Abstract
We have produced pure Sn coatings from an alkaline bath plating. The plating bath was composed of sodium stannate and sodium hydroxide with sorbitol as an additive. The experiments were performed with a potentiostat/galvanostat at various current densities from 5–25 mA/cm2. The morphology of the coatings, thickness, plating rate, and microhardness were evaluated. Furthermore the wetting of the Sn coatings on a Cu substrate was also assessed by area spread ratio measurements after reflow at 250 °C. The resultant coatings were very smooth and shiny. Initially, the plating morphology was uneven and a nodular type, which further improved with increasing current density up to 15 mA/cm2. The plating rate and thickness were the maximum at a current density of 15 mA/cm2. The coatings had higher strength and solderability at 15 mA/cm2 due to the improved microstructure and plating rate.
Highlights
Microelectronic circuits are very sensitive to the formation of unwanted metallic outgrowths over time
While most studies have focused only on microstructure and whisker growth, in this study, we evaluated the wetting of the deposits as a function of current density
The that belonged to Cu6 Sn5 intermetallic compounds (IMCs), which may come from the adherent various peaks in the XRD spectrum were matched with the JCPDS file 04-0673 and 45-1488 substrate [13,14,15,16]
Summary
Microelectronic circuits are very sensitive to the formation of unwanted metallic outgrowths over time. These metallic outgrowths are termed as whiskers, which originate due to high residual stresses inside the coatings. These whiskers can cause short-circuiting of electronic circuits if not controlled properly [1,2]. The prime factor is the build-up of stresses in the deposits due to the non-uniform chemistry of the deposits, external environment and corrosive factors [3] The coating techniques such as vapor deposition, evaporation, sol–gel, or laser deposition require expensive tooling and great control during the experiment. Acidic baths are more popular due to their important role in high-quality surface finish, but require sophisticated disposal systems [7,8,9,10,11]
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