About ¼ or a fourth of the way, you can stop at San Mateo, CA. This is about 15 minutes south of San Francisco.
About ⅔ or two thirds of the way, you can stop at Mountain View, CA. This is about half an hour southeast of San Francisco, or about 17 minutes northwest of Campbell.
About ¾ or three fourths of the way, you can stop at Sunnyvale, CA. This is about half an hour southeast of San Francisco, or about 15 minutes northwest of Campbell.
If you drive straight through without stopping at all, the total distance is 50 miles. The distances shown above don't include local roads to get into each town, so if you're planning a long road trip, make sure you factor in traffic and road conditions, rest stop breaks, and interesting detours along the way. If you're in a rush, you can do the trip with zero stops, and your total travel time would be around 54 minutes.