SMTA International Conference Proceedings

Electroless Palladium as a PCB Surface Finish - The Re-Introduction

Author: Jim Trainor
Company: OMG Electronic Chemicals
Date Published: 10/24/2010   Conference: SMTA International

Abstract: Electroless palladium (E-Pd) used as a surface finish applied to PCBs had a brief but successful run during the late 1990’s, primarily used in the automotive industry for radios, engine control modules and transmission modules. Its success was based on multi-functionality compared to other Cu basis surface finishes and for its cost effectiveness compared to ENIG. Soldering to Palladium had never been considered a simple drop in replacement to HASL but once a profile had been developed, good wetting with reliable and consistent solder joints were formed. Millions of assemblies were run using E-Pd as a surface finish, with one large PCB supplier producing 20,000 + panels per week for one customer alone. The demise of the use of E-Pd was based more on economic reasons rather than anything technical, the breakup of the former Soviet Union and the lack of stability in that region impacted the delivery of Palladium. The price rose from a baseline of $148/oz to a level far in excess of gold at the time – Pd hit a high of around $1200/oz compared to $350/oz for gold! The uncertainty of supply and the increased cost resulted in its demise as a surface finish. For the users of Pd who embraced its great potential this was an unwelcomed outcome.

Fast forward to today and in 2010 there are two key items in favor of the return of Palladium as a surface finish:

Speculation by the general public in gold and other precious metals that is driving cost ever skyward. The advent of Pb-free soldering has removed the need to develop special profiles to solder to Palladium – it is truly a drop in replacement for more expensive ENIG or less robust Immersion Silver, Immersion Tin or OSP.

Palladium has as a surface finish the potential to offer:

1) all the benefits of gold without the cost

2) the need for nickel as a barrier layer and its associated potential problems

3) assembling lead free removes the need to create special profile when soldering to Palladium applied directly to bare copper.

The reliability of the solder joint is based on the formation of CuSn Intermetallic Compounds. As will be seen from the data presented here, Palladium is a multifunctional deposit that is easy to apply in the PCB Fab house, benign with regards to negative impact on the PCB materials, may be the answer to creep corrosion that is seen in emerging markets and lastly is cost effectiveness. This is a first in a series of papers on the subject of Pd from OMG and is presented to provide a large quantity of information, in some cases only summary data is provided due to space limitations. Detailed test results are available upon request and/or will be presented in future papers.

Key Words: 

Surface Finish, Electroless Palladium, Solder Joint Reliability, Switch Contact

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