Implementing Lead-Free Electronics

Citation

Willis, B. (2005), "Implementing Lead-Free Electronics", Soldering & Surface Mount Technology, Vol. 17 No. 2. https://doi.org/10.1108/ssmt.2005.21917bae.003

Implementing Lead-Free Electronics

Implementing Lead-Free Electronics

Jennie S. HwangMcGraw-Hill Professional Engineering470 pp.10 chapters with diagrams and photographs

Keywords: Electronic engineering, Books, Solder

Jennie is one of the most well known figures in the industry and in the last 10 years has been heavily involved in lead-free introduction and training workshops worldwide. This is her second lead-free textbook; her first was published in 2001. With the challenges ahead every lead-free reference source is a benefit to engineers (Plate 3).

Jennie has produced a reference source covering the A-Z of lead-free which has been specifically printed with a large typeface to make quick reference easier. It is laid out specifically as a quick reference guide to the reader. It lists all the figures and tables that are included in the book in the opening pages. The first chapter provides an overview of the environmental legislation in Europe, US and Asia and with it the experience gained so far and the research projects that have been undertaken. It also outlines some of the basic engineering considerations for lead-free production.

Plate 3 The lay-out has been designed to be a quick reference guide to the reader

Jennie Hwang does cover many of the basics of paste, printing, reflow and wave, but there are some subtleties even in the fundamental steps that need to be addressed. Using separate storage for waste paste, using separate squeegee blades, separate storage for bar and wave solder dross. Accurate monitoring of material usage particularly bar which is the biggest expenditure in the lead-free process.

Component and PCB finishes in chapter 5 has been a hot topic for the last 5 or 6 years, partly this has been the move to find a lead-free alternative and partly to avoid solder levelled finishes. Although there are still concerns over the use of tin on components this looks like the industry direction and tin is gaining interest as the PCB finish for the future. Jennie Hwang provides an overview of the options and then illustrates results and the experience in the industry.

Reflow soldering is covered in chapter 6 considering and demonstrating parameters and profiles achieved in different convection reflow ovens. It is fair to say that practical experience in the industry shows that existing professional ovens can do lead-free; the only impact is throughput speed and slower cooling rates with existing technology. The chapter briefly mentions vapour phase soldering, which is being more openly discussed in Europe for lead-free. It is expected to see how VPS grow but by how much, 10-15 per cent of usage is to be expected. After all VPS is being used in Japan for thermally demanding boards and has been for the last 4 years. The chapter features example sections on 0201 and gull wing connections produced with SnAgCu and SnAgCuIn. This reviewer has successfully processed OSP, gold and silver boards with both the aforementioned alloys, the results with VPS proved very successful with delta T's of less than 5°C.

Chapter 9 outlines and illustrates some of the common process defects experienced in manufacture, some of these are often seen for the first time when moving to lead-free. Fortunately most of the issues have solutions or they have been proven to be cosmetic and not reliability issues. Fillet lifting is a prime example that has been known for a number of years based on the work done at Osaka University and NIST in the USA. Reliability testing has demonstrated that fillet lifting is not an issue so much so that the latest issue of IPC 610 defines it as a process indicator. The book as a whole provides some good images from wave and reflow with different alloys. This may be used as a reference for quality control during process introduction. They will complement other documents available in the industry.

Chapter 10 looks at lead-free reliability data. It is fair to say that lead-free alloys have been tested on test modules with a range of different temperature cycles. Unfortunately it is difficult to compare results from different test boards and different test parameters hence the interest in developing computer models with the correct acceleration factors.

I still feel that the text could have benefited from some more practical advice at a shop floor level, more Do's and Don'ts, also slightly less emphasis on anyone particular alloy family.

Bob Willis