Ultrasonically enabled Low Temperature Electroless and Immersion Metallisation AmirahKassim The Functional Materials Applied Research Group Coventry University
Ultrasonically enabled Low Temperature Electroless and Immersion Metallisation 3 year project, started in October 2010 Funded by: IeMRC Objective: to reduce the plating temperatures used in electroless and immersion plating by the application of ultrasound
Ultrasonically enabled Low Temperature Electroless and Immersion Metallisation Electroless and Immersion plating processes used in Photovoltaic and Printed Circuit Board manufacture Process Electroless Copper Electroless Nickel Immersion Silver Immersion Gold Temperature ( o C) Comments 30 70 Contains formaldehyde 50 90 40 90 80 90 High temperatures required for good deposition rate
The effect of sound on the chemistry of a solution Human Hearing Ultrasound Diagnostic Ultrasound 10 3 10 4 10 5 10 6 10 7 20kHz 2MHz Extended range ultrasound for sonochemistry
COMPRESSION COMPRESSION COMPRESSION COMPRESSION RAREFACTION RAREFACTION RAREFACTION RAREFACTION RAREFACTION 5000 o C 2000 ats BUBBLE FORMS GROWS IN SUCCESSIVE CYCLES REACHES UNSTABLE SIZE VIOLENT COLLAPSE
Acoustic cavitation in a liquid: NEAR A SURFACE Boundary Layer Solid Surface Asymmetric collapse Rush of liquid from one side produces a powerful jet of liquid targeted at the surface.
Acoustic cavitation in a liquid: NEAR A SURFACE Video courtesy of University of Twente, Netherlands. and Shimadzu Europa GmbH, Duisburg, Germany
Acoustic cavitation in a liquid: NEAR A SURFACE Electrochemical Effects Thinning of diffusion layer Improved mass transport Improved solution movement Electrode cleaning Degassing
Effect of ultrasound on plating rate Workers Plated Metal Reducing Agent Plating rate Abyaneh et al Increase Nickel Hypophosphite complexing agent= low Mallory Nickel Hypophosphite lowthiourea concentration Masuoka and Nickel Hypophosphite Hayashi Yang et al Nickel Hypophosphite Decrease complxing agent = high highthiourea concentration Touyeras et al Copper Formaldehyde Zaho et al Copper Formaldehyde
Ultrasonic frequency = 530kHz Data reproduced by kind permission of; F. Touyeras et al Ultrasonics Sonochemistry 10 (2003) 363 368
Improved mass transport Thinning of diffusion layer Crystal structure formed under ultrasonic conditions in the initial stages of plating (Abyaneh et al) Localised heating in the diffusion layer (Toyeras et al) Activation of catalyst Degassing
Conditioner 5 minutes 30-60 o C Rinse 5 minutes Pre-dip 1 minute RT Catalyst 5 minutes 30-50 o C Rinse 5 minutes Accelerator 2 minutes RT Rinse 3 minutes Electroless Copper 25-60 minutes 30-70 o C
Pd Pd Pd Oxidation HCHO 2e - Pd Pd Pd Pd Pd Reduction Cu 2+
Copper deposit on the surface of the substrate.
Electroless Copper 3350-1 (Chestech Ltd) EDTA based Solution subjected to ultrasonic irradiation of different frequencies continuously for 4 hours. Ultrasonic Frequency Copper Conc. after 4 hours Copper Conc. after 48 hours Control (Mechanical Stirring) 20 khz (20 % Amplitude) 100% 100% Precipitated NA 40 khz 100% 100% 582 khz 100% 70% 863 khz 100% Precipitated
20 khz - Precipitates copper from solution after 4 hours Effects of cavitation destroy chemicals in electroless formulation e.g. EDTA, stabilizers 40 khz Stable after 4 hours and 48 hours Precipitated 100% Cu in solution Precipitate, 70% Cu in Solution High frequency (583/850 khz) unstable Radical formation oxidation of chemicals in electroless formulation
Experimental Procedure Electroless Copper 3350-1 (Chestech Ltd) 1 litre Catalyst 3344 (Chestech Ltd Pd/Sn colloid) Substrate Unclad epoxy laminate (IsolaDuraver 104) Temperature - 25, 30, 35, 40, 45 and 50 ºC Plating Time 25 minutes Agitation - Ultrasound (40 khz) or Magnetic Stirring Ultrasonic Bath Langford, Model 475TT 40 khz Power density 90.3 W/litre
Responses 1. Weight gain Dry epoxy panels in oven for 24 hours at 120 ºC Weigh Process through Electroless Copper Weigh Dry epoxy panels in oven for 24 hours at 120 ºC From weight gain calculate plating rate. 2. Morphology Scanning Electron Microscope
Plating rate µm/25min Main effect on plating rate is temperature particularly above 40 ºC Ultrasound had a slight negative effect at low temperature Slight improvement at 35 ºC and above
Ultrasonic Microjets Pd Pd Ultrasound scrubs surface and removes catalyst Pd Lowers plating rate Pd Pd Particularly problematic at low temperature longer initiation time Pd Pd At high temperature (50 ºC) ultrasound always produces good results short initiation time Pd
Plating rate µm/25min Plating rate rises as delay time increases to 7 minutes 10 minute delay causes plating rate to drop since almost half the plating time is without agitation
After 10 minutes ultrasound most of catalyst removed from surface
Plating rate µm/25min 7 minute delay best plating results with ultrasound at all temperatures Ultrasound with 7 minute delay at 40 ºC gives plating rates higher than silent plating at 45 ºC
Silent 40 ºC Ultrasound
Conditions: Frequency= 40kHz 7 minute delay Ultrasound reduces plating temperature Reduces energy needed
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