-
- News
- Books
Featured Books
- smt007 Magazine
Latest Issues
Current IssueBox Build
One trend is to add box build and final assembly to your product offering. In this issue, we explore the opportunities and risks of adding system assembly to your service portfolio.
IPC APEX EXPO 2024 Pre-show
This month’s issue devotes its pages to a comprehensive preview of the IPC APEX EXPO 2024 event. Whether your role is technical or business, if you're new-to-the-industry or seasoned veteran, you'll find value throughout this program.
Boost Your Sales
Every part of your business can be evaluated as a process, including your sales funnel. Optimizing your selling process requires a coordinated effort between marketing and sales. In this issue, industry experts in marketing and sales offer their best advice on how to boost your sales efforts.
- Articles
- Columns
Search Console
- Links
- Events
||| MENU - smt007 Magazine
Making the Move to Lead-free Requires Teamwork
December 31, 1969 |Estimated reading time: 3 minutes
The reality of the reduction of hazardous substances (RoHS) regulations has many manufacturers in the United States seeking alternative materials for their products. Manufacturers who compete in the global marketplace must be prepared to with the regulations. Regardless of the debates over the science justifying the regulations, manufacturers need to explore alternative products and processes to enable compliance.
Manufacturing products contain even trace elements of lead will need to be replaced. Suppliers have been working diligently to develop lead-free materials. One of the current alternative alloys to lead is a combination of tin/silver/copper (Sn/Ag/Cu) that proven effective. This article will briefly focus on two critical areas for a successful transition to the lead-free process.
Reflow Soldering Because solder paste is a dominant material used to attach components to a board, it is important to understand what effects of transitioning to a lead-free process will have on the solder paste. When examining solder paste, several characteristics such as print performance, tack and working life and powder sizes will remain relatively unaffected by the change.
The density, however, will be affected because lead-free densities are typically lower. This means the percentage of solids will need to be lower to obtain the same solder volume. At the same time, the surface tension of the molten solder is higher and will affect the self-wetting properties and the spread of the molten solder. In addition, wetting of lead-free solders is significantly different than that of traditional tin/lead solders (Sn63). The Sn63 has a bright, smooth finish and tends to wet areas significantly beyond the printed area. In contrast, lead-free solders typically wet a much smaller area given the same printed area. Additionally, the appearance of the solder joint is typically duller than Sn63 and not as smooth, especially under air reflow.
This change means that quality inspectors will need to be retrained to better evaluate "accept and reject" assemblies. Automatic inspection equipment also may have to be re-calibrated to compensate for the reduced wetting.
Many lead-free solder pastes have been shown to provide increased wetting performance and improved cosmetic performance under a nitrogen atmosphere. Therefore, the decision to use nitrogen for reflow will become yet another issue.
Users will need to consider the performance of their existing ovens. Lead-free solders require peak reflow temperatures around 245°C, much higher than the 215°C-peak temperature associated with Sn63. In many cases, older ovens may have difficulty maintaining a suitable temperature gradient across the entire length of the board. This problem could be further compounded on boards where component densities are not uniform. The goal is to keep the temperatures as close to 245°C as possible. However, an inefficient oven may have some components hitting 260°C or greater, while others are barely reaching the 245°C threshold. Depending on the temperature reached, there is the possibility for component and board degradation.
Labeling: Segregating Materials and AssembliesThe transition from tin/lead-based to lead-free is unlikely to occur in one easy step. During this move to lead-free processing, labeling will be a major area of focus. A transition toward a mixture of tin/lead-based and lead-free components before the final step to a completely lead-free assembly process is more likely to occur. Therefore, a key issue will be identifying lead-free materials, components and assembled boards from their tin/lead-based counterparts. This will be required to ease identification at both the assembly and repair, during in-house and field service stages. Components with both tin/lead-based and lead-free elements will need to use separate part numbers so assemblers can make sure the correct component is being used on the correct assembly.
In addition to ensuring that compliant assemblies are shipped in accordance with the new regulations, segregation of lead-free assemblies and components will eliminate a mixing of tin/lead-based assemblies and components until they have been fully qualified as lead-free.
Temperature ratings are also a concern. Assemblers must know the "do not exceed" temperatures of the devices being used to protect against damage. To address this, NEMI, JEDEC and IPC are working on a standard for future implementation.
Resources are Available These are just two of the many challenges facing assemblers in the transition to lead-free assemblies. Fortunately, there are several sources, such as NCMS, NEMI, IPC, Solder Products Value Council, SMTA and Soldertec, where comprehensive information can be gained. Assemblers must remember that they also can rely on the industry suppliers to provide them with the necessary technical data to enable compliance with the pending regulations. Working together and sharing information will ease the transition for all those involved in the lead-free process.
Brian Bauer, SMT business manager for Heraeus' Circuit Materials Division, may be contacted at (610) 825-6050; email: 4cmd.com.