An open hole and a finished via-in-pad surface are different
Placing a via inside a component land can shorten a connection or provide a useful thermal path. It can also create an opening into which solder moves during assembly. The design decision therefore needs both a routing review and an attachment-process review.
Do not assume that “via in pad” automatically means the hole is filled and copper capped. Likewise, a via covered by solder mask is not the same as a flat solderable land. State the required finished structure in the fabrication requirements and confirm it with the assembler.
Define the fill and cap requirements
A filled and capped construction uses a controlled fill and a finished copper surface over the via. Material choice, void control, planarity and the cap are process requirements that need agreement. Conductive fill, non-conductive resin fill and copper-filled microvias should not be treated as identical structures.
Manufacturer guidance distinguishes filling and capping from simpler plugging or tenting. Use a recognized construction description and any applicable agreed standard, with enough detail to remove ambiguity. A vague note such as “plug all vias” does not define the surface needed under a fine-pitch component.
Review the package and complete board construction
- Identify the exact package and land-pattern requirements.
- Show the via location, layer span and relevant dimensions.
- Specify the surface and planarity needed for assembly.
- Review stencil, paste and inspection implications.
- Confirm the fabrication sequence, cost and qualification evidence.
Via-in-pad is useful when it solves a real routing or thermal problem, but it can add manufacturing complexity. Where routing permits an alternative, compare the total construction and assembly risk rather than assuming that the most compact geometry is automatically the best production choice.
Verify the result and control changes
Agree on how the finished feature will be assessed, including any relevant fill, cap or surface evidence. Electrical continuity alone does not prove that the soldering surface is suitable, and a smooth visible surface does not establish every internal characteristic.
For the first assembly, correlate hidden-joint or soldering results with the released via construction. If a change is required, update the board and assembly documentation together. Preserve the accepted material and process requirements for repeat orders so a later supplier does not replace a defined via-in-pad structure with a different, cheaper interpretation.