The Institute for Interconnecting and Packaging Electronic Circuits Number 2215Sanders Road·Northbrook,IL60062-6135 2.3.26 Subject IPC lonizable Detection of Surface Contaminants (Dynamic Method) Date Revision 11/94 IPC-TM-650 A Originating Task Group TEST METHODS MANUAL lonic Conductivity (5-32a) 1.0 Scope with an initial conductivity of about 0.1 micromhos (10 megohms). 1.1 Purpose This test method establishes a procedure for Water/alcohol systems are used when nonpolar soils might determining the amount of surface ionic soil on a printed board or printed board assembly. The soil must be soluble in Various alcohols have been used successfully. The preferred water, alcohol or some mixture of both. The determination can systems use either N-propanol or isopropanol as the alcohol be made on either a quantitative or a qualitative basis. solvent. Because of the high dielectric constant of the alco- hols, excessive alcohol in the mixture will generally degrade 1.2 Restrictions The equipment used does not differenti- the sensitivity of the measurement. To obtain maximum sen- ate between specific ionic specie. It determines their presence sitivity and to insure sufficient alcohol to readily remove all and ranks them according to their ionic mobilities. Salts with nonpolar residue, the recommended mixtures are 40% (by higher ionic mobilities are weighed heavier than salts with volume) N- propanol and 60% water or 50% (by volume) iso lower ionic mobilities. propanol and 50% water. Mixtures with as high as 75% by volume is isopropanol havebeensuccessfully used. 1.3 Application This method has application as a quality control tool and as a method for developing and evaluating 5.2 calibration Once the fluid in the system has estab- cleaning process parameters.As a quality control tool, it can lished a stable level of conductivity,aprecise quantity of cali- be used to inspect parts to determine if they conform to pre- bration solution is injected into the test solution. The system determined levels of cleanliness. In process development this then integrates the variables of test solution conductivity: procedure can be used to evaluate solvent and process effi- pumping rate, sample area and time into a contamination level ciency and also to set levels of acceptable cleanliness. specified as equivalent micrograms of sodium chloride (per sq.) of the sample. 2.0 Applicable Documents None 5.3Testing Once the system has been calibrated in accor- 3.0 Test Specimen Any preproduction or production bare dance with 5.2, the test specimen is immersed in the sample printed board or printed board assembly. tank. Care must be taken not to handle the sample or any of the appliances used to insert it into the tank. Finger dirt con- 4.oTestEquipmentAdynamic measurementdevice tains highly mobile ionic soils and may give spurious readings. which extracts the ions from the surface being measured and During the course of the measurement, the conductivity of the checks conductivity of a rinse solution. Solvent is pumped through a recirculating loop which includes a plastic tank, solution will depart from the baseline of conductivity and then gradually return. When it has returned to the baseline, no conductivity cell and ion exchange column to remove all additional soil can be removed and the measurement is com- traces of ions from the solvent before entering the tank. The plete. conductivity cell used is temperature compensated to avoid reading variations caused bytemperature changes.Ameter- The curve for that sample is then integrated as per section 5.2 ing pump pumps the solution through the loop at a constant and the calibration curve is used to determine the amount of rate. A recorder is used to follow the change of conductivity contamination on the part. with time. (See notes). 5.4 Evaluation Without a sample in the tank, a condition 5.0Procedure will be established in which the conductivity of the solvent, as measured by the conductivity cell, will atta