Mill inner layers (2nd and 3rd layer) Place prepreg (insulative adhesive layer) on both sides of the board, and attach outer layers (1st and 4th layer) on respective sides Apply pressure and heat in a press machine Drill holes with a prototyping machine Through Hole plating Mill outer layers (1st and 4th layer)

It will take more than 3 days just for above process!

When you apply pressure and heat using a press machine to the board sandwiched with prepregs and outer layers, you have to carefully consider flow path of melted prepreg. Otherwise, the thickness of the board becomes uneven and adversely affects milling quality of outer layers (3rd and 4th layer).

3. Once a multilayer board is made, you have to test conductivity between inner

layers and outer layers. In a laboratory environment, you have to use a circuit tester and check the conductivity of every single contact point one by one. This is very tedious and time consuming.

4. Considering above, the system cost as well as process cost are very expensive.