You should never put an NSP file directly onto the SD card. It's an inefficient use of time (it takes double the time, since you have to put it onto the SD and install it) and space (since you require twice the space of the actual file: space to hold the NSP and space to install the title to).
Use something like TinWoo, Awoo-Installer, or even blawar's Tinfoil to install an NSP file that's on your computer over a USB or FTP connection. For example, use NS-USBloader on your computer where the NSP file is located, and use TinWoo on your Switch.