A custom LED PCB may look simple at first: define the board size, calculate the required number of LEDs, and arrange them across the available space.
In a real OEM product, however, LED placement cannot be considered independently from the mechanical design.
Mounting holes may occupy positions where LEDs would ideally be placed. A connector can affect both LED spacing and PCB routing. Internal housing structures may restrict where certain components can be located. Even a relatively small mechanical feature can influence the final LED arrangement if it appears in the wrong position.
This is why LED PCB layout is not simply a matter of fitting components onto a board.
The ideal LED layout and the final mechanical layout are not always the same.
In LED PCB design, mechanical requirements and LED placement therefore need to be considered together.
1. PCB Dimensions Are Only the Starting Point
When an OEM customer already has a finished or partially developed housing, the PCB dimensions and mounting-hole locations may already be defined.
In this situation, NKT may receive information such as:
- PCB dimensions,
- mounting-hole positions,
- 2D dimensional drawings,
- CAD drawings,
- or PDF drawings.
The LED module then needs to be designed around those existing mechanical conditions.
But not every project begins this way.
Sometimes the customer has not finalized the housing and asks NKT to propose the LED PCB dimensions and mounting-hole arrangement.
In these projects, NKT can develop the PCB around factors such as the required LED quantity, LED arrangement and overall board dimensions, then provide the proposed drawing to the customer for confirmation.
Therefore, the mechanical starting point can be different from one OEM project to another:
Existing housing
→ PCB follows defined mechanical constraints
or
Housing not yet finalized
→ PCB layout can help define the module's mechanical configuration
This flexibility can be important during custom LED module development.
2. Why Can a Small Mounting Hole Affect LED Placement?
A mounting hole normally occupies only a small percentage of the total PCB area.
The issue is usually not how much board area the hole consumes.
The more important question is:
Where is the mounting hole located?
Imagine that the preferred LED arrangement places an LED at a certain position to maintain relatively even spacing across the board.
If a mounting hole must occupy that same position, the LED has to move.
That change may then affect the spacing between neighboring LEDs.
Therefore, a small mounting hole can influence the LED layout even though it occupies very little PCB area.
This distinction is important.
Mechanical constraints do not necessarily make a large portion of the PCB unusable. Instead, their specific locations can conflict with preferred LED positions or PCB routing.
3. What Happens When a Mounting Hole Conflicts With LED Uniformity?
When NKT develops an LED layout, the LEDs are normally arranged as evenly as practical for the application.
But mechanical requirements can sometimes prevent a perfectly uniform arrangement.
A mounting hole is a typical example.
If the preferred LED position conflicts with a required mounting hole, there are two possible situations.
The housing is still flexible
If the customer's housing has not yet been finalized, NKT may ask whether the mounting-hole position can be adjusted.
Some customers place greater importance on light uniformity and may agree to move the mounting point if the product design allows it.
The housing is already fixed
If the housing has already been tooled or the mounting structure cannot be changed, moving the hole may not be practical.
In that case, the mechanical condition remains fixed and NKT adjusts the LED layout around it, trying to maintain the most uniform arrangement possible within the available constraints.
This leads to an important OEM design principle:
When mechanical constraints conflict with LED placement, the right solution depends on which product requirements are still flexible.
The relationship between LED spacing and the resulting light distribution is discussed further in LED light uniformity.
4. Mounting Holes Are Not Automatically Large Keep-Out Areas
The term keep-out area can sometimes create the impression that a large section of an LED PCB must always remain empty around every mounting hole.
That is not how NKT normally approaches the problem.
Mounting holes are handled according to the applicable PCB design rules and necessary clearances.
The practical layout issue is often much simpler:
Can an LED or another component be placed where we want it without conflicting with the mounting requirement?
If yes, the rest of the PCB can continue to be used normally.
If not, the affected component placement or routing needs to be adjusted.
This is why NKT does not normally treat mounting holes as a reason to reserve unnecessarily large unused PCB areas.
5. Connector Position Can Affect Both LED Placement and Routing
Connectors create a different type of layout constraint.
