M538: Surface Mounting Instructions - Footprint Guidelines

Surface mount board layout is a critical portion of the total design. The footprint must be the correct size to ensure proper solder connection interface between the board and the package. With the correct pad geometry, the package will self-align when subjected to a solder reflow process and will also allow for just enough excess surface area for adequate solder filleting. The following recommended footprints are suggested guidelines only and may require ground plane modifications for electrical and/or thermal considerations. When an increase in ground plane size is necessary, solder mask over bare copper (SMOBC) should be utilized to contain solder and eliminate alignment problems during solder reflow. Electrical and/or thermal considerations may also require the board to contain plated vias located under the surface mount package. When this is necessary, the recommended via diameter is 0.3mm with a pitch of 1.0mm. To prevent solder wicking inside the via during reflow, solder mask pads are recommended over all vias located under the package. The solder mask diameter should be 100 microns larger than the via diameter. Blind or filled vias also work well as an alternative to solder mask to further enhance thermal conduction.