Issue link: https://iconnect007.uberflip.com/i/881969
24 SMT Magazine • October 2017 occasion, how do you rework it when you have to start from scratch? It's not an easy solution all the time." The challenge is not only with the surface- mount components that are getting even small- er. "We also have the other end of it where we have the through-hole side and parts that are bigger and boards that have multiple ground planes," says Burns. "When you get into very, very thick boards with a lot of ground connec- tions, power planes and a whole separate set of issues with the heat profile and the thermal transfer, you need to get an adequate solder connection. We've had some instances where we've tried to hand-solder things and there's so much thermal mass that it makes it virtual- ly impossible. So, a designer adding the thermal mass and the thermal planes for the circuits to operate correctly doesn't always lend to good solder connections or ease of process for solder- ing. We try and automate the things as much as we can through wave solder or through se- lective soldering process, just to give us the ad- vantage of the mechanical push of the solder up through the holes in addition to the heat. But the thermal planes are a huge issue. The oth- er issue on that is the same concept that you get with the pad geometry in surface-mounts. You have to make certain that the hole side, the diameter of the hole and the diameter of the leads aren't too close together so that you have enough room to physically allow the solder to move through the hole." Roush says pre-heat helps to address the is- sues with dealing with thick boards. "Redesign- ing some of the tips, we've spent a lot of time in the past few months really looking at that as we've done testing in other areas, and found that through the course of the matter, getting barrel fill in the through-hole is really an ongo- ing issue. We've had customers who had never cross-sectioned their boards and they thought they were doing a pretty good job, and realized that they were actually not getting the barrel fill they thought they were getting. I think, some- times it comes down to a little patience from an operator's standpoint. We've found that because they can see the top where they're going to feed the solder in if they're using wire and it looks like it's re-flowing, they're not patient enough to let the thermal energy go all the way down to the bottom of the barrel before they start feed- ing solder and then when it backs up they think it must be full," he explains. "There's a little pa- tience involved in that, which doesn't necessar- ily come through until you have enough expe- rience to realize that you've got to get that en- ergy all the way through the barrel and the cor- responding pin location. But pre-heat definitely helps and then re-looking at how the tip designs are done. I know the tendency is to use a small selection of tips to do a majority of the jobs, but in those applications, redesigning or doing something that's a little outside the box or cus- tom to that application may help get more ther- mal energy in there more efficiently. We've seen a growing trend of that. We've seen that we've guided customers into different tip selections because they're doing that through-hole ap- plication and they weren't patient enough and they needed more energy to get there, and that was the end solution. It's a combination of tip geometry, asking them to just wait even a frac- tion of a second longer than they think they really need to, to allow that thermal energy to soak through." Burns agrees. "Patience is a big thing. One of the main points we touch on in the solder- ing classes that I teach is being patient. I can give you an example but sometimes even that doesn't matter when it comes to some of these designs. We had a board out here that the oper- ator couldn't get to flow, so I walked down and watched the process. In this case, we had two different soldering systems, and we were using the highest thermal energy tips we have from one of the systems. Two tips at the same time on the board. After about 40 seconds, we could get solder to flow through the hole. So, a signif- icant amount of patience, a lot of time, a lot of ACHIEVING THE PERFECT SOLDER JOINT: THE MANY PERSPECTIVES ON SOLDERING " One of the main points we touch on in the soldering classes that I teach is being patient. "