Flexible connection for reflow free super fine pitch QFP SMT components

Owing to the limitation of the fine pitch and the fine area array assembly, fine pitch package or micro BGA are facing challenges such as miniaturization, high density and assembly problems along with the rapid development of the high-density electronic packaging and surface mount assembly. The major limitation of the fine pitch packages is around 0.3mm. Exceeding this limitation encounters reliability issues for the manufacture of packaging leads, solder pads on PCB and the reflow soldering, especially the interconnection failure, such as bridging, solder ball and cold solder joint. More novel interconnection methods are urgently needed to be found in order to overcome these obstacles. In our work, a conductive silicone rubber used to achieve the electrical interconnection between the packaging leads and solder pads on PCB is studied. The pitch is reduced within 0.1 to 0.05 mm when the interconnection of the conductive silicone rubber is adopted, and the characteristics of the current carrying capacity and the continuity resistance have greatly improved. Thus, the size of the integrated circuit (IC) package can be greatly reduced, and the surface mount density can be greatly increased after using this new interconnection technology. Herein, we investigated two types of conductive silicone rubber interconnections for SOP and QFP packages. The conductive silicone rubber is placed between the devices leads and solder pads. For the first type, using a specially designed the mechanism presses QFP with conductive silicone rubber on the bottom of QFP's leads on to the PCB to fix the connection. The second type is to design a connector which can clamp the QFP leads and the conductive silicone rubber, achieving the interconnection between PCB and SOP and QFP leads. Devices interconnection can be greatly improved through the above two types of connection. This work is aimed to study new connection method about QFP package in order to reduce the size of the packages and increase the density of the assembly. Experiment indicates that this conductive silicone rubber interconnection is able to withstand high temperature change, chemical corrosion and vibration and shock. Meanwhile, it is possible to avoid the interconnection failure during the reflow. Considering the advantages of conductive silicone rubber interconnect technology by a unique design, this flexible connection of QFP is feasible.