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The Needs for, and Problems Experienced While Developing a Successful Low Palladium Activation System for Electroless Copper Deposition



The Needs for, and Problems Experienced While Developing a Successful Low Palladium Activation System for Electroless Copper Deposition
This paper summarizes experiences gained while developing a new cost effective Palladium containing ionic activation system.
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Authored By:


Chrsitian Wendeln, Lutz Stamp, Gerson Krilles, Matthias Dammasch, Roger Massey.
Atotech GmbH, Berlin

Summary


The electroless deposition of Copper is widely used within the printed circuit board industry as it offers a simple and reliable method for metallizing holes, which subsequently enable multilayer PCBs. While the process as a whole continues to develop since its adoption, one point that has remained common is the need to activate those materials on which the Copper does not naturally deposit, namely the glass fiber bundles and epoxy matrix. Such activation processes are typically based on Palladium as this has been long proven to be a reliable method, however its use does not come without some penalties. The activation step is acknowledged to be one, and in some cases, the most expensive step within the electroless Copper process as a whole, and this is due to the cost of the Palladium metal itself. Historically this has always been a concern, but with the current cost of Palladium exceeding that of Gold, the desire for a “low cost” activator has increased dramatically in recent years.

Over the years, many suppliers have developed alternative processes utilizing conductive polymers or variations of carbon, and while these have been accepted within the market and have generally been found to operate at a lower cost, with decades of reliability data, and countless installations worldwide, the metallization of through holes with electroless Copper remains the preferred method for many applications. Hence the need for a “low cost” but high performance, Palladium based activator step remains as strong as ever.

This paper summarizes experiences gained while developing a new cost effective Palladium containing ionic activation system, we review the successes and issues found with early generations and then show that building on these experiences, a successful, low Palladium activation system can be provided that satisfies both the technical and commercial demands of today’s PCB market.

Conclusions


With the current high price of Palladium not showing any signs of decreasing in the near future, in order to minimize ongoing process operational costs, there is increasing pressure to reduce the Palladium content used in electroless Copper activation processes. While a number of low, or reduced Palladium activators have been introduced previously, they have generally seen limited market acceptance due to poor or inconsistent performance.

A new low Palladium activation process has been developed, which overcomes the issues reported with earlier generations, and is shown to offer comparable performance to the current high Palladium containing equivalents. The testing reviewed within the paper, shows that the Palladium adsorbed onto a range of dielectric materials can be maintained at a stable level across the operational life of the process bath, and is, not only equivalent to that arising from traditional activation series, but is sufficient to enable a reliable and robust electroless Copper deposition.

Initially Published in the SMTA Proceedings

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