PCB fabrication
- Gerber or ODB++ fabrication data and the board outline
- Layer stackup, material identity, finished copper and board thickness
- Drill data, impedance targets, surface finish and inspection requirements
Engineering Reference
PCB Drilling & Via Structures
A hole needs a purpose, a dimension and a layer span. Keep drill-tool and finished-hole requirements distinct, then define plating, pad structure, protection and acceptance for each hole family in the fabrication package.
Capability register
Scope and conditions
Read each value together with its board type and review conditions.
- 0.1mmMechanical drill reference
- Rigid published entry; tool/finished review
- 0.075mmLaser drill reference
- Rigid and rigid-flex; depth review
- 20:1Mechanical aspect ratio
- Rigid only; laser limit is separate
Published limits apply to their stated board type. Layer count, copper weight and minimum geometry require a combined engineering review.
Capability register
Mechanical and laser drilling register
The figures are board-type-specific process entries. State the actual processed depth and whether the specified dimension is drilled or finished.
On smaller screens, scroll within the table to see every column.
| Parameter | Published capability | Applies to | Review conditions |
|---|---|---|---|
| Minimum mechanical drilling | 0.1mm | Rigid, flex and rigid-flex entries | Plated/non-plated status, drill vs finished size, depth and tolerance |
| Minimum laser drilling | 0.075mm rigid/rigid-flex; 0.1mm flex | Respective board types | Dielectric depth, layer span, pad, fill and final hole definition |
| Mechanical aspect ratio | 20:1 rigid; 10:1 flex; 12:1 rigid-flex | Mechanical drilling | Use the actual processed depth and diameter; no automatic combination of limits |
| Laser aspect ratio | 1:1 | Rigid and rigid-flex entries | Separate from mechanical-hole figures |
| Press-fit hole tolerance | ±0.05mm | PCB entries | Finished-hole definition, connector requirement and measurement |
| PTH tolerance | ±0.075mm | PCB entries | Finished plated diameter and critical-hole exceptions |
| NPTH tolerance | ±0.05mm | PCB entries | Finished non-plated diameter and drawing datum |
| Countersink tolerance | ±0.15mm | PCB entries | Specify the controlled countersink dimension and drawing geometry |
Engineering review
Blind vias: identify the external-to-internal span
A blind connection is specified by its start and end layers.
Provide a separate drill family for each span, with hole size, pads and the required finished condition. The material depth and build sequence must be reviewed with that span.
The 20L reference includes 1–4 / 17–20L blind connections. The RF examples include other spans; none of these examples establishes a universal blind-via depth or maximum order.
Engineering review
Buried vias: coordinate the internal structure
A buried connection is completed within the stack rather than opening on the finished external surfaces.
Show the internal start/end layers and keep the layer numbering consistent between drill data and stackup. Define pads, clearances, plating and any filling requirement before later layers cover the structure.
The capability list includes blind-buried via boards. A new buried-via design still requires review of the proposed lamination sequence and the evidence needed for acceptance.
Engineering review
Via-in-pad: specify the required finished pad
The component land and the via are one assembly interface.
Identify which pads contain vias, the via layer span and the required fill or cap. State the finished surface requirement and the inspection criteria relevant to the component attachment.
Do not treat an unspecified covered hole as an approved filled-and-capped pad. Provide the package and land-pattern requirements so fabrication and assembly can review the same structure.
Engineering review
Backdrill: define the layers to remove and preserve
Use a controlled drawing and drill map for the backdrill operation.
Identify the drilling side, start/end relationship, backdrill diameter, target residual stub and keepout from retained connections. State which values are critical acceptance dimensions.
The 14L RO4003C + HTG example records 1–4 / 1–9L backdrill entries. These are spans in that project, not a general residual-stub or depth-tolerance specification.
Engineering review
Annular ring: review the pad and hole together
No single universal minimum annular-ring value is inferred from the capability table.
Provide pad diameter, drill/finished diameter, layer and registration-sensitive areas for each critical hole family. Identify any drawing-specific breakout or acceptance requirement.
The review must consider the actual copper, hole structure and layer registration. Keep annular ring separate from trace/space and hole-to-line dimensions in the drawing.
Engineering review
Castellations: define the edge connection
An edge-plated feature needs both the hole data and the finished outline.
Show the intended finished half-hole geometry, copper layers, plating/finish and the relationship to the routed edge. Provide critical tolerances and the mating or soldering interface.
Send the full panel and outline concept where available. Manufacturing sequence, holding features and acceptance of the exposed edge are reviewed for the proposed construction.
Engineering review
Plated slots and mechanical features
Distinguish a plated electrical slot from a non-plated mechanical opening.
Dimension finished slot width, length, end geometry, location and tolerance. Mark plated status and the connected copper layers, and avoid conflicting dimensions in drill and routing files.
For connector or press-fit slots, provide the mating-part drawing and the measurement requirement. Confirm any countersink or counterbore as a separate controlled feature.
Engineering review
Via protection: name the intended condition
Protection controls what remains exposed after fabrication.
Mark which via families are open, mask-covered, plugged, filled or capped as required by the design. Identify sides and local exceptions rather than relying on a board-wide note.
Coordinate the protection with solder-mask openings, finish, assembly lands and the required inspection. The selected structure and acceptance criteria must be agreed in the release package.
Engineering review
Hole and via RFQ checklist
Make every hole family traceable from data to drawing.
- Data
- Fabrication and drill files, plated/non-plated separation, all start/end layers and the released stackup.
- Requirements
- Finished vs drill dimensions, tolerance, pad structure, slots, edge features, fill/cap and backdrill instructions.
- Acceptance
- Critical connector/press-fit criteria, requested cross-sections or other evidence, and any allowed engineering adjustments.
RFQ checklist
Send the files that define your build
Include the drawing revision and acceptance requirements. The engineering review confirms the manufacturable combination before quotation.
PCB assembly
- PCB fabrication package and an itemized BOM with manufacturer part numbers
- CPL / pick-and-place data, assembly drawings and component polarity
- Component sourcing scope, programming files and the agreed test procedure
Engineering FAQ
Questions before you quote
Is the smallest drill value the finished plated hole size?
The table is a drilling entry. State whether your requirement is a drill-tool or finished diameter, with plated status and tolerance, so engineering can reconcile it.
Can 20:1 be used for laser microvias?
No. The 20:1 entry is rigid mechanical drilling. The rigid and rigid-flex laser aspect-ratio entry is 1:1.
What is needed for backdrill review?
Provide side, span, diameter, retained connection, target residual stub, keepout and the acceptance dimensions in a controlled drawing.
Does via protection automatically mean filled and capped?
No. State the required condition explicitly for each via family, including sides and exceptions. Filling, plugging, covering and capping need distinct instructions.