Small Transport; Low Wing; 2 Turboprop Eng
Air Traffic Control Fully Certified
Air Traffic Control Time Certified In Pos 1 (yrs) 7.0
Communication Breakdown; Situational Awareness
ATC Issue All Types; Conflict NMAC
Air Traffic Control Issued Advisory / Alert
Airspace Structure; Human Factors
Aircraft X was on approximately 7 mile final on the ILS at 2900 feet when they were handed off to AFW from Approach.  As soon as Aircraft X was switched the Conflict Alert alarm went off.  There was an unknown aircraft crossing from east to west 6 miles north of the field.  The unknown aircraft was at 2600 feet climbing.  The unknown aircraft was directly in front of Aircraft X.  I issued a traffic alert to Aircraft X.  Aircraft X reported traffic in sight and passed over the aircraft about 200 feet above it.  This happens often here at AFW and is happening more frequently with our increase in traffic. An adjacent non towered airport is 5 miles northeast of AFW airport; outside the Class D airspace.  Many times aircraft depart this airport westbound and stay clear of the D airspace and never call AFW tower.  These aircraft routinely cross the final approach fix at 2500 feet; the same altitude as IFR Aircraft on the ILS for AFW.  If the Class D airspace was extended to the north these aircraft would have to cross further north or call AFW so that we could use altitude to separate them.
A AFW Tower Controller reported an arriving aircraft on an instrument approach had a NMAC with an unidentified VFR aircraft departing a satellite non towered airport.