90 days is the speedy trial rule on a misdemeanor and if the State fails to file within 90 days the Defendant is entitled to discharge. The State can only hold an individual in jail for up to 33 days without the filing of an Information. On the 30th day a Motion for Release should be filed and if no charges are filed by the 33rd day, the Defendant shall be released. Even if the defendant is released, the State still has the full 90 days to file. I suggest you consult with a local Criminal Defense attorney to discuss your boyfriend's case in further detail and learn all of his rights and options. Good luck.
Everything attorney Fluke said above is correct.
I would add, however, that 17 days without formally filing the charges is completely normal. Many times, if the Defendant is not in custody, the arraignment is set 30-45 days after the arrest in misdemeanor cases.
Best of luck to your boyfriend.