The design for manufacture of high density DSP package

The mania for mobility applications such as smart-phones, tablet PCs, and personal computers is sweeping all over the globe. In order to insure the performance of a new product, the Design for Manufacture (DFM) plays an important role on a package design both in research stage and mass product stage. The substrate process capabilities, assembly process capabilities, material properties, and package structure are the main factors for DFM. In this paper, a high density DSP (Digital Signal Processing) package is showed as an example for the DFM methodology. For this typical high density WB-BGA package, the warpage control is the key point for DFM not only in substrate process but also in assembly process. The molding compound (MC) is used for protecting die. Molding or dispending process is the main step for assembly process. The coefficient of thermal expansion (CTE) mismatch and the material shrinkage cause the substrate deformation. If the substrate deformation large enough, it will affect cold solder joint between substrate and PCB (Printed Circuit Board), and the electrical performance and reliability. To evaluate the deformation by molding or dispensing process, the cooling down stage from 125 °C to 25 °C was simulated by EDA tool. The warpage of test samples with different molding height were measured here to estimate the real DSP package design. The difference of simulation data and measurement data are little. If the molding height is large enough, the structure deformation mainly depends on the molding structure. To improve the warpage, a copper ring is used in dispensing technology for DSP package. The significant signals were tested by oscilloscope and logic analyzer to verify the performance of DSP package, and the performance of the DSP was satisfied with the target.