Define standard for this project
Standard is not a universal set of dimensions. Establish the candidate supplier's ordinary material, copper, drilling, and routing options for the intended board. Use those as a comparison baseline and keep the same electrical, mechanical, and assembly requirements for an HDI alternative.
A conventional layout that depends on unusually fine traces or marginal via lands may already be demanding. Conversely, an HDI design with generous geometry may be straightforward within an appropriate qualified process.
Use a real package escape study
Check the device's ball map, unused positions, power groups, and allowed pin assignments. NXP's non-HDI WLCSP application note gives device-specific examples showing why package organization matters. Do not transfer those example dimensions directly to another package.
Attempt the difficult routes first. Include plane connections and decoupling placement so the study represents a complete electrical design. A fanout that exports signal pins while leaving power access unresolved has not demonstrated feasibility.
Compare the consequences that affect the product
For an illustrative handheld instrument, a conventional option may require more board area, while HDI may preserve the desired outline. Compare that area tradeoff with enclosure freedom, test points, connector access, and assembly yield considerations. A board that fits the enclosure but cannot be probed or serviced may create new product costs.
- Keep the same component and connector placement assumptions.
- Compare usable routing channels, not just line counts.
- Review return paths wherever layers change.
- Ask for quotations against equally complete acceptance requirements.
Choose by demonstrated need
Record the constraint that forces HDI if it is selected. That reason becomes a useful design rule during later changes. If the conventional option meets every requirement with comfortable margin, HDI can remain an alternative for a future size reduction instead of being introduced without a measurable benefit.
Adjacent-layer access, one connection at a time
Dielectric · geometry + material
Core or build-up dielectric
Illustrative only. Copper thickness, dielectric construction and via spans require a reviewed stackup.
Common questions
Does fine package pitch always require HDI?
No. Pin population and escape arrangement also matter. Use the exact component's documentation and a routing study.
Can HDI reduce the number of layers?
It can in some layouts, but this is not guaranteed. Additional access may reduce routing demand while reference and power requirements still set the layer count.
References & further reading
Method & assumptions · General design guidance. Validate the proposed construction and acceptance criteria for your project.