Testing Methodology
Standardized laboratory procedures evaluate the dimensional stability of printed solder paste deposits when exposed to thermal and ambient conditions. The print slump ipc tm 650 test provides a quantitative measurement of how much a printed pattern spreads before the solder melts. This standard defines the copper test pattern and the stencil thickness used to run the evaluation.
Technicians inspect the resulting deposits under magnification to determine the minimum spacing that resists bridging.
Defect Prevention
Pad bridging represents the main manufacturing defect prevented by verifying paste resistance to spreading under heat. When paste with low slump resistance is used, the deposited material spreads across the solder mask during the preheat phase of reflow. Solder paste slump is more pronounced in fine-pitch applications where the distance between adjacent pads is extremely small.
The print slump ipc tm 650 test evaluates both cold slump at room temperature and hot slump at elevated temperatures to cover all pre-reflow conditions. High slump values indicate that the paste has low yield stress, which allows gravity or temperature to flatten the brick.
Paste Evaluation
Stencil printing optimization depends on using paste with high slump resistance. Formulators adjust the rheological additives in the flux vehicle to prevent wet solder deposits from collapsing on the board. Rheometers measure the viscosity and yield stress of the formulation to ensure consistency between production batches.
Solder paste that passes the test maintains its height and shape, ensuring the printed volume stays within the target tolerance.
