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National Chung Hsing University Institutional Repository - NCHUIR > 工學院 > 化學工程學系所 > 依資料類型分類 > 碩博士論文 >  銲點表面處理層之選擇與利用固態接合製程之界面反應

Please use this identifier to cite or link to this item: http://nchuir.lib.nchu.edu.tw/handle/309270000/154314

標題: 銲點表面處理層之選擇與利用固態接合製程之界面反應
The Choice of Surface Finishes for Solder Joint and the Interfacial Reactions by Solid-State Bonding
作者: 林吉甫
Lin, Chi-Pu
Contributors: 陳志銘
化學工程學系所
關鍵字: 表面處理層;固態接合;介金屬化合物;應變
Surface Finish;Intermetallic Compounds;Solid-state Bonding;Strain
日期: 2012
Issue Date: 2013-11-21 10:12:52 (UTC+8)
Publisher: 化學工程學系所
摘要: 近年來環保意識抬頭,綠色材料議題備受重視,由於鉛會危害環境以及人體健康,所以歐盟在2006年立法禁止含鉛的電子封裝製程,傳統在印刷電路板上表面處理的技術熱風整平(Hot Air Solder Leveling, HASL)因利用錫鉛共晶的組成而被禁止,許多替代的處理層像化鎳浸金(Electroless Nickel/Immersion Gold, ENIG)、化鎳化鈀浸金(Electroless Nickel/Electroless Palladium/Immersion Gold, ENEPIG)、浸鍍銀(Immersion Silver)、浸鍍錫(Immersion Tin)與有機保銲劑(Organic Solderability Preservatives, OSPs)因而興起。
在封裝製程中常利用迴銲銲接的過程將銲料熔融並與基板反應接合,在此過程下基板上的表面處理層亦會熔融到液態的銲料內,造成界面反應主要為銲料的錫與基板的銅層進行液固的反應。然而在可撓曲式的印刷電路板以及光學封裝中,常用固態接合的技術利用以錫為主的銲料將晶片與基板接合,而非運用迴銲的製程。因此表面處理層仍會殘留在銲點界面處形成錫/表面處理層/銅的三層結構。本研究則探討當表面處理層仍存在於錫/銅的界面處時,在固態熱處理下對其反應的介金屬化合物生成動力學之機制與型態的影響。
由於現今的電子產品都朝向輕薄短小的趨勢,可藉由撓曲式的印刷電路板來減少封裝的體積。在撓曲的過程中,銲點界面處的反應亦會遭受到形變的影響,因此在本論文中亦研究在施加壓縮與拉伸應變並改變應變曲率的大小,並與不受應變界面反應的結果相比較探討應變對錫/表面處理層/銅三層結構界面反應的影響。
在積體電路的封裝中,界面反應並不僅只在銲料與基板間,其反應亦受到晶片端之金屬層交互擴散的影響。在覆晶技術的凸塊下金屬層(Under Bump Metallization, UBM)常運用銅層以及鎳層,由於銅層具良好的導電性常被用於印刷電路板上的金屬線,因此運用於基板端,鎳則具有良好的銲接性以及擴散阻隔的能力,亦經常運用在晶片端之阻隔層,錫則為無鉛銲料中主要的成分,因此在覆晶銲點中常形成鎳/錫/銅的三明治結構。本論文藉由導入表面處理層在鎳/錫/銅的三明治結構內,在固態熱處理下,研究表面處理層對界面反應交互擴散的影響。
本論文得到的結果認為銀表面處理層能夠增加銲料接點的可靠度外亦能減緩形變對界面反應的影響,鈀表面處理層跟錫與鎳反應會生成過厚的(Pd,Ni)Sn4層,使銲點機械性值大幅下降,然而在銲料中添加適量的銅,則能減緩(Pd,Ni)Sn4層過度的成長,改善其可靠度。
The technology of surface finishes for printed circuit boards (PCBs) is seeing a dramatic shift from hot air solder leveling (HASL) towards alternative finishes such as electroless nickel/immersion gold (ENIG), electroless nickel/electroless palladium/immersion gold (ENEPIG), immersion silver, immersion tin and organic solderability preservatives (OSPs). This trend is driven by the worldwide environmental pressure to ban the use of lead for electronic assemblies, as well as the demands of modern assembly technology, which require a higher co-planarity of the surface finish for surface mount assembly.
For flexible PCB and optoelectronic packaging, solid-state bonding rather than reflow is commonly used to join the chips to the PCB with Sn-based solders, after which the surface finishes layer remains at the joint interface and participates in the interfacial reactions at the solder joints. Solder joint samples composed of a Sn/surface finishes/Cu trilayer were prepared to study the interfacial reactions.
Besides, flexible PCBs are usually bended in order to reduce the packaging volume, making the solder joints subject to strain. Therefore, it is of interest to investigate the Sn/surface finishes/Cu tri-layer interfacial reactions under the influence of strain. In this study, the Sn/surface finishes/Cu trilayer on polymer board was subjected to compressive and tensile strain aged at 150℃ and 200℃ to investigate the formation and morphology of intermetallic compounds.
However, the interfacial reactions not only exist at solder/Cu interface, it also effect by the opposite diffusion couple. In modern integrated circuit (IC) packaging, the under bump metallization (UBM) used in flip-chip technologies is often composed of two different types of metal pads. Cu is commonly used as a metallization layer on the printed circuit boards (PCB). Ni has good solderability and is also a good diffusion barrier. Therefore, it is commonly used as a barrier layer on the chip-side metallization. Sn is the primary element of the Pb-containing and Pb-free solders, hence the Ni/Sn/Cu sandwich-type structure is often formed in the flip-chip solder joints. Therefore, morphological evolution, phase formation, and kinetic behavior of the intermetallic compounds formed at the interfaces were investigated to understand the cross-interactions in the Ni/Sn/Cu samples with a surface finish layer.
In this dissertation’s conclusions, the Ag surface finish not only could enhance the reliability of solder joint, but also retard the influences of interfacial reactions under strain. On the contrary, the Pd surface finish would react with Sn and Ni to form thick (Pd,Ni)Sn4, it would make the mechanical properties decrease drastically. However, adding some Cu in the solder could retard the (Pd,Ni)Sn4 growth excessively and improve the mechanical strength.
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