Casimir: Resistivity of Solvent Extract (ROSE) testers measure ionic contamination by washing boards with a DI water/IPA solution. (No-clean people: Stop and go on to something else.) The testers are process control instruments used to monitor a relative contamination (cleanliness) level, established as a comparison with a quality baseline. ROSE testers can be dynamic or static. EMPF studied Rose testing and testers ("An In-Depth Look At Ionic Cleanliness Testing," RR0013, August 1993) and found the dynamic to be more accurate.
Most testers measure resistivity, rather than conductivity. The concentration of ionized material varies linearly with the conductivity of a solution, where the resistivity of the solution is non-linear.
DYNAMIC TESTERS: Ionograph and Zero-Ion measure the resistivity of the solution leaving the test tank, deionize it, return it to the tank, and continue, until the solution resistivity returns to the initial baseline. The tester calculates dissolved contamination from the time versus resistivity sample curve. This approach depends on:
� Working the solution for long times at high conductivities where the CO2 absorption from the air highest and least predictable. � Ability of DI columns to remove all the ions in a single pass. � Instantaneous differentiation of ionic materials.
... possibly over-estimating the contamination level. Additionally, if set-up with a very high resistivity baseline, the test time can be very long and may end-up detecting ions from substrate materials and components, which have little to do with controlling assembly processes.
STATIC TESTERS: The Omega Meter, Contaminometer, among others measure the resistivity (or possibly conductivity) of the solution leaving the test tank, return it to the tank, and continue, until the resistivity (or conductivity) of the solution declines to a baseline. The tester calculates the accumulated ions in the solution. These testers are:
� Less sensitive to CO2 absorption than dynamic testers. � Generally, more accurate, except that - if the volume of solution was too small - there is a risk of saturation, resulting in a low reading. � Able to have lower test times. Some testers of this type: - Stop the test automatically when conductivity stops rising, reducing test time, rather than testing for a fixed time period. - Extrapolate (automatically by software ) with a reasonable accuracy to the end point, if a test has ended, but the conductivity is still rising.
Operators like Omega Meters
Our old, sadly departed (from SMTnet) friend Brian Ellis makes a static tester and talks about the differences between tester types on: http://www.protonique.com/psagraph/files/statdy.htm.
As the manufacturer of the Zero-Ion, I must correct one statement made by Dave F.
According to the EMPF report sited in Dave�s response, �Static� based systems actually are more susceptible to carbon Dioxide adsorption than �Dynamic� based systems.
Please allow me to quote directly from the EMPF Executive Summarry, page 1 paragraph 3.
�Carbon dioxide can dissolve in water to form carbonic acid. This can weakly ionize into H+ and HCO3- ions which can / will then affect ionic readings. The presence of this ionic build-up during a static extraction will contribute to the overall ionic reading. In most cases, such contributions will be small, representing only a small error in the measured results� The dynamic systems are continually deionizing the solvent, therefore removing the small amounts of CO2 before it has a chance to accumulate a measurable amount.�
Mike: I'm just glad I got away with the rest of the stuff I said. You are 100% correctamuno that the report said what you stated. I don't believe that the authors understood the process of absorbing CO2 in ionless water, nor the impact of that chemical reaction on resistivity metering. Further, the report makes a backhanded recognition of that by saying words to the effect that further testing is necessary to characterize the effects of CO2.