The cleaning strength or solvency of non-aqueous cleaners usually is measured by an industry benchmark called the Kari-Butanol test. In the Kari-Butanol lab test, a standardized test material called butanol — a thick, rubbery, eraser-like gum — is immersed in the solvent for a certain period of time under controlled conditions (e.g., temperatures, pressures, etc.). The lab technician then measures the remaining gum to determine the quantity of material that was dissolved by the solvent. It’s simple, fast and easy.

TriggerGrip™ system being used with a strong solvent to clean a PCB
TriggerGrip™ system being used with a strong solvent to clean a PCB

The result of the test is an index called the Kari-Butanol value. This is usually reported on MicroCare product spec sheets as “Kb value.” A higher Kb value is better and means the cleaner is more aggressive or active. Mild cleaners have low scores in the tens and twenties; powerful cleaners like the old chlorinated solvents have ratings in the low hundreds. Soft, mild MicroCare cleaners like the Alcohol-Enhanced Flux Remover – ProClean™ have Kb values in the mid-30s. Stronger cleaners, like the Heavy Duty Flux Remover – SuprClean™, will have values of 75-130.

Special Note: You cannot compute a Kb value for a water-based cleaner, and you cannot compute a pH value for a solvent cleaner. Aqueous cleaners are profiled using the pH test for acidity or alkalinity. Different chemistries require different tools.

The Kari-Butanol process is an old test and is well-suited to old-style industrial cleaners. In the old days, using a Kb value to compare the old industrial cleaners like methylene chloride, perc, TCA and trike made sense because of the types of parts which were being cleaned (big) and the types of contamination they were trying to remove (crude). There also was another trade-off from these strong solvents — they often had compatibility problems with plastics and other components. But today’s world is different. None of those old-style solvents are used today in any precision cleaning application. Even more importantly, very few people are trying to remove heavy, rubbery gunk — at least, not from a PCB, a medical device, the Space Shuttle or some ultra-small BGA chip. So the Kb test is somewhat obsolete.

In the place of the Kari-Butanol test most engineers are substituting systematic testing procedures, rigorously testing solvents on their components, their contamination and their cleaning processes. This makes sense because it’s a test of real-world conditions. Often, the results are unexpected: the relatively mild Vertrel® solvents clean as well as or even better than cleaners with much higher Kb values. Informally, we call these surprising results “operational Kb values.” In these real-world cleaning of oils and fluxes, many MicroCare solvents clean much more effectively than the Kari-Butanol test would suggest while maintaining excellent materials compatibility.

Don’t be concerned if your favorite MicroCare solvent has a moderately low Kb value. We’ve tested the cleaners and they work great. Give them a try. For precision cleaning applications, MicroCare products are your best choice.

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