Analysing electroless nickel plating baths

Automated on-line analysis system performs all liquid handling steps such as taking sample aliquots, dosing of reagents, titration and cleaning.

Electroless nickel layers are normally nickel-phosphorus alloys.

For the reductive chemical deposition of nickel with phosphorus inclusions, sodium-hypophosphite is used as the reducing agent (reductant).

To apply even nickel layers to the workpieces, the content of nickel, reductant and the alkalinity have to be determined periodically.

For the determination of the ingredients an automated ProcessLab system can be used.

All liquid handling steps such as taking sample aliquots, dosing of reagents, titration and cleaning are performed by pumps and burets controlled by processLab.

A sample aliquot is transferred either to the vessel for alkalinity and nickel analysis or to the vessel for reductant content determination.

General features of the ProcessLab system include the following.

* Alkalinity, nickel and hypophosphite determination in one system.

* Barcode reader offers automatic method selection by using predefined barcodes.

* Optional liquid level sensors monitor the reagent level and call for manual intervention when required.

* Additional terminals for the I/O controller allow to transmit or receive external signals, for examples a result that is sent to a remote PCS (Process Control System).

An incoming signal can be a density value from a density meter.

This system is very flexible and can be adapted very easily to any specific needs, said Metrohm UK.

If necessary an additional reagent cabinet is available and ProcessLab can be placed on top of it.

There is sufficient space for all reagents, which makes ProcessLab even more practical.

Calibration and storage of the electrodes are as follows.

* The electrodes need no calibration as only inflection point titrations are carried out.

* The electrodes should be stored in demineralised water, for longer times store the pH electrode and Pt Titrode in KCL 3 mol/L and the Cu ISE in a clean and dry place.

Performing the analysis - the sample is filled into a barcode-labelled beaker and put onto the sample processor.

After starting the tiamo method the barcode is scanned and the appropriate analysis tracks are selected (tiamo identifies the predefined barcode string).

With this method no sample table and no manual sample information is used and urgent samples can be inserted at any time.

* Alkalinity determination - titration with HCI - the sample aliquot is filled up with demin.

Water and titrated to the first inflection point with hydrochloric acid standard solution against a combined pH-glass electrode.

As soon as the first inflection point is reached, tiamo calculates the results and, depending on the barcode, either triggers cleaning of the vessel or continues with the nickel determination.

* Nickel determination - titration with EDTA - the addition of a defined amount of buffer pH=10 and titration with EDTA standard solution to one inflection point against a combined Cu-sensitive electrode.

When the titration is finished the vessel is cleaned; the tiamo calculates the result and creates the database entry.

* Hypophosphite determination - -titration with iodine and thiosulfate - a defined amount of iodine solution is added to the sample aliquot and acidified with sulphuric acid.

After the wait time the iodine that has not reacted with the hypophosphite is titrated to one inflection point with thiosulfate standard solution against a Pt Titrode.

When the titration is finished the vessel is cleaned; tiamo calculates the result and creates the database entry.

Literature is as follows.

* Gros, Prof Dr Leo, Bruttel, P, von Kloeden, M (2005) Practical titration, Metrohm Monograph 8.029.5003.

* Haider, Dr C, Electrodes in Potentiometry, Metrohm Monograph 8.015.5003.

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