PROCESS DEVELOPMENT FOR 01005 LEAD-FREE PASSIVE ASSEMBLY: STENCIL PRINTING

摘要

For some years now, an area ratio of 0.66 or greater has been the criterion for stencil apertures to achieve acceptable volume control in the printed solder paste “brick,” for small apertures Meeting this criterion, in the stencil printing process, has been a constant concern as the volume consistency of the solder paste brick is among the most critical metrics in determining high yields in the assembly process. With the advent of 0201 and most recently 01005 passives components, meeting the area ratio target of 0.66 is a challenging task; especially with a 5 mil thick stencil and a Type 3 powder solder paste. These tiny passive technologies and minimalist IC packages like 0.4mm CSPs have created a need to re-evaluate the area ratio criterion of 0.66 and other related issues. In light of this need, we developed a series of designed experiments (DOEs) evaluating Type 3 and Type 4 solder pastes, varying aperture designs for 0201, 01005 and 0.4 mm CSPs, and 3 and 4 mil thick laser cut and E-Fab stencils. In these experiments we determined optimum print parameters for the various combinations of pastes, components, aperture design, and stencil fabrication mentioned above. Our results also suggested new criteria for area ratios. We believe that with the concurrent implementation of leadfree assembly, this work could not be more timely.