-- [ From: michael carano * EMC.Ver #2.10P ] -- HELLO NANCY, THE THICKNESS RANGE OF MOST OSP FORMULATIONS ARE IN THE RANGE OF.12-.35 MICRONS. THIS THICKNESS RANGE GENERALLY PROVIDES SUFFUCIENT PROTECTION. PLEASE NOTE , HOWEVER, THAT THE THINNER THE OSP DOES NOT NECESSARILY MEAN THE LEAST IN SOLDERABILITY PROTECTION. AS FAR AS TESTING THE THICKNESS, I AM MOST FAMILIAR WITH AN ORGANIC ACID DISSOLUTION TEST WHERE YOU DISSOLVE THE COATING OF OFF A COUPON A COLLECT THE FLUID. THEN, A UV-VIS METHOD IS EMPLOYED AGAINST A STANDARD AND THE THICKNESS IS DETERMINED FROM THAT. LET ME KNOW IF YOU NEED FURTHER INFOMATION.