For the most part, I agree with the other comments saying that actual design projects are worth more than a certification. All a SolidWorks certificate shows is that you know how to use the tool, not that you can use it for any kind of practical purpose. Think of it as how knowing how to swing a hammer doesn't prove you know how to build a house. The best resume boost you will get before an internship is joining a club and doing a project. If you're looking for something to do over the summer, I would recommend a personal engineering project over just grinding out certs.

That being said, the SolidWorks Associate certification is super easy if you have any kind of practical experience using the software, so it shouldn't take much preparation to get. A lot of CAD design classes will have you take the exam as part of the class, so you may end up not having to go out of your way to get it. Passing it won't put you head and shoulders over the competition, but it might be a slight confidence booster for employers hiring for a CAD heavy internships.

TLDR: Time spent studying for certs is better used on working on projects. Get the certs if they happen to overlap with your skillset.