Declan. I copied the next text from the EMPF home page which you can find at:(I hope that is OK Toni) http://empf.arl.psu.edu/products/is4000/ You have to access this home page to be able to see the graphics and more interesting features of this equipment. Anyone considering Statistical Process Control of Solder Paste System should check this out. If you need further information contact Michael Frederickson Phone: (317) 655-EMPF(3673), Fax: (317) 655-3699 [log in to unmask] Alex Basauri Statistical Process Control of Solder Paste System Courtesy of Alpha Metals Manufacturers who monitor solder paste characteristics during surface mount circuit assembly procedures are ultimately concerned with obtaining a high yield of reliable solder joints. The solderability of a given paste system under reflow conditions is, at present, not measured directly using any one given technique. An existing quality control test for paste includes the measurement of viscosity as a means of establishing the thixotropic behavior required for printability. In addition, the issue of solderability is addressed most directly via the solder ball test, reflecting the level of oxidation of the powder in the paste, and the wetting test, which acts as a barometer for the ability of the flux to create a solderable surface. However, none of these tests can monitor paste viability in-situ within the flow of manufacturing. As an alternative, the evaluation of solder pastes using AC impedance measurements has been found to be feasible in studies conducted at Marquette University and the EMPF. The use of impedance techniques to characterize material properties is widespread. It consists of the application of a small-signal voltage of varying AC frequency to a given material through suitable electrodes. The resulting current flow is then measured, and the impedance is determined as the ratio of the applied voltage to the measured current at each frequency. Such data is quite useful for materials comprised of regions of differing electrical behavior, as is the case for solder paste because each region will impede current in a manner that will predominate only over a given frequency interval. When the impedance is plotted, per Figure 1, a spectra is observed which is derived from these current-limiting attributes (microstructural and/or chemical reactio n-based). Figure 1 Further, these attributes can be accentuated using different probe configurations (2, 3, or 4 probes). Each of these impedance mechanisms is interpreted as an appropriate combination of resistors and capacitors, and the entire material is represented as an equivalent circuit. Once obtained, this circuit, as seen in Figure 2, delineates the microscopic electrical nature of the paste and acts as a reference model against which the degradation of paste viability in manufacturing can be judged. Figure 2 Alex Basauri [log in to unmask] Trimble Navigation LTD The GPS Solution!! 645 N. Mary Avenue B6 Sunnyvale, CA 94086 (408) 481-8751 (408) 481-6077 Fx *************************************************************************** * TechNet mail list is provided as a service by IPC using SmartList v3.05 * *************************************************************************** * To unsubscribe from this list at any time, send a message to: * * [log in to unmask] with <subject: unsubscribe> and no text. * *************************************************************************** *************************************************************************** * TechNet mail list is provided as a service by IPC using SmartList v3.05 * *************************************************************************** * To unsubscribe from this list at any time, send a message to: * * [log in to unmask] with <subject: unsubscribe> and no text. * ***************************************************************************