Issue link: https://iconnect007.uberflip.com/i/1010078
AUGUST 2018 I SMT007 MAGAZINE 15 the cleanliness and for sensitive electronics. That is something that typically they are not involved with. Just those architectures and having to lay out those signals and the I/Os can make it more difficult just to clean. Shaughnessy: So, they need to be in communication from the start. Because I don't think they put this thought in the cleaning process; I don't hear many designers talking about that. Camden: You'll see a group of four or five supercaps right next to four or five QFNs. You a disruption of the water flow where it can't get repeatably underneath those QFNs, which are already hard to clean. So, those types of things just aren't thought of. This is the circuit that needs to go on, but when you look at the placements—that's something that needs to be thought of if you're going to clean your boards. Solis: Layout is extremely important. Here's an example. There are QFNs very close to plated through-hole. Now, in our analysis, we were able to detect the through-hole flux that's flowing underneath the via under the QFN. Because the organic acids are so different in the surface mount versus the through-hole flux, we were able to detect and verify that they are getting cross contamination from the through- hole process into the surface-mount QFN. Shaughnessy: That's interesting. I am sure people will be surprised to read that because I really don't think they put a whole lot of effort into designing for cleaning. Barry Matties: You guys focus on reliability, training, process audits. What typical problems you encounter in your audits as you go into these facilities? Solis: There's one interesting thing that pops out on, let's say, a few times that I have walked the line: the conception that brush cleaning for solder balls is a positive, a value-added step. I've seen operators dry brushing at the flux in the final architectures. They are taking large paint brushes and dipping them in bowls of alcohol. The problem with that is the flux that is already benign, just because it had the look that there's a little residue there, they start scrubbing it, and they have no idea that they are breaking down and solubilizing fluxes. We call it contamination relocation. They are making it much worse, but it is perceived that alcohol cleans things, that alcohol dissolves things. But they just relocate what was good flux, now they basically shove it to the nearest surface mount architecture, so now you have collateral contamination. Camden: The spot you are working on is clean, and then half-an-inch square around it is extremely dirty. Solis: Now, you have a super concentration of flux and resin from weeks and weeks, or days and days, of dipping it back and forth, and now they are spreading it on clean boards. Matties: Why is this a prevalent problem? Solis: I think a lot of people can't get to the thought of no-clean, and they just accept that it is a blanket term. In many factories, a lot of engineers really don't understand what no-clean really is and how it behaves. Often, they don't even go back and ask their flux suppliers on how they can learn more about this. Camden: The problem is it is not a repeatable process. If you have a hundred boards and they all fail in the same manner a hundred times, that's an easy thing to diagnose. When you are looking at rework or repair, they are not part of standard assembly operations, and they aren't usually documented in the same manner. It's really because rework is not always a repeatable process, and because you are not doing touch up on 100% of boards. Operator A may be doing a perfect job every time; Operator B may not be doing a perfect job every time; so, of the hundreds of boards that are touched up, even out of those, only a small percentage of failures will have that as the root