彎曲及熱負載下之超薄型晶片軟膜異方性導電膠接點可靠度及可撓曲性研究

Reliability and Flexibility Investigation of Ultra-Thin Chip-on-Flex (UTCOF) with Anisotropic Conductive Adhesive (ACA) Joints under Bending and Thermal Loading

陸蘇財(Su-Tsai Lu)

指導教授 ： 陳文華

國立清華大學/工學院/動力機械工程學系/博士(2011年)

https://doi.org/10.6843/NTHU.2011.00037

摘要

中文摘要
展望未來消費性先進電子產品的應用，高密度和可撓曲接點的需求快速增加。本論文旨在探討超薄型晶片軟膜(ultra-thin chip-on-flex, UTCOF)異方性導電膠(anisotropic conductive adhesive, ACA)接點在承受彎曲及熱負載下的可靠度及其可撓曲性，除應用ANSYS有限單元套裝軟體發展一準確的三維數值分析模型外，並經由實驗驗証及參數化分析，期建立UTCOF接合構裝技術之設計準則。
由於ACA膠材的收縮特性和其導電顆粒之彈塑性質將影響ACA接點之電阻值，本論文乃利用三維有限單元模型，配合接觸力學分析，對熱壓合製程後之ACA接點電阻值導電機制進行分析，並與ACA接點電阻值驗証結果相互驗証，此研究結果將可供準確預估ACA接點的可靠性。
在高密度COF的研究中，本論文提出一新型的複合凸塊(compliant bump)接合結構，搭配雙層式ACA膠材，並完成20 m間距接合架構的可行性驗証，1,000小時高溫高濕(85°C/85%RH)溫濕儲存 (temperature-humidity storage test, THST)和1,000次之溫度循環(temperature cycling test, TCT)測試。
在UTCOF的接合實驗相關參數研究，本論文完成了晶圓薄化及晶圓切割，除探討不同晶片厚度(25 m, 35 m, 50 m)對超薄型晶片撓曲能力之影響，並對製程溫度對兩種不同ACA膠材(ACA-P, ACA-F)之固化特性，探討膠材在不同固化程度下之界面接合力及接點電阻值。此外，不同接合壓力下金凸塊(Gold bump)和複合凸塊的接點電阻值和導電顆粒變形亦予分析。ACA接點在熱負載下之可靠度，係利用7,000小時長時間85°C/85% RH THST來分析，並藉由不同測試環境下之靜態彎曲和四點彎曲負載來試驗其可撓曲性，不同測試環境下的失效樣品，亦將藉由掃描式電子顯微鏡(scanning electron microscopy, SEM)橫截面觀察其失效機制。此外，兩種UTCOF接點在四點彎曲負載下之失效機制並以有限單元數值分析配合探討。
本論文所建立的可撓曲UTCOF和高密度COF接合技術成果，將可為軟性電子構裝技術發展及量產設計之參考。

關鍵字

超薄型晶片軟膜 ； 異方性導電膠 ； 可靠度 ； 可撓曲性 ； 有限單元數值分析 ； 軟性電子構裝

並列摘要

Abstract
For future advanced applications in consumer electronic products, the need of high-density and flexible interconnects increases rapidly. In this study, the reliability and flexibility of ultra-thin chip-on-flex (UTCOF) interconnects using anisotropic conductive adhesive (ACA) were investigated. A rigorous three-dimensional (3-D) numerical analysis model was performed using the ANSYS program. Moreover, experimental and parametric analyses of UTCOF interconnects were evaluated to establish the design rule of ACA-bonded UTCOF interconnects.
Due to shrinkage of ACA resin and elastic-plastic characteristic of conductive particles, the effect of contact behavior in ACA joints on the contact resistance of the fabricated UTCOF interconnects after thermo-compression process was also estimated using a three-dimensional finite element model. The contact resistances obtained from the analysis results were in good agreement with experimental results, and can be used to predict the reliability performance in ACA joints.
A process for manufacturing 20 m-pitch compliant-bumps was proposed for COF structure using 2-layer ACA material. The reliability of the fabricated COF interconnects was evaluated by performing an 85°C/85％ relative humidity temperature-humidity storage test (RH THST) for 1,000 hours and a -55°C~125°C thermal cycling test (TCT) for 1,000 cycles.
For UTCOF interconnects, the effect of chip thickness (25 m, 35 m, 50 m) on the fracture strength of the ultra-thin silicon chip was estimated. Both the ACA-P and ACA-F materials were assembled at different bonding temperatures to study the temperature effects on the curing percentage and adhesion by differential scanning calorimeter (DSC) measurement and peeling test, respectively. Meanwhile, the relationship between curing conditions and electrical contact resistance was examined. Moreover, the bonding pressure effects on the electrical performance and deformation degree of conductive particles within the ACA resin were also explored. The contact resistance of daisy chain was measured to examine the bonding quality through the 80 m pitch dummy test samples using micro Au (gold) bump (GB) and compliant bump (CB). The reliability of the fabricated UTCOF interconnects bonded with selected ACA joints was evaluated by long-term 85°C/85％ RH THST for 7,000 hours and their flexibility was performed by static bending under various testing environments and 4-point bending tests. The interfaces between ultra-thin silicon chip and substrate for failed samples from THST and 4-point bending tests were then inspected through the cross-section scanning electron microscopy (SEM) works. Finite element analysis (FEA) was also conducted to interpret the failure mechanism of the UTCOF interconnects under 4-point bending test.
Based on the results achieved, the UTCOF with ACA joints presented in this work would be reliable for serving as flexible interconnects for consumer electronic products. Also, the manufacturing technology for high-density and flexible UTCOF interconnects with ACA joints was thus established.

並列關鍵字

Ultra-thin chip-on-flex (UTCOF) ； anisotropic conductive adhesive (ACA) ； reliability ； flexibility ； finite element analysis (FEA) ； flexible interconnects

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