Laser drilling forms small interlayer openings by removing material at selected locations. For an HDI PCB, the design question is not simply which laser is used. The dielectric, copper condition, target layer, hole geometry and subsequent cleaning and metallization must form a compatible process.
Define the hole as a finished feature
State the start and target layers and identify how depth and diameter will be measured. A tapered opening can have different dimensions at the entry and target. If a supplier quotes a nominal laser-hole size, ask which dimension that number describes and what tolerances apply to the finished connection.
Material response and copper preparation influence hole formation. The process must expose the intended target surface without leaving an unsuitable interface for later copper deposition. Machine specifications alone do not establish that the complete manufacturing sequence is qualified for the selected stackup.
Review inputs and evidence
| Input | Why it matters |
|---|---|
| Dielectric construction | Sets the material and depth that the drilling process must handle |
| Target copper and pad geometry | Defines the landing interface and registration margin |
| Hole distribution | Helps the fabricator evaluate the actual pattern and local process demands |
| Post-drilling preparation | Connects the formed opening with reliable metallization |
Think beyond the drilling step
A clean-looking opening is an intermediate feature. The finished interconnect depends on preparation, copper deposition and the subsequent processing history. Ask how the supplier verifies the final structure, not only how it measures the drilled hole.
For an illustrative design, a reduction in build-up dielectric thickness may help hole formation while also changing impedance and trace geometry. Treat that as a coordinated stackup revision. Engineering should review all affected features before approving the revised construction.
Prepare the RFQ
Include a layer-specific drill schedule, the proposed materials, hole and pad requirements, and any critical structures needing representative acceptance evidence. Flag unusual transitions or tightly packed arrays so the supplier can review them explicitly.
Record approved alternatives in the drawing. If the supplier proposes changing hole geometry or target-pad dimensions, check the impact on escape routing and nearby copper. The approved manufacturing proposal should become part of the released package. Laser types, machine models and qualified minimum dimensions for this site's operator are [NEEDS CLIENT INPUT]; this guide does not imply ownership of a particular drilling system.
Continue the engineering review
- Microvia aspect ratio design tradeoffs
- HDI PCB materials selection
- Copper-filled microvia processing
- 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.