Paste Depletion
Gradual loss of material describes the reduction in the amount of solder paste successfully transferred from a stencil to a printed circuit board over multiple print cycles. This solder volume decay often occurs because the paste dries out or becomes trapped in the apertures of the stencil. Monitoring this trend is essential for preventing the formation of insufficient solder joints during the reflow process.
Stencil Interaction
Viscosity changes as the volatile components in the flux evaporate over time. As the paste becomes stiffer, the material no longer flows cleanly into the small holes of the metal mask. This leads to a steady drop in the deposited amount, a phenomenon known as solder volume decay.
Automated inspection systems track the height and area of each deposit to detect when the transfer efficiency falls below a set threshold. Sophisticated software calculates the volume from these separate measurements to warn operators of a potential shortfall before the printer runs out of usable material.
Joint Quality
Failure to address this issue results in weak mechanical connections and intermittent electrical faults. Regular cleaning cycles for the stencil and the addition of fresh paste can slow the progress of the problem. If solder volume decay is not corrected, the final assembly may fail to meet the requirements of ipc class three standards.
