First, Joe McCarthy was a US Senator from Wisconsin, not a judge, and therefore any actions taken by him to uncover "Un-American" activities were done so through congressional investigations and not trials.

McCarthy originally claimed there were over 200 communists in the State Department, but that number ended up changing a LOT. He made later claims ranging from about 80-10 communists in the State Department. He never produced any real evidence that there were. McCarthy lost most credibility during the Army-McCarthy Hearings in 1954, when he accused the US Army of coddling communists. He was censured shortly thereafter. Throughout his crusade, there's no evidence to suggest that McCarthy himself ever uncovered any communists or spies.

History.com sums it all up pretty well here