Eliminating Whisker Growth by Indium Addition in Electroplated Sn on Copper Substrate

Recent Advances in Mitigation of Whiskers from Electroplated Tin

“…As seen in Fig. 3a, 75 no whiskers with aspect ratio (AR = length/diameter) greater than 5 grew in the 3-lm Sn-In-Sn sample, although under the same processing conditions, a high density of whiskers grew in the pure Sn and Sn-Sn-Sn samples. Similar whisker mitigation has been reported for a 1.6-lm Sn-In-Sn sample with 7 wt.% In over a 1.5-year period, where a focused ion beam (FIB) cross section revealed a columnar microstructure.…”

“…Recent work has demonstrated that addition of 6% to 10% indium prevents growth of long whiskers from electroplated Sn coatings during isothermal aging at room temperature. [74][75][76] Unlike with Pb additions, where whisker growth is mitigated but not eliminated, addition of In at this concentration level completely eliminates whisker growth.…”

“…The efficacy of In for mitigation of whisker growth in 1-lm-, 3-lm-and 6-lm-thick electroplated Sn was assessed by comparing whisker growth rates in Sn doped with (6 wt.% to 10 wt.%) In versus pure Sn processed under identical conditions. [74][75][76] Since an electrolyte was not available initially for codepositing Sn and In, Sn-In samples on Cu substrates were made in three layers (i.e., Sn-In-Sn), followed by a diffusion heat treatment to homogenize the through-thickness composition, for comparison with a control trilayer Sn-Sn-Sn sample and a monolithic Sn coating of the same thickness (1 lm, 3 lm, or 6 lm). As seen in Fig.…”

“…In thicker films, a combination of columnar and equiaxed grains is observed. 75 Collaborators at Technic have conducted cyclic thermal shock tests (À 55°C to + 85°C, three cycles per hour) as per JEDEC standard JESD20A on coplated Sn-10%In samples. They found zero whisker growth after 1500 cycles, even though the acceptance standard for this test is whiskers of less than 40 lm length, further confirming the efficacy of In for eliminating whisker growth.…”

Electrodeposition of Sn–In Alloys Involving Deep Eutectic Solvents

“…Quite recently it has been shown that the addition of a certain amount of In can contribute to the elimination of whiskers growth in electrodeposited Sn on copper substrates under ambient temperature aging. Therefore, in terms of Sn whisker mitigation, In seems to represent a better additive than Pb [9,13,14]. In addition, due to their physico-mechanical and chemical properties, including low melting temperature, low stress, superior thermal fatigue resistance, Sn-In alloys are suitable for making connections by soldering in the assembly of integrated circuits and micromodules [15][16][17].…”