Start with the layers that must connect
A via provides an electrical connection between conductor layers. A through via spans the board thickness; a blind via reaches an internal layer from an outer surface; a buried via connects internal layers without opening at the finished outer surfaces. Microvia construction is a further technology choice with its own geometry and processing limits.
Terms such as thermal via, via-in-pad, tented or filled describe a purpose, location or treatment rather than an entirely separate layer-reach category. One feature can have several of these descriptions. Write the complete requirement instead of choosing a name from a list of supposedly interchangeable via types.
Balance routing benefit with fabrication complexity
Smaller or selectively spanning vias can make dense escape routing possible, but they affect drilling, registration, lamination and inspection. Stacked and staggered structures also create different construction questions. Review the topology with the fabricator before routing the whole board around an assumed capability.
Specify the relevant hole and pad geometry, layer span and board construction. Distinguish the finished opening from the drill-tool size. Do not assume that a nominal via size from a calculator or a previous two-layer board is suitable for a different stackup.
Review electrical, thermal and assembly effects
The connection’s behavior depends on its geometry and surrounding return structure, not simply the number of vias on a net. Consider unused stubs, reference transitions, current distribution and thermal paths where they matter to the circuit. Simplified estimates should be checked against the real construction and operating conditions.
A via within a solder land can affect paste and solder behavior unless its treatment is explicitly defined. Tenting, plugging, filling and copper capping are different operations. Tell the fabricator and assembler what finished surface is required, especially beneath a component.
Release and verify the intended structure
- Show via groups and their layer spans in the stackup or fabrication documentation.
- State finished geometry and plating requirements where critical.
- Identify covering, filling and capping separately.
- Agree on appropriate inspection, electrical test and any qualification evidence.
- Require review before a topology or construction substitution.
Keep the approved via structure with the released design. A manufacturer’s proposed change can affect routing, assembly or reliability, so it should not be treated as a cosmetic CAM edit. Verify the first build against the agreed evidence before relying on that construction for repeat production.