Dr. Ron Lasky: A Solder Alloy and Solder Paste Overview

Estimated reading time: 3 minutes

The I-Connect007 editorial team spoke with Dr. Ron Lasky about why the world has not embraced some of the exciting alloys that companies like Indium Corporation have developed. He also provides an overview of solder alloys, including the difficulty of qualifying SAC305.

Nolan Johnson: Ron, thanks for joining us in this conversation. What’s your role in the industry?

Dr. Ron Lasky: My day job is as a professor of engineering at Dartmouth, and I also work with Indium Corporation as a senior technologist.

Barry Matties: When thinking of solder paste, is there a critical performance metric that you think is often neglected?

Lasky: Yes. There is something that’s a critical performance metric in solder paste called “response to pause.” If you have to shut the line down for some time because you have to put components on the pick-and-place machine or some other task, some solder pastes will stiffen up, and you can’t use the first print. You have to print once, wipe the board, and print it again because the solder paste stiffens up. That’s called a poor response to pause. A better solder paste—and this is one of the things my colleagues at Indium Corporation understand—has a good response to pause. In other words, you can leave the solder paste on the stencil for an hour or more, and it doesn’t make a difference.

One customer changed to Indium Corporation’s solder paste and no longer had to do this wiping of the board when they stopped the line every couple of hours to do something. In the past, each of these times, the paste would stiffen, and they had do to the “print-and-wipe” procedure. At the end of the day, it ended up being 20 minutes or more of lost production in an eight-hour shift; it was a bigger deal than might first appear. The new solder paste improved their productivity a couple of percentage points, but it improved their profitability 8–9%. With cost estimating software I had developed, I was able to calculate all this, and we ended up writing a paper on the topic.

Dan Feinberg: Do you see a significant change in the volume of solder that is being used as a percentage basis—not by tonnage or anything—for a solder paste versus bar solder for wave soldering?

Lasky: Solder paste has become more dominant, and that’s the case because certainly surface-mount technology, for a lot of our products, is the only thing used. I don’t think there are any cellphones that use wave soldering.

Feinberg: No, I wouldn’t think so at all.

Lasky: But don’t discount bar solder. Twenty-five years ago, some people said, “Wave soldering and through-hole are going to go away. We shouldn’t even pay attention to those,” but that’s nonsense. They’re not going to go away probably ever.

Feinberg: One of the things with through-hole is that with the change in the last decade to lead-free solder, the flexibility of the solder has reduced significantly. And when you have a component that’s mounted through a through-hole and then soldered versus placed on a pad and then soldered, the reliability is significantly better with the through-hole.
This behavior hasn’t mattered so much until the reliability needs have increased, which they have increased significantly in the last 36 months, thanks to autonomous driving and the volume of electronics in transportation. That may be slowing down the decrease in wave soldering, although—from an economic stand-point—it makes no sense. We’re kind of at a crossroads right now.

Lasky: I have to push back a little bit on that. I would agree that one of the reasons wave soldering is not going to go away is some of our electronics products have a lot of plugs. Some of those plugs want through-hole for mechanical strength.

Feinberg: That’s true.

Lasky: A lot of the components that are made that are critical for autonomous driving only come in surface mount formats because you can’t beat SMT’s interconnectivity. If some-body said, “We want to make an Intel micro-processor be through-hole,” it wouldn’t be possible because there are too many interconnects, and you can’t make through-holes that small. I agree with most of your thoughts on through-hole, but we’re going to have to make surface-mount reliable enough for situations like this.

To read the rest of this interview, which appeared in the May 2020 issue of SMT007 Magazine, click here.