“No-Clean” Flux Residues Detection With Impedance Measurements

The no-clean flux-residues pose a high-reliability risk, thus controlled strictly in the modern electronics assembly industry. A series of customized surface insulation resistance (SIR) experiments and ac impedance analysis under various test patterns demonstrate the dramatic impact of the partial activation of the fluxes unevaporated solvents, and non-decomposed activators on the reliability of the final assembly. Although the mainstream no-clean pastes and liquid fluxes are qualified under all the standard SIR and electrochemical migration (ECM) reliability tests, the solder mask-filled SIR patterns are more realistic and the test results more accurate. The spaces are filled with solder masks; thus, the ionic migration analysis is more complex. From this perspective, we demonstrate a thorough examination of these more realistic structures with the classic dc SIR method and ac impedance measurements. This study examined the impact of no-clean flux residues on capacitance and resistance in the case of solder mask-filled comb patterns.