Most high-reliability products have a Pb-solder exemption or are out of scope under the RoHS Directive, and the companies that manufacture these products are evaluating the impact of Pb-free SAC solder assembly on the reliability of these more demanding applications. The complex assemblies found in high-reliability products often feature broad component mixes and pose many thermal challenges as a result of board thermal properties and the resulting thermal gradients across the assembly.
Pb-free assembly is already challenging for manufacturers due to the high temperatures required and the resulting tighter processing windows. When assembling complex assemblies, these challenges are exacerbated by the variability of component mass, large size and high layer count of PWBs, the need to rework, and the high likelihood of mixed through-hole, surface mount, and back side assembly.
"New soldering materials, maximum qualified component temperatures and primary attach and/or rework equipment all need to be addressed relative to reliability in the face of Pb-free assembly requirements," said Joe Smetana, principal engineer, Advanced Technology, for Alcatel and co-chair of the task force. "These recommendations were developed to communicate the needs of the high-reliability segment to the supply chain and the relevant standards groups that must address these needs."
Key recommendations include the following.
In the meantime, a few steps can be taken to improve processing.
Use the following techniques to improve rework processes:
The International Electronics Manufacturing Initiative's mission is to assure leadership of the global electronics manufacturing supply chain. Based in Herndon, VA, the industry-led consortium is made up of approximately 70 manufacturers, suppliers, industry associations and consortia, government agencies, and universities. iNEMI roadmaps the needs of the electronics industry, identifies gaps in the technology infrastructure, establishes implementation projects to eliminate these gaps (both business and technical), and stimulates standards activities to speed the introduction of new technologies. The consortium also works with government, universities and other funding agencies to set priorities for future industry needs and R&D initiatives.
For additional information about iNEMI, visit http://www.inemi.org . The recommendations are available on the iNEMI website at http://www.inemi.org/cms/projects/ese/High_Rel_RoHS.html .
Agilent Technologies Inc.
Cisco Systems Inc.
Delphi Electronics & Safety
Jabil Circuit Inc.
Sun Microsystems Inc.