無鉛表面處理銲墊之低銀含量錫銀銅銲錫球格陣列構裝接點性質研究

The Study on Low-Ag Content Sn-Ag-Cu BGA Solder Joints with various Pb-free Surface Finishes

陳衿良(Chin-Liang Chen)

指導教授 ： 莊東漢

國立臺灣大學/工學院/材料科學與工程學研究所/博士(2010年)

https://doi.org/10.6342/NTU.2010.03537

摘要

針對Sn-Ag-Cu無鉛銲錫成分中，銀含量過高所導致之種種缺失，本研究嘗試以直接降低銀含量之方式，並於所得之低銀含量銲錫合金中，再額外添加微量之鎳及鍺元素，觀察Sn-3Ag-0.5Cu(SAC305)、Sn-1Ag-0.5Cu(SAC105)及Sn-1Ag-0.5Cu-0.06Ni-0.01Ge(SAC105NG)三組銲錫合金，與有機保銲膜(OSP)、化鎳金(ENIG)及化鎳鈀金(ENEPIG)等無鉛表面處理銲墊，經迴銲及高溫時效處理後，各組接點之界面反應情形，此外，針對不同銲錫合金與無鉛表面處理銲墊之機械強度，本研究則利用推球測試(BS)、拔球測試(CBP)及新發展之快速推球測試(HSBS)加以評估。
實驗結果顯示，Sn-Ag-Cu銲錫接點之推球及拔球強度，將因其成分中之銀含量降低，而有明顯下降之情形，但當微量之鎳及鍺元素添加進入銲錫合金後，將可有效提升其機械強度，且對Sn-Ag-Cu-Ni-Ge五元合金而言，其接點之推球及拔球強度，於高溫時效處理後之劣化情形，將優於習用之高銀含量Sn-Ag-Cu銲錫；另一方面，不同於推球及拔球測試所導致之接點內部延性破斷，在接點之快速推球測試中，其所呈現之破斷模式，將屬於斷裂於接點界面之脆性破斷，故不同反應系統所生成之界面介金屬化合物，其外觀形貌、化學成分及厚度等，均將影響個別接點之快速推球強度，其中，對銲錫與OSP表面處理銲墊作用之接點而言，降低銲錫成分中之銀含量，將可有效提升接點之快速推球強度，然而，當反應系統改為銲錫與ENIG表面處理銲墊時，整體接點之衝擊耐受度，反而將因銲錫中銀含量之減少，而有略為劣化之情形，此外，針對本研究額外添加之鎳及鍺元素，其效應將導致整體接點之抗衝擊能力明顯下降，另一方面，相較於習用之ENIG表面處理銲墊，具有額外無電鍍鈀層之ENEPIG表面處理，將可有效提升銲錫接點之衝擊耐受度。

關鍵字

低銀含量錫銀銅銲錫 ； 無鉛表面處理 ； 球格陣列構裝 ； 界面反應 ； 機械性質測試 ； 化鎳鈀金 ； 快速推球強度

並列摘要

Due to concerns about the drawbacks leading from the high-Ag content in the Sn-Ag-Cu Pb-free solders, the Ag content of the Sn-Ag-Cu solder is directly lowered in the present study. In addition, minor Ni and Ge elements are doped into the solder alloy to further optimize the properties of the low-Ag content solder. Interfacial reactions between each kind of solder alloy (Sn-3Ag-0.5Cu(SAC305), Sn-1Ag-0.5Cu(SAC105), and Sn-1Ag-0.5Cu-0.06Ni-0.01Ge(SAC105NG)) and various Pb-free surface finishes (Organic Solderability Preservative(OSP), Electroless Nickel Immersion Gold(ENIG), and Electroless Nickel Electroless Palladium Immersion Gold(ENEPIG)) after reflow and high temperature aging treatment were observed, and the mechanical strength of the solder joints were evaluated via Ball Shear(BS), Cold Ball Pull(CBP), and the newly-developed High Speed Ball Shear (HSBS) tests.
The results show that the ball shear and cold ball pull strengths of the Sn-Ag-Cu solder joints decrease obviously as the Ag content of the solder alloy reduces; however, after the minor Ni and Ge elements were doped into the solder alloy, the mechanical strength of the Sn-Ag-Cu-Ni-Ge solder can effectively be improved, and the degradation of the ball shear and cold ball pull strengths after high temperature aging treatment is less apparent in this five-element alloy than in the high-Ag content Sn-Ag-Cu solder. Unlike the ductile fracturing through the solder balls which is revealed in the ball shear and cold ball pull tests, the high speed ball shear test causes the solder joints to fracture along the interfacial intermetallic compounds. Thus, the morphology, chemical composition, and thickness of the interfacial intermetallic should all be considered to be factors influencing the high speed ball shear strength of each solder joint. For the case that the solders react with OSP surface finish, the high speed ball shear strength of the solder joint increases with the decreasing of the Ag content. On the contrary, the shock resistance of the solder joint deteriorates as the Ag content reduces when the surface finish changes to the ENIG as well as the minor Ni and Ge elements doping into the solder alloy. On the other hand, for the ENEPIG surface finish with an extra electroless palladium layer, its shock resistance can effectively be improved as comparing to the traditional ENIG metallization.

並列關鍵字

low-Ag content Sn-Ag-Cu solder ； Pb-free surface finish ； BGA package ； interfacial reaction ； mechanical property test ； ENEPIG ； high speed ball shear strength

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