應用同軸式垂直轉接於高頻覆晶傳導線之設計及量測

Abstract

本論文中，新穎的同軸式垂直轉接覆晶傳導線已被成功地製作出來，並具有直流到40 GHz的寬頻特性。 對傳統垂直轉接的覆晶傳導線而言，主要的缺點在於受限的電流路徑，尤其在高頻時會導致寄生效應。同時，為了提升覆晶封裝的可靠度，通常會施以底膠的填充，但底膠材料的填充常使得傳導線在毫米波段下的損耗增加。為了達成具寬頻特性及低損耗的傳導線設計,在本論文中提出了兩種同軸式的垂直轉接，並且研究及證明其在高頻覆晶上應用的可行性。 兩種同轉式垂直轉接在高頻覆晶結構上的應用已在本研究中製作出來及驗證其高頻特性。藉由full-wave 3D 模擬軟體，同軸式垂直轉接的有效物理結構參數對高頻的影響已被探討。其中，對此二種同軸式垂直轉接而言，改變內外金屬導體半徑的比值以及高阻抗的補償設計，可大幅改善傳導線的反射特性。且在底膠填入後影響的研究中，可發現只有增加很小量的損耗，代表使用同軸式垂直轉接的傳道線，可成功的降低因底膠的填入對高頻特性的影響。由量測結果可知，使用同軸式垂直轉接的高頻覆晶傳導線擁有從直流到40 GHz良好的反射特性(小於 20 dB)，且在高頻傳導線應用中具有很大的潛力。

In this study, novel designs of flip-chip interconnect structures using the vertical “coaxial-type transitions” have been successfully fabricated and demonstrated to show the broadband interconnect performance from DC to 40 GHz. The major disadvantage in the conventional flip-chip interconnect structure is the finite current paths which induce additional parastics, especially at high operating frequencies. Meanwhile, underfill is necessary to ensure the joint reliability; however, it induces more loss in the millimeter wave range as compared to low frequency range. To achieve the goal for broad band application and low loss transition property, the two coaxial-type transitions for interconnects are proposed and fabricated to demonstrate its feasibility for microwave applications in this study. The two proposed coaxial-type transitions in the flip chip interconnect structure have been fabricated for demonstration. The effects of the physical parameters in the two coaxial-type transitions on the reflection property have been investigated with full wave 3-D simulator. The parameter of ratio (R) and the high impedance compensation showed great improvements on the reflection properties at transitions in both the proposed coaxial-type transitions. The injection of underfill showed only very small increase in loss, which means the degradation of RF performance was successfully reduced with the proposed coaxial-type transitions. The measured results of the flip chip interconnect structure with the coaxial-type transitions showed excellent performance of better than 20 dB return loss from DC to 40 GHz. The proposed coaxial-type structure is proven to be of great potential for high frequency interconnect applications.