低介電常數與低消散因子感光聚醯亞胺之合成鑑定

Synthesis of Photosensitive Polyimide with Low Dielectric Constant and Low Dissipation Factor

吳炳翰(Ping-Han Wu)

指導教授 ： 陳文章

國立臺灣大學/工學院/化學工程學研究所/碩士(2019年)

https://doi.org/10.6342/NTU201900703

摘要

近年來，聚醯亞胺在軟性印刷電路板領域中已引起許多關注，它因為良好的熱穩定性、抗化學溶劑腐蝕性以及良好的機械性質而能夠被用於印刷電路板的基板或覆蓋。但在傳統的聚醯亞胺圖案化過程較為繁雜，因此我們需要引入新穎感光壓克力交聯系統，透過負型光阻的模式來幫助顯影成像。另一方面在高頻傳輸是一個十分重要的領域，而當中有個最嚴重的問題便是高頻傳輸下的訊號遺失及能量損耗，所以我們需要引入具有較低介電常數與消散因子的單體來合成聚醯亞胺，傳統的芳香環聚醯亞胺介電常數多高於3.5，消散因子則高於0.02 (於一兆赫茲頻譜)，此一數值是無法應用於新穎的商業化高頻傳輸材料當中的，因此著實需要開發低介電常數與消散因子的聚醯亞胺材料。
本研究第二章，我們成功引入含氟原子的基團於聚醯亞胺高分子中，透過C-F鍵結極低的極化率使得電子在特定電場中並不會過度震盪導致訊號損失而能降低介電常數與消散因子，我們也比較不同的商品化二酐及二胺，透過位置與鍊段長度的不同最適化出最佳性質的聚醯亞胺，此一系統的介電常數最低可降至2.5以下，且消散因子能降至0.005~0.008(於一兆赫茲頻譜)。並且我們發現到降低了介電常數與消散因子的聚醯亞胺在熱穩定性質與機械強度上仍可以維持與傳統聚醯亞胺相近的數值，感光性方面解析度約為50微米左右。
本研究第三章，透過合成引入高立障之二胺單體增加整體結構的自由體積，使得空氣部分在整體高分子中佔有更多的比例，空氣的介電常數為1，因此可以透過增加自由體積來達到降低介電常數與消散因子的目的。不過本方法也有一個新的難題在於雖可降低介電常數至2.8、消散因子0.01，但立體障礙過大的分子使得反應性較差且成膜性不佳，讓我們在製膜應用上遇到極大的阻礙，因此仍需要混入其他單體提升反應性，使成膜性得到強化。
本研究第四章，透過混摻我們的聚醯胺酸(聚醯亞胺前驅物)至一些填充物以及染劑中，我們將高分子製成油墨配方，以工業用網版印刷將其覆蓋於電路板上進行測試，檢測其是否易於處理操作，結果顯示做成油墨配方的高分子仍然具有相當的熱穩定性與機械性質，且介電性質仍在一定的範圍內，而這個油墨配方也能夠完美的進行感光顯影，讓整個印刷電路板的製程能夠更簡便、更實惠。

關鍵字

感光聚醯亞胺 ； 高頻應用 ； 低介電常數 ； 低消散因子 ； 軟性印刷電路板 ； (阻焊)覆蓋層 ； 網版印刷

並列摘要

In modern days, photosensitive polyimides (PSPIs) have been attracting great attention in flexible printed circuit (FPC) industry. Polyimide can be used as a substrate or cover layer due to its’ high thermal stability, high chemical resistance, and excellent mechanical properties. However, it is difficult to make pattern on a printed circuit, so we introduce acrylate cross-linker to get a negative-working patterns formation. On the other hands, for the future printed circuit with higher transmission frequency, some problems must be overcome. The signal loss under high frequency transmission is the main purpose of introducing monomers with low dielectric constant (Dk) and low dissipation factor (Df). Conventional polyimides with aromatic rings usually give more than 3.5 dielectric constant and 0.02 dissipation factor (@10G Hz).
In chapter 2, we successfully introduce fluorinated group in the polymer chain. Due to the low polarizability of a carbon-fluorine bond, we minimize the electrons oscillation under a specific electric field. We compare different commercialized fluorinated dianhydrides and diamine to optimize the properties of the polyimide film. The polyimide film we made shows great dielectric constant around 2.5 and dissipation factor around 0.005~0.008 (10G Hz). On the other hands, thermal properties and mechanical properties remain the same as conventional polyimides with proper photosensitivity.
In chapter 3, we synthesize bulky diamine to increase the free volume in our system. By increasing the free volume, we can introduce more air in our polyimide chain. The dielectric constant of air is 1, so increasing air content can reduce the dielectric constant and dissipation factor. However, the bulky chain makes the free-standing film brittle. Although we can still reduce Dk and Df to around 2.8 and 0.01, the poor mechanical properties make it difficult for us to use as a printed circuit cover layer. We need to synthesis copolymer to strengthen film integrity.
In conclusion, we successfully synthesized some polyimides with enough low Dk, Df, and proper film properties. After blending our poly (amic acids) with some filler and dye to do ink test, we demonstrate the easy-processable characteristic of our polymer, we use industrialized screen printing process to test our polyimide ink film. The result shows great dielectric properties and mechanical properties, which is enough for applying in the flexible printed circuit cover layer (solder resist). These splendid polyimides can also combine with our acrylate photosensitive system, which makes the process easier, cheaper and can save more time in laminating layers on PCB.

並列關鍵字

photosensitive polyimide ； high frequency ； low dielectric constant ； low dissipation factor ； flexible printed circuit ； solder resist (cover layer) ； screen printing

參考文獻

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