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ROSE (Resistivity Of Solvents Extracted) testing was developed in the 1960s as a quality assurance and process monitoring method and is still regularly used today. Unfortunately, profound changes in the processes and materials used in the electronic assembly industry have a significant impact on the usefulness of the test. This article will discuss what ROSE test results really mean and when they are—and more importantly, are not—useful.
What does the data mean?
ROSE testing is performed by submerging an entire electronic assembly into a solution of DI water and IPA (isopropyl alcohol). Results are given as µg/cm2 of NaCl equivalence and represents the amount of solulizable ionic contamination present on the entire assembly. The reading is derived by simply measuring the resisitivity of the solution over time; the test does not identify specific ions present.
Limitations in this test method have been realized as many current flux residues are not particularyly soluble in the test solution (the test was developed for wave-soldered through hole hardware soldered with RMA fluxes). Additionally, low component clearances make it difficult to remove and detect trapped ionic contamination.
When is it useful?
Depending on the complexity of the assembly and the materials used, the ROSE test method can still be a reasonably effective process monitoring tool. With an established baseline in place, ROSE testing can provide useful feedback if a process errata results in a change in cleanliness.
Is ROSE testing a good predictor of reliability?
Unfortunately, ROSE testing is not (and in our opinion, never really was) a good predictor of product reliability. With shrinking components and increased density, decreasing pitches, and ever expanding presence of high-sensitivity circuits, cleanliness is more important now than it has ever been. Foresite routinely links field failures to small pockets of localized contamination (e.g. no-clean flux is not fully heat-activated after wicking under a selective solder pallet) which simply can not be detected by fully submerging the assembly and averaging the results over the entire surface area of the board.
ROSE testing can still be useful in a limited manner as a process monitoring tool, but relying on a test developed over fifty years ago for determining cleanliness of wave-soldered through hole boards processed with RMA flux to predict reliability of current electronic assemblies is asking for trouble.