Issue link: https://iconnect007.uberflip.com/i/1293772
82 SMT007 MAGAZINE I OCTOBER 2020 levels are now present in the other two areas. Performing localized cleanliness testing was key to shining light on those "shadows." The chemical signature shows that the flux uses a weak organic acid, and at these levels in the PTH/capacitor, areas are at an increased risk of electrical leakage or even dendrite growth. This same board was put through an inline wash process, and the second set of IC data shows acceptable levels of ionics across the board. A large batch of boards processed like this had to be recovery cleaned before shipping to the customer because of that increased reli- ability risk. It's what we had to do to get that darn teenager off the porch. This method of localized cleaning is like running your vacuum without a bag, or you could also say contami- nation relocation. Please say it as a matter of fact. It's my "Git-r-done," if you will. The simi- larities stop there. The good news is there is a simple way to enhance this same basic cleaning method while reducing the spread of IPA and solu- bilized residues onto neighboring compo- nents. Instead of dipping the end of the acid brush into a bottle, soak a lab wipe with IPA and then place that wipe over the area that needs to be cleaned. Then, you use the brush on top of that wipe to clean as normal (Figure 2). The wipe will absorb the flux/ solvent mixture (Figure 3), not allowing the solution to transfer to neighboring compo- nents and become a potential risk for electri- cal leakage in the field. The wipe is then simply discarded. It's important that a new wipe is used for each individual cleaning process. A wipe or brush will collect residue over time, so using a new wipe eliminates cross-contamination. As with any assembly process, you need to create objective evidence that the process is effective using some sort of cleanliness or environmen- tal exposure testing. Conclusion It might be close to Halloween, but there isn't any reason to be afraid of what your cleaning process is doing to reliability if you shine enough light on the process. And should teenagers try and haunt your porch this year, give them full-size candy bars instead of a has- sle. Everyone likes candy. SMT007 Eric Camden is a lead investigator at Foresite Inc. To read past columns or contact Camden, click here. Figure 2: Lab wipe and brush. Figure 3: Lab wipe after localized cleaning.