A catheter includes a shaft for insertion into an organ of a patient, an extendable distal-end assembly, and two or more strengthening elements. The extendable distal-end assembly is coupled to the shaft and includes multiple splines, at least one spline includes a flexible circuit board having one or more electrodes disposed thereon, the circuit board is configured, when the distal-end assembly is extended in the organ, to conform to a surface of the organ so as to make contact between the electrodes and the surface. The strengthening elements are distributed along the circuit board of the spline and are configured to mechanically strengthen the spline.
