In the previous article entitled "Capped vias" technology for HDI PCBs we anticipated the importance of the perfect flatness of the over-plating of the "filled vias".
With regard to this aspect, it is due to emphasize that in the application of this construction technique, the definition, with the customer, of the side of the PCB where the greatest flatness is required is of great importance.
It is necessary to refer to the IPC standards or to the customer specifications to validate the product for all the characteristic aspects of this technology:
- Capped Thickness, thickness of the copper deposited on top of the filling resin greater than 12um in accordance with the IPC class 3 standard;
- Dimple Value, depression of the copper pad less than 76um in accordance with the IPC class 3 standard;
- Bumps Value, overgrowth of the copper pad below 50um in accordance with the IPC class 3 standard;
- Wrap Thickness, overlap of the plating of the filled hole, greater than> 5 um in accordance with the IPC class 3 standard;
In order to obtain the best design and subsequent manufacturing result, it is of the utmost importance on the one hand to provide PCB designers with technological support by guiding them already in the definition phase of new projects with respect to the choice of the best technique on the market and, on the other hand, equip themselves with the most up-to-date technologies and production processes.