Development of ultra-thin low warpage coreless substrate

Coreless substrate is a promising next generation substrate. Coreless substrate has very low z-height, which means such substrate will be lighter, smaller and it will have very short interconnection, fine linewidth, and good power integrity. But the major challenge for coreless substrate manufacturing and assembly processing is reducing warpage. In this paper, we introduced a novel coreless substrate with 100μm thick and very low warpage. A novel low cost manufactory process for the substrate was also developed. In order to achieve low warpage coreless substrate, new materials were used. Mostly ABF or PI was used as coreless substrate stack material. In this paper PP was used as main material, and the glass fiber cloth in PP supporting the substrate reduced warpage. SAP process was used manufacturing coreless substrate; particular fixtures were made for the manufacture process. The through-holes were 40μm diameter ablated by UV laser. The copper layer was 30μm thick. Two types of coreless substrate were fabricated using different PP materials for different application. Type I coreless substrate using common PP film is constructed by one layer PP film (40μm) and two 30μm Cu layers. The application is for interposers and high frequency applications. The PP using in type II has low dielectric loss; the dielectric loss angle tangent is 0.0060 at 1GHz. Type II substrate can be used in high frequency device manufactory and packaging. The electrical test structures were designed and tested. A 2.13GHz micro-strip filter was designed and manufactured using type B coreless substrate.