Peebos In essence, the purpose of measuring resistivity in your cleaning process is to maintain quality in your manufacturing process. Electronic circuit assemblies that have ionic contaminants (salts such as tin,lead, copper and finger etc..) on their surfaces may become somewhat unreliable particularly when exposed to condensation or high humidity. Why? Because water dissolves salt and salt is conductive, so your electronic circuit may behave in a somewhat unintended and unpredictable way. If the resistivity meter on your cleaner is reading low values, say less than 0.1 megohm, then you may have dirty assemblies; whereas if the reading is greater than 1 megohm, then you will be likely to have cleaner and therefore perhaps, more reliable assemblies. The current ANSI / IPC- J-STD-001 manufacturing standard, uses resistivity measurements to help control your process. It refers to a maximum recommended limit of 1.5 microgrammes per square centimetre (10.06 microgrammes / square inch) sodium chloride equivalence on your assembly. This measurement comes about from taking a reading of test solution resistivity before and after the test and then extrapolating this result and by calculation express it as a measure of salt (ionic) contamination. To get a much more thorough explanation of this, get a copy of the above spec and IPC-TM-650. There are some questions that you should consider, e.g.: Suppose some of my assemblies have much more flux residues than others, will they all be cleaned to the same level? You really need to "cleanliness test" individual assemblies because you have only measured the rinse water resistivity and maybe the rogue assembly got through the process before the cleaner had got hold of those nasty residues. So if I clean to 10.06 megohms / inch2 I am OK? Not necessarily. By definition, the spec is saying it is acceptable to leave UP TO 10.06 microgrammes of salt on every square inch but if you are into fine line - fine pitch, sophisticated packages, COB, BGA etc., and working in a hostile environment, then this level will almost certainly be too high. Hope this helps and if you want more, let me know Best regards Graham Naisbitt ---------------------------------------------------------------------------- ---------------------------------------------------------------------------- ----- [log in to unmask] Concoat Ltd Alasan House, Albany Park Camberley GU15 2PL UK Application Engineers in Chemical Compounds to the Electronics Industry -----Original Message----- From: Peebos <[log in to unmask]> To: [log in to unmask] <[log in to unmask]>