It was determined in a screening study that some currently available cleaning formulations did not completely remove flux residues from lead-free solders in post-solder defluxing proce ;ses. Additional work has been initiated using two no-clean flux formulations with a conventional tin/lead eutectic solder paste as a baseline. Reflowed boards were cleaned using a variety of different chemistries and processes, and cleanliness after defluxing was assessed by J-STD-001B SIR and ionic contamination testing. Ionic contamination is found to be a much more effective criterion than SIR when dealing with no-clean solder paste systems. Results indicate that higher reflow temperature results in a poorer cleaning efficiency, obviously due to the greater extent of residue charring. The deterioration of cleaning efficiency accelerates with increasing temperature. The cleaning efficiency of the lead-free system is poorer than the SnPb system, due to higher reflow temperature, higher activity of tin, and more complicated flux chemistry of lead-free flux system. Overall, the semi-aqueous cleaning system is, quantitatively, the most efficient cleaning chemistry, followed in order by the neutral pH aqueous system, the saponified aqueous system, and a co-solvent vapor degreasing system. For Pb-free cleaning, he semi-aqueous chemistry is the only effective cleaning chemistry of those tested. Overall, the centrifugal process was the most efficient, followed in order by spray-in-air (batch), spray-in-air (in-line), and vapor degreasing. However, the ranking of process efficiency may be affected by the cleaner concentration and cleaning tims factors. In the former case, a higher cleaner concentration is observed to be associated with higher cleaning eff ciency as well, thus contributing to the ranking of process efficiency. For Pb-free cleaning, the ranking of processes becomes batch spray > in-line spray > centrifugal > vapor degreasing. The cleaning process is not as critical as cleaning chemistry, and the semi-aqueous cleaner is superior in cleaning efficiency when dealing with Pb-free cleaning. Also, based upon visual observations alone, the aqueous saponifier with in-line spray-in-air process and co-sohent vapor degreasing process were the only two chemistry/process combinations that resulted in boards that appeared completely clean for each paste at each reflow profile.
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