電鍍銅在自退火過程中的微結構變化對基板翹曲的影響

In-situ Characterization of the Microstructure Transition of Electroplated Cu During Self-Annealing and Its Effect on the Substrate Warpage

楊舒評(S.P. Yang) ； 胡麗萍(L.P. Hu) ； 楊政憲(C.H. Yang) ； 李承翰(C.H. Li) ； 何政恩(C.E. Ho)

《鑛冶：中國鑛冶工程學會會刊》 64卷4期 (2020/12) Pp. 71-83

https://doi.org/10.30069/MM.202012_64(4).07

摘要

印刷電路板（printed circuit boards, PCBs）的翹曲（warpage）一直是決定電子封裝（electronic packages）品質的關鍵因子。本研究透過X光繞射（X-ray diffraction, XRD）和電子背向散射繞射（electron backscatter diffraction, EBSD）等原位追蹤（in-situ）技術，以進行電鍍銅（electroplated Cu）之微結構演變探討。同時，也採用了shadow moiré和懸臂樑（cantilever）等分析方法針對基板翹曲及其應力演變進行即時觀測。透過這一系列的分析觀察，我們發現在自退火（self-annealing/room-temperature annealing）的情況下，電鍍銅晶體將發生巨幅轉變而引發顯著的應力釋放（stress relaxation），終致PCB基板發生翹曲。此外，研究也發現電鍍時所使用的電流密度將是影響電鍍銅自退火的重要因子，故可藉此以調控PCB的翹曲程度。高溫退火之預處理則可加速電鍍銅的再結晶，使得銅的微結構快速趨於穩定狀態。上述作用機制從未在文獻中被報導過，此一新知預計將可作為擬定PCB翹曲問題之緩解策略。

關鍵字

電鍍銅 ； 自退火 ； 印刷電路板翹曲 ； 內應力 ； 晶體轉變

並列摘要

The warpage of printed circuit boards (PCBs) has been a serious reliability concern in electronic packaging applications because of the flatness requirement of electronic assemblies. Electroplated Cu might play a key role in the PCB warpage. The objective of the present study was to systematically investigate the microstructure/ stress evolutions of electroplated Cu during self-annealing and the dependence of the PCB warpage on the Cu microstructure transition. The Cu crystallographic evolution, including the grain size and orientation, was in-situ characterized by means of X-ray diffraction (XRD) and electron backscatter diffraction (EBSD). Additionally, the phase-shifting shadow moiré and cantilever methods were employed to conduct non-destructive, real-time measurements of the PCB warpage. These characterizations showed that a remarkable crystallographic transition upon Cu self-annealing induced a stress relaxation, leading to the PCB warpage without thermal processes. Moreover, the plating current density was an important factor of the Cu self-annealing behavior and the high-temperature annealing pretreatment accelerated Cu recrystallization and stabilized the Cu microstructure, providing a possible mitigation strategy for the PCB warpage.

並列關鍵字

Electroplated Cu ； Self-annealing ； PCB warpage ； Internal stress ； Crystallographic transition