Sn Whiskers: Causes, Mechanisms and Mitigation Strategies

Major Driving Forces and Growth Mechanisms for Tin Whiskers

“…2.1) of growth rate versus applied pressure shows that the whisker growth rate is accelerated by the application of mechanical stress. Other studies [3][4][5][6] have repeatedly confirmed that mechanical stress can enhance whisker growth. Oxidation has also been proposed as an alternative driving force, but we believe it can be discounted as the primary cause by experiments that show that whiskers still form under high vacuum conditions where oxidation will not occur [7].…”

“…The Sn-based layers were grown over Cu layers that were vapor deposited via electron-beam deposition on oxidized Si (100) substrates. Further details of the deposition process can be found in [6,18].…”

“…Other sources of stress that have been identified are not as easily removed; these include residual stress [6] due to the initial plating [8], thermal-expansion mismatch during thermal cycling [9], electromigration and intermetallic compound (IMC) formation between the Sn and Cu layers [6,[10][11][12].…”

“…Numerous measurements [6,[10][11][12][15][16][17][18] have shown that IMC formation leads to stress in the Sn layer. Lee and Lee [11] were the first to show this quantitatively by using wafer curvature to measure the buildup of compressive stress in the Sn layer.…”

Microstructural Investigations of Low Temperature Joining of Q&P Steels Using Ag Nanoparticles in Combination with Sn and SnAg as Activating Material

“…Whisker formation in the joining seams was often observed (Figures 19 and 20). Such whisker growth is known from the use of lead-free Sn solders with copper substrates [28]. It is assumed that in particular external or internal stresses lead to the formation of whiskers.…”