The Modeling and Prediction Study of BLP Device Solder Joint Three-Dimensional Shape

Abstract

Solder joint shape refers to geometry that molten solder can be achieved with spreading and wetting along the metal surface in the junction between components solder pins and printed circuit board (PCB) pad, to the metal surface contact angle and solder fillet shape[1]. BLP (Bottom Leaded Plastic) [2] which is not a type of thin out-line surface mount device(SMD) without the side lead is widely used in manufacturing of new generation memory such as SDRAM \ RDRAM \ DDR. For this non-lead SMD, the shape and reliability of solder joint is the focus of the study. In this paper, we select the C-BLP of 28-pin device as the research object, complete the forming model of solder joint shape based on minimum energy principle and the solder joint shape theory by using Surface Evolver software, and analyze two critical process parameters (solder volume and solder pad width ) impacting on the solder joint shape. The study results show that the solder volume and pad width have a significant impact on the three-dimensional shape of BLP solder joint. The law of which is that: in the case of the other fixed parameters, as the increase of the solder volume, solder joint surface gradually changes from the relatively flat to the convex, solder joint gradually changes from the completely soldered to the partly soldered in the pad connections, and solder joint heights are gradually decreased; in the case of the other fixed parameters, as the increase of the pad in width, the solder joint surface gradually changes from the convex to the flat, solder joint gradually changes from the completely soldered to the partly soldered in the pad connections, and solder joint heights are gradually decreased. The actual solder joint shape designs of BLP devices can be instructed based on predicted results.