The density of platinum and palladium powders for thick film pastes

Abstract

Density is one of the key powder metal properties for materials such as platinum used extensively in the microelectronics industry for hybrid circuits and discrete devices. Of the three major density measurement systems typically used, reliance in the industry is usually on the Scott density and tap density methods. Because of the inate operator variability with the Scott approach contrasted to the excellent coefficient of variance achieved with the tap density method, the latter is preferred. While many precious metal powders can be adequately tested at 1,000 taps, platinum (and many flake materials) require extended taps (3,200 is often specified) to reach the ‘true’ apparent density. Smaller volumes of materials can be normally tested using a 10ml graduate. However, for low surface area powders (larger particles) there is a significant difference in resultant values due to graduate size. Sintering, although it does produce a bi-modal crystal structure, can be used to increase the surface area. The particle size distribution also changes significantly. Very little has been published in recent years because the general instrumentation is basically simple and there have been no major breakthroughs. Manufacturers rely on their own experience using the pycnometer, Scott density and/or tap density. Platinum and palladium require more energy to disperse the particles than other precious and non-noble powders. Each material must be evaluated separately to assure meaningful results.