Choose the enclosure before routing the PCB, then freeze both designs against one mechanical drawing. A board outline alone cannot prove fit. You also need mounting coordinates, connector envelopes, component heights and an assembly path. For an illustrative 3 × 5 in [76.2 × 127 mm] PCB, the enclosure must accommodate everything around that rectangle. Use the circuit board and battery enclosure sizing article for general space planning; this checklist focuses on the interfaces you must settle before board release.
Establish the usable internal envelope
Start with the environment, then choose a candidate enclosure with a dimensioned drawing. Lightweight indoor equipment may suit plastic. Metal may suit different mechanical, shielding or installation requirements, but it changes the antenna plan.
Our custom enclosures include polycarbonate in standard molded sizes, cut to your layout. Custom cutouts do not mean a custom molded shell. Establish the available shell geometry before committing the PCB outline.
Check these dimensions on the actual enclosure drawing:
- Minimum usable internal width and length at the board's mounting height, not just at the lid opening.
- Distance from the mounting surface to the lowest lid feature.
- Positions and heights of bosses, ribs, gasket channels and fasteners.
- Space occupied by an internal mounting plate or adapter plate, if used.
- Wall thickness and its variation wherever connectors or controls pass through.
- Access needed to install the board without scraping components against the enclosure.
Do not treat external dimensions as usable dimensions. Tapered plastic walls can also make the available footprint change with height.
Record the required environmental protection separately from the dimensional requirements. Any enclosure rating we specify is a manufacturer rating; our enclosures are not UL listed.
Put the board and enclosure on one coordinate system
A hole pattern described from several unrelated edges is difficult to inspect and easy to reverse. Establish shared references before exchanging drawings.
- Define the mounting plane and two perpendicular reference edges.
- State which view shows the coordinates, such as looking into the open enclosure.
- Dimension the board outline, mounting holes and connector centerlines from those references.
- Identify hole diameters, fastener sizes and any slots explicitly.
- Include enclosure tolerances, board fabrication tolerances and mounting play in the fit review.
- Reserve clearance around screw heads, washers, mounting posts and installation tools.
Do not assume a screw hole is also an accurate locating feature. Clearance holes allow movement, which affects the position of board-mounted connectors at the wall.
If the enclosure's mounting pattern does not match the board, settle the adapter arrangement before routing. The PCB mounting article explains mounting approaches; the release drawing must identify which arrangement you actually selected.
Keep copper and components away from mounting hardware according to the electrical design requirements. Mechanical clearance is not a substitute for required electrical spacing.
Freeze the DB25 and power interfaces
A DB25 connector needs more space than its mating face suggests. Its mounting style determines where that space sits.
A board-mounted right-angle connector ties the PCB position directly to the wall opening. A panel-mounted connector with internal wiring relaxes that alignment, but needs space for terminations and wire routing.
Check the complete connector assembly:
- Exact connector part and manufacturer's recommended panel opening.
- Flange, mounting hardware and permitted panel thickness.
- Connector body and solder tails inside the enclosure.
- Mating plug, backshell and cable bend outside the enclosure.
- Access to retention screws with adjacent cables connected.
- Any required gasket and its compression or mounting requirements.
Do not use a generic DB25 outline as the production cutout. Different mounting arrangements can require different openings and hardware.
Check whether the connector can enter its opening during board installation. A connector trapped behind the wall may fit perfectly in the final model but remain impossible to assemble.
For an optional power inlet, define plug insertion depth and internal termination clearance. If power enters through the DB25, review contact ratings, conductor size and fault protection separately. Connector shape alone establishes none of these.
Adding a connector or reset control also changes the enclosure boundary. The article on enclosure ratings after mounting devices explains why the completed assembly needs its own review.
Calculate the complete board stack
Depth often fails after width and length appear settled. Include the underside of the lowest board and the tallest feature above the highest board.
The following is an illustrative stack, not a catalog enclosure specification. It assumes two boards with no underside components extending below the lower board.
| Stack element | Example height |
|---|---|
| Mounting plane to lower PCB underside | 0.25 in [6.35 mm] |
| Lower PCB thickness | 0.063 in [1.60 mm] |
| Clear gap between PCB surfaces | 0.40 in [10.16 mm] |
| Upper PCB thickness | 0.063 in [1.60 mm] |
| Tallest component above upper PCB | 0.35 in [8.89 mm] |
| Illustrative mechanical clearance above components | 0.10 in [2.54 mm] |
| Required usable height for this example | 1.226 in [31.14 mm] |
An enclosure with only 1 in [25.4 mm] of usable height cannot contain this stack. An enclosure measuring that depth externally offers still less usable height.
Before approving the stack:
- Use the fully mated dimensions of board-to-board connectors.
- Include solder joints, leads and underside components.
- Check overlapping components within the gap between boards.
- Allow for connector seating variation, board bow and enclosure tolerances.
- Confirm that electrical spacing and cooling requirements exceed any illustrative mechanical allowance where necessary.
A nominal gap that disappears at the tolerance limits is not a reliable fit.
