A microvia capture pad provides copper around the connection at the receiving layer. The target pad and the hole must remain correctly registered within the chosen construction. Reducing a pad to free routing space can consume manufacturing margin, so pad dimensions should be reviewed together with hole geometry and registration allowances.
Use a complete tolerance view
For a simple concentric circular illustration, the radial copper allowance is half the difference between pad and hole diameters. Real acceptance depends on the specified measurement, feature shape, process variation and applicable criteria. Do not use the nominal arithmetic as proof that the manufactured feature will meet requirements.
Distinguish the entry pad from the target pad where their functions or dimensions differ. A tapered hole and a multilayer registration problem cannot be fully described by one diameter copied into every layer's rule.
Pad review inputs
| Input | Question it answers |
|---|---|
| Hole geometry | Which part of the formed or finished feature is being compared? |
| Pad dimensions | How much landing area is provided on each relevant layer? |
| Registration allowance | What variation must the construction accommodate? |
| Nearby copper | Does the complete pad envelope leave sufficient routing clearance? |
Evaluate the real routing benefit
An illustrative BGA fanout may gain a channel by shrinking capture pads. Before accepting that change, ask the fabricator to review the resulting geometry and compare another escape route or layer allocation. The apparent routing improvement can be offset by a process exception that affects the entire board.
Also check reference planes and antipads. A pad that fits between signal traces may create a larger interruption in a nearby plane. Include all relevant copper layers when judging the connection's footprint.
Freeze approved pad rules
Record pad dimensions, allowable via spans and tolerances in the fabrication package. Confirm that the layout's via definitions match the drawing and drill data. Avoid leaving unused or obsolete via templates available in the released project if they could be mistaken for approved structures.
When the supplier proposes a pad change, review its effect on routing and electrical behavior before approval. Preserve the accepted geometry with the stackup revision. Minimum capture-pad dimensions and registration capabilities for this site's operator are [NEEDS CLIENT INPUT]; this article supplies a review framework, not factory limits.
Continue the engineering review
- PCB microvia design fundamentals
- Fine-pitch BGA fanout with microvias
- Microvia aspect ratio design tradeoffs
- HDI PCB engineering hub
Review your HDI requirements
Share the board revision, proposed stackup, quantity and open questions. Include the requirements discussed in this guide so the project review starts with the same assumptions.