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The Low Dk and Df Photosensitive Insulation Material for Low Transmission Loss Packages
Keywords: interposer and fan-out package, photosensitive insulation material, low Dk and Df
Today’s packaging technologies require high density connections among the different kinds of devices, especially between DRAM and logic. To realize it, the 3D vertical integration of DRAM on logic and side by side integration using silicon interposer ( 2.5 D ) with TSV ( Through Silicon Via ) have been studied. However, TSV technology faces some issues such as poor high-frequency properties and high fabrication cost. Organic interposer ( 2.1D ) with embedded high density wiring or fan-out package is one of the key solutions for the trend of electronic package development. For 2.1D, the organic materials with excellent electric performance have been also required in order to realize the packages for next-generation mobile communication( 5G ) and high-speed interconnection. Current thermosetting materials with low Dk( dielectric constant ) and Df( dielectric tangent ) are limited to via size larger than 20 μm by the laser compatibility. The cost of laser equipment is another bottleneck to be solved. On the other hand, photosensitive insulation material demonstrates fine via by photolithography process, however photosensitive insulation material is generally not applicable for high frequency applications because of the poor electrical properties. To realize the organic interposer and fan-out package for both high frequency of transmission signals and high density interconnection, we have newly developed photosensitive insulation materials having low Dk and Df as well as excellent lithographic and insulation properties. The material was designed using our accumulated resin solubility technology of core materials. The Dk and Df of the material showed 2.5 and 0.0060 at 10 GHz, respectively using SPDR( Split Post Dielectric Resonator ) method equal to or more excellent values than thermosetting resins. Then, the material showed 140 degrees C as glass transition temperature ( Tg ) without filler. Generally, thermosetting or thermal plasticity resins of low Dk and Df have compatible excellent electro property and high Tg in containing high volume surface-treated silica filer. The circuitry was fabricated by combination of the developed material and sputter or electro-less plating technique on smooth resin surface. Sputter layer thickness were 50 nm of Ti and 150 nm of Cu, respectively. The peel strength between the material and seed layer was more than 0.7 and 0.5 kN/m, respectively even on smooth surface roughness as 50 nm. These strong peel strength provide the good yield for assembly and mechanical reliability. Furthermore, the material will be applicable not only semiconductor process bat also panel process. The material was compatible with SAP( Semi-Additive Process ) and trench process, and demonstrated via connectivity less than 10 μm and Line/Space less than 5/5 μm. The fabricated circuitry using the material also passed biased-HAST( Highly Accelerated Stress Test ) criteria over 200 hours at 130 degrees C and 85 % condition. This excellent insulation reliability was caused by lower coefficient of moisture absorption than 0.2 % and lower concentration of ionic impurity than 20ppm. The elongation was > 50 % obtained and internal stress of cured material showed very low as 1.5 MPa at room temperature in comparison with thermosetting resin being almost 10 to 20 MPa. From these material properties, the circuitry using this material realizes both low warpage and mechanical reliability such as three times reflow at 260 degrees C after moisture sensitivity level 2 ( MSL2 ) and 1,000 cycles of thermal cycling test ( TCT ) from -55 degrees C to 125 degrees C. From these results, we have developed novel photosensitive insulation material compatible with excellent electrical property and fine circuitry. It is expecting that developed material contributing to realization of organic interposer and fan-out package for both high frequency of transmission signals and high density interconnection on next-generation mobile communication( 5G ).
tsukuba, ibaraki

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