Issue link: https://iconnect007.uberflip.com/i/1002143
JULY 2018 I PCB007 MAGAZINE 53 Lindland: That's a good question, and I would say probably not—they don't know it. And the more information you could provide would help tremendously. The other thing, too, as Tom said, with our equipment and what's go- ing on now, you're able to apply your solder mask and meet a target thickness. That allows us to do some of the higher end and more dif- ficult panels, whereas 20 years ago, it wasn't really specified. There wasn't that real target, and there wasn't a real requirement as a solder mask equipment manufacturer, to meet that. As it's gotten tighter, we've been very effective and very successful at doing that. Matties: I would think if you discover in your assembly process that the mask is too thick, that's an enormous amount of waste. I don't know what the outcome is with thick mask. Is the board absolutely rejected at the assembly level if the mask is too thick? Lindland: You're right. If that is happening at the assembler, it's way too late. And that's where people have tombstoning and other problems with their components. And yet, if the design- er would specify what the desired thickness is, I think everyone would be more successful. Goldman: You know, it always comes down to communication. No matter what the subject is, it still comes back to communication, doesn't it? Matties: I think there's communication. But in some cases, there are new standards or needs that creep up that we're not aware of until it's too late. And so it's not just communication, it's being aware of the trends and the require- ments or the impact that you have on the pro- cess. Shaughnessy: And then the manufacturer will fix this problem, and sometimes they don't even tell the designer. Matties: Yes. That feedback loop needs to ex- ist. We're seeing more and more demand for HDI, especially here in North America; we're seeing more people move into that. Are there any considerations for HDI as it relates to sol- der mask? Lindland: It's all about the mask thickness. It really is, because with an HDI panel, you have tighter tolerances all the way around, from your copper heights to your panel thickness, hole sizes, everything. It puts tighter demands on the entire process, and for solder mask, it's a very process-oriented system where you re- ally rely on how you clean the panel, how you apply the mask, how you tack cure it, how you expose it, how you dry it, handle it, everything, to get the results you need. And the demands have gotten tighter in the last few years, and the ability to put the mask on very evenly on a wide range and do different things is much more difficult for a lot of shops. Matties: Is that based on the equipment that they have or is it also based on the discipline that they have? Lindland: A lot of it is that the equipment was designed 20 years ago, and a lot of advance- ment hasn't been made, or they haven't made a lot of investment in new. Meeker: Well, the equipment was originally de- signed to replace flatbed screen printing. And in the North American market, which is all pat- tern-plated, there's a lot of high and low cop- per plating across the entire panel. The origi- nal goal was to put the solder mask on real- ly thick and consistently over even where you have a variation of 2−3-mils in traces, so you have something that was more tolerant to un- even copper plating. Throughout the rest of the world, everything is panel-plated, so it's not as big an issue as it is here with pattern plate. That was the original goal, so the ear- lier machines were made to put it on thick, It's all about the mask thickness.