Can Age and Storage Conditions Affect the SIR Performance of a No-Clean Solder Paste Flux Residue?

摘要

The SMT assembly world, especially within the commercial electronics realm, is dominated by no-clean solder paste technology. A solder paste flux residue that does not require removal is very attractive in a competitive world where every penny of assembly cost counts. One important aspect of the reliability of assembled devices is the nature of the no-clean solder paste flux residue. Most people in this field understand the importance of having a process that renders the solder paste flux residue as benign and inert as possible, thereby ensuring electrical reliability. But, of all the factors that play into the electrical reliability of the solder paste flux residue, is there any impact made by the age of the solder paste and how it was stored? This paper uses J-STD-004B SIR (Surface Insulation Resistance) testing to examine this question. Two commercially available SAC305, Type 4, no-clean solder pastes—one with a ROL0 and the other with a ROL1 J-STD-004B classification—were subjected to two different storage conditions (room temperature and refrigeration) and aged for varying lengths of time. After aging, the solder pastes were printed and reflowed using the same common reflow profile and then submitted to SIR testing to see what, if any, difference could be detected in their SIR performances. The reason for testing both a ROL0 and a ROL1 was to see if differences in chemistry could have an impact on how a solder paste ages relative to SIR performance.