Prove the installation and service paths
Final position is only one part of fit. Every board, connector and fastener needs a practical route into that position.
Use an unpowered mechanical mock-up or representative parts to check the sequence:
- Insert the board without bending it or forcing connectors against the wall.
- Reach every mounting screw with the intended tool.
- Attach internal cables without trapping them beneath the board.
- Close the lid without loading components, cables or connector bodies.
- Remove the board without dismantling unrelated equipment.
- Reach reset controls and programming connections as intended.
Keeping external connectors on one face often simplifies installation. Opposite faces can also work, but connectors on adjacent faces deserve an explicit assembly-path check.
Define how a reset button operates through the enclosure. Include actuator travel, alignment, wall thickness and protection against unintended operation. A hole that admits a tool is still an opening in the enclosure boundary.
Do not rely on a cable or connector to hold the PCB in position. Support the board and provide cable restraint appropriate to the installation.
Reserve antenna and thermal space
Wi-Fi placement can invalidate an otherwise complete mechanical design. A metal enclosure strongly attenuates radio signals, so do not assume an internal antenna will provide dependable coverage.
Plastic avoids that metal barrier, but nearby wiring, ground planes and components can still affect antenna performance.
Freeze these requirements before routing:
- Antenna position and orientation within the enclosure.
- The radio or antenna manufacturer's copper and component keepout requirements.
- Separation from conductive mounting parts and cable bundles.
- An external antenna interface, if required and supported by the radio design.
- Antenna cable routing, bend limits and connector access.
For an external antenna, use the enclosure antenna feedthrough article to plan the sealed boundary. Address mechanical loads using the antenna mounting article.
Also record board dissipation and maximum ambient temperature before freezing the enclosure. Leave space for the chosen heat path. The sealed-enclosure component layout article covers the thermal placement decisions; do not use spare volume as proof of adequate cooling.
Close the mechanical release checks
Release the PCB only after the enclosure and board drawings agree. Keep a dated revision pair so later changes cannot silently break the interface.
- Board outline fits the minimum usable envelope.
- Mounting coordinates and hardware agree across both drawings.
- Connector openings align throughout the tolerance range.
- Board stack clears the lid, ribs and fasteners.
- Cables fit with their required bends and strain relief.
- Assembly and removal paths have been demonstrated.
- Antenna keepouts and the thermal arrangement remain unobstructed.
- Any change to mounting, connectors or board thickness triggers another fit review.
A physical fit check before a larger production release is more useful than another visual inspection of the PCB outline alone.
What to send with the enclosure quote request
Send a coordinated mechanical package rather than a board width and length. Use the cutout designer to lay out openings, check spacing and export the layout with your request.
Include:
- Required material, installation environment and enclosure protection requirements.
- Candidate enclosure drawing, or required usable dimensions if the shell is not selected.
- Dimensioned PCB outline, mounting coordinates and complete height envelope.
- Connector drawings, panel thickness limits and internal and external clearance envelopes.
- Cutout locations referenced to named enclosure datums.
- Antenna position, cable routing and thermal provisions.
- Assembly sequence, service access and critical tolerances.
- Drawing revisions, quantity and any required evaluation or listing documentation.
Keep PCB fabrication and assembly deliverables separate from the enclosure specification. A mechanical fit package does not define component procurement, board population or functional testing. Settle those responsibilities separately, then release the enclosure and PCB against the same approved interface drawing.
Enclosures for this job
Catalog sizes that suit the job this article answers, picked from its subject; open one for its full specifications.
| Enclosure | Material | Outside H x W x D / display | Rating |
|---|---|---|---|
| 10 × 8 × 6 in | 304 stainless | 10 x 8 x 6 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
| 12 × 10 × 6 in | 304 stainless | 12 x 10 x 6 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
| 16 × 12 × 8 in | 304 stainless | 16 x 12 x 8 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
Questions
Should the enclosure be selected before the PCB is designed?
Choose a candidate enclosure before routing, then coordinate both designs against a shared mechanical drawing. Freeze usable internal dimensions, mounting coordinates, connector positions and height limits before releasing the PCB. Recheck fit whenever a later change affects one of those interfaces.
Will a 3 × 5 in enclosure fit a 3 × 5 in PCB?
No. Those dimensions describe only the board outline. The usable enclosure space must also accommodate mounting hardware, connector bodies, component heights, cables and installation access. External enclosure dimensions cannot establish whether the board fits inside.
How much enclosure space should be reserved for a DB25 connector?
There is no universal allowance. Use the selected connector drawing, including its body, solder tails, mounting hardware and permitted panel thickness. Check the mating plug, backshell, cable bend and screw access outside the enclosure as well as the space inside.
Can the Wi-Fi antenna stay inside a metal enclosure?
Do not assume an internal antenna will provide reliable coverage through a metal enclosure. Plan an external antenna interface supported by the radio design, or evaluate a suitable nonmetallic enclosure. Follow the antenna keepout requirements and verify performance in the completed assembly.
