FAQ Search

Q.  After Cleaning a PCB, How Do I Analyze, Measure or Track Cleaning Results and Product Reliability?

It is very hard to determine how clean is clean enough.  Everybody's boards are different, everybody's materials of construction are different, everybody's product expectations are different.  So you need to think long and hard about what is the best measure of cleanliness for your output.

That being said, there are three common ways to check for cleanliness. The first is a simple visual inspection – if there are no visible flux materials and no white residues, most people just call it “clean enough.” Not very sophisticated, but it works.

At the other end of the scale is Surface Insulation Resistance testing. A full SIR test takes 28 days, a big machine and serious system calibration; one of the industry leaders is Thermotron. Most users simply farm out the test to a research lab. The result of an SIR test is a measure of the resistance of electrical flow across the traces on a PCB caused by conductive contamination, such as the ionics from fluxes. High resistance is good and means the board is clean.

A less precise but faster and far more user-friendly measurement of cleanliness is ionograph testing. This process requires the board to be immersed in a bath of deionized water for 15 minutes or so. After the water has had a few moments to circulate around the components, the water automatically is tested for ionic contamination. Since the DI water will dissolve ionics from the boards, any change in resistivity of the water would indicate the relative dirtiness or cleanliness of the board. The Omegameter 600SMD probably is the industry standard for ionic testing. The system provides an accurate, repeatable and rapid method for determining cleanliness and complies with industrial specifications including MIL-STD-2000A, IPC-TM-650 and ANSI/J-STD-001B. A quick Google search or a visit to TechNet will help clarify these options.

Released 9/8/2008