The low Dk/Df polyimide adhesives for low transmission loss substrate

Abstract

The advance of wireless communications and broadband technologies is dramatically progressing with the remarkable growth of the market of information technology equipments such as mobile phones and tablets. In order to meet ever-enlargement of transmitting data, transmission frequency in circuits tends to become high and the integrity of a high-frequency signal can be damaged by transmission loss. In high frequency circuits, two kinds of factors decide transmission loss. One is conductor (circuits) loss; the other is dielectric (insulating materials) loss. The former relates to skin effect of circuits. Skin effect is a tendency for an alternating current to flow mainly near surface of conductors. The general improving measure of conductor loss is smoothing a surface of circuits. However, smoothing a surface of circuits tends to weaken the adhesion between copper circuits and insulating materials. Accordingly, it is difficult for copper circuits to fulfill both smooth surface and good adhesion to insulating materials. Dielectric loss depends on current frequency and dielectric constant (Dk) and dielectric tangent (Df) of dielectric materials insulating conductive materials. Consequently, as current frequency become high, dielectric loss tend to increase, and the general improving measure of this loss is using low Dk and low Df materials. Hence Low Dk and Df materials with good adhesivity to smooth surface of copper are required for high frequency PCBs. We recently developed the novel solvent-soluble polyimides. Moreover, by using these materials, we got the low Dk, low Df adhesives with high heat resistance and good adhesivitiy to smooth copper such as rolled copper foils. In this presentation, we will report on properties of our polyimides and their adhesives and the trans mission loss evaluation of the substrate using the adhesive of these polyimides.