We investigated the imidization of a polyimide (PI) and the formation of Cu nanoparticles in a PI film by curinga precursor of PI (polyamic acid (PAA) dissolved in n-methyl-2-pyrrolidinone) in a reducing atmosphere in the rapid thermal annealing (RTA) system. A Cu film was deposited onto the SiO2/Si substrate, and the PAA was spin-coated onto the Cu film. After the PAA reacted with the Cu film, soft-baking was performed to evaporate the solvent. Finally, the PAA was imidized to PI at 450 degrees C by curing in a reducing atmosphere with the RTA. Fourier transform infrared spectroscopy showed that the PAA was successfully imidized by the RTA. X-ray diffraction patterns revealed that Cu nanoparticles formed by RTA curing at 450 degrees C for 5 minutes in a reducing atmosphere, and transmission electron microscopy showed that Cu nanoparticles about 6.5 nm in size were uniformly dispersed in the PI film. Curing by RTA is an attractive method because it takes only a few minutes.
Shielding against electromagnetic interference (EMI) is becoming increasingly important as electronics such as wearable devices, sensors, IoT, and smartphones become smaller, faster, and weigh less. Package level EMI shielding has several advantages over board level shielding, such
as a higher packaging density and better design flexibility. We developed a new fan-out package structure using back-side under bump metallurgy (UBM) and a substrate (or metal carrier) to improve the thermal characteristics and reduce die shift. UBM and the substrate (or metal carrier), which
consisted of highly conductive metals, is effective for EMI shielding. We study EMI shielding effects of UBM and the substrate (or metal carrier). To determine the EMI shielding of the UBM structures, Ti (17 nm thick) and Cu (70 nm thick) were sequentially deposited on a glass substrate using
a direct-current (DC) magnetron sputtering system. Then Cu was electroplated or Ni-P was electroless plated with various thicknesses up to 10 µm. Samples were measured under 100 MHz and 1 GHz with 0 dB conditions using a spectra analyzer, which is a near-field measurement equipment.
In unpatterened UBM, increase in the Cu or Ni thickness resulted in further enhanced EMI shielding. When the thickness of Cu UBM or Ni-P UBM was bigger than 5 µm or 3 µm, respectively, the UBM exhibited good EMI shielding. A double layer of Cu strips was formed on
the back side of the chip to enhance EMI shielding. The larger the overlap between the Cu strip and the upper and lower layers, the better the EMI shielding effect. When this overlap was larger than 0.5 mm, the EMI SE was similar to that of a single unpatterned Cu layer. We demonstrated good
EMI shielding in the double-layered structure with a large overlap width between the upper and lower Cu strips, and expect better moisture release in such structures.
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