In many NKT projects, the customer does not specify an exact connector position, allowing NKT to determine a suitable location during PCB layout.
When selecting that position, several factors may be considered together:
- LED arrangement,
- PCB routing,
- available board space,
- connection direction,
- and accessibility during product assembly.
The connector itself may occupy only a relatively small area, but its position can still interrupt an otherwise uniform LED arrangement.
Its pins and associated traces can also influence nearby routing.
For this reason, connector placement should not be treated as an afterthought.
At the same time, the connector should not automatically be given priority over the optical layout.
The objective is to find a practical position that works with both the electrical design and the physical product.
Connector location deserves a deeper discussion of its own, so we will cover that separately in another LED module design article rather than turning this article into a connector-design guide.
6. Housing Structures Can Create Additional Layout Restrictions
Mounting holes and connectors are not the only mechanical constraints that can affect an LED PCB.
The internal structure of the customer's product can also matter.
For example, an enclosure may contain:
- an internal post or structural feature,
- a raised section of the housing,
- or an area where a taller PCB component would interfere with the enclosure.
A customer may also specifically define an area where components cannot be placed.
When this information is available before PCB design, NKT can take those restrictions into account during layout.
This is one reason why mechanical drawings are useful even when the electrical requirements of the LED module appear straightforward.
7. What If the Customer Does Not Provide Complete Mechanical Information?
Not every OEM project begins with a complete mechanical drawing.
A customer may initially provide only a general PCB size or basic product requirement.
In that situation, NKT will normally ask whether the customer already has defined dimensions and mounting-hole positions.
If the customer has them, the drawings can be provided for the PCB layout.
If the customer has not yet determined them and wants NKT to propose the arrangement, NKT can develop the PCB dimensions and mounting-hole layout based on the LED quantity and arrangement, then send the drawing to the customer for confirmation.
Therefore:
PCB size alone may not be enough to finalize an LED layout when the module must fit an existing mechanical design.
The amount of mechanical information required depends on how far the customer's product design has already progressed.
8. Why Can Mechanical Interference Still Appear During Prototyping?
Even when drawings are available, mechanical interference can occasionally be discovered during prototype evaluation.
For example, a PCB component may interfere with an internal housing structure that was not fully considered during the initial layout.
This does not happen frequently in NKT projects, but it is one reason physical prototype validation remains useful.
When interference is found, the first question is usually:
Can the PCB layout be adjusted without changing the customer's housing?
If moving a connector or another PCB component can resolve the issue, changing the PCB is often the more practical solution.
This is especially true when the customer's housing has already been tooled.
Changing a molded housing can involve additional tooling work, cost and a more complicated modification process. A PCB layout adjustment may therefore be much simpler.
This is one of the practical purposes of prototype validation before production.
9. Can Mechanical Constraints Reduce the Number of LEDs That Fit?
Yes, but this is not a common situation in NKT projects.
Occasionally, the combination of board dimensions and mechanical restrictions means that the originally considered LED quantity cannot be arranged practically.
When this happens, NKT does not automatically force the same number of LEDs onto the PCB.
Instead, the next step is to confirm the customer's actual performance requirement.
For example:
If the original lumen or power target is flexible
→ the customer may accept the revised module configuration.
If the target output must be maintained
→ NKT may evaluate whether another suitable LED can provide higher output within the application requirements.
Another possibility is to reconsider the LED operating current, provided the selected LED and module design allow it.
The appropriate response therefore depends on the customer's priorities rather than on a fixed rule.
For a deeper explanation of how output requirements affect the number of LEDs in a module, see LED quantity.
10. Why Not Simply Increase LED Current When Space Is Limited?
Increasing current can sometimes increase LED output, but it should not be treated as an automatic solution to a mechanical layout problem.
Higher LED current can affect:
- electrical loading,
- luminous efficacy,
- thermal conditions,
- and the operating point of the LED.
Therefore, if mechanical constraints reduce the number of LEDs that can reasonably fit, NKT first considers the customer's required output and available LED options before deciding whether a different operating current is appropriate.
The important distinction is:
The maximum allowable LED current is not automatically the preferred operating current for the module.
