Material Composition
Electronic assembly materials combine fine metallic spheres with a chemical paste to enable both mechanical and electrical connection during reflow. Solder paste is printed onto copper pads of a printed circuit board before components are placed, acting as both an adhesive and a source of metal for the joint. This compound consists of powder alloy mixed with a flux medium that cleans the board surfaces during soldering.
Rheological Characterization
Printing paste onto fine-pitch pads requires precise viscosity and yield point control. The behavior of solder paste under pressure determines how well it flows through the stencil apertures and releases onto the board. If the paste is too thick, it will not fill the aperture, leaving insufficient solder on the pad.
If it is too thin, the paste will slump, leading to solder bridging after reflow.
Print Performance
Printing quality depends on stencil thickness, squeegee pressure, and the physical properties of the print material. Using a high-quality solder paste prevents common defect modes such as bridging, solder balling, and open circuits. Modern optical inspection machines measure the volume of each deposit to ensure that the correct amount of material is present.
This inspection helps catch printing problems before the board goes to the assembly and reflow stages. By adjusting print parameters to match the material paste properties, manufacturers achieve high yields and stable joints.
