強化銀墨水之附著性，具有明顯的效果，可以進一步提升銀墨水之附著性。 本研究藉由上述所獲得之銀墨水列印參數，列印單層RDL與多層RDL結構，並透過不同層數之銀焊墊進行打線接合與推拉力測試驗證。研究結果證實所列印之銀電路與焊墊具有可重複性，其線寬與焊墊尺寸，分別約為25-28 µm與 100-110 µm。而添加了高分子層的多層RDL結構，在僅有一層銀焊墊時，即可達到100%打線良率，並可通過推拉力測試規範的標準值。但是單層RDL結構的銀焊墊則需列印至三層時，才能達到相同的強度，說明打線接合良率與金球受力強度會受到銀焊墊厚度與高分子層影響。此外，本研究中列印800顆含三層銀焊墊的多層RDL結構封裝體，進行放量可靠度測試(RA)。研究結果證實，RDL封裝體在正常溫濕度與高低溫環境中具有良好的可靠度，其溫度循環測試(TCT)與高溫儲存測試(HTSL)的良率可達到100%。但當濕度提高至85%RH以上之高壓高濕的環境測試時，會加速濕氣從結構的缺陷與層與層間滲入，使得封裝體容易有分層與電性失效問題，導致較低的可靠度，高加速溫濕度測試(HAST)的良率下降至96%，而具100%RH之高溫水蒸汽壓力測試(或稱壓力鍋測試, PCT)良率更是下降至76%。 最後，經過綜合評估分析，雖然AJP技術在生產速度上仍不及傳統製程，距離實際量產應用還有許多設備與成本問題需要考量，但由於其具有免光罩直接結構列印、多範圍材料選擇與少化學廢料等優點，且經本研究證明其可成功應用於RDL結構封裝體製造，擁有高度的技術可行性與可靠度。因此，與傳統製程的複雜度與高成本相比下，仍具有一定的優勢與發展潛力，有機會實際應用於業界。

In this study, Aerosol Jet printing (AJP) was successfully used to replace the traditional process to complete the multi-layer RDL structure package, and it was proved to be feasible. This study utilizes solvent to adjust the concentration of nanoparticles silver ink, and the result proves that the ink has good atomization and stability when the ratio of silver ink and solvent is 2:1 (Ag: PGME). The high-quality silver lines can be successfully printed with the proper parameters of sheath gas and atomizing gas flow rate, and the line width can be controlled at 20-30 µm according to requirements. The silver ink has good electrical conductivity, transmission stability and adhesion after sintering at a temperature above 180℃ for 1 hour by direct temperature sintering method. The minimum average resistivity reaches 2.22×〖10〗^(-6) Ω‧cm, about 2 times that of bulk silver, and the adhesion grade reaches 5B. In addition, the adhesion of silver ink was also enhanced by adding polymer ink, which has obvious effect and can further improve the adhesion of silver ink. This study utilizes the silver ink printing parameters obtained above to print single-layer RDL and multi-layer RDL structures, and conduct wire bonding and shear-pull test verification through different layers of silver pads. The results demonstrate that the printed silver circuits and bond pads are repeatable, with line widths and pad sizes of approximately 25-28 µm and 100-110 µm, respectively. The multi-layer RDL structure with added polymer layer can achieve 100% wire bonding yield rate when has only one silver bond pad, and can pass the standard value of the shear-pull test specification. However, the silver bond pads of the single-layer RDL structure need to be printed to three layers to achieve the same strength. It shows that the wire bonding yield rate and the force strength of the gold ball are affected by the thickness of the silver bond pad and the polymer layer. Furthermore, we printed 800 multi-layer RDL structure packages with three-layer silver bond pads for Reliability testing (RA). The study results show that the RDL package has good reliability in normal temperature and humidity and high-low temperature environments, and the yield rate of the Temperature cycle test (TCT) and High temperature storage test (HTSL) can reach 100%. However, when the humidity is increased to above 85%RH, the reliability of the RDL package is reduced due to the pores and defects between the layers. The yield rate of Highly accelerated stress test (HAST) dropped to 96%, and the yield rate of Pressure cook test (PCT) with 100% RH dropped to 76%. Finally, after a comprehensive evaluation and analysis, although the production speed of AJP technology is still lower than the traditional process, there are still many equipment and cost issues to be considered before the actual mass production application. However, due to its advantages of mask-free direct structure printing, wide range of material selection and less chemical waste, and this study has proved that it has technical feasibility and reliability, it can be successfully applied to the manufacture of RDL structure packages. Therefore, compared with the complexity and high cost of the traditional process, AJP still has certain advantages and development potential, and has the opportunity to be practically applied in the industry.