Boric Acid is not something that you should be putting in your dogs ears. This could damage the tissue and delay healing. Straight white vinegar is really good for chronic ear infections. Start out with a weakened solution and slowly make it stronger until it's straight. Also give him a spoonful of yogurt everyday to prevent infections from flurishing.
Boric Acid is often used as an antiseptic, it can be mixed with rubbing alcohol and applied to the ear to kill germs. This boric acid mixture is actually safer to use than hydrogen peroxide when applied correctly because it does not kill healthy tissue like peroxide does.