A CASE STUDY FOR TRANSITIONING CLASS A SERVER MOTHERBOARDS TO LEAD-FREE
Authors: R. Schueller, Ph.D., W. Ables, and J. Fitch, Ph.D. Company: DfR Solutions and Dell Inc. Date Published: 1/31/2009
Abstract: The EU RoHS legislation currently has an exemption to allow the continued use of lead based solder in Class A servers until at least 2010. There are industry proposals in place to extend this exemption to 2012 or beyond due to the added challenge of producing highly reliable lead-free server assemblies. Dell has surpassed the requirements of this legislation by transitioning all recently released Class A server printed circuit board assemblies to lead-free. This case study paper will outline the process followed, the testing performed, the material changes made, and the challenges that were met and overcome in this dedicated year-long effort by a large team of people. A great deal of reliability testing was performed to ensure there was no compromise to the expected life of the product. The most significant challenge was in selecting a PCB surface finish. Immersion silver has been ruled out due to its susceptibility to creep corrosion. OSP finish did not provide sufficient wetting capability after two surface mount passes. In the end, lead-free Hot Air Solder Level (HASL) finish was selected due to its superior solderability and testability. However, laminate material, alloy type, and process conditions had to be carefully selected to ensure compatibility with this surface finish. Since September, 2007, all Dell’s newly released server motherboards were built lead-free and all quality targets have been successfully met.