Will the dogs live together in the same household? Or are they just meeting on visits?
Generally, it's a good idea for dogs to meet on "neutral territory"--meaning not in the house or yard of either dog. Take them both to a park or other place near the home where they can meet, sniff, get to know each other...and then walk home together.
Obvioulsy, the 3 month old Yorkie is tiny and fragile. You'll need to keep pretty close supervision on both dogs until your 100% sure of how they are playing together. The small dog could be injured (or worse) if they play gets too rough.
I have both big dogs and a small dog--and they all get along great. So I think after a period of time you'll be able to trust your two together as well. Just don't push it, and don't hesitate to step in and make the larger dog know that he has to be gentle.