- 學位論文
印刷電路板銅蝕刻製程之均勻化改進研究-水坑效應排除與非等向性提昇
Improving the copper etching process in printed circuit board manufacturing–prevent the puddling effect and enhance anisotropic etching
摘要
印刷電路板（Printed Circuit Board, PCB）產業的銅蝕刻製程始終存在不同類型的蝕刻問題，其中最被廣泛研究的莫過於光阻下方銅膜（俗稱銅皮）的底切問題。底切的形成與蝕刻行為的等向性有絕對的關係，評估底切的程度通常是以蝕刻因數的大小做為參考，而蝕刻因數的大小則取決於銅線兩倍高度與上下線寬差的比值，而影響蝕刻因數大小的參數則包括蝕刻液類型、濃度、流速、溫度等。歷經多年的研發，非等向性蝕刻的技術仍未完全發展完備，而新的問題隨著新式蝕刻技術的開發而產生。採取輸送帶進材的濕式噴灑蝕刻製程的PCB製造業，目前幾乎均面臨銅膜中心位置的水坑效應（Puddling Effect）問題。此一水坑效應會使銅膜週邊位置的蝕刻深度大於中心位置的蝕刻深度，造成銅膜蝕刻面的均勻度不足，進而影響末端產品的品質。 有鑒於目前多種常用之銅蝕刻製程均無法有效解決水坑效應的問題，或者解決問題的同時必須增加可觀的額外設備與維護支出，我們於是積極尋找更有效的替代方式，目前發現較為可行的作法是以平板式噴嘴於蝕刻液面上或下直接在板材表面提供近距離而垂直入射的激流（Jet Stream），板材進料則仍可透過輸送帶水平式行進，以維持高產量。本項沉浸式或非沉浸式激流蝕刻技術的效果是由於改變蝕刻液在銅箔基板上的流動方式，而使得Puddling Effect 現像消除，且流速增加與流向垂直亦可在銅箔基板(CCL)與蝕刻液噴射處成垂直區域造成極高的腐蝕速度可達每分鐘375 µm，相較於濕式噴灑蝕刻機台的蝕刻速率本實驗機台蝕刻能力約為其五~六倍，以噴嘴高度4 mm(相較於銅箔基板的水平面)、流量為70~75 LPM之條件下有最佳之蝕刻速率，且在線路蝕刻方面在線寬線距(L/S)為250 µm/100 µm條件下具有甚佳之蝕刻因子，蝕刻因子最高可達7。基於上述實驗的結果，預期在轉移至產線後將能有效增加產率與蝕刻品質。另一方面也對業界常用氣體與溶銅量對蝕刻液的影響進行分析，其望了解氣體、溶銅量對製程所造成的影響，以便於控製蝕刻品質。
並列摘要
Various problems have constantly emerged during the copper etching process in the manufacturing industry of printed circuit board (PCB). The most common one is the undercut phenomenon beneath the etch resist resulted from undesirable isotropic etching. The etch factor is generally used as an indicator for evaluating the degree of undercut in an etching process and is a function of the copper line thickness and of the difference between the lower and the upper line width. Environmental parameters such as etch solution type, solution concentration, flow velocity, and temperature have a deterministic impact on the magnitude of an etch factor. The undercut problem does not cease to occur in the absence of an ideally anisotropic etching although it has indeed been alleviated after years of intensive research. On the other hand, new problems emerge along with new etching techniques. The PCB manufacturers that adopt the spray etching process in combination with conveyors are forced to deal with the annoying puddling problem. The puddling effect caused by insufficient mass transfer of the etch solution at the center portion of a board could lead to an unacceptable etch depth difference between the edge area and the center area and a loss of uniformity of etched copper film. Most of the available copper etching processes cannot efficiently resolve the puddling effect. The only one that has a satisfactory solution unfortunately calls for extra auxiliary equipment and a tremendous amount of maintenance work and cost. An alternative resolution to the problem has been developed and evaluated and the new technique is deemed feasible based upon a full-scale theoretical analysis. The principle is to adopt a jet stream to speed up the etching process by a higher flow rate and to enhance the anisotropic etching by a higher and more direct impact force from the stream. According to current research findings, the puddling effect seen in traditional etching processes was completely eliminated. The etching efficiency of this new technique is much higher that those by other traditional processes. The optimal etching rate is 375 µm/min under 4 mm jet distance at a flow rate of 70~75 LPM in FeCl3 solutions. The etching factor has attained a relatively large value of 7 which is much better than those obtained from currently available techniques. Base on these experimental observations, the new system is expected to increase throughput and to enhance etching factors in on-line application.