To make the back plate transparent in render image, you should apply material as "glass" for your model
Otherwise, the image of your model after rendering remains as solid color even though you change its appearance with tranparency
This is totally possible and easier than you think. I am assuming you are wanting to render an image with a transparent background, to overlay onto another image or composition.
First you need to make sure your model is on a 100% black background. Go to the Scenes Tab, uncheck "Show Environment Image" and then click the 'Background Color' block to change the background color to 100% black. This helps remove any unwanted artifacts around the edges of your model.
Finally, all you have to do is include an Alpha Channel (transparent background) with your render. In the render options, set image format to TIFF or PNG and check "Include Alpha."
Thanks Brian, this is exactly what I need.