A control module for an electrical stimulation system includes a casing defining a sealed inner compartment; an electronic subassembly disposed in the inner compartment; and a header portion coupled to the casing and having a connector to receive a proximal end of a lead or lead extension. The connector includes conductive contacts to electrically couple to terminal contacts on the lead or lead extension. The control module also includes a feedthrough assembly coupling the casing to the header portion. The feedthrough assembly includes a non-conductive ceramic block coupled to the casing, conductive feedthrough pins passing through the ceramic block and electrically coupling the conductive contacts of the connector to the electronic subassembly, a metal braze coupling the feedthrough pins to the ceramic block, and at least one glass layer disposed on at least a portion of the ceramic block and in contact with at least one of the feedthrough pins.