The proceeds of the current tax levies and future state aid receipts or other school funds which may become available must be applied to the extent necessary to repay such certificates and the full faith and credit of the district shall be pledged to payment of the certificates. Certificates issued in anticipation of receipt of aids shall mature not later than the anticipated date of receipt of the aids as estimated by the commissioner, but in no event later than three months after the close of the school year in which issued. Certificates issued in anticipation of receipt of taxes shall mature not later than the anticipated date of receipt in full of the taxes, but in no event later than three months after the close of the calendar year in which issued. The certificates must be sold at not less than par. The certificates must bear interest after maturity until paid at the rate they bore before maturity and any interest accruing before or after maturity must be paid from any available school funds.