IPC - Association Connecting Electronics Industries
Scope
PurposeThese tests are used as process control tools@ they can be used to inspect printed wiring boards or printed wiring assemblies and determine if they conform to the monitoring level of the user??s performance specification. Bulk ionic cleanliness testing may be accomplished by measuring the ionizable surface contaminants extracted by the following three methods:1. Manual extraction method2. Dynamic extraction method3. Static extraction methodRestrictions Measurements of ionic conductivities do not differentiate between different ionic species. They simply measure conductivities (or resistivities) which can be related to amounts of ionic materials present in solution. There is no identification of the contribution to the total conductivity readings of any individual ionic species which may be present in the solution. For measurement of individual ionic species (type and level of residue) see IPC-TM-650@ Test Method 2.3.28@ Ionic Analysis of Circuit Boards@ Ion Chromatography Method.For simplicity@ amounts of ionic materials in solution can be expressed by a conductivity factor which is equivalent to the measured conductivity contributed by a known amount of a standard strongly ionized salt such as sodium chloride (NaCl). Ionic residues are therefore usually expressed as equivalents of sodium chloride in micrograms per unit surface area (?g NaCl Eq./cm2) of the sample. This does not imply that the contamination is NaCl but@ rather@ it exhibits a conductivity function which is equivalent to that of the expressed amount of sodium chloride if it were in solution instead of the ionic soil.These tests will not measure any surface ionic materials which are not brought into solution because of insolubility@ physical entrapment or inadequate exposure to the extracting solvent. Additionally@ non-ionic components of the soil will not be measured.Application Caution should be exercised in comparing results between different test equipment as well as the different test methods. These methods are applicable as quality control tools in evaluating the parameters of materials and cleaning process@ in terms of how they affect the final cleanliness of the board or assembly. As process control tools@ they can be used to inspect printed wiring boards or printed wiring assemblies and determine if they conform to the requirements of the user??s performance specification. It is important to understand@ no calculation factor can exist to convert data from one style of commercial tester to another due to the great differences in system responses. See IPC-TR-583. This means it is very difficult to compare data from different machines.These procedures can also be used to assist in-process development as general residue indicators@ to evaluate flux cleanability@ solvent efficiency and general improvements of process parameters.?