|The Toxics Use Reduction Institute (TURI) and the University of Massachusetts Lowell (UML) have been providing training, information, and research to help the New England Lead-Free Consortium find new lead-free technologies.
Consortium members contribute time, materials, facilities, funding, and expertise to jointly develop and implement testing of lead-free alternatives. Companies from outside Massachusetts have joined the Consortium as the European Restrictions on Hazardous Substances RoHS regulation deadline has drawn closer.
The Consortium has proven to be a successful working partnership between industry, academia, and government. With the assistance of the EPA, the Consortium broadened its geographic scope to the New England region for Phase III, the testing of production printed wiring board. The following companies and agencies are involved in the New England Lead-Free Consortium: University of Massachusetts Lowell; Massachusetts Toxics Use Reduction Institute (TURI); EPA Region 1-New England; Tyco Electronics (M-A/COM) in Lowell, MA; Benchmark Electronics in Hudson, NH; Dynamics Details, Inc. in Newburyport, MA; Teradyne, Inc. in North Reading, MA; Texas Instruments in Attleboro, MA; Raytheon Company in Tewksbury, MA; Schneider Electric in North Andover, MA; Skyworks Solutions, Inc. in Woburn, MA; Textron Systems in Wilmington, MA; American Power Conversion in West Kingston, RI; and Stentech in Salem, NH.
The Phase III testing of lead-free printed wire boards (PWB) closely resembling real world production boards was a monumental effort that involved examining the manufacturing issues of implementing lead-free electronics.
Each of the 40 double-sided boards had 20 layers with a 16 x 18 inch footprint that contained approximately 1,700 components. The 68,000 total components were supplied by 8 consortium members, Raytheon, Textron, Teradyne, Skyworks Solutions, Benchmark Electronics, American Power Conversion, Texas Instruments, and M/A-COM.
The Consortium selected the following materials and processes for the Phase III lead-free testing:
1. Solder paste: These are two suppliers of tin/lead and lead-free solder paste. The lead-free solder paste from both suppliers contains the SAC 305 (tin/silver/copper) alloy and no-clean flux.
2. Component finishes: A variety of lead-free component finishes are being used on the boards. They include: nickel/palladium/gold, palladium silver, gold, nickel/gold, tin/nickel, tin/silver/copper, tin/bismuth, tin/copper, and tin.
3. Board surface finishes: Three lead-free board surface finishes are being evaluated: Electroless nickel immersion gold (ENIG); Immersion silver; and Organic solderability preservative (OSP).
The printed wiring boards were designed by Benchmark Electronics and manufactured by Dynamic Details, Inc. Stentech manufactured the two stencils. The wiring board visual inspection was conducted at Benchmark Electronics; visual inspectors conducted 100 percent visual tests on all solder joints.
The boards then went through accelerated reliability testing to simulate the thermal and other environmental stresses that a printed wire board would need to endure throughout a typical product life. The reliability tests were divided evenly: half of the PWBs went to thermal cycling at Raytheon’s facilities in Andover, MA, and the other half went to highly accelerated life testing (HALT) at Teradyne’s facilities in North Reading, MA. To measure solder joint strength, pull tests were performed prior to and after the thermal cycling and HALT testing. The pull tests were conducted at the University of Massachusetts Lowell.
The results were mixed but encouraging. Lead-free electronics assembly and solder joint strength were comparable to lead, but the through-hole assembly did not perform as well.
The next steps for the Consortium include developing control strategies for potential lead-free electronics failure modes and conducting further testing for through-hole components. Results should be available by June 2006.
A major issue with transitioning to lead-free electronics is the copper dissolution that occurs during rework of components. In the August issue of Circuits Assembly magazine, an article by the New England Lead Free Consortium describes a project that TURI, Benchmark Electronics, and Mercury Computer Systems undertook to demonstrate that rework is possible on lead-free boards with minimal copper dissolution.