Miniaturization of electronic devices has been strongly pursued to facilitate ubiquitous computing. High-density packaging technology is a promising candidate for reducing device size. For producing high-density packaging, metallization is an important process. Electroless nickelphosphorus plating, the most popular metallization method, is available for insulator materials such as silicon nitride (SiN) and polyimide (PI). For this study, we investigated three materials for substrates, PI as a resin, SiN as a passivation film, and aluminum (Al) as a metal. The values of adhesion strength between the electroless Ni-P film and three substrates were evaluated quantitatively using a stud pull test. A commercially available weak alkaline degreasing agent (aluminum cleaner NE-6; Meltex Inc.) is effective for metallization of PI, SiN, and Al simultaneously without a zincate process. These three materials are common used for a wafer level chip size package (W-CSP), which is a newly developed high-density packaging technology. Using the degreasing agent, we obtain sufficient adhesion strength for three substrates: PI, SiN and Al.The optimum concentration of the degreasing agent is 45 g/dm3 for all substrate materials. Results show that the electroless Ni-P plating process is suitable for metallization of high-density packaging.
An electrochemical measurement cell that enables the measurement of the rest potential, potentiostatic polarization, and anodic polarization curve of an electrode under wet etching was developed under wet etching by spray. The Cu electrode was fabricated by screen printing to simulate a printed circuit board. Its cross-section was analyzed using optical microscopy after electrochemical measurements. Measurements of the Cu electrode rest potential were conducted under wet etching with different flow rates. The Cu electrode rest potential was shifted to noble potential when the flow rate of spray was high under wet etching. Results show that the Cu electrode dissolution was explained by the mixed potential theory. The Cu electrode cross-section after the potentiostatic polarization showed that the cross-section shape was controlled by the polarization potential. Furthermore, the current densities of the potentiostatic polarizations showed good agreement with that of the anodic polarization curves. The details of the Cu electrode dissolution behavior under wet etching by spray using the electrochemical measurement cell are discussed.
Transparent heat-mirror insulation films comprising a multilayer of AlN/Al/AlN were fabricated using new magnetic hollow-cathode sputtering. Electrical and optical properties of multilayer films were examined. Visible transmission of 78 % (at 0.5 μm) and infrared transmission of 30 % (at 1.0 μm) were obtained for a three-layer film of AlN (30 nm) / N-doping Al (9 nm) /AlN(30 nm)on PET films.