Press-fit PCB hole requirements should start with the exact connector pin and its current drawing, not with a generic drill size or tolerance. Release the connector’s specified finished plated-hole dimensions together with its plating, finish, board-thickness and assembly requirements. Then agree who will verify the holes, support the board during insertion, evaluate the force profile and authorize any rework.
A compliant pin needs the intended interference with the plated barrel. If the finished hole, barrel construction or insertion process differs from the connector maker’s requirements, a hole that appears dimensionally acceptable may still produce an unqualified interface.
For a broader explanation of how fabrication affects hole dimensions, see PCB finished hole size and drill tolerance. For a different application context, see press-fit technology for power and cooling systems.
Why the finished hole controls the interface
A compliant press-fit contact is designed to deform as it enters a plated through-hole. The resulting contact depends on the relationship between the pin and the hole, including the copper barrel and surface finish. The board must also tolerate the insertion process without damage that compromises the connection.
Several dimensions and conditions interact:
- Finished-hole diameter: The available space for the pin after plating and the applicable finish.
- Copper barrel: Its construction affects the mechanical and electrical interface. Barrel condition matters, not just the opening diameter.
- Surface finish: The material and thickness can affect the final opening and contact interface.
- Board thickness: The connector must be compatible with the engagement length and the board construction.
- Insertion support: The fixture must support the board where the connector is pressed without interfering with pins or components.
- Insertion behavior: Force and displacement can reveal process deviations when interpreted against an agreed connector-specific plan.
These factors are related, but they are not interchangeable. A finished-hole measurement does not prove barrel integrity, correct insertion or long-term connector performance.
Amphenol’s TB-2026 Rev G, Section 4.1, calls for inspection of blocked holes and finished plated-hole size for its VHDM connectors, while noting that drilling and plating also matter. That is useful evidence of the interaction, but it is a VHDM-specific document—not a universal hole specification for every press-fit connector.
Start with the exact connector documentation
Ask the connector maker for the drawing and application information for the exact contact and connector revision being released. Do not assume that connectors with similar-looking pins use the same PCB hole, finish or insertion requirements.
Confirm at least:
- The connector and pin part numbers, drawing revision and any applicable options.
- The finished-hole size and tolerance, including how the requirement is defined and inspected.
- The required copper plating, allowed surface finishes and any restrictions on the barrel.
- The supported board-thickness range and relevant pin engagement or protrusion requirements.
- The insertion tooling, board support and force-displacement guidance.
- The approved inspection, removal and rework instructions, including any limits on reuse.
Resolve conflicts between the connector drawing, PCB fabrication drawing and assembly instructions before fabrication. If the connector maker permits alternatives, record the approved alternative and its revision rather than substituting a preferred shop practice silently.
Drill diameter is not finished-hole diameter
The drill creates the initial opening in the laminate. Subsequent processing forms the plated barrel and applies the specified finish. The fabrication supplier therefore needs to choose and control its drilling and plating process so that the finished feature meets the released requirement.
Do not place a connector’s finished-hole requirement in a drill table without identifying it as a finished dimension. Equally, do not calculate a production drill size simply by adding an assumed plating allowance. The actual process, finish and feature geometry must be considered by the fabricator.
A release package should make these distinct:
- Design target: A nominal value used to describe the intended feature, if the drawing defines one.
- Acceptance limits: The permitted finished-hole range and any associated geometric or inspection requirements.
- Fabrication drill: The supplier’s process input, unless the parties have specifically agreed otherwise.
- Measured result: A result obtained using the specified method, location and decision rules.
A nominal value is not automatically the midpoint of the limits, and it is not an acceptance range by itself. A drawing tolerance is also not permission to ignore plating, finish or connector-specific conditions.
