Study on reliability of embedded passives in organic substrate

Embedded passives represent a promising solution regarding the reduction of size and assembly costs of system in package (SiP). In addition, the benefits also include improvements in electrical performance and reliability. Although embedded passives are more reliable by elimination solder joint interconnects, they also introduce other concerns such as deformation and component instability. More layers may be needed to accommodate the embedded passives, and various materials within the substrate may cause significant thermo-mechanical stress due to coefficient of thermal expansion (CTE) mismatch. Due to the embedded substrate include viscoelastic material, the Maxwell model was applied to describe the viscoelastic behavior of embedded capacitor in the FR4 substrate series, and the constitutive equations of the Maxwell model were obtained. The three dimensional finite element model of embedded capacitor is developed. And the thermo-mechanical deformation of embedded capacitor is investigated after accelerated thermal cycling (-55degC to 125degC) based on the American military standard (MIL). The result shows that the maximum displacement takes place at the both sides of the middle edges. And the deformation leads to the distance of capacitor electrodes increase, which results in decrease of capacitance. The biggest reduction of capacitance is approximate 10% after thermal cycling, but embedded substrate is baked before thermal cycling can prevent the capacitance from decreasing and the change of capacitor is less than 5%. From 100 MHz to 1 GHz, the signal integrity of micro-via is investigated and the model is developed. The signal micro-via including one ground-via have obvious resonance peaks around the 1 GHz. Compare with one ground-via, the resonant peak of micro-via including four ground-via that array symmetrically can be inhibited. In addition, the insertion loss and return loss of the micro-via including four ground-vias are less than that including only one g- round-via.