The electrophoretic deposition (EPD) process successfully applied for the deposition of quarternized polyetherimide (q-PEI) emulsion on the Cu surface in the relatively low voltage range of 2~7 V. Allowing the rheological movement of q-PEI suspension drops to move to the cathode, this voltage level allowed q-PEI (or PEI) coating to be in the thickness range in a few micrometers within 300 sec. The coating thickness increased with the applied voltages and seemed to reach a plateau with time seemingly allowing a stable control of EPD operating conditions. The low-voltage in EPD minimized the violent water electrolysis or gas evolution, and subsequently the quality of the deposited PEI layer was excellent with the RMS roughness in 15~35 nm. The thermally transformation of q-PEI to PEI was confirmed using FT-IR. Based on the electro-rheological theory of suspension drops under electrical potential, the key operation parameters of EPD, i.e., deposition time and applied voltage, were thoroughly investigated by measuring the thickness, surface roughness, and cross-section images of specimens. This work demonstrated that the low-voltage EPD could minimize the gas evolution rates and, thus, provide a high-quality PEI coating on metal surfaces without pinholes, voids, or delaminated areas within a reasonable span of EPD processing time.