Editing Copper electroplating (section)

=== Alkaline cyanide ===

Alkaline cyanide baths have historically been one of the most commonly-used plating chemistries for copper electrodeposition.<ref name="Flott" /><ref name="Bandes Review">{{cite journal |last1=Bandes |first1=Herbert |title=The Electrodeposition of Copper |journal=Transactions of the Electrochemical Society |date=1945 |volume=88 |issue=1 |pages=263–278 |doi=10.1149/1.3071688 |url=https://iopscience.iop.org/article/10.1149/1.3071688/meta |access-date=April 9, 2022|doi-access=free }}</ref> Cyanide copper baths typically provide high covering and [[throwing power]], allowing uniform and complete coverage of the substrate, but often plate at lower [[current efficiency]].<ref name="PFCu" /> They produce a metal finish favored for its [[Diffusion barrier|diffusion blocking]] character. Diffusion blocking is used to improve the long term adherence of different metals, e.g. chromium and steel. It is also used to prevent the second material from diffusing into the substrate.

Cyanide baths contain [[cuprous cyanide]] as the source of copper(I) ions, [[sodium cyanide|sodium]] or [[potassium cyanide]] as a source of free cyanide that complexes with cuprous cyanide to render it soluble, and [[sodium hydroxide|sodium]] or [[potassium hydroxide]] for increased conductivity and pH control.<ref name="JackHorner">{{cite journal |last1=Horner |first1=Jack |title=Cyanide Copper Plating |journal=Plating & Surface Finishing |url=https://www.nmfrc.org/pdf/p1199l.pdf |access-date=July 24, 2022}}</ref> Baths may also contain [[Rochelle salt]]s and [[sodium carbonate|sodium]] or [[potassium carbonate]], as well as a variety of proprietary additives.<ref name="PFCu" /> Cyanide copper baths can be used as low-efficiency strike-only baths, medium-efficiency strike-plate baths, and high efficiency plating baths.<ref name="Barauskas" />

==== Bath composition ====
{| class="wikitable"
|-
! rowspan="2" | Chemical Name
! rowspan="2" | Formula
! colspan="2" | Strike<ref name="Barauskas" />
! colspan="2" | Strike-plate<ref name="Barauskas" />
! colspan="2" | High-efficiency plate<ref name="Barauskas" />
|-
| Sodium || Potassium || Sodium || Potassium || Sodium || Potassium
|-
| [[Copper(I) cyanide]]||  CuCN  || 30 g/L || 30 g/L || 42 g/L || 42 g/L || 75 g/L || 60 g/L
|-
| Sodium or [[potassium cyanide]]||  NaCN or KCN  ||  48 g/L || 58.5 g/L || 51.9 g/L || 66.6 g/L || 97.5 g/L || 102 g/L
|-
| Sodium or [[potassium hydroxide]]||  NaOH or KOH  ||  3.75–7.5 g/L || 3.75–7.5 g/L || colspan="2"| Control to pH 10.2–10.5 || 15 g/L || 15 g/L
|-
| [[Rochelle salt]]s ||  KNaC<sub>4</sub>H<sub>4</sub>O<sub>6</sub>·4H<sub>2</sub>O  || 30 g/L || 30 g/L || 60 g/L || 60 g/L || 45 g/L || 45 g/L
|-
| [[Sodium carbonate|Sodium]] or [[potassium carbonate]]||  Na<sub>2</sub>CO<sub>3</sub> or K<sub>2</sub>CO<sub>3</sub>  ||  15 g/L || 15 g/L || 30 g/L || 30 g/L || 15 g/L || 15 g/L
|}

==== Operating conditions ====
* Temperature: 24-66&nbsp;°C (strike); 40-55&nbsp;°C (strike-plate); 60-71&nbsp;°C (high-efficiency)<ref name="Barauskas" />
* Cathode current density: 0.5-4.0 A/dm<sup>2</sup> (strike); 1.0-1.5 A/dm<sup>2</sup> (strike-plate); 8.6 A/dm<sup>2</sup> (high-efficiency)<ref name="Barauskas" />
* Current efficiency: 30-60% (strike); 30-50% (strike-plate); 90-99% (high-efficiency);<ref name="Barauskas" />
* pH: >11.0<ref name="PFCu" />

==== Toxicity ====

Commercial platers typically use a copper cyanide solution, which retains a high concentration of copper. However, the presence of free cyanide in the baths makes them dangerous due to the [[Cyanide poisoning|highly toxic nature of cyanide]]. This creates both health hazards as well as issues with waste disposal.<ref name="Barauskas" />