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无电解镍镀液中的碘酸盐

AN-V-195

2021-09

zh

Polarographic determination of iodate stabilizers

化学镀镍是表面处理行业中一项重要而成熟的工艺。过去，人们广泛使用添加少量铅来稳定镀液。随着近年来对消费品（尤其是电子产品）中使用铅的限制越来越多，人们开发并引入了替代稳定剂。作为铅替代品的稳定剂之一是碘酸盐。它可以作为单一添加剂使用，也可以与铋或锑结合使用。这种方法可以通过极谱法直接测定镀液样品中的碘酸根含量。该方法简单快捷、灵敏可靠。

In the past, lead was commonly used as a stabilizer in electroless nickel plating processes. The regular and precise determination of the stabilizer concentration is essential to keep the plating process under stable conditions and to run the process successfully. As restrictions on the use of lead in consumer products (particularly electronics) have grown in recent years, alternative stabilizers were developed and introduced. One of the stabilizers used as a lead replacement is iodate (IO3- ). 

Electroless nickel plating is used in various industrial production processes (e.g., production of hard disks, and for protection against corrosion or wear). The ENIG (electroless nickel, immersion gold) and ENEPIG (electroless nickel, electroless palladium, immersion gold) processes in the production of printed circuit boards (PCB) are very reliant on the success of this method as electroless nickel plating is the first step in the process. 

Polarography can be used to determine the iodate content after dilution in supporting electrolyte and has been established as a straightforward, sensitive, selective, and interference-free method for this application. 

Electroless nickel plating bath

Figure 1. 884 Professional VA.

After diluting the sample in electrolyte, the polarographic determination of iodate is carried out on the 884 Professional VA with the Multi-Mode Electrode pro as working electrode using the parameters listed in Table 1. The concentration of iodate is determined by two additions of standard addition solution.

Table 1. Parameters for the iodate determination
Parameter Setting
Working electrode DME
Mode DP – Differential Pulse 
Start potential -0.1 V
End potential -0.7 V 
Peak potential iodate -0.34 V
  • Working electrode: Multi-Mode Electrode pro with standard glass capillaries
  • Reference electrode: Ag/AgCl/KCl (3 mol/L) reference electrode with electrolyte vessel. Bridge electrolyte: KCl (3 mol/L) 
  • Auxiliary electrode: Platinum rod electrode
Figure 2. Determination of iodate in an electroless nickel bath with two standard additions.

The determination of iodate in electroless nickel plating baths can be carried out in a simple and straightforward manner. The method is selective and free of interferences. It is suitable for concentrations in the low mg/L range. 

Table 2. Result
Sample  Concentration IO3-  [mg/L] 
Electroless nickel bath  2.5
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Internal reference: AW CH4-0475-092007

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