![]() A large global solder paste manufacturer may run this viscosity test several hundred times in a given week. Test methods TM-650 2.4.34 and 2.4.34.2 lay out the viscosity test and measurement process. Industry standards, such as IPC J-STD-005, require solder paste manufacturers to specify, measure and report the viscosity of solder paste as a quality assurance procedure. These range from high shear rates as the metallic squeegee forces paste through the stencil's apertures, to low shear rates where gravity is the only force acting on it.ĭiagram of a spiral viscometer. As the paste is applied to the PCB, through a stencil, it experiences a complex series of shear forces. Paste flux gel is a viscous material which is blended with solder powder to create solder paste. Solder paste is a complex material made up of very small spheres of tin-based alloy, called solder powder, and solder flux gel. Today, with advances in measurement technology, SMT yields can be more accurately predicted by analyzing solder paste. In the past, viscosity was measured by the force of resistance on a rotating spindle, inserted into the paste sample. Many of the problems can be traced back to the interaction of the process equipment and the flow quality of the solder paste. ![]() ![]() Mitch Holtzer, Global Director of Customer Technical Support, Alpha Assembly SolutionsĪccording to dozens of published surface-mount process studies, up to 80 percent of defects occur when solder paste is stencil-printed onto a bare board. ![]()
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