BY FRANK GRANO
The electronics industry is making steady progress toward developing lead-free assembly processes to meet the EU's Restriction on Hazardous Substances (RoHS) directive, which calls for the elimination of lead and other hazardous substances from new electrical and electronic equipment by July 2006. To date, industry efforts have concentrated on finding a lead-free replacement for the commonly used tin-lead (SnPb) solder and proving the replacement's reliability. The current lead-free solder targeted by most of the industry is the tin-silver-copper (Sn-Ag-Cu) alloy, which has a 34° to 36°C higher melting point than lead-based solders.
If all development activities were completed tomorrow and the electronics assembly industry declared itself ready for RoHS, could the switch be made overnight by simply changing the assembly process and the materials used? Unfortunately, the answer is no. There remain many issues that the industry must address. Achieving global compliance with the RoHS directive will require significant infrastructure changes.
At the product level, the electronics industry must develop standards to determine compliance with RoHS and related chemical restriction requirements. The U.S. electronics industry has formed a working group to define a “best management” standard to demonstrate compliance. Currently, this work is led by a multi-industry trade coalition and organized by the Electronics Industry Alliance (EIA) and the American Electronics Association (AEA).
At a more basic level, however, industry must define the assembly process, determine component specifications and develop acceptance criteria to implement new lead-free manufacturing and repair processes. With the RoHS implementation date only two years away, industry must act quickly to develop and validate standards for lead-free processes and products.
In the familiar world of SnPb-based soldering, standards exist for virtually every aspect of the assembly process and for the materials and components used. These standards cover acceptance criteria for finished products and a number of other aspects to ensure that assembly materials and components are compatible with the assembly process. There are currently more than 100 IPC and JEDEC standards that provide well-defined parameters for assembly materials, components, solderability, cleanliness, fabrication, assembly and more.
Lacking new process and materials standards, how can an assembler ensure that the products being manufactured are acceptable and, more importantly, reliable? Very simply put, unless the assembler already has experience with the process, it can't be done. Standards are the backbone for industry testing and acceptance criteria, but since the current standards bodies and most of the electronics assembly industry don't have the expertise in lead-free soldering, how will the job get done? It will only happen if companies with lead-free experience provide expertise to the groups developing the new standards. This is presently limited to a few OEMS and the EMS community, so participation from all companies is imperative.
The National Electronics Manufacturing Initiative (NEMI), an industry-led consortium, has organized a project team to focus industry efforts on development of materials and process standards for lead-free assembly. NEMI is calling on the resources of its broad-based membership, along with other industry leaders with lead-free experience, to define specifications that will lead to rapid development of IPC and JEDEC standards. The goal is to develop specifications and criteria based on a cross section of industry expertise.
The first step is to define the conditions that will exist when assembling a board with a lead-free soldering process. This definition must cover all aspects of assembly — SMT, rework, wave solder, manual rework, etc. It also must include the soldering temperatures for all component types, covering soldering joints, package materials and PCAs.
Based on this definition, it will be possible to identify and prioritize the industry standards that must be revised, or define new standards. There may need to be a new type of standard that actually defines the soldering criteria for assembling a board using a lead-free process. Such a standard cover the entire assembly process and would go a long way toward assisting manufacturers new to the process in getting started.
Given the timeframe, industry must focus on a core group of standards. NEMI has identified two key standards: IPC-610 (workmanship standards) and J-STD-020 (MSL document). Initial efforts are focusing on these two standards, then the group will identify additional specifications to be updated.
To date, the industry push is to develop soldering processes. It is now time for companies experienced in lead-free processes to address the additional needs of the assembly community, which includes standards that can be used on a day-to-day basis on the factory floor and throughout the supply chain.
 |
FRANK GRANO, principal process engineer, may be contacted at Sanmina-SCI, 13000 South Memorial Parkway, Huntsville, AL 35807; (256) 882-4903; e-mail: [email protected]. Grano also chairs NEMI's RoHS Assembly Process Specifications Project.