This relationship between LED current, output and efficiency will be discussed separately in a later article so that the current topic remains focused on PCB layout.
11. Mechanical Layout and Optical Layout Have to Work Together
For an LED module, component placement is not purely an electrical problem.
LED position also affects how light is distributed across the final product.
Ideally, LEDs can be arranged with appropriate spacing across the required illuminated area.
In practice, the PCB may also need to accommodate:
mounting holes
connector
housing structures
component clearances
PCB routing
These constraints can prevent a perfectly symmetrical LED arrangement.
NKT therefore uses engineering layout experience to achieve the most practical arrangement within the actual product constraints.
NKT does not perform optical simulation as part of this layout process.
Where light distribution needs to be confirmed in the finished application, prototype evaluation and the customer's final product testing remain important.
12. What Should an OEM Provide Before LED PCB Layout Begins?
If the product's mechanical design already exists, useful information can include:
- PCB dimensions,
- mounting-hole dimensions and positions,
- 2D dimensional drawings,
- CAD drawings,
- PDF mechanical drawings,
- connector requirements,
- and relevant housing restrictions.
Not every project requires exactly the same information.
If some mechanical details have not yet been determined, they do not necessarily need to exist before the LED module project can begin.
NKT can propose PCB dimensions, mounting-hole positions or component arrangements where appropriate and provide the design to the customer for confirmation.
The important point is to identify which mechanical conditions are already fixed and which can still be adjusted.
13. So, How Do Mechanical Constraints Affect LED PCB Layout?
Mounting holes, connectors and housing restrictions usually do not matter because they consume a large percentage of PCB area.
Their influence is often positional.
A small mounting hole can occupy an ideal LED location.
A connector can interrupt LED spacing or affect nearby routing.
An internal housing structure can prevent a taller component from occupying an otherwise suitable position.
The resulting design process is therefore not simply:
PCB size → place LEDs
A more realistic process is:
Product Requirements
↓
PCB Dimensions and Mechanical Information
↓
Mounting Holes + Housing Restrictions + Connector
↓
LED Placement + PCB Routing
↓
Check Spacing and Mechanical Compatibility
↓
Resolve Conflicts Where Necessary
↓
Customer Confirmation
↓
Prototype Validation
For custom OEM products, the objective is not to create the theoretically perfect LED pattern in isolation.
The objective is to create an LED PCB layout that works inside the real product while maintaining the required electrical and optical performance as closely as practical.
That is an important part of application-specific LED module design.
FAQ
Do mounting holes significantly reduce usable LED PCB area?
Usually not.
A mounting hole normally occupies only a small portion of the PCB. Its greater impact may come from its location. If the hole occupies a preferred LED position, the surrounding LED arrangement may need to be adjusted.
Can mounting-hole positions be changed to improve LED spacing?
Sometimes.
If the customer's housing is still under development, NKT may ask whether a mounting point can be moved when it conflicts with the preferred LED arrangement.
If the housing has already been tooled or the mounting position is fixed, the PCB layout normally needs to adapt to the existing mechanical design.
Who determines the connector position on a custom LED module?
It depends on the project.
In many NKT projects, the connector position is determined during NKT's PCB layout process. LED arrangement, routing and customer assembly access can all be considered when choosing the location.
If the customer specifies the connector position, the PCB is designed around that requirement.
What information should an OEM provide for LED PCB layout?
If available, PCB dimensions, mounting-hole positions and mechanical drawings are useful starting points.
NKT commonly works with 2D dimensional drawings, CAD drawings and PDF drawings.
If the customer has not yet determined the PCB dimensions or mounting points, NKT can propose them based on the module requirements and submit the design for customer confirmation.
What happens if a PCB component interferes with the housing?
If the conflict can be resolved by moving the PCB component or adjusting the PCB layout, that can be more practical than changing an already-tooled housing.
The appropriate solution depends on which mechanical features are fixed and which parts of the module can still be modified.
Can mechanical constraints affect LED quantity?
Occasionally.
If the required LED quantity cannot be arranged practically within the available mechanical conditions, NKT can discuss the output requirement with the customer and evaluate options such