Oxidation and Topography of Powder in Pb-free Solder Paste

摘要

With Pb-free soldering materials 'Heat' is the most important parameter. Despite the fact that our industry has to switch to Pb-free technology, the ever increasing demands for higher quality in the final electronic product is the driving force to achieve more consistent material performance. The introduction of Pb-free technology has presented additional challenges to deliver more batch-to-batch consistency of solder paste. It is not only the consistency of the flux system with a higher thermal stability that has received more attention but also, as described in this paper, a number of surface properties of the powder, impacting the interaction with the flux system, that have recently received greater recognition as important parameters. Surface roughness and the differences in the alloy between the mass of the solder particle and its specific surface area not only impact the wetting properties of a solder paste but also its rheology and consequently its printing properties.rn1. We strongly believe that getting more control over the oxide content becomes a key element in the successful application of Pb-free solder paste.rn2. An oxygen content analysis with the high temperature fusion furnace method seems to be an insignificant procedure. Although it may claim a level of repeatability, its resolution is considerably lower than the oxide level analysis by the fusion-in-oil principle.rn3. The ratio of fines in a particle range has a significant impact on the oxide level.rn4. Air oxidation doesn't have such an influence on oxide level at ambient temperatures.rn5. Solidification seems to have a minor influence on oxide level and yet quite a significant one on topography of solderrnpowder.rn6. Even if it would turn out that AFM would be a fundamentally correct method to establish both oxide layersrn(indirectly) and surface-topography, we would still require a justification of the cost per analysis versus the potentialrnto detect process variations.rn7. If AFM data only become meaningful when supported by EDX results, this technique has no chance to become arnfeasible detection routine. However, it will still be functional in supporting and guiding process improvements.