A novel high performance substrate and the processes thereof

This paper introduces a novel high performance substrate for digital and RF application. Instead of line width, we indicated that the size of VIA land is the key issue to improve routing density. In a practical example, if the VIA land can be reduced to 30 um, with 15/15 um line/space width, a bump grid array which has 3 rows and 105 um pitch can be easily fanned out by just one layer. For the target of high routing density, we develop a novel process and successfully meet the aforesaid criteria. Accordingly, the design of flip chip substrates become easy and the cost of advanced packaging can be reduced. In the application of high performance and RF system, crosstalk and EMI are important issues. Accordingly, we make thinner dielectric layers, the thinner gap between signal traces and ground plane, to reduce crosstalk between two signal traces and EMI issues. Moreover, because of the continuity of 50 ohm impedance, the line width is confined by an electronic relation with the thickness of dielectric layer. In other words, reducing the thickness of dielectric layer can also reduce the width of signal traces. Therefore, thinner thickness of dielectric layer makes higher routing density. By our novel processes, we can produce 8um thickness for any layer. For a practical example, the thickness of our 8-layer substrate is just 90um. In addition, foldable character is another benefit of thin thickness. A foldable system can be realized by our substrate. Based on the common design rule of flexible substrates, the radius of bending curvature is 10 times of the thickness of substrates. Thus, a thin substrate like ours has excellent flexibility. A real test has demonstrated that the flexibility of our substrates can sustain more then 100,000 times bending in 1 mm radius of bending curvature. Summarizing aforesaid matter, our substrate has high density, thin thickness and foldable character. Introducing a temporary solid carrier in the processes is the originality of this sub- strate. Because of its rigidity of dimension, precise alignment and thin film process can be easily done on the carrier. Thus, our substrate can be made and achieve so many attractive properties. Furthermore, a fully functional SiP system made by our substrate is demonstrated to evaluate the practicability.