Issue link: https://iconnect007.uberflip.com/i/1526114
SEPTEMBER 2024 I SMT007 MAGAZINE 13 Murling: Jetting is normally faster than dis- pensing, and you can normally jet smaller and more consistent solder paste deposits. Is that actually true? Lasky: If so, why would anybody want to dis- pense anymore? Murling: ink of jetting as the next genera- tion of dispensing. Dispensing is more widely understood point-to-point. It is important to realize that when I refer to these processes, it is in the context of dispensing or jetting solder pastes. ere are other materials that require this technology, such as underfills, epoxies, adhesives, etc. As I mentioned earlier, jetting can process a full circuit board; however, it is slower than a printing operation. If you are one of the low- volume manufacturers where a single com- ponent could cost thousands of dollars, it may make sense to jet the board as opposed to printing it. is is where the economies of scale come into play. Quality manufactur- ing equipment is rarely cheap. Make sure you do your research so you are getting the right equipment for your manufacturing. What needs to be done with solder formulation to support printing vs. dispensing vs. jetting? Murling: On the formulation side, we defi- nitely need to consider it. On the Mycronic head, for example, there's normally some type of heat applied to lower the overall viscosity so the solder can be shot through the air and deposited appropriately. Flux is reactive to heat, so it takes careful consideration when exposing solder-based flux to heat for a long time. Developing a flux chemistry that can handle these process chal- lenges is an important design consideration. Powder size is also a large consideration. e finer the needle or the final orifice for jetting, the finer the powder must be. is is to make sure that the solder is homogenous through- out the entire syringe, as well as being compat- ible with the other solders you're using on your board. ese are all constraints we take into consideration while developing solder pastes. If you're picking a different formulation for the different dispensing approaches, happen to use different methods when prototyping, and then move into production with a differ- ent application method, how much of a consideration is that? Does the design team need to specify it? Murling: From a reliability perspective, flux normally defaults to IPC-J-STD-004C—SIR and ECM testing are the current industry stan- dard tests to determine reliability of flux res- idues, whether that's reliability with that sol- der paste alone or in combination with other materials. is testing is used commonly for no-clean formulas because they are intended to be le on the PCB post-reflow. We do see SIR requests for water-soluble formulas that are intended to be cleaned post-reflow, so this testing really verifies your cleaning process. Really, how clean is clean? From a metallurgical reliability perspective, though, the user normally dictates the mission profile, which would determine the proper alloy choice. It is important to make sure that the alloy you are using in your dispensing and Dr. Ron Lasky