Comparative analysis of your process engineering
Mark Thompson has been manufacturing bare panels for over 30 years. He is currently installing circuit boards at Monsoon Solutions, a high-tech design office near Seattle, WA. With Mark’s extensive practical knowledge of PCB manufacturing, he brings a unique perspective to PCB design.
In this discussion with the I-Connect007 editorial team, Mark shares what is important from a process engineer perspective, and how to stay on top of evaluating and benchmarking your process. workmanship, as well as ideas for his new role as a designer.
Barry Matties: Mark, now that you’re a PCB designer, after decades of manufacturing, what’s the most surprising thing you’ve learned?
Marc Thompson: Oh, my God, there are quite a few. For years I have preached things like, “Don’t design to the minimum because of the engraving offsets based on the weights of the copper.” But now I find myself going through this because I lack space. I design it in 4/4 and I’m like, “Well, my God, if I do that, now I’m going to have to burn it to make up on half an ounce of copper, and it’s going to be four and a half and three and half, which means they’re going to be relegated to three-eighths of an ounce copper foil. And that could be a problem for the power functions. This can be a problem for the part itself, and it may not live with it. So that’s one of the things I learned.
I also learned a lot about component placement and cavity design. We’ve already talked about footprints and the importance of having a good footprint. And honestly, the footprints themselves are pretty much the same. What changes is the yard, the distance around the component you’re actually putting on the board, and that distance dictates how much space you have. There might be a high part, and you might need a human, to have a finger in there and reach and hand weld something on a very high part. So it becomes a problem, and that’s one of the other things I’ve learned.
In fact, it’s almost like I erased my 25 years at Prototron and over 30 years in PCB manufacturing when I started designing. I have to completely rethink the game and deal with a lot more variables. The design is certainly not a point-to-point connection of networks. It is so much more than that. It is to understand these nets; it is to understand power. What’s the very first thing I look at when I look at a board? I am looking at the power functions. I ask questions about the mechanics. When we make a kick off call with a customer, the very first thing I say is, “What sort of mechanical considerations do you have? “
Along with this, there are also power functions. If they have high current power considerations then I need to make sure the trace width will be large enough. I’ll use a site like Saturn and precompute the width of this trace, then I can plan things ahead. In fact, this is one of the things that I learned here recently, very intimately: when I place parts, I allow myself enough space to drop vias to be able to make interconnects. Because if this is a six layer map and I don’t have a lot of room on the outer layers depending on the part geometries and available space, I’m going to have to switch to an inner layer . And by doing that, that means I’m going to have to have a via. I have to account for that via width and buffer size associated with that via all the way up the stack. I also take care of the casting polygons. It’s a big one.
Matties: Law. Is there something you used to preach there that you’d say now, “Wait, I’ve been thinking about that now that I’m on this side, and let’s do it on this side.” way ? “
Thompson: I’ll give you an example. As a manufacturer, you want things to look nice and clean. If they have metal on the edge, you’ll try to clip it on. Where don’t you put it back? You don’t clip it back onto an RF launch, a coplanar waveguide-like structure that goes all the way to the edge of the card and has to go all the way to the edge of the Z axis of that particular card, and it has to stay. Thus.
Matties: It’s interesting. Thanks for sharing this. With your manufacturing background, you are in a truly unique position as a PCB designer.
Thompson: I am. I can’t tell you how many conversations I’ve had with the designers here at Monsoon about manufacturing issues. Often times they ask me what is the minimum hole size with a particular buffer size. And these are very simple questions, but they are very useful if you don’t know the answer.
To read the full interview, which appeared in the April 2021 issue of PCB007 Magazine, click here.