Issue link: https://iconnect007.uberflip.com/i/1207026
FEBRUARY 2020 I SMT007 MAGAZINE 81 After that, you have to con- sider the pick-and-place pro- cess and how the components would be placed, including if there's skewing of the compo- nents or if the placement pres- sure is too great or not enough; all of that can affect how the material is going to reflow. Then, you would focus on the reflow process. You have to optimize each process sepa- rately. You can't look at just one process and say, "Print- ing is great, so we're good to go." It's not going to work well for you if you ignore one or more parts of the manufacturing process. The placement has the least number of eyes on it from a solder paste standpoint, but it comes into play when you're talking about miniaturization and small components. Matties: We have heard that there are now more opens than bridges because people aren't put- ting enough paste down. When your custom- ers are working in fine pitch and high density, are they doing an inspection process before- hand? Nash: With mobile and automotive manufac- turing—or any type of circuit board manufac- turing, for that matter—most people implement SPI into their process. It's a piece of equipment that could save you costly rework and ensure that you have process optimization on the print- ing side of things. In my career at Indium Cor- poration, I've heard a couple of different per- centages—anywhere from 60% to 98%. I don't know what the true number is, and I don't know of a study that's been done on this, but the majority of defects at the end of the line can be the result of printing process errors. Matties: Rectify it before it becomes waste. Nash: That's exactly why a lot of people are putting SPI equipment into their lines to try to optimize the printing process to avoid defects at the end of the line and costly repairs. It is an important step toward cost reduction. In many cases, people look solely at the cost of the solder paste, but they forget that total cost includes the cost of materials, manufacturing, and rework. Matties: The cost of a recall is extraordinarily high. An open may not be something that affects the whole line, but it can be catastrophic; in some cases, human life is at risk. Nash: That's an important note to make. What's the cost of a failure in the field? You don't want something like that to happen because that's usually in the millions of dollars when it could have been corrected by optimizing your pro- cess and choosing a material that is optimal for your assembly rather than basing the material decision solely on cost. Matties: And traceability is getting easier and easier as time goes by as well, so liability trick- les down the supply chain. Nash: The other important thing to mention regarding miniaturization is Z miniaturiza- tion as well. Many people are trying to pack circuit board designs into a thinner package. If you look at cellphones from 2000 to 2020, they have gotten thinner. Cavity printing was a topic a few years ago. People are doing that, but many are doing stuff in cavities with jetting materials or dispensing materials rather than printing processes. Z-axis is also going to be more challenging because you have to heat the flux properly. You don't want an unactivated flux underneath the component, which could cause a catalyst for dendritic growth formation. Designing materials that have electrical, ther- mal, and mechanical reliability is important. Matties: What advice do you give companies from the outset before they move into this type of technology? Chris Nash