iNEMI members call for unique part numbers to differentiate ball metallurgies on Pb-Free BGA components

The International Electronics Manufacturing Initiative (iNEMI), an industry-led consortium, announced that a majority of its OEM and EMS members strongly support unique part numbers for BGA components to differentiate any Pb-free ball metallurgies other than SAC 305 or SAC 405, including low silver, added dopants such as nickel, and other SAC (or non-SAC) alloy compositions.

iNEMI members supporting this position include:  3M, Agilent Technologies Inc., Alcatel-Lucent, Analogic, Celestica Inc., Delphi Electronics & Safety, Hewlett-Packard Company, Huawei Technologies Co. Ltd., Intel Corporation, Jabil Circuit Inc., Microsoft Corp., Micro Systems Engineering Inc., Plexus Corp., Sanmina-SCI Corporation, Solectron Corporation and Tyco Electronics Corporation. 

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). Changes include reductions in silver down to as low as 0.3% and addition of other metals, such as nickel. Concerns about these changes in metallurgies prompted iNEMI to release the following statement:

While variations in alloy metallurgy may improve mechanical shock performance, they can also impact the manufacturing process in a number of ways. Since these changes can affect form, fit and function of the device, they should be documented by the issuance of 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.  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.  "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."

Peter Tomaiuolo, corporate technology director for Celestica, agrees.  "Knowing what metallurgy is used by a particular manufacturer is not enough. It is equally or more important to be able to identify and track this difference on our manufacturing floors. We also would like component suppliers to proactively declare the timelines of proposed changes to device construction, including sphere metallurgy, ahead of the MPN and PCN release."

Supporting this position Courtney Ryan, Jabil's senior vice president of supply chain stated, "We are convinced that the only practical way to accomplish this requirement is through separate part numbers that can clearly identify RoHS compliance and manufacturing process compatibility." 

"Admittedly, proliferation of part numbers can add complexity and cost to the supply chain," said Jon Heard, director, technology commodity management, Alcatel-Lucent.  "However, when a change affects form, fit and/or function, we know of no other foolproof method to ensure predictable sourcing, manufacturing and field deployment of electronics hardware.  Alternate ball metallurgies that have different characteristics in assembly and mechanical performance clearly warrant separate part numbers."

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.

"The proliferation of solder ball metallurgies only makes it more difficult to close the remaining knowledge gaps for Pb-free conversion of mission-critical applications.  Reliability experts are still working to fully understand the long-life performance of SAC 305/405 and have limited data on some of the alternate ball formulations. A change in metallurgy without the ability to track the change through MPNs will only make Pb-free conversion more difficult and could delay the process," says Mike Davisson, RoHS technical program manager for Agilent Technologies.

For additional information and further discussion 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" http://thor.inemi.org/webdownload/projects/ese/EMSF_Guidelines_BGA_metallurgy.pdf