Described embodiments include apparatus that includes a catheter and a tip electrode, at a distal end of the catheter, shaped to define a plurality of microelectrode apertures. The apparatus further includes at least one printed circuit board (PCB) disposed within a lumen of the catheter, and a plurality of microelectrodes coupled to the PCB and at least partly situated within the microelectrode apertures, the PCB being configured to carry signals from the microelectrodes. Other embodiments are also described.