Decision table: what each result can—and cannot—establish
| Decision point | Evidence to use | What it can establish | What it cannot establish alone |
|---|---|---|---|
| Choose the hole requirement | Exact connector drawing and application document | The released connector-specific interface | That the PCB has been fabricated or assembled correctly |
| Select fabrication inputs | Fabricator’s process review against the finished-hole requirement | A planned route to the specified finished feature | Acceptance based on drill diameter alone |
| Check finished holes | Agreed gauge or measurement method, locations and limits | Whether checked features meet the dimensional decision rule | Barrel integrity, insertion quality or full-lot acceptance without the agreed plan |
| Examine a cross-section | Agreed destructive section and evaluation criteria | Local evidence of barrel construction or the assembled interface | The size and condition of every hole, or the full three-dimensional interface |
| Evaluate insertion | Approved tooling, support and force-displacement plan | Whether the observed insertion meets the agreed process criteria | Long-term performance or connector qualification by itself |
| Accept rework | Connector maker’s instructions and project authorization | Whether the proposed action is permitted under the agreed conditions | That a generic removal or reinsertion procedure is safe |
A hypothetical finished-hole check
Assume, solely for illustration, that a connector drawing permits a finished-hole diameter from 0.90 mm through 1.00 mm. This is not a recommended press-fit specification.
The window is:
- Upper limit minus lower limit: 1.00 − 0.90 = 0.10 mm
- Midpoint: (0.90 + 1.00) / 2 = 0.95 mm
If the drawing actually designated that midpoint as nominal, the same illustrative limits could be expressed as 0.95 ± 0.05 mm. A real drawing may use a different nominal convention.
Now assume three separate finished-hole measurements:
| Measurement | Difference from midpoint | Comparison with the assumed window |
|---|---|---|
| 0.94 mm | 0.94 − 0.95 = −0.01 mm | Inside |
| 0.99 mm | 0.99 − 0.95 = +0.04 mm | Inside |
| 1.01 mm | 1.01 − 0.95 = +0.06 mm | Outside: 0.01 mm above the upper limit |
These comparisons assume the reported values represent the finished-hole dimension required by the drawing, using the agreed measurement method and decision rules. The result of 1.01 mm is outside the assumed window; it should be addressed through the project’s nonconformance process.
The two in-window readings do not establish production acceptance. Three readings do not characterize a lot, and the example says nothing about blocked holes, plating, insertion force or connector qualification. Sampling, measurement uncertainty and acceptance decisions must follow the actual project plan.
Specify plating, finish and board construction
A finished diameter is only one part of the plated-hole requirement. Give the fabricator the connector maker’s applicable requirements for barrel copper and surface finish, along with the board’s construction and thickness.
The release should identify whether the hole dimension applies after the final finish and how it is to be checked. The connector maker should clarify any restrictions on finish material, thickness or other barrel conditions. The fabricator can then review whether its proposed process is compatible with those requirements.
Also check the connector’s board-thickness and pin-engagement conditions against the actual stackup. An otherwise acceptable hole may not be suitable if the board is outside the connector’s supported thickness range or if the pin and support fixture interfere with features on the opposite side.
Include hole locations, relevant keepouts and connector orientation on the drawing or in controlled assembly data. The guidance in fabrication drawing essentials can help organize these requirements, but the connector-specific information should remain identifiable.
Plan board support and insertion before release
Press-fit assembly is not just a hole-size check performed at the end of fabrication. The assembly team needs the connector drawing early enough to review the board, tooling and insertion sequence.
The support fixture should be designed around the actual board and connector geometry. Review:
- Where support is needed under the insertion area.
- Clearance for pins, protrusions and components on the opposite side.
- Board flatness and the risk of local bending during insertion.
- Connector orientation, seating features and access for the press tooling.
- Whether adjacent components or earlier assembly operations limit support.
- The insertion sequence for the actual connector arrangement.
The connector maker’s instructions govern the permitted insertion method. The assembly supplier should identify fixture or access concerns before the PCB and tooling are released; the customer or design owner should resolve any necessary board changes.
Agree on the force-displacement plan
An insertion force trace can help distinguish normal insertion from a process problem, but only when its limits and interpretation are defined for the connector and process. Ask the connector maker what force-displacement information is relevant, where limits apply and what action is required if a trace falls outside them.
The project agreement should state whether traces are collected, for which assemblies, how exceptions are dispositioned and what records are delivered. Do not substitute a generic force value for the connector maker’s guidance, and do not assume a normal-looking trace alone proves a qualified connection.
HilPCB’s through-hole assembly service includes review of press-fit requirements against the connector specification. The scope of tooling, insertion monitoring, inspection and records should be agreed for the particular project; review should not be interpreted as automatic 100% validation.
Choose inspection methods for the question being asked
Pin gauge or dimensional measurement
A calibrated hole gauge, such as an appropriately specified pin or go/no-go gauge, can provide a direct check of accessibility or conformance to defined hole limits. A go/no-go result is a decision against the gauge sizes; it is not necessarily a numerical diameter measurement.
