Part number changes ahead for lead-free BGAs

Many suppliers are moving away from SAC 305/405 ball metallurgies in order to improve the ability to survive mechanical shock (e.g. drop test of portable products), said iNEMI. These changes include reductions in silver down to as low as 0.3% as well as the addition of other metals such as nickel.

These changes in metallurgies have raised several concerns in the industry, resulting in a call for separate part numbers primarily because the additional ball metallurgies will have difference characteristics in assembly and mechanical performance. While variations in alloy metallurgy may improve mechanical shock performance, they can also impact the manufacturing process in a number of ways, said iNEMI. The industry consortium believes since these changes can impact the form, fit and function of the device, they should be documented by a part change notice (PCN) and should be associated with a change in manufacturing part number (MPN).

In this way, the manufacturing assembly process can be properly controlled and optimized prior to actual assembly to ensure repeatable and reliable attachment of the BGA to the next higher assembly and to help minimize ship holds due to unknown parts, explained iNEMI. "While JEDEC identifies BGA solder ball material composition as an example of a major change (see JESD46C), we recognize that some further guidelines may need to be developed around triggering the PCN and/or change to MPN."

"It is inevitable that solder ball metallurgies will change as industry learns more about the performance of Pb-free technologies," said Jim McElroy, CEO of iNEMI, in a statement. "However, use of these different compositions will most likely require changes in reflow profiles and corresponding adjustments to the assembly process. The lower-silver compositions have a higher melting point than SAC 305/405 alloys, which moves the melting range higher. Based on assembly process margins (especially for large complex boards), low-silver compositions could also impact the MSL rating. In order to maintain reliable assembly processes manufacturers must know the metallurgical characteristics of the components they are using and be able to differentiate parts."

EMS companies are also calling for component suppliers to provide timelines of proposed changes to device construction including sphere metallurgy ahead of the MPN and PCN release.

In 2004, iNEMI called for the use of unique part numbers for RoHS compliant components, as defined by JEDEC/IPC standards. The consortium is also calling for continued availability of SnPb BGAs for use in high-reliability products, which are currently exempt from, or out of scope of, the EU RoHS Directive. Manufacturers of these high-reliability products will continue to use SnPb processes until long-life reliability concerns regarding Pb-free are resolved, and Pb-free BGAs are not compatible with these processes, said iNEMI.

For additional information about transitioning to alternate metallurgies, see the EMS Forum's recently published Guidelines for Suppliers Transitioning to RoHS Compliant Ball Grid Array (BGA) Packages with Low-Ag SAC Alloys.