a ceramic substrate has , on its surface , a multilayer wiring division , on which micro cantilever type probes are fixed . the multilayer wiring division has the first conductor layer , which includes through - hole junction pads , flatness improvement rings surrounding the through - hole junction pads and a grounding region further surrounding the flatness improvement rings . since the flatness improvement rings are located around the through - hole junction pads , the surface of the first insulating layer , which is located above the first conductor layer , is free from severe undulation even near the through - hole junction pads . accordingly , the multilayer wiring division has less irregularity in shape as a whole , and thus the probe mounting pads on the surface of the second insulating layer do not slope but keep almost horizontal . the probe unit substrate according to the invention has an advantage of less surface undulation and having non - sloping probe mounting pads without using a complicated manufacturing process .