Lead-Free Soldering Print E-mail
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Written by Bob Willis   
Monday, 27 August 2007 08:41
Lead-Free Soldering
By Jasbir Bath, Editor, Solectron

Jasbir Bath has gathered a good mix of industry and academic authors to cover each step in the path to RoHS compliance. With Jasbir working for Solectron Corp., the main focus is manufacturing and the impact of lead-free technology. A fairly easy read, it is suitable for engineers and non-technical staff to get a balanced overview and the hands-on story.
Ten chapters and 299 pages take the reader through the overview of the legislation in US, Europe and Asia to the implementation of international standards. Each of the building blocks of manufacture is covered in a practical way, including the materials and reliability. The book provides a good introduction to the issues and covers many of the issues engineers often neglect.
Two engineers from Atotech cover solder finishes in detail, illustrating the importance of each selection. Recent surveys have shown that the change in PCB finish can often be one of the most common reasons for failure in lead-free manufacture, ahead of delamination, cosmetic and via failure. Hugh Roberts and Kuldip Johal use a simple methodology to outline the finishes. It is fair to say a large percentage of the text is devoted to gold processes.
Karl Sauter of Sun Microsystems discusses laminates for printed board manufacture. Sun has been actively involved in the discussions on materials, and has spent many years investigating Conductive Anodic Filament phenomena because of the complexity of their product design. The sections deal with the available test methods to assess materials and an interesting case study of accelerated thermal stress testing. There are advantages to new laminates on complex products; however, not all products require high Tg materials.
The assembly section by Sundar Sethuraman discusses the possible changes in manufacture to accommodate lead-free with the potential issues faced by any engineer tasked with product conversion. Sethuraman highlights the need for more profiling and a review of this process. Many engineers have become a little blasé in the need for correct temperature monitoring. One of the surprises is that there is no section covering the growth of selective soldering and the issues associated with lead-free. It fair to say that many companies have adopted pin-in-hole reflow, but selective is growing in popularity.
Wave soldering is deservedly given its own chapter because of the difficulty in converting the process and the many issues it raises in manufacture. Each process step, fluxing, pre-heat, handling and solder bath materials are considered, along with the interaction of materials and process conditions. Advice is given on well-known wave soldering issues like fillet lifting, fillet tearing, pad lifting, and the increased incidence of shorting that can occur in manufacture. Each of the process indicators is mentioned and how the IPC standards criteria change with lead-free joints.
Bath’s first book concludes with pages reviewing the content and emphasizing the work that still needs urgent attention. Although much has been achieved in the last ten years, many questions go unanswered. The final pages stress how we have changed our whole manufacturing process, but to whose benefit?
Last Updated on Tuesday, 28 August 2007 05:02


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