Combine ingredients for dry rub in a small dish, set aside.
Place ribs face down on a working surface. Use a knife to carefully remove membrane from ribs. Discard. Cut racks of ribs in half or thirds to ensure they fit into instant pot. Rub ribs with dry rub mix until generously seasoned.
Place onions, garlic, liquid smoke, worcestershire sauce, and broth in bottom of Instant Pot. Place rack into Instant Pot. Place Ribs on their side onto the rack.
Select manual pressure, and cook ribs for 27 minutes. Allow to natural release for 5 minutes before opening the valve to release remaining pressure.
Place ribs on a foil lined baking sheet. Brush with barbecue sauce if desired, and broil or grill until sauce is set and browned, about 5 minutes.