Stencil Design for Lead-Free Reflow Process

Following the trend toward miniaturization, manufactured components across end-user industries such as electronics, automotive and other industrial applications are becoming smaller in size. From July 2006 has came into force the RoHS Directive on the restrictions of the use of certain hazardous substances in electrical and electronic equipment. In Tele and Radio Research Institute was pursued works to face the problem of lead free assembly implementation due to RoHS Directive. We put the special attention to miniature components. In the paper there are presented the result of investigation of stencil design, solder paste printing process and solder paste wetting and spread characteristics for both the smallest components on the board (including 0201 and 01005 component) and the largest components on the board. A quality assessment consisting of solder wetting/spread and coalescence, volume and shape of printed solder paste (3D inspection) as well as cross-section of solder joints were performed.