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MARCH 2019 I SMT007 MAGAZINE 107 ity of a product than a human with unfettered access to flux. If a part is difficult to solder, the answer is clearly more flux, right? While that may be technically correct, it's among the dumbest things in the history of electronics as- sembly. There are a couple of good ways to use flux for hand operations, and they are to use the flux that is part of the cored wire or tacky flux used mostly for BGA rework. When using a cored wire with the proper feed rate, any flux residues will be near benign. The reason for recommending tacky flux is the application is very controlled, and the risk of flux spread- ing to neighboring components is much lower than using a bottle of liquid flux. Flux spread to surrounding components is a killer to reli- ability because it will be as active as flux gets next to right out of the bottle. After some hand operations, there is a de- sire to clean any residues, which is another questionable operation. If it's no-clean flux and coating or RF issues are of no concern, just leave it in place. That's smart. If cleaning is required, it's very important to be mindful of where any effluent is being deposited. It's essential to effectively rinse the area that was just washed with IPA or some sort of solvent. Just be smart and see where all the effluent is draining. If that is under other components, they are now at an increased risk for electrical leakage. It's vital to use the right amount of flux and know where 100% of that is spread- ing, and if cleaning is part of the process, be sure it's effective and rinsed properly. The final part of the assembly process that needs to be considered, at least for this month, is packaging. The points to consider are proper handling and using clean ESD bags/trays for shipping. I have seen many facilities reuse ESD bags that can collect processing residues and general debris over time. They can also lose their ESD properties due to damage. The same goes for trays used anywhere in the process in- cluding moving station to station or packaging to be sent to the next supplier. Throughout all of the process steps I have mentioned, one more thing to think about is proper handling. Wearing gloves is essential, but knowing how to wear gloves is as im- portant as anything else. Gloves should be changed any time an operator wipes their face, touches raw flux, or rubs a saltlick for some reason. Contamination is easily transferred to the PCBA surface and will greatly increase the risk of electrical leakage or electrochemical migration-related issues in the field. It's smart to know how easily any assembly process can affect reliability. SMT007 Eric Camden is a lead investigator at Foresite Inc. To read past columns or contact Camden, click here. The second annual Real Time with… IPC APEX EXPO Show & Tell Magazine is a supplement to our other monthly magazines and brings you exclusive, in-depth coverage of the recent event. This year, we feature 150+ pages of great content including multiple event photo galleries, video interviews, attendees' thoughts, reviews from our guest contributors and I-Connect007 editors, interviews with award winners and other industry experts, and cover- age of the successful IPC STEM Student Outreach program. I-Connect007 Publishes Second Annual Show & Tell Magazine— All About IPC APEX EXPO 2019 Download magazine here.

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