HDI PCB manufacturing combines a planned interconnection structure with repeated imaging, lamination, hole preparation and copper deposition. A smaller hole is only one part of the process. The fabrication package must tell the supplier which layers connect, which vias are filled, where copper thickness matters and what evidence is required before shipment.
Translate the layout into a process route
Start with the finished stackup and a separate via-span table. Identify mechanically drilled holes, laser-drilled connections and any buried structures formed before the final lamination. Give each structure an unambiguous name that matches the drill files and drawing. A supplier should be able to explain how those features are made without inferring the designer's intent from overlapping drill symbols.
The order matters. An inner connection that becomes inaccessible after lamination must be fabricated and inspected earlier. Additional build-up stages can change registration allowances, copper distribution and the thermal history of the material. Ask the fabricator to return a marked-up construction proposal before the layout is frozen.
Specify evidence with the purchase package
| Deliverable | What it should resolve |
|---|---|
| Approved stackup | Layer sequence, finished thickness, materials and controlled-impedance geometry |
| Via construction drawing | Layer spans, fill or cap requirements and permitted arrangements |
| Inspection plan | Sampling, representative coupons, acceptance criteria and record retention |
| Deviation register | Every approved departure from the released design and its owner |
An illustrative manufacturing review
Suppose the layout has a surface BGA escape into layer 2 and another connection continuing to layer 3. A note saying “HDI vias” does not explain whether the two connections are stacked, staggered or replaced by another supported construction. The reviewer should return a drawing of the proposed path and describe any pad or spacing changes. Engineering then evaluates the routing and reliability implications before accepting it.
That discussion is more useful than asking for a universal minimum hole size. Production limits depend on the complete construction, material and inspection requirements. A demonstrated feature on one sample board does not establish the same capability for every stackup.
Release decisions
Separate bare-board acceptance from assembly acceptance. Agree how electrical test results, material identification and any required performance evidence will accompany the shipment. Define what happens if a proposed material becomes unavailable. The approved alternate should be reviewed against electrical and manufacturing requirements before it enters the build.
Keep the supplier's approved manufacturing proposal with the released revision. If a later quote changes the stackup, compare it as an engineering change rather than treating it as the same product at a different price. Verified fabrication limits, production locations and certifications for this website's operator remain [NEEDS CLIENT INPUT].
Continue the engineering review
- Sequential lamination in HDI fabrication
- HDI DFM release checklist
- How to evaluate an HDI PCB manufacturer
- 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.