Agree on the gauge design, calibration, insertion method, checked side and locations, and how the result will be recorded. The plan should account for the finished surface and avoid damaging or contaminating the barrel. A gauge check can help identify a blocked or undersized opening, depending on the method, but it does not by itself verify the complete barrel or the assembled contact.
Destructive cross-section
A cross-section can provide local evidence of the plated barrel and, if performed on an assembled interface, the contact region. It destroys the selected sample and shows only the plane examined. Section preparation and the position of that plane matter; a section is not automatically a reliable substitute for the specified finished-hole gauge.
Agree in advance which samples may be sacrificed, what features will be evaluated, the acceptance criteria and who receives the results. Use the method to answer a defined question rather than treating a section as proof that all holes or all assembled interfaces are acceptable.
For the wider inspection package, PCB first article inspection discusses how to organize evidence around released requirements. A first-article plan should not be confused with ongoing lot acceptance or connector qualification.
Put responsibilities in the release and RFQ
The design owner coordinates the requirements, but each party has a distinct role. Make those roles explicit in the RFQ and project agreement.
| Party | Responsibility to agree and document |
|---|---|
| Customer or design owner | Release the controlled PCB and assembly data; identify the connector; resolve drawing conflicts; approve changes and deviations. |
| Connector maker | Provide the applicable connector documentation and clarify pin, hole, plating, finish, insertion and authorized rework requirements. |
| PCB fabricator | Review and manufacture against the released finished-hole and board requirements; raise process or inspection conflicts before proceeding. |
| Assembly supplier | Review tooling access and board support; perform the agreed insertion and inspection operations; report exceptions. |
| Agreed inspection authority | Apply the specified methods, sampling and decision rules, and retain or deliver the records defined by the project. |
Include these fields in the release or RFQ:
- Connector manufacturer, part number, pin variant and drawing/application-document revisions.
- PCB fabrication and assembly drawing revisions, stackup and finished board thickness.
- Connector hole locations, finished-hole limits, definition of the finished state, plating and permitted finish.
- Applicable geometric, blocked-hole and barrel requirements from the connector documentation.
- Required gauge or measurement method, sample selection, decision rules and record format.
- Insertion tooling, support and sequence requirements, plus force-displacement monitoring and exception criteria if required.
- First-article or other inspection scope, including any destructive samples and required evidence.
- Nonconformance contacts, deviation approval authority and disposition process.
- Connector-maker instructions for removal, replacement and rework, including any authorized reuse limits.
For pricing and a manufacturability review, submit the controlled package through request a quote. If requirements or responsibilities need clarification before release, contact HilPCB.
Control deviations and rework
If a hole check, plating inspection or insertion trace does not meet the agreed requirement, isolate the affected material and use the project’s nonconformance process. Record the feature or assembly involved, the requirement and revision, the observed result and the proposed disposition.
Do not assume that enlarging a hole, soldering a press-fit contact, removing and reinserting a pin, or replacing a connector is acceptable. Each action can change the barrel or contact interface. Obtain the connector maker’s applicable instructions and the customer’s authorization, then define any required follow-up inspection. Reuse or rework limits are connector- and process-specific; they should not be invented from a generic rule.
Frequently asked questions
Is a press-fit hole specified by drill size?
Normally, the connector interface is controlled by the finished plated-hole requirement. The fabricator selects and controls drilling and processing to achieve that requirement unless the project specifies otherwise.
Does an in-tolerance hole guarantee a good press-fit connection?
No. Plating, finish, board thickness, barrel condition, insertion support and the connector-specific process also matter. Qualification requires the evidence defined for the actual connector and application.
Can a go/no-go gauge replace a cross-section?
Not generally. A gauge checks the feature according to its defined fit and method; a cross-section provides local destructive evidence of the barrel or interface. Choose each for the question it can answer.
What should be done with an out-of-window measurement?
Follow the agreed nonconformance process. Confirm the applicable requirement and measurement method, identify affected material, and obtain an authorized disposition rather than assuming the part can be reworked.
Who defines press-fit removal and reinsertion limits?
Use the exact connector maker’s instructions and the project’s approval process. Do not apply a generic reuse or rework cycle to an unspecified connector.