Electromigration vs SIR

Abstract

The IPC‐SF‐818 surface insulation resistance (SIR) test data taken with the use of a variety of halide‐free, no‐clean fluxes are analysed against Bellcore TR‐NWT‐000078 electromigration (EM) test data. Neither test results show correlation with bulk flux resistivity, flux water extract resistivity, flux residue moisture pick‐up, and flux corrosivity without bias. However, in the case of rosin fluxes, the insulation resistance behaviour in both SIR and EM tests is a function of the pH value of fluxes. This phenomenon is more significant in the SIR test. In the case of low‐residue, no‐clean fluxes, only the SIR test displays such a pH dependent relationship. Data suggest that the 50 volts bias voltage used in the SIR test may be responsible for this, and can be explained with a high‐bias‐voltage‐induced electrolysis mechanism which is further promoted by a high pH environment. This failure mechanism is absent in the EM test which utilises 10 volts bias voltage, and probably will not occur under the normal 5 volts application conditions. Overall, the SIR test seems to be more stringent while the EM test appears to be more realistic.