PCB technologies / PROJECT FIELD GUIDE

HDI PCBs

Support dense component escape routing with an intentional via strategy.

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ENGINEERING → PROCUREMENT → PRODUCTION

THE PRACTICAL ANSWER

What to know before you decide

HDI PCBs use fine interconnections and microvia structures to route dense packages within limited space. The central decision is the connection architecture, not simply the smallest hole offered. Start with the component escape problem, compare simpler alternatives and then review the lamination sequence and via interfaces with the fabricator. A compact layout should be supported by evidence for the proposed construction, especially when several microvia levels or demanding thermal exposures are involved.

01 / DECISION GUIDE

Make the trade-offs explicit

Prove the escape requirement

Identify the package pitch, pad geometry and inner-ball routing demand. Test whether changes to fanout, layer allocation or placement can resolve the problem before selecting a more complex build. Keep a marked escape study with the RFQ. This gives the fabricator a specific engineering challenge to review rather than an open-ended request for maximum density.

Draw every via span and sequence

Show microvia, buried and through-hole connections on a stack-up diagram. Distinguish staggered from stacked arrangements and identify the interfaces carrying current between structures. The number of build-up cycles affects the manufacturing plan. Avoid using a shorthand such as HDI as the entire specification, because substantially different constructions can share that label.

Ask for evidence relevant to the structure

Discuss the intended assembly exposures and operating environment, then ask what process qualification or coupon evidence supports the proposed via arrangement. Geometric feasibility alone does not establish long-term performance. If the available evidence does not match the planned structure, consider a simpler architecture or a targeted validation build before accepting the design for production.

Coordinate pads, vias and assembly

When a microvia shares a solder land, define its surface treatment and the assembler's expectations. Confirm that the selected land geometry remains compatible with component guidance. Routing density, manufacturability and soldering requirements meet at the same small feature; reviewing them separately can produce a board that is routable but difficult to assemble consistently.

02 / SIDE BY SIDE

Compare the choices

HDI PCB microvia design — planning considerations
Architecture choice	Potential benefit	Review focus
Through-via baseline	Simpler process where routing permits	Escape feasibility
Single build-up microvia	Access to an adjacent layer	Dielectric and pad geometry
Staggered microvias	Avoid selected stacked interfaces	Space and routing demand
Stacked structures	Dense vertical interconnection	Interface reliability evidence
Every-layer approach	High interconnect freedom	Complete process and qualification scope

03 / REVIEW BEFORE RELEASE

Questions that prevent rework

Selecting the smallest feature everywhere

Use advanced features only where needed. Unnecessary density can constrain yield and sourcing without helping the circuit.

A stack-up without a via map

Layer count does not explain the build sequence. Show all connection spans and interfaces.

Reliability inferred from one successful prototype

A functioning sample does not establish performance across assembly cycles or the intended service environment. Define relevant validation.

04 / COMMON QUESTIONS

Get a clear answer

Does every fine-pitch BGA require HDI?

Not necessarily. Escape feasibility depends on pitch, pad geometry, signal count and available layers. Evaluate the actual fanout before selecting a microvia architecture.

Are stacked and staggered microvias interchangeable?

No. They use different space and interfaces and can carry different manufacturing and reliability considerations. Review each proposed construction with the fabricator.

What should an HDI RFQ include?

Include the package escape region, stack-up, via-span diagram, pad treatment, intended thermal exposure and requested reliability evidence, in addition to the normal fabrication package.

Technical references

Check each source’s scope and revision against your project requirements. Confirm the proposed construction with your manufacturing partner.

YOUR PROJECT / YOUR NEXT STEP

Build a useful project brief

Create an HDI architecture review brief. The output is not a microvia reliability approval.

Use this planning aid to prepare a review. It does not approve a design or estimate a price. Selections are processed locally and are not submitted by this tool.

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Useful next steps

01 / Capabilities