Attended Six Sigma BB Certification classes, but didn't got certificate– how to mention this on resume?

I have Attended Six Sigma Black Belt Certification Classes, but didn’t got Certificate, due to meet tough targets and deadlines demands of my Job at that time. Now can some gentleman tell me that how can i positively just mention Six Sigma process knowledge only, and avoid being asked about certificate on demand. Or else how can i just mention SSBB knowledge in an impressive why, while i don’t have certificate?