A probe card assembly can include a probe head assembly having probes for contacting an electronic device to be tested. The probe head assembly can be electrically connected to a wiring substrate and mechanically attached to a stiffener plate. The wiring substrate can provide electrical connections to a testing apparatus, and the stiffener plate can provide structure for attaching the probe card assembly to the testing apparatus. The stiffener plate can have a greater mechanical strength than the wiring substrate and can be less susceptible to thermally induced movement than the wiring substrate. The wiring substrate may be attached to the stiffener plate at a central location of the wiring substrate. Space may be provided at other locations where the wiring substrate is attached to the stiffener plate so that the wiring substrate can expand and contract with respect to the stiffener plate.