AbstractThe main aims of this project were to:- * Use ultrasound to enhance the plating rate of an electroless copper process at low temperatures
* Replace formaldehyde by using another reducing agent, which is more environmentally beneficial to the industry.
The effects of ultrasound on the electroless copper plating of epoxy substrates using different frequencies (40 and 850 kHz) has been investigated at different temperatures (25, 30, 35, 40, 45 and 50ºC) with different reducing agents (formaldehyde and glyoxylic acid) and in the presence and absence of air bubbling. The conventional plating rate in this process is (1.25µm /25 minutes) at 46ºC. Ultrasound was applied during the plating process and also with an added delay at the start of the plating process. Several parameters were monitored such as plating rate (via calculation of weight gain), stability of the plating bath (UV) the reflectance percentage (Gloss Meter), test of substrate surface by scanning electronic microscope (SEM) and X-ray Photoelectron Spectroscopy (XPS). The adhesion of the copper layer on the substrate surface also was examined. The results obtained clearly indicate that use of 40 kHz sonication leads to the highest plating rate at 35 and 40ºC when a time delay of 7 minutes is introduced before applying ultrasound. The deposition rate increased from 1.43µm/25 minutes to 1.65µm/25 minutes at 35oC and from 1.86µm/25 minutes to 2.54 µm/25 minutes at 40oC. Sonication was also found to be unhelpful at 25 and 30 ºC where the deposition rate was found to decrease at these temperatures at both frequencies (40 and 850 kHz) from 0.75 µm/25 minutes to 0.27µm/25 minutes at 25oC and from 1.18µm/25 minutes to 1.11µm/25 minutes at 30oC. Introduction of air bubbling reduced the plating rate but enhanced the copper bath stability at 40ºC. All results showed that the plating rate was much higher with formaldehyde than with glyoxylic acid. SEM results also show that application of ultrasound causes a fine grain structure which impacts on the colour of the substrate surface, as the gloss meter results show.
Unfortunately UV results indicate that with sonication it appears that the stability of the electroless plating bath is much reduced with copper precipitating out of the solution after sonication. This indicates that the use of this technology may prove problematical in ‘real life’ conditions.
|Date of Award||2013|
|Supervisor||Larysa Paniwnyk (Supervisor), Andrew Cobley (Supervisor) & John Graves (Supervisor)|
- copper plating