HDI engineering
Via-in-Pad for HDI PCB: Fill, Cap & Assembly Requirements
Via-in-pad places an interconnect inside a component land. It helps dense routing, but the via treatment and finished pad surface must support soldering. 鈥淰ia-in-pad鈥� alone is not a complete fabrication instruction.
The practical decision
Specify the via type, layer span, fill/cap construction and finished land requirements. Review the pad as both an electrical interconnect and a soldering surface, using one agreed fabrication and assembly detail.
- LocateComponent land + via span
- SpecifyFill + cap + surface
- ReviewFootprint + paste + soldering
- InspectCriteria + records
Via treatment terms are not interchangeable
Through vias and laser microvias may use different processes. Define the intended construction rather than copying shorthand from another board. Mask over an opening is not the same thing as a filled, planarized and copper-capped pad.
| Condition | Meaning | Still needs definition |
|---|---|---|
| Open via in a land | An opening intersects the soldering surface | Solder loss and process suitability |
| Tented via | Mask covers an opening according to the process | Suitability for the actual land and assembly |
| Filled via | Material occupies the via | Fill material, extent, void criteria and surface |
| Filled and capped | A specified fill has a conductive cap | Cap construction and surface acceptance |
| Copper-filled microvia | Defined plating fills the microvia | Target/stack interface and surface requirements |
| Via-in-pad assembly land | A component solders over the treated via | Footprint, finish, paste design and joint inspection |
Specify the complete drawing detail
Identify the affected via type and component lands, layer start/stop, hole and pad dimensions, fill/cap treatment, finish and agreed pad surface limits. Require a documented review if a supplier proposes another construction. A web illustration cannot establish universal dimple, protrusion or void limits.
| Drawing item | Purpose | Review partner |
|---|---|---|
| Layer-pair definition | Connects the land to the correct layer | PCB design and fabrication |
| Treatment detail | Defines filling/capping route | Fabrication engineering |
| Finished land | Defines the soldering surface | Fabrication and assembly |
| Component footprint | Provides solder-joint context | Design and assembly |
| Inspection scope | Assesses construction and completed joints | Engineering and quality |
Check the via dimensions separately using the microvia design review.
Example: moving a via beneath a BGA
Illustrative design change: replacing a dogbone escape with a via inside a BGA pad triggers review of the via treatment, land geometry, surface and assembly process. Use the BGA land, annulus and routing-channel worksheet for the package-specific geometry. Reusing the old paste drawing without checking the changed pad can leave an important part of the revision unreviewed. Confirm that fabrication and assembly data describe the same approved release.
Separate construction from joint-inspection evidence
Construction records address the via and land; assembly inspection addresses the resulting joint. Neither record answers every question about the other process. Keep the separate microvia reliability review for stacked structures. Consult component-supplier land-pattern and assembly information alongside the agreed fabrication detail.
For the assembly side, review the BGA assembly process and the actual component requirements.
Working document
Prepare your handoff checklist
Open the editable text worksheet, save a copy and record the requirement, owner and evidence for each item. Keep unanswered points visible when requesting review.
- Component lands and exact footprint revision
- Via type and start/stop layers
- Hole, pad and clearance dimensions
- Fill material/process and cap requirements
- Finished surface and acceptance limits
- Finish and soldering requirements
- Assembly and paste revisions
- Construction and joint-inspection scope
- Approved exceptions and released revision
The Contact page is a separate enquiry step. Attach your completed worksheet and relevant files there using its available submission options; this page does not automatically transfer your answers.
Questions before you release the files
Can an open via remain in a solder pad?
It needs process-specific review. An opening can change solder flow and joint formation. CAD permission is not manufacturing approval.
Is copper-filled microvia the same as resin-filled through via?
No. They are different structures and processes. Specify the actual via and complete treatment.
Does via-in-pad always mean stacked microvias?
No. Via-in-pad describes location in a component land; stacked describes relationships between levels. Define both where applicable.
Continue with the next engineering task
Technical references
Original package/assembly references; use the documentation for the exact component in your design.