The introduction of Pb-free has led to countless tomes on the subject. One, however, stands apart as a pragmatic, ready-made guide for process engineers. The succinctly titled Lead-Free Soldering is a tidy look at the entire SMT process, including design and test, from the perspective of the line engineer. Editor Jasbir Bath recently spoke with Circuits Assembly’s Mike Buetow.
CA: Have you read other books on lead-free soldering?
JB: I have looked at others in general. They’re a little too detailed than they need to be. Some process engineers want to get right down to the facts. They don’t have time to read a whole book. We tried to make the chapters fairly short so they could be readable, but also have information that you could pull out immediately. The book’s trying to get to the general details: what's happening before, now and in the future.
CA: What was the development process like?
JB: When you start it, you seek out authors for each chapter. Each individual author gave me a draft outline. I went back and forth on the plan and how to bring up details. The plan was, when I went to the different authors, I asked for 20 pages; don’t break the bank. Give me a general opinion on each area: intro, details, a little discussion, and the conclusion. We tried to have a reasonable order and focus on what people would want to know. I went through a lot of drafts and tried to see what someone else wanted to see and what makes sense – from the eye of the reader.
CA: How did you get together with Springer?
JB: When I first had the interaction with Springer – it was in 2005 – and they were interested in articles. I presented the idea; there are many books on lead-free soldering, but this one had to be more practical. I looked through an initial draft and picked out 10 subjects, including reflow, wave, laminates and reliability. When you’re a process engineer, you need to know something about everything. Then I said, Who would be the best person to write each chapter? Then the chapter author would give me an outline of each general subject. Then we worked on the headings. Then I said, OK, go write it.
CA: Some of the chapter authors – Jean-Paul Clech, Karl Sauter, Carol Handwerker, yourself – are widely known. Others – many of whom are also at Solectron – are less so. What was your intention to involve your coworkers?
JB: Because I’m at Solectron, I know these people and how they work. We have an advantage on some process areas in that we may have seen things that others haven’t. We wanted the best for SMT wave and reflow. I took the rework myself, but for some SMT and wave, we seemed to have a reasonable handle on what’s going on because we deal with cellphones, laptops and servers. And this was a good opportunity for some of them to get this under their belt.
CA: Certain chapters – Chapter 6, for example – include a fair amount of formulas. Others are discussion-oriented. Why the difference in approach?
JB: I always try to push more on the practical. In some of these areas, you had to go more into the fundamentals in order to go into the practical. I was always reviewing it: Does it make sense? Is it readable? In general, I am trying to pull back and say, “Give me the whole picture.” For someone who’s an expert, it’s a challenge; they want to get to the finish line. I had to say, “Push on the practical side.”
CA: Many of the authors are involved in trade consortia like iNEMI. How was the reaction from that side?
JB: I said to each author, “You write your opinion as to what’s going on in your particular area.” The authors, because they were part of it, could use the information. We were very cognizant we could not use data that was not published. It was all public domain.
CA: One of the aspects that impressed me was the depth of the cited literature.
JB: Some chapters had more references than others. It shows sometimes the direction the authors wanted to take, where they get the information and references. During the editing process, we emphasized having a source.
In terms of my involvement, I was relying a lot on the authors to work in literature when it was needed. Often when I read it, I was a reviewer. I would say, “Does that make sense? Do you want to temper that, rather than in black-in-white in most cases this will occur.” There was a lot of back and forth on this, to try to give a balanced opinion on things. If you want to go through a minefield, look at the surface finishes chapter. These specific authors didn’t want to step on anyone’s toes. They wanted to be objective.
CA: Why a supplier for the Surface Finishes chapter?
JB: I was looking for someone who could give a reasonable opinion on surface finishes. I went to Kuldip [Johal, the chapter coauthor] at Atotech, and knew based on background, when they present at conferences, they try to be balanced. They try to be upfront. I wanted to be sure I had someone who would give a good account of this area, not bias it. The person who knows the most about surface finishes is probably the supplier. I wanted it to say, this finish is good in this, this and this application.
CA: Why include the processing sequences?
JB: When I went through the draft, Hugh [Roberts, the chapter coauthor] and Kuldip felt it rounded out the chapter to put those details in. It was better explained by going into more detail on how those finishes plated. I left it to them.
CA: Some believe the lack of self-centering mandates higher accuracy machines. Where do you stand on that today?
JB: If you’ve misplaced it, if it’s gross, it would affect both SnPb and lead-free. It really goes back to how repeatable and calibrated the placement machines are. People like to blame lead-free if there’s a defect. We haven’t come across any major points in our production process that say that.
CA: I also noticed the book steered away from the controversial aspects of lead-free.
JB: If it was something that was pushing the envelope, I said, “You may want to rephrase it.” When you’re reading it, you can create certain controversy. When you have something that’s not always factually correct, you want to be careful to state that “in the majority of cases, this is what you can expect.” When you read something, you want to get to the point but not stir the hornet’s nest.
CA: Which area was the hardest to develop?
JB: The rework chapter was based on my personal experience. And there wasn’t much work on rework done in general. So I tried to put in as much as I had.
CA: One area covered in many places but not by a standalone chapter is components.
JB: When I was writing, I had Components to be marked in, but the authors I wanted had conflicts or moved out of industry. If I were to do it again, I would include a chapter on component solderability. Next time [laughs].
CA: Chapters 3, on reflow, doesn’t cover design rules, but Chapter 4 (wave) does. Why is this?
JB: What we found was that the design side for wave seemed more critical. Wave was considered to have changed more than SMT. SMT design rules don’t change in general.
CA: The Laminates Chapter includes nominal discussion of IST, but has a case study on HATS, which is a controversial test method. Does this suggest a preference?
JB: The HATS case study was included as a preference of the author [Karl Sauter]. He was giving his opinion on where the industry is moving.
CA: Indeed, the case study shows a lack of correlation with the HATS results.
JB: We still wanted to give both sides. We didn’t want to sugarcoat it.
CA: Over the process of writing a book, what did you learn?
JB: I learned you have to follow deadlines [laughs]. In October 2005 we started with a draft. By October 2006 we got the OK from Springer. We took it easy from January to August 2006, then realized we had to get it done. We worked hard on it two or three months, making sure we enforced timelines. Even when you give authors time to do this, you still have to chase a bit. You are always learning to be flexible and always meet deadlines. The other thing I learned was about editing: the template, doing the editing, what kind of JPGs, the font, the different annotations, how you insert them.
CA: Are there plans for a follow-up?
JB: There are other things to do: new areas in lead-free soldering, things that aren’t covered here. I need a holiday for a bit. I think we covered a lot of the subjects here in general lead-free soldering that would be good to talk about at the process level.
CA: How was Solectron throughout the process?
JB: Solectron was very accommodating. Most of the work was done on my own time. I think the opinion was, Make sure you’re OK with it. Writing a whole book would be tough. Being an editor was more manageable.
Editor’s note: Lead-Free Soldering, Jasbir Bath, editor, 299 pp., available in the SMTA and IPC bookstores. List price: $129.