Wolfgang Hansal

Pulse plating of nickel: influence of electrochemical parameters and composition of electrolyte

Abstract In this paper, the influence of the electrochemical parameters and the composition of the electrolyte on the properties of the deposits in pulse plating of nickel will be discussed. The characteristics and the electrochemical behaviour of a nickel sulphamate bath with and without organic additives were derived from fundamental electrochemical experiments. Plating experiments using pulsed current for the deposition revealed the resulting layer properties. The addition of organic bath additives strongly influences the properties of the deposited nickel layers. While the hardness of the layers can be considerably improved by organic additives in the plating electrolyte, these additives can interfere with the freshly deposited nickel surface during the off-time of the pulse sequence.

Influence of pulse plating parameters on morphology and hardness of pure tin deposit

Abstract In the present work, the electrochemical deposition of tin coatings using pulse plating techniques was investigated. Based on fundamental electrochemical experiments, pure tin coatings were deposited by using direct and pulsed current. Both types of deposits were compared with each other and the effects of the pulse plating parameters, i.e. duty cycle, frequency and current density were investigated. Matt layers with wide powdery areas are obtained with direct current. At low current density and low duty cycle (10%), the pulsed current improves this aspect of the deposit by reducing the formation of powdery deposits. At higher duty cycles, the increase in the frequency additionally improves the hardness of the coating.

Effects of pulsed current on plasma electrolytic oxidation

Abstract In this paper, the effects of different current pulse parameters on the resulting PEO layers are described. The properties of the layers were assessed optically, with a scanning electron microscope, and the corrosion resistance has been measured. It is shown that the polarity and the frequency of the applied current has a high influence on the properties of the resulting layers. Unipolar pulses with low frequencies produce rougher layers with reduced corrosion protection. Different additives were added to the electrolyte in order to improve corrosion resistance of the resulting layers. Some of the additives, especially if based on tungstate and molybdate resulted in a colouring effect of the layer. This colouring effect is most pronounced when low frequencies and unipolar pulses are used. Higher frequencies and bipolar pulses create smoother and denser layers with higher corrosion resistance. The highest corrosion resistance was obtained by combining addition of tungstate and high frequency bipolar pulses.

Control of silver throwing power by pulse reverse electroplating

The influence of electroplating parameters on throwing power (TP) is studied in additive-free silver cyanide solutions under direct current and pulse reverse electroplating conditions. It is found that the best TP is obtained when no agitation of the electrolyte is applied. The most important parameters for controlling the TP are the cathodic current density, the anodic to cathodic charge ratio, and the ratio between the anodic and cathodic current densities. Guidelines for process optimisation are given.

Silver Metallization on Porosified LTCC Deposited by Pulse Plating Technique

Present microelectronic devices especially when including high frequency applications are in need of highly integrated metallization technologies. Silver is considered as a future interconnection material for such devices and systems due to its low bulk resistivity of about 1.6 μΩ·cm at 20°C. Conventional thick film metallization techniques on low temperature co-fired ceramics such as screen printing are only partly capable of meeting the requirements in terms of lateral resolution and precision. Furthermore, on advanced surfaces such as porosified composite LTCC, also thin film metallization techniques (e.g. sputtering) meet their limits due to a poor coverage and hence, a low electrical conductivity. In this study, it is shown, that bipolar pulse plating of silver is capable of bridging the pores of the surface of the porosified substrate without penetrating them. The plated metallizations feature very fine grains with an average diameter of approx. 90 nm and a maximum up to 250 nm. The film resistivity...

Nanoparticle incorporation in plasma-electrolytic oxidation

One remaining problem of thicker PEO based topcoats on light metal substrates is the enhanced porosity with increasing layer thickness. While modern deposition techniques such as pulsed anodisation counteract this phenomenon, a simple current signal based approach cannot completely eliminate this problem. In the process described in this paper the pulse anodised PEO layers are modified by the incorporation of functional nanoparticles and the effects of such embedded nanoparticles on the resulting microstructure of the layer are studied. The examination of the layer properties was performed using scanning electron microscopy, electrochemical techniques and X-ray diffraction methods. The dependency of corrosion resistance on the presence of nanoparticles in the layer as well as the alloy composition of the substrate and the applied current signal is shown.