CircuiTree - August 2008 - (Page 21)

[ Tech Talk ] The beneﬁcial effect of reduced additive consumption has been observed for many years when anodes were bagged to prevent anode ﬁlm particles from contaminating the bath. Menard and Wurm considered different shielding materials and constructions. They dismissed diaphragms and membranes because they can deteriorate with time and have a tendency to plug. First, a plastic grid was used as a shield. The grid had only very small contact points with the anode to preserve a large active anode surface area. The additives trapped between the grid and the anode degraded fast but additive replenishment due to agitation was much reduced so that additive consumption at the anode was also much reduced. When the plastic mesh was replaced by a non-active titanium mesh of similar conﬁguration, a threefold further reduction in additive consumption was observed. This effect was explained by the fact that the metal shield, being in contact with the active anode, acquires the potential of the anode and thus repels the positively The beneﬁcial effect of reduced additive consumption has been observed for many years when anodes were bagged to prevent anode ﬁlm particles from contaminating the bath. charged additives before they can get near the anode. Another beneﬁcial effect was observed. The shielding of the anodes resulted in a more uniform plating thickness across the panel. The rising oxygen bubbles act as a shield at the upper portion of the anode that reduces the current density in this region and leads to lower plated copper thickness in the upper portion of a panel. It was observed that in the presence of an anode shield, larger bubbles form. Thus, the total bubble cross section area is much smaller with large bubbles for a given volume of gas and therefore the shielding effect near the top that reduces the current density is much reduced, leading to improved copper thickness uniformity. ■ References 1. Dow, W.-P., and Chen, H.-H., “A Novel Copper Electroplating Formula for Laser-Drilled Microvia and Through-Hole Filling,” Circuit World, 30/3, 2004. 2. Dow, W.-P., Yen, M.-Y., and Chen, H.-H., “ThroughHole Filling By Copper Electroplating for SiP,” CircuiTree, February 2007. 3. Dyar, et al., “A Low-Cost Semiconductor Metallization/Planarization Process,” Plating & Surface Finishing, March 2004. 4. Yeh, C.-C., Lan, K.-H., and Dow, W.-P., “Microvia Filling Plating Technology for IC Substrate Application,” Circuit World, 30/3, 2004. 5. Menard, S., and Wurm, J., “Reduced Additive Consumption in Base Metal Plating Baths,” Circuit World, 30/3, 2004. Karl H. Dietz is CircuiTree’s technical editor. Email karl.h.dietz@USA.dupont.com 797 VA Computrace CVS with unsurpassed precision • Improved bath monitoring • Reduced operating costs • Modular setup 797 VA Computrace for Cyclic Voltammetric Stripping (CVS) For the determination of organic additives such as • Brighteners • Levelers • Suppressors www.metrohm.com U.S.A. 800-645-3050 CANADA 800-263-8715 www.brinkmann.com info@brinkmann.com Titration • Ion Chromatography • VA Trace Analysis • ProcessLab • Automation circuitree.com • August 2008 CT06084Met-797.indd 1 21 4/21/08 11:52:47 AM http://www.metrohm.com http://www.brinkmann.com http://circuitree.com

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CirciuTree - August 2008 Contents My Line Industry Review Tech Talk Flexible Thinking Creating Connections Between Electronics Design and Manufacturing Happy Thoughts View From the Middle Market Outlook Fein Lines IPCA Showcase Technical Product Spotlights Classified Ads Upcoming Events Ad Index Buyers Guide

CircuiTree - August 2008

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