Stencil Openings and Bond Pads Design Considerations for High Density Solder Paste Printing Process for Assembly of Display Panel

摘要

We discuss the design considerations of the stencil openings and the dimension of the bond pads on the PCB for the solder paste printing in the assembly process of high density LED display panel. Stencil printing process for solder paste application is commonly adopted for high density discrete bond pads on PCB substrate. In order to achieve high assembly yield when the size and pitch of the bond pads are much reduced to around ~100μm and 150μm respectively, the design guidelines for the size of openings and thickness of the stencil for obtaining a desirable printed volume of solder paste can be determined with the considerations of the layout of solder mask and its thickness as well as the bond pads geometry and dimensions on the PCB. We will also highlight how the printing transfer efficiency of the solder paste is affected by (i) stencil design such as size and aspect ratio of the stencil openings, stencil thickness, the aperture-area to wall-area ratio of the opening, tension on the stencil, (ii) bond pads design on PCB such as pad size, solder mask thickness, solder mask clearance around pads and (iii) solder paste selection with considerations of type of solder paste, flux viscosity, flux residue and its cleanability.