無鉛焊料對最終表面處理技術介面合金共化物之研究

Analysis of Intermetallic Layer in the Final Finish with Lead Free

陳致宏(Chin-Hong Chen)

指導教授 ： 蔡德華

國立臺北科技大學/工程學院/化學工程研究所/碩士(2007年)

摘要

有鉛焊料中所含的鉛為嚴重環境污染物，目前改為無鉛焊料是勢在必行，對於電子等相關產業必定會引起相當大的動盪。另外由於目前無電鍍鎳金 （Electroless Nickel Immersion Gold, ENIG）仍為有按鍵之電子產品最終表面技術最佳選擇之製程，但是中磷鎳容易帶來黑墊困擾，目前產業界正積極研發其他最終表面處理技術來取代中磷鎳金製程進而解決黑墊問題。
本研究主要使用無鉛焊料（SAC305）針對印刷電路板製程之最終表面處理部分進行回焊後，將形成之介面合金共化物（Intermetallic Compound, IMC）進行熱循環方式測試。最終表面處理製程部分則選擇直接金（Direct Immersion Gold, DIG）、高磷含量無電鍍鎳金（High Phosphorous Electroless Nickel Immersion Gold, HP-ENIG）、無電鍍鎳鈀金（Electroless Nickel Electroless Palladium Immersion Gold, ENEPIG）個別放入中央處理器（Central Processing Unit, CPU）所選用之球柵陣列封裝（Ball Grid Array, BGA）之板材製成試片，再置於高溫烤箱中，利用不同溫度條件來探討各製程中介面合金共化物（Intermetallic Compound, IMC）之微結構變化及銲點強度差異。
根據實驗個別探討三種最終表面處理製程，每個製程均探討以無鉛焊料SAC305進行焊接後，形成之介面合金層在定溫時效下生長現象;及觀察定溫時效下未植無鉛錫球待焊表面部分之外觀變化與晶格;並分析討論定溫時效下植無鉛錫球部分進行錫球推拉力測試並進行失效模式分析討論。

由實驗結果觀察得知，在無電鍍高磷鎳金IMC layer（Ni,Cu）6Sn5觀察部分，於加熱至600hrs時，開始有鬆散不紮實現象發生，其可能為影響銲點強度要因之一;在直接金製程定溫時效下IMC layer觀察，加熱至100hrs可發現銅層與Cu6Sn5之間，產生另一IMC layer Cu3Sn，並可發現有40%推力斷面出現在IMC layer，其IMC layer Cu3Sn也可能為影響銲點強度要因之一;在無電鍍鎳無電鍍鈀金製程定溫時效下IMC layer（Ni,Cu）6Sn5 +Pd觀察，加熱至200hrs時，IMC結構開始由樹枝狀結構變化成塊狀結構。

關鍵字

無鉛焊料 ； 最終表面處理 ； 表面黏著技術

並列摘要

Sn-Pb solder should be replaced by lead free solder in the future applications because the previous one contains one of the notorious environmental killers, lead. Apparently the replacement will make a strong impact to entire electronic industry. In addition, a better final finish technique should be developed to replace the Electroless Nickel Immersion Gold (ENIG) technique for the keyboard manufacturing industry because the latter suffers from the problem of black pad caused by medium phosphorus.
This study mainly used the lead free solder (SAC305) in the reflow process of the final finish, and test the formed Intermetallic Compound (IMC) with a thermal recycle method. During the final finish process, the materials of Direct Immersion Gold (DIG), High Phosphorous Electroless Nickel Immersion Gold (HP-ENIG), Electroless Nickel Electroless Palladium Immersion Gold (ENEPIG) were individually put on the panels made by CPU-picked Ball Grid Array (BGA), to product experimental test pieces. Then the pieces were put in an oven with several different high temperature settings to investigate their microstructure changes and welding strengths of the intermetallic compounds obtained by different processes.
Finally,this study investigates individually three different final finish processes. The investigations for each process include (1) the growth phenomenon in a certain temperature of the intermetallic which was formed after welding with SAC305; (2) the surface structure and crystal grid changes in a certain temperature before the surface was welded with lead free balls; (3) lead free Ball shear/Ball Pull tests in a certain temperature and tests of failure mode and effect analysis.
The result shows that: there are some loosening phenomenon are observed after the IMC layer of High Phosphorous Electroless Nickel Immersion Gold was heated up to 600hrs, maybe the loosening is one of the factors which causes the change of solder strength. For the Direct Immersion Gold procedure in fixed temperature, there are some IMC layer Cu3Sn are formed after the IMC layer was heated up to 100hrs, and about 40% cross section of ball shear formed in the layer. Probably, it weakens the solder strength. For the Electroless Nickel Electroless Palladium Immersion Gold procedure in fixed temperature, the IMC structure turns from dentritic structure to lump structure after 200 hrs heating.

並列關鍵字

Lead free solder ； Finial finish ； SMT

參考文獻

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