Engineering resources
Aspect ratio as a process review input
Aspect ratio is a compact description of a hole geometry. It is useful for screening a PCB construction, but it does not prove that the hole can be drilled, prepared and plated reliably. A ratio without a defined numerator and denominator can also send two reviewers to different conclusions.
Declare the calculation convention
For a mechanically drilled through-hole, a common manufacturing expression divides board thickness by production drill diameter. Eurocircuits explicitly identifies the production tool in its aspect-ratio definition. When reviewing another supplier, confirm its convention rather than assuming that a CAD finished-hole value is the same input.
Blind and buried structures need the relevant drilled depth, not automatically the entire final board thickness. Sequential constructions should be reviewed at the stage when the feature is produced. Keep those structures on separate rows of the hole table so a favorable through-hole calculation does not conceal a different via geometry.
Two ratios for one hypothetical hole
Geometry example, not a capability claim. A board is nominally 2.00 mm thick. The finished hole requirement is 0.25 mm, and the proposed production tool is 0.30 mm. Using the tool gives 2.00/0.30 = 6.67. Using the finished diameter gives 2.00/0.25 = 8.00. The geometry has not changed; the reporting convention has.
Now consider a provisional maximum thickness of 2.10 mm. At the same proposed tool diameter, the calculation becomes 7.00. Record which thickness case is being evaluated. Do not round a value down simply to fit a published limit. The fabricator must still review the complete construction and applicable acceptance requirements.
| Input | Record | Reason |
|---|---|---|
| Depth | Nominal and relevant upper condition | Identifies the drilled section |
| Diameter | Finished requirement and proposed tool separately | Prevents convention errors |
| Material stack | Exact grades and copper structure | Connects geometry to processing |
| Acceptance | Hole-wall and reliability requirements | Defines evidence beyond the ratio |
Use the result to ask better questions
Ask how the proposed hole structure will be qualified, which representative sections or coupons will be evaluated, and how any change to the tool or stack will be approved. Also review pad geometry and registration. Increasing a drill diameter may improve the ratio while reducing available annular ring; reducing board thickness may conflict with connector fit.
Start with the distinction between finished hole and drill tool sizes. Submit the hole table alongside the fabrication package, so the ratio remains a documented input to review rather than a stand-alone promise of manufacturability.
Project review
Send your drawing and project requirements for a fabrication review. Identify the board revision, intended material and any acceptance requirements with your attachments.
Sources and scope
References checked 9 October 2026. The worksheets and hypothetical examples are original editorial guidance. They do not establish production settings, material availability or approval of a particular construction.