Article

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

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Abstract

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.

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... Ultrasound agitation propagates through acoustic cavitation producing a mechanical effect on the surface by acoustic streaming, micro-jetting. Shock-wave formation provides better mixing and dispersion of reactants [173,174]. The benefits of ultrasound agitation reported by several researchers are mass transport enhancement [175,176], thinning of the diffusion layer [176], localized heating, [175] and de-gassing [176][177][178]. ...
... Ultrasonic agitation enables low temperature deposition without affecting film morphology and properties [174,179]. With low temperature operation, growth rate enhancement is due to the "scrubbing" of acoustic cavitation as shown in Fig. 8. Based upon detail experimentation, the employment of a 7-min delay time prior to introduction of ultrasound is more effective than continuous process to achieve high growth rates at low operating temperatures (40°C) [174]. ...
... Ultrasonic agitation enables low temperature deposition without affecting film morphology and properties [174,179]. With low temperature operation, growth rate enhancement is due to the "scrubbing" of acoustic cavitation as shown in Fig. 8. Based upon detail experimentation, the employment of a 7-min delay time prior to introduction of ultrasound is more effective than continuous process to achieve high growth rates at low operating temperatures (40°C) [174]. Moreover, by employing ultrasound, effective deposition is possible even when catalytic concentration is relatively low for the surface activation process [179]. ...
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  • J González-García
  • M D Esclapez
  • P Bonete
  • Y V Hernández
  • L G Garretón
  • V Sáez
J. González-García, M.D. Esclapez, P. Bonete, Y.V. Hernández, L.G. Garretón, V. Sáez, Current topics on sonoelectrochemistry, Ultrasonics 50 (2010) 318-322.