無鉛銲錫成分與綠漆通孔尺寸對FCBGA元件可靠度影響之研究

Investigation of the Lead-free Solder Compositions and the Solder Mask Opening Sizes on the Reliability of the FCBGA Components

鄭武輝(Wu-Hui Cheng)

指導教授 ： 陳永樹

元智大學/工程學院/機械工程學系/碩士(2006年)

https://doi.org/10.6838/YZU.2006.00061

摘要

FCBGA元件因具備高效能及高腳數之特性，因而成為構裝技術之主流，而電路板層級元件之失效位置常見於銲錫接點處。由於近年綠色科技之倡導及歐盟法規限定，無鉛銲錫如錫銀銅合金已廣泛應用於錫球接點之材質，因此本研究即針對63Sn37Pb、Sn3.0Ag0.5Cu及Sn4.0Ag0.5Cu三種錫球材質之FCBGA元件進行可靠度彎曲測試，並藉由韋伯分佈探討其可靠度行為之差異。
研究結果指出於循環彎曲測試中，無鉛銲錫之元件相較於錫鉛共熔合金提供較高之平均壽命，但其元件具有變異性較大之壽命分佈。而於一次下壓彎曲測試中，則後者材質具有較佳之抗彎矩強度。此外本研究亦探討0.4 mm及0.525 mm兩種綠漆通孔尺寸對於FCBGA元件可靠度之影響，結果得知無論銲點材質為何？0.525 mm之綠漆通孔尺寸設計皆具有較高之可靠度。此外，並於循環彎曲測試後，統計其失效位置及失效模式，得知0.4 mm綠漆通孔尺寸之失效位置位於錫球上方靠近基板處，而0.525 mm綠漆通孔尺寸之失效位置則為錫球下方靠近電路板之位置。而於一次下壓彎曲測試之失效模式，則兩者之破壞位置相同，皆為錫球下方之銲墊與電路板界面破裂而剝離。
此外，於有限元素分析中計算角落錫球於循環彎曲測試之塑性應變區間並計算其疲勞壽命。其估算結果相符於彎曲測試之平均壽命，因而證實有限元素模型之正確性。而藉由分析所得之累積應變能密度，結合循環彎曲測試之結果，得以建構本研究中FCBGA元件之疲勞壽命模型，並適用於計算不同綠漆通孔尺寸之累積應變能密度，藉此得知FCBGA元件之綠漆通孔尺寸與疲勞壽命之關係。而研究結果對於封裝結構設計之可靠度工程極具應用價值。

關鍵字

有限元素分析 ； 疲勞壽命 ； 無鉛銲錫 ； 綠漆通孔尺寸 ； 覆晶球柵陣列構裝 ； 彎曲測試

並列摘要

FCBGA components provide higher I/O counts and better performance, and become the major trend in the recent packaging technologies developed. The failure locations of the board level assembly are frequently observed at the solder connections. Also, due to the environmental concern and the green electronics regulations, the lead-free solder alloy such as Sn-Ag-Cu is often used to replace the traditional tin-lead solder alloy in the electronic applications. This study then focuses on the investigation of reliability differences for the FCBGA components with 63Sn37Pb, Sn3.0Ag0.5Cu, and Sn4.0Ag0.5Cu as the materials of the solder balls.

The results indicate that in the cyclic bend test, the FCBGA components with lead-free solder have the better average fatigue life than those with tin-lead solder. However, the results for the former have more variations than the latter. But in the monotonic test, the latter is better in resisting the bending forces. Also, the package design with 0.4 mm and 0.525 mm solder mask (S/M) opening sizes were also studied with the bend test. The results show that FCBGA components with larger opening sizes perform better in their reliability. Moreover, the failure locations and failure modes of FCBGA component under the cyclic bend test are identified with the failure analysis. The results reveal that the failure locations for 0.4 mm S/M opening size are at the top of the solder ball on the substrate side and are at PCB side for those with 0.525 mm S/M openings. On the contrary, for all the tests, those failures in the monotonic tests are pretty much the same to occur at lower locations on the PCB side at the interface of the solder pad and PCB itself.

Finally, the finite element analysis (FEA) is used to calculate the plastic strain range of the corner solder balls under the cyclic bend test. Later, by combining the results with the fatigue model to predict the reliability of solder joint, it is found that the analyzed results are consistent with the failure mode analysis and test statistics. This indicates that the FEA Model is accurate enough and could be applied further. It is then used to calculate the plastic strain energy density accumulated per bending cycle within the critical solder joint and the results is also compared with the experimental results. The resulting fatigue model for the FCBGA component is then obtained. It is then possible to use this model to change the solder mask opening sizes in predicting the corresponding fatigue life. The results are believed to be worthy for the application in the FCBGA component reliability assessment.

並列關鍵字

Bend test ； Fatigue life ； FCBGA ； FEA ； Lead-free solder ； Solder mask opening size

參考文獻

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