Ti/Ni(80%)Cr(20%) Thin-Film Resistor With a Nearly Zero Temperature Coefficient of Resistance for Integration in a Standard CMOS Process
A thin-film resistor out of Ni(80%)Cr(20%) for integration in a standard complementary metal-oxide-semiconductor process with a temperature coefficient of resistance (TCR) below 10 ppm/K was realized by applying a thin Ti layer underneath. The Ti-layer thickness and the temperature and duration of furnace annealing after deposition were optimized in different experiments. The combination of 5-nm Ti + 10-nm NiCr and a 30-min heat treatment at 350degC in a forming gas ambient was found to yield a sheet resistance of about 140 Omega/sq and a TCR of below 10 ppm/K. The long-term drift of the sheet resistance after 1000 h at 200degC was about 0.3%. A transmission electron microscopy analysis was conducted to investigate the structure of the film and a possible change during annealing. An Auger analysis was conducted for film surface analysis.
Effect of Chromium Concentration on the Electrical Properties of NiCr Thin Films Resistor Deposited at Room Temperature by Magnetron Cosputtering Technique
NiCr films, 100 nm thick, were prepared on SiO 2 (600 nm)/Si substrates at room temperature as a function of chromium concentration by the cosputtering technique. The crystalline nature and electrical properties of the NiCr films were investigated as a function of chromium concentration. The films with a chromium concentration up to 39% showed a crystalline structure having a low resistivity, a high root-mean-square (rms) roughness, and positive temperature coefficient of resistivity (TCR) values. The films with a chromium concentration above 39% exhibited the amorphous structure with negative TCR values. The TCR values of the films with a chromium concentration of 39 and 42% are approximately +10 and -9 ppm/K, respectively. The TCR values approaching zero can be established by controlling the chromium concentration in the NiCr films.
Failure analysis for poor solderability of Au surface of PCB
Nonwetting is one of the common problems and is always rejected in electronic assemblies. ENIG pads of a PCBA exhibited nonwetting after lead-free reflow soldering. With the aid of stereomicroscope, SEM&EDS and XRF, a series of analysis was performed. And after visual inspection, surface and cross section analysis, thickness measurement and solderability test, it can be inferred that oxidation of plating surface was the main reason for nonwetting, and corrosion in Ni plating caused an adverse impact on solderalibity.