Persistence and Consistence. Reward good behavior. Every time you notice your puppy potty on the potty pad......throw him a big party with treats
You are already off to a good start if he is using the potty pads 80% of the time......you just need a little reinforcement to get it to that 100%
You may have to close your door at least until he is 100% potty pad train. Take him to the potty pads and say "potty" when he potties, praise him and give him a treat........rinse and repeat until he gets it. If he potties where he isn't supposed to just clean the spot with nature's miracle or something similar and not scold him. If you scold him, he will only potty in secret somewhere else.
Reward good behavior, ignore bad behavior.......works every time but it does take some patience and understanding. Eventually he will catch on a learn that pottying on the potty pads is a good thing and will go just to the potty pads exclusively.
It took a little bit of time, but my Duchess is 100% potty pad train and she still goes outside. It didn't confuse her at all. I love that she has a place to potty indoors while I'm away but she will still potty outside. In fact, she prefers to poop outside and will wait all day until I come her to walk to poop but if I wait too long to walk her, she will poop on the potty pad.
She is so trained to using the potty pad that even she when she has the occasionally bout of colitis, she will try her best to make it to the potty pad.
Also my Duchess will stop using the potty pads if they become to soiled so i have to change them often. I also use the washable pads to save on money and the enviroment