If the life estate deed exists before you put the mortgage on record, it will impact the mortgage lien position. Most mortgage lenders will want the life estate extinguished or they may consider having the owner of the life estate sign the mortgage to validate the lien and allow it to take priority over the life estate.
If you already have a mortgage in place and wish to create a life estate, you'll need to review the terms of your mortgage. Look for a "due on sale" clause. This type of clause would give the lender the right to demand payment in full if you transfer any ownership interest without their permission.
I would presume the life estate deed would be created by an attorney, so your attorney can review your mortgage and give you the proper advice.