SOLDER JOINT DESIGN OPTIMIZATION OF QUAD-FLAT PACKAGE WITH GULLWING LEADS UNDER ACCELERATED THERMAL CYCLING AND POWER CYCLING

Abstract

Ever growing complexity in designing of Integrated Circuits and accommodating high number of Interconnections in the device is the main source of motivation in today’s world of IC devices. Quad Flat Package (QFP) with Gullwing leads is spearhead technology which enables high connectivity levels required to be customized in most convenient and advantageous form. Gullwing leads have the advantage of having a large area in contact with solder and also work as mechanical springs. They also make it easier to inspect and rework. Lot of work has been carried out on inspecting the reliability of solder joints in QFP packages under Accelerated Thermal Cycling (ATC) as the only load. Devices go under a loading condition when you switch it on and off numerous times. This type of load is known as Power Cycling. Past studies have shown that some of the organic packages fail early in power cycling but perform better in ATC [1]. In predicting life of the package, we usually consider Accelerated Thermal Cycle (ATC) in which we believe temperature is uniform through-out. But by taking Power Cycling into account we have non-uniform temperature in the assembly where die is the only source of heat generation. In this paper, Solder joint reliability of QFP with Gullwing leads is evaluated by using Finite Element Analysis (FEA) under two Loading conditions and the combination of two. For design optimization, our main focus is on the shape of solder. From past studies its concluded that amount of solder affects the reliability of solder joints. Geometry of QFP package with different solder shapes, angles and Gullwing leads were modeled using Ansys Design modeler tool. These models were then subjected to ATC and Power Cycling to assess the stress distribution and the plastic work in the solder joints. We leveraged this comparative study to predict best solder profile design by analyzing results obtained from simulations to lessen the solder wreck and increase life of the package.