低介電常數與低損耗因子之光固化3D列印樹脂開發

Abstract

由3D列印技術代表的積層製造概念藉由極其簡短的製程步驟，製造時間與極少的材料浪費已經對傳統製造業產生劃時代的改變。在許多3D列印技術中，光固化3D列印機的成本最低，但是其壓克力樹脂列印成品擁有最好的列印精確性與最強的層間結合力因此吸引了越來越多學術界與產業界資源投入探究其可能的應用領域，其中包括客製化電子產品製造。本論文旨在改進光固化3D列印應用在電子產品製造的兩大缺點，即低介電性以及在非平面物體上形成純銅線路的高難度挑戰。在第二章中帶有非極性以及立體障礙功能之金剛烷結構的雙官能基壓克力單體被混入三官能基交聯劑單體組成的樹脂浴中成功的印出無翹曲與裂痕的薄膜以及高解析度的物體，其介電常數與損耗因子也大幅地降低(2.77/0.02 @ 10GHz)。本章節對單與雙官能基具有立體障礙功能的壓克力單體在交聯劑高分子網路結構中之交聯行為差異性的探討為接續低介電損耗因子的光固化3D列印樹脂配方研發提供了理論基礎。為了降低光固化壓克力高分子結構先天的高介電損耗因子，非極性分子二乙烯基苯被導入壓克力樹酯中以大幅增強其介電性能，在第三章的研究應用電腦模擬選出立體障礙更強的單官能基壓克力單體甲基丙烯酸酯雙環戊烷與二乙烯基苯及三官能基交聯劑單體形成新的3D光固化列印樹脂配方，以此配方所列印出來的物體不僅完全沒有翹曲與裂痕，並且其列印精確度相比市售光固化樹脂毫不遜色，更重要的是其展現了極低的介電常數與損耗因子(2.63/0.007 @ 10GHz)與優異的熱穩定性CTE (α1/α2= 49/75 ppm/oC)，此表現已相當於用在生產5G傳輸用印刷電路板的低耗損等級(Low Loss)基板材料。最後在第四章，光固化3D列印物體表面的溝槽設計成功讓電鍍銅線路在其非平面表面上形成，應用此方式以及第二章與第三章所開發之樹脂配方分別被用來製造曲面電路板以及訊號完整性測試用微帶線(Micro-strip Line)測試板。兩者分別通過無鉛製程用迴焊爐測試以及展現非常優良的高頻訊號完整性 (S21 <2dB up to 4.6GHz)，此研究成果成功地展現光固化3D列印在製造高品質與信賴性電子裝置的潛力。

Additive manufacturing (AM) materialized by 3D printing technology has been reshaping the traditional manufacturing industry with its extremely simple process flow, short fabrication time and little material waste. Among a variety of 3D printing techniques, liquid-crystal display (LCD) 3D printer has the lowest machine cost but its products from acrylate-based resin photo-polymerization exhibits the highest accuracy and strongest layer to layer adhesion. Therefore, more and more industrial and research endeavors are devoted to exploring its potential applications including customized electronic device fabrication. This dissertation aims at solving LCD 3D printing technique’s biggest disadvantages in electronic device fabrication: poor dielectric properties for prevailing polymethyl methacrylate/methyl acrylic acid-based resin and difficulty of pure Cu trace formation on printed object’s nonplanar surface. At first (Chapter 2), steric hindering acrylate monomers with non-polar adamantyl structures were added into tri-functional cross-linker resin bath to successfully eradicate its higher crack and warpage tendency, enhance its dielectric constant (Dk) and dissipation factor (Df) performances (2.77/0.02 @ 10GHz) without compromising the excellent thermal stability (coefficient of thermal expansion (CTE) α1/α2= 66/83ppm/oC). Mono and bi-functional steric hindering monomer’s cross-linking behaviors were studied to pave the way for the following resin formula development. In Chapter 3, the non-polar divinyl benzene (DVB) monomer was introduced to reduce acrylate polymer’s inherent high polarity. The mono-functional monomer with the strongest steric hindering was selected based on software simulation to form an optimum resin formula together with DVB and cross-linker. The printed samples demonstrated very low Dk/Df (2.63/0.007 @ 10GHz) and CTE (α1/α2= 49/75ppm/oC), comparable to Tier 4 mid-loss PCB dielectric materials utilized to produce PCB for 5G applications. Lastly, trench structures on LCD 3D printed boards were design in Chapter 4 to enables reliable pure Cu circuit to be formed on the non-planar printed polymer surface. With trench type Cu circuit, curvilinear circuit board and micro-strip line test vehicle fabricated by resin formulas developed from Chapter 2 and 3 passed reflow (lead free temperature profile) and exhibited excellent signal integrity (<2dB S21) up to 4.6GHz respectively, demonstrating LCD 3D printing technique’s potential in reliable, high quality electronic device fabrication.