Tin whiskers are one of the headaches of the soldering world. In a word, they stink.
At least, that’s one takeaway I got from Graham Naisbitt’s presentation during IPC/SMTA High-Reliability Cleaning and Conformal Coating Conference. Naisbitt didn’t really say tin whiskers stink — rather he explained that many people try to reduce the likelihood of tin whiskers using a test with a sweet-smelling acronym, ROSE.
Actually, he doesn’t think that the resistivity of solvent extract (ROSE) test really works in this context. “It’s wrongly referred to as a cleanliness test. But it’s designed to measure soluble ionic content, which can be a contributor to tin whiskers,” said Naisbitt, who works at Gen3 Systems Limited.
Instead, he proposed using process ionic contamination testing (PICT). PICT starts with a mixture of isopropyl alcohol and deionized water to determine the extent of contaminants on the board.
PICT’s real value is that it focuses on process control. This helps ensure that the same contaminants are removed every time. That’s far more reliable and repeatable than attempting to prove cleanliness, which requires the difficult task of ensuring that all possible contaminants are removed.
Naisbitt presented details on testing techniques that can help prevent ionic contamination from providing a base for tin whiskers, making his case that PICT should replace ROSE. He closed his talk with a question that caused a moment of pause before drawing a collective groan: Is a ROSE still a ROSE when it’s PICT?