The top, i.e. the signal layer (0.0014 in. width) is followed by a prepreg layer with a thickness of 0.0091 in. and dielectric constant of 4.2. The top layer is copper material.

View UMC 55NM SP-RVT with 2.5V device DDR23 COMBO PHY CMD/ADDR Block for 2 layer PCB board usage full description to... see the entire UMC 55NM SP-RVT with 2.5V device DDR23 COMBO PHY CMD/ADDR Block ...

DDR23 COMBO PHY CMD/ADDR BLOCK ; UMC 40LP/RVT LowK Logic Process with 2.5V device for 2 layer PCB board usage ...

But as you can see above, there are additional choices when it comes to multi-layer boards. #1 is a through via connecting all of the layers. #2 is a blind via; it stops part way through the board.

Comparing Stackups The 2-layer PCB stackup can be clearly demarcated. Layer 1, or the top layer, is described as a signal layer. The 0.0014-in.-thick layer is made of copper material; the copper ...