由電流驅使之錫晶鬚成長之研究

Abstract

在微電子構裝工業中，近來因為環境保護的考量，所以使得無鉛銲錫逐漸地取代傳統的有鉛銲錫。而在大部份的無鉛銲料中，錫的成分比例皆超過95%。因此由電流驅使的錫晶鬚之成長將成為無鉛銲料構裝中最重要的研究課題之一。本論文中，利用5000Å的錫條在700 Å的鈦膜之上的Blech構造來研究純錫的電遷移效應。所使用的電流密度為7.5 ×104 A/cm2及1.5 ×105 A/cm2。經過通電後我們觀察到在陽極部份產生錫晶鬚及突出物，陰極部份則產生孔洞。此外，為了研究溫度的效應，試片在通電時分別置於室溫及50°C下。在室溫下，電流密度1.5 ×105 A/cm2時錫晶鬚的成長速率大約為3 Å/sec,在50°C下則為7.7 Å/sec。在電流密度7.5 ×104 A/cm2室溫下時速率為0.4 Å/sec。本論文中，錫晶鬚成長速率與通電的時間及電流密度及通電時環境溫度成函數關係，由電流驅使的錫晶鬚之成長機制將被討論。

Lead-free solders are replacing traditional SnPb solders gradually due to environmental concern in microelectronic packaging industry. In most lead-free solders, tin is the richest element and weighs over 95% of the solders. Therefore, tin whisker growth driven by electrical currents would be one of the most crucial reliability issues in lead-free microelectronic packaging. Blech structure is used to investigate the electromigration effect in pure tin, in which 5000 Å tin strips are on 700 Å titanium films. Current density of 7.5 ×104 A/cm2 and 1.5 ×105 A/cm2 are applied in the Blech samples. We observed tin whiskers and hillocks on the anode side and voids on the cathode side. The average growth rate of tin whiskers is measured as a function of current density. Also, to investigate temperature effect, samples are stressed at room temperature and 50°C respectively. The average growth rate is about 3 Å/sec at the current densities 1.5 ×105A/cm2 at room temperature, and the rate is 7.7 Å/sec at 50°C. The rate is 0.4 Å/sec at the current densities of 7.5 ×104 A/cm2. The average growth rate of tin whisker as a function of time, current density and temperature are presented in this thesis. The mechanism of tin whisker growth driven by electrical force is discussed.