Measuring the Cleanliness of Electronics With A Single Number
For years, the electronics industry has been looking for a single number that indicates the cleanliness of electronics. That number was thought to be the equivalent concentration of NaCl, a result of ROSE testing specified in MIL and IPC standards - a number that has been widely used and trusted.
But ROSE test results have not been shown to correlate with reliability in the field. The results are a gross process indicator, at best.
The shortcomings of bulk resistivity cleanliness testing such as ROSE can be problematic. Two major shortcomings of ROSE testing are:
The result represents an average cleanliness value for all surfaces of the sample. But contaminants aren’t usually evenly distributed across all areas of electronics, and often, there are higher spot concentrations in product areas that are critical to performance and reliability.
The result is a measurement of the change in resistivity of the test equipment’s solution volume. This dilutes any contaminants and only indicates changes in conductivity - not corrosiveness.
Because of these shortcomings, we’ve commonly heard statements such as this: “my product passed cleanliness testing but failed in the field. Why?” These shortcomings were major drivers that led Foresite to develop the C3 Critical Cleanliness Control®.
The current generation of C3, the C3/C.I., utilizes a new, single, cleanliness number – the C3 Corrosivity Index™ (C.I.).
The C3/C.I. calculates and displays the C.I. value for the present test and the C.I. pass/fail limit for the programmed test parameters in use. Thus, a single cleanliness value for the selected, critical, localized, electronics area of interest is generated and can be graphed on the C3 display for a selected group of tests, over a selected time period.
The C.I. facilitates SPC (statistical process control), showing any trending in product cleanliness, a major factor in product reliability. A high C.I. value or an increase in the C.I. over time can indicate a process that is out of control or is headed that way.