| 摘要: | 隨著電子產品朝向小型化、輕薄化、多功能化和高密度化發展，作為元件間功能整合的電路板上所組裝的元件密度越來越高，導致高密度電路板的功耗和發熱量也隨之增加。如做為傳導電訊的金屬阻抗過大，將使電路板散熱不良，進而導致元件過熱，從而降低產品的效率、壽命與可靠性。為了解決這一問題，銅箔基板(Copper Clad Laminate, CCL)是印刷電路板(PCB)製造中的關鍵材料。CCL是由玻璃纖維和其他增強材料浸泡在樹脂中，並在其單面或雙面覆銅所製成，它廣泛應用於電視、廣播、電腦和行動通訊等電子產品中。隨著科技的進步，CCL在航空航天、通訊設備、消費性電子產品和LED照明等領域中的應用範圍也不斷擴大，它為各產業的電子產品提供強大的支持和基礎。
在使用CCL是重分佈層(Redistribution Layer, RDL)的PCB製程中，其銅箔層的封邊係依賴濕式蝕刻製程來保護和固定銅箔分離層。該法主要是在選定位置的周圍以光阻進行保護，經曝光顯影後，蝕刻去除上層約5 μm厚的銅箔和部分下層銅箔，然後將蝕刻後的表面封住，以保護分離層的高分子材料，避免在後續製程中產生分離。
本研究旨在研發一種使用紅外光雷射封合薄銅箔基板的雷射焊接法，檢視其取代前述濕式製程的可行性，以利於後續嵌入式電路基板(Embedded Trace Substrate, ETS)製程。研究主要對兩層厚度分別為5 μm和18 μm的銅箔進行疊焊，比較了使用波長為 1064 nm、最大功率20 W的脈衝式雷射 (Pulsed laser)與波長為1070 nm、最大功率500 W的連續式雷射(Continuous wave laser)的焊接效果。期望是能減小熱影響區且盡可能不傷及銅箔底下的有機材，並能在100 mm/s的焊接速度下形成穩定且均勻的焊道。
為了確保接合強度，我們以顯微鏡和焊接強度測試儀對樣品進行表徵檢測和接合強度測試。結果顯示，以脈衝式雷射焊接後剝離強度可達2.54 N/cm，連續式雷射剝離強度最高可達0.98 N/cm，此兩結果均高於高分子膠的剝離強度，也顯示以雷射直接進行薄銅箔焊接，在強度與時效應可滿足實際製程之需要。除了提供精確、高效的薄銅箔封合外，此法也相對環境更友善。;As electronic products continue to develop towards miniaturization, lightness, mul-ti-functionality, and high density, the density of components assembled on circuit boards for functional integration between devices is also increasing. This leads to higher power consumption and heat generation in high-density circuit boards. If the impedance of the metal used for conducting signals is too high, it will result in poor heat dissipation on the circuit board, causing the components to overheat, which in turn reduces the efficiency, lifespan, and reliability of the products. To address this issue, Copper Clad Laminate (CCL) has become a key material in the manufacturing of Printed Circuit Boards (PCBs). CCL is made by impregnating glass fibers and other reinforcing materials in resin and then coat-ing one or both sides with copper. It is widely used in electronic products such as televi-sions, broadcasting, computers, and mobile communications. With technological ad-vancements, the application scope of CCL has also expanded in fields like aerospace, communication equipment, consumer electronics, and LED lighting, providing strong support and foundation for electronic products in various industries.
In the PCB process that uses CCL as the Redistribution Layer (RDL), the edge sealing between the copper foil layers relies on a wet etching process to protect and fix the copper foils from separation in the subsequent processes. This method mainly involves protecting the selected area with a photoresist, and after exposure and development, the upper layer of approximately 5 μm thick copper foil and part of the lower copper foil are etched away. The etched surface is then sealed to protect the polymer material of the separation layer, preventing separation in subsequent processes.
This study aims to develop a laser welding method that uses infrared laser sealing on thin copper foil substrates, examining its feasibility as a replacement for the aforemen-tioned wet process to facilitate subsequent Embedded Trace Substrate (ETS) processing. The research focuses on welding two layers of copper foil with thicknesses of 5 μm and 18 μm, comparing the welding effects using a pulsed laser with a wavelength of 1064 nm and a maximum power of 20 W and a continuous wave laser with a wavelength of 1070 nm and a maximum power of 500 W. The goal is to minimize the heat-affected zone and avoid damaging the organic material beneath the copper foil while forming a stable and uniform weld at a welding speed of 100 mm/s.
To ensure bonding strength, samples were characterized and tested using a micro-scope and welding strength tester. The results show that the peel strength after pulsed laser welding can reach 2.54 N/cm, and the maximum peel strength with continuous wave laser welding can reach 0.98 N/cm. Both results are higher than the peel strength of polymer glue, demonstrating that direct laser welding of thin copper foil can meet the requirements of actual processes in terms of strength and durability. In addition to providing precise and efficient sealing of thin copper foil, this method is also relatively more environmentally friendly. |
