Issue link: https://iconnect007.uberflip.com/i/1389320
40 SMT007 MAGAZINE I JULY 2021 use either an alternative solvent or water-solu- ble fluxes and pastes for cleaning or to move on to a "no-clean" process by using low residue or no-clean fluxes and pastes. Current technology using no-clean or low- residue fluxes is eliminating the need for clean- ing. However, the use of no-clean flux requires a clean work environment and a culture change that not only affects the user but their suppliers as well. In addition, the use of no-clean fluxes may require a controlled soldering atmosphere to provide a process window compatible with their lower activity. e use of no-clean fluxes is increasing due to the environmental concerns of using fluxes that require cleaning and the disposal of used solvents containing lead. But we also need to keep in mind that no-clean flux is not as active as other types of flux and hence the soldering results may be less than desired unless ade- quate steps are taken not only internally at the company but also by component and board suppliers. Conclusion No matter what fluxes, cleaning materials, or processes are used, they all need to meet the same requirements. When using more active fluxes, cleaning should be done with appropri- ate solvents to remove any contaminants that can cause field failures due to dendritic growth and corrosion. But how do you know when it is clean enough? If you asked a similar question about solder joints causing reliability prob- lems in the field, it would be easier to answer because the accept/reject criteria in J-STD- 001 and IPC 610 is well established. But it is not that simple when it comes to deciding how clean is clean even though the requirements are established in these two standards. We will discuss cleaning requirements in our next col- umn. Stay tuned. SMT007 Ray Prasad is the president of Ray Prasad Consultancy Group and author of the textbook Sur- face Mount Technology: Princi- ples and Practice. Prasad is also an inductee to the IPC Hall of Fame—the highest honor in the electronics industry—and has decades of experi- ence in all areas of SMT, including his leadership roles implementing SMT at Boeing and Intel; help- ing OEM and EMS clients across the globe set up strong, internal, self-sustaining SMT infrastructure; and teaching on-site, in-depth SMT classes. He can be reached at smtsolver@rayprasasd.com and reg- ularly offers in-depth SMT classes. Details about classes can be found at rayprasad.com. To read past columns or contact Prasad, click here. Table 2: Cleaning solvents for different types of fluxes. (Source: Ray Prasad, Surface Mount Technology, Principles and Practice, 2nd Edition, Table 13.5)