Circuits Assembly - November 2007 - (Page 32)

RoHS Transition Pb-Free Manufacturing from a Tier III EMS Perspective Greg Caswell How one company made the switch. MS firms have been involved in the Pb-free transition for a considerable time. In fact, one might say the process has reached a level of maturity. Early adopters were faced with myriad issues such as solder paste availability, board materials, surface finishes, component terminations, parts numbering and logistics, processing temperatures, and the lack of reliability data. This level of change was daunting even for the larger EMS firms, but had a major impact on smaller firms that lacked abundant engineering resources. So how did we do it and how has the process matured? VirTex began its transition in 2004 to be ready for the July 1, 2006, European Union deadline. To examine the process, it is necessary to break it down into each element, examine the changes, and define what has been accomplished by the industry to move from initial utilization to a more refined set of materials and processes. Solder paste. When the process transition was started, it made sense to go from SnPb eutectic to a Pb-free eutectic (e.g., SAC 309 or SnAg3.0Cu0.9) material. Manufacturing several circuit card assemblies revealed excessive component tombstoning. A move to a lower copper content (0.7%) reduced tombstoning significantly, but it was the move to SAC 305 that provided the results we were looking for: tombstoning occurring on less than 0.5% of the subject 0402 and 0201 components. Many other companies that followed this path achieved the same results, and SAC 305 became the de facto standard for SM reflow and wave. In general, Pb-free solder materials do not wet as well as E the standard SnPb compositions, but have achieved a level of acceptability. The greater use permits industry to accumulate reliability data and focus on process improvements and enhanced reliability. Components. Several issues became obvious as various devices were switched to RoHS compliant materials. These issues included parts numbering, materials, lead finish or ball composition, and compatibility with higher temperatures associated with Pb-free assembly. In the 2004 timeframe, it was necessary to take a customer bill of materials (BoM) and manually crosscheck the parts to those that met Pb-free manufacturing requirements. Many parts, such as passives, were available in Pb-free equivalents for years and, as such, the part numbers remained the same. Other suppliers put a notification on their Web sites; still others changed their part numbering schemes. The result: a logistical nightmare. Today, most distributors have a customer-accessible database that quickly permits the uploading of a BoM and cross-referencing of Pb-free part numbers. Finally, it became necessary to take leaded parts headed toward obsolescence, remove the lead finish and recoat using Pb-free materials. VirTex accomplished this with the help of Six Sigma Corp., which stripped and refinished the parts. This action provided our customers a year to redo software and incorporate new devices into their designs. Another issue is the ability of parts to withstand the almost 40°C increase in reflow temperatures for Pb-free processing. In many cases, components, such as connectors, were RoHS-compatible (meaning that the seven banned materials were not present in the new part), but were not compatible with the Pb-free manufacturing process. These parts would either melt or warp at the higher temperatures. Today, most 32 Circuits Assembly NOVEMBER 2007 circuitsassembly.com http://circuitsassembly.com

Table of Contents Feed for the Digital Edition of Circuits Assembly - November 2007

Circuits Assembly - November 2007 Contents Caveat Lector Industry News Market Watch Talking Heads Focus on Business Global Sourcing On the Forefront Screen Printing Better Manufacturing Pb-Free Manufacturing from a Tier III EMS Perspective ‘Living Documents, Subject to Change’ Creating Ideal Solder Joints An Alternative Drying Process for MSDs ‘Customer Satisfaction is More than a Score’ Optoelectronic Substrates: Will They Happen? Tech Tips Wave Soldering Process Doctor Test and Inspection Getting Lean Materials World Equipment Advances Product Spotlight Assembly Insider Technical Abstracts Ad Index

Circuits Assembly - November 2007

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