Issue link: https://iconnect007.uberflip.com/i/1207026
86 SMT007 MAGAZINE I FEBRUARY 2020 nent. It causes challenges with the solder beading performance, or tombstoning occur- rences might increase. There are still some corners that people try to cut to save a little bit of cost, which could open up major cost impli- cations on the back end with rework. Shaughnessy: What advice would you give to designers and the EEs upfront other than com- municating with you earlier? Nash: It's not just communicating early; it's also about communication throughout because the manufacturing engineers are the ones deal- ing with the problems in real-time. They come back to the suppliers and say, "We have chal- lenges with this. We can't fix it with the current material. What else do you have?" Then, we try to work with them on both the material and process improvements to eliminate the issue. But if you redesigned your pads for these com- ponents, you wouldn't have the problems with this current solder paste that you're using. The ideal scenario would be a continuous conver- sation, or regular meetings, between the man- ufacturing engineers, design for manufacturing engineers, and design engineers. Happy Holden: I noticed in our reporting of the CES Show that more and more consumer prod- ucts are wearables, which requires high-den- sity circuit boards. Is assembling products like that the same type of challenge as packaging or SiP assembly? Nash: The technology around SiP assembly and heterogeneous integration is what people are calling higher-density circuit board manu- facturing. For example, they might be trying to put a Wi-Fi and Bluetooth module into one package, and that will help with the circuit board density. Before, you might have had two separate packages doing the same thing as the SiP would do. However, they're also trying to generalize these technologies and make them more cookie-cutter, as well as customizable, so that you can take three or four different things and plug it into one, but those three or four dif- ferent things are standardized. One customer might put two in one, and another customer might put five in one package, but the ability to do that is there. That way, you can put a lot more stuff on, including four or five different SiP packages on the same circuit board in half the footprint. Holden: Does it take specialized solder paste if you're going to embed the component inside the circuit board where it's going to go through lamination and even later surface assembly? Nash: If you think about it from a packaging standpoint or SiP, for instance, you use the sol- der paste to build a mini circuit board, and then you use some sort of molding compound to mold over the package to protect it for a number of different reasons, whether it's pro- prietary or environmental. Some flux technology has to be compatible with the over-mold, or people clean off the flux residue to eliminate the compatibility uncer- tainty altogether. The majority of people build- ing SiP over-mold the package, but most of them use either a water-soluble flux vehicle in a solder paste where they can clean it with DI water or a no-clean material and a solvent- based cleaner. The same holds true for any coating materials or encapsulation materials, whether it's a pot- ting compound, conformal coating compound, or molding compound. You need to do your due diligence up front and make sure if you are going to leave the solder paste flux residue behind, that you have some knowledge that the materials are going to be compatible. In other words, the conformal coating or molding com- pounds are going to be compatible, electrically and/or mechanically (adhesion) with the no- clean flux residue that's already present. Again, the same holds true for the circuit board. Is the solder mask compatible with the molding, compound, conformal coating compound, etc.? Matties: This has been very helpful, Chris. We appreciate your time. Nash: Thank you. SMT007