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A Closer Look at Lead-free Solder
November 15, 2005 |Estimated reading time: 4 minutes
By Michelle M. Boisvert, SMT Managing Editor
— I can no longer consider myself a newbie in the SMT industry. Last week, I got my feet wet in the soldering side of things. At the recent "Lead-free Technology Forum and Workshop," presented by Dage Precision Industries and hosted at the Circuit Technology Center in Haverhill, Mass., I had the chance to hand-solder thru-hole components onto a board using lead-free solder. Though I didn't feel sure-footed enough to solder the surface mount components, nor do I foresee any outsourcing contracts coming my way anytime soon, I now can say I have encountered the "Lead-free Experience."
The EU's deadline of July 1, 2006, for RoHS compliance is less than eight months away, which has many companies upping the lead-free-compliance ante. Phil Zarrow of ITM Consulting offered attendees a slightly humorous, but straightforward look at the mandate during "Lead-free: Get With It or Get Out of the Way." Zarrow's presentation examined the ins and outs of working with lead-free alloys. The speaker also touched on how lead-free will affect all departments, including facilities, field support, sales and marketing and training. While one ideal solution to operating a lead-free line would be to have separate facilities for lead-based and lead-free work, small- to medium-sized companies most likely will not have this luxury. Balancing and managing a facility that works with both alloys will be a challenging area for these companies. Some suggestions included maintaining separate part numbers for same-function alloys, focused training for personnel and creating segregated storage spaces. Zarrow also noted manufacturers need to get through the first four stages of lead-free: Denial, Anger, Bargaining and Depression, and move on to the Acceptance stage because RoHS is here and it has been enacted.
During "Implementing Lead-free Materials and Processes," David Suraski of AIM Solder outlined how the migration to lead-free will affect each step of the manufacturing process, from material selection through final assembly. Component concerns range from availability issues, such as a narrowed selection field for parts, to reliability woes brought on by elevated melting temperatures for lead-free solders during the soldering process. A component's internal thermal damage may not be easily detectable using electrical tests. These damages can possibly cause field failures after assembly. The component's moisture sensitivity level (MSL) also is an issue requiring tweaks to storage and handling procedures.
When considering which lead-free alloy to implement, Suraski urged attendees that there is no drop-in solution, noting the NCMS' multi-year, multi-million-dollar study of 70 alloys in search of one lead-free solution. The study found no such solution existed. Suraski also highlighted several available lead-free solutions and data on each. Tin/lead and lead-free compatibility also was discussed, and suggestions for a smooth dual-alloy line were given.There are several noted differences between tin/lead and lead-free solders, as well as inspection parameters for lead-free BGAs. David Bernard, Ph.D., of Dage Precision Industries, noted this in his presentation, "X-ray Inspection of Lead-free Assemblies." The overall optical appearances of lead-free solder joints are different than tin/lead counterparts. Lead-free tends to give a less shiny, dull, grainy appearance compared to eutectic joints. Inspection technicians must be trained to understand these differences, as they may not necessarily mean there is a defect. Technicians also should be trained to recognize the wetting (or lack of wetting) characteristics of lead-free alloys. Lead-free solders also experience increased voiding levels; however, these voids may not always mean a failure. The IPC's 610D standard for acceptability of electronic assemblies sets voiding limits at 25% before a joint is considered a failure. Bernard stressed the use of X-ray inspection for lead-free alloys because it inspects optically hidden joints, such as BGAs and flip chips, as well as SMT components where the general look of the joint is not familiar, i.e. shiny. Bernard explained the differences between 2D and 3D inspection; and demonstrated Dage's XiDAT (X-ray Integrated Digital Acquisition Technology) XD7600, which enables oblique angle views of up to 70° for any position and 360° around any point of the inspection area (measuring 18 × 16"). The XD7500 can inspect PCBs containing BGA and CSP devices.
During "Lead-free Rework and Repair: Hands-on Soldering," Charles Dennehy, president of Circuit Technology Center, outlined some of the issues the company has been dealing with on the rework side. Bill Seaman of Circuit Technology Center led attendees out onto the floor to further discuss some experiences the company has had in the way of lead-free solder rework, as well as problems they have encountered. Bill Butman, training director of AssemTech Skills Training in Acton, Mass., guided attendees through the aforementioned "Lead-free Experience," allowing them to solder thru-hole and surface mount components onto a board using lead-free solder.
Even industry experts are unsure exactly how the transition to lead-free will play out. One imperative step to a smooth transition will be making sure that all players in the assembly process, from component suppliers to inspection technicians, through rework and repair techs are familiar with product supplies and anticipated outcomes. Companies need to get everyone in the component supply chain involved, specifically purchasing agents. It seems that RoHS and all related lead-free questions have manufacturers realizing that the way they're used to doing things is changing. It seems everyone will need to learn, re-learn and experience something different when it comes to lead-free.