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36 SMT007 MAGAZINE I MAY 2018 Article by Joe Russeau, PRECISION ANALYTICAL LABORATORY and Mark Northrup, IEC ELECTRONICS For decades now, the electronics indus- try has had a growing need to understand the impacts of chemical residues on PCB and PCBA reliability. Residues left from flux and other process chemistries can potentially lead to premature failure of assemblies once in the field. Understanding where such residues orig- inate and their impact on product function is paramount to mitigating product failures due to cleanliness issues. One tool that has been used for decades to evaluate printed board and assembly cleanliness has been the resistivity of solvent extract (ROSE) test. The ROSE test was developed in the early 1970s by the Naval Avionics Warfare Center in Indianapolis, Indiana. The early test used a squeeze bottle containing a solvent comprised of 75% 2-propanol and 25% deionized water (75/25). The surface of an assembly was rinsed with the 75/25 mixture and any material (e.g., flux) easily soluble in the mixture was dissolved and captured in a beaker. The resis- tivity of the captured solution was measured, and the result was expressed in terms of sodium chloride equivalents (NaCl eq.). Later versions of the test were automated and a 10.06 micro- gram (µg) of NaCl eq./in 2 (1.56 µg of NaCl eq./ cm2) limit was eventually ascribed to the test. That limit became enshrined in various mili- tary specifications, such as MIL-P-28809 and WS-6536 and eventually became the indus- try pass/fail standard. The limit persists today and is used across a wide base of material sets, from bare boards to assemblies to components. Over the last two to three years, there has been considerable discussion within various IPC committees about the role of the ROSE test in today's assembly environment. The transi- tion from predominantly water wash processes to "no clean" has meant the advent of very different flux compositions. The question has been posed—on numerous occasions, we might add—as to whether the ROSE test is still a viable option for evaluating PCB and PCBA cleanliness. There have essentially been two camps of thought on the subject: those who want to continue using the test and re-invent it as a process control tool and those that think the test has run its useful course. To update the test, IPC's J-STD-001 commit- tee commissioned a subgroup of users and subject matter experts to determine if there was a best-practices use that would bolster its continued application. Two conclusions

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