Bare printed wiring board materials require changes from today’s typical standard dicy cured FR4 materials in order to support lead-free assembly. The High Density Packaging User’s Group has completed a study of via reliability through air to air thermal cycling after various SnPb and lead-free reflow profiles. Six different materials, with different numbers of reflow profiles were studied in this test through 6000 accelerated thermal cycles. Data from this testing will be presented that clearly shows that all materials claimed to be lead-free compatible are not created equal. A review of relevant material properties vs. the results will also be attempted.

Introduction and Background

Previous testing and publications have detailed some of the impacts of Pb-free soldering on bare printed circuit board materials and plated through hole reliability [1,2,3,6]. The High Density Packaging User’s Group (HDPUG) consortium has run a series of projects to better determine the effects of Pb-free soldering on the plated through hole integrity and long term reliability. This second phase of testing looks at long term reliability based on accelerated testing using air to air thermal cycling after typical SnPb and SnAgCu reflow profiles. (Additional testing using liquid to liquid testing was also completed, but will not be addressed here.)

This work was done by a number of different companies. The test boards were designed by Alcatel with inputs from Sanmina-SCI. The test plan documentation was completed by Alcatel, with various team member inputs. Bare board fabrication was done by Sanmina-SCI at their San Jose facility. Test board preconditioning reflow and wiring was completed by Flextronics. Air to air thermal cycling and monitoring was done by the Sanmina-SCI Reliability Engineering Lab. Finally, failure analysis was completed by the Sanmina-SCI PART Lab. Materials used in the board fabrication were provided by Isola, Nelco, and Polyclad. 

This work was started in mid-2003. At that time, there were a limited number of bare board materials specifically designated as Pb-free compatible and a number of these were new and unavailable for testing. Since this time, additional materials have been introduced specifically designed for improved performance in Pb-free soldering. All of the materials studied here remain production available materials today.

 This report was presented at APEX 2006.

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