MIX half of the lime juice, 1/2 cup of the mayo, the dressing mix and mustard in medium bowl until well blended. Add crabmeat, 1/2 cup of the cracker crumbs and the onions; mix lightly.
SHAPE into 18 (1/2-inch-thick) patties; coat with remaining cracker crumbs.
COOK patties, in batches, in large nonstick skillet on medium heat 2 min. on each side or until browned on both sides and heated through. Meanwhile, mix remaining 1/2 cup mayo, the remaining lime juice, the lime zest and sour cream until well blended. Serve with crab cakes.