Low-frequency ‘delay time’ ultrasound and its effect on electroless Cu metallisation of a Pd activated dielectric material

• Continuous ultrasound only increases plating rate at high electrolyte temperatures.
• Continuous ultrasound removes Pd from catalysed substrate.
• ‘Delay time’ ultrasound increases plating rate at lower electrolyte temperatures.
• ‘Delay time’ ultrasound reduces porosity of electroless Cu deposit.
• ‘Delay time ultrasound has no effect of crystal structure of electroless Cu deposit.

The effect that the presence of low-frequency ultrasound has on the deposition rate of an electroless Cu plating process for the metallisation of a Pd activated dielectric material has been preliminarily studied. Continuous ultrasound during electroless Cu plating had little effect on the deposition rate compared with the standard process under mechanical agitation due to the detrimental effect of cavitation on removing Pd from the dielectric materials. However, the introduction of a ‘delay time’ prior to the introduction of ultrasound resulted in an increase of the deposition rate of up to 26% (7-min delay time) and suggested that low frequency ultrasound could enable a reduction in electroless copper operating temperatures without a significant decrease in plating rate. Cu coatings produced in such conditions exhibited a significantly enhanced surface coverage with reduced porosity without any undesired effect on the crystal structure.