A test coupon for measuring a dielectric constant of a memory module substrate has a plurality of test pattern layers each having a long trace and a short trace formed thereon. A first test pattern layer has an exposed surface and a second test pattern layer is formed internally. The first test pattern layer has probe pads respectively connected to the long and short traces of the first and second pattern layers. Probe pads of the first test pattern layer are connected to a via contact of the second test pattern layer by via holes. The via contact of the second pattern layer is connected to the long and short traces of the second pattern layer. The test coupon is used to measure the dielectric constant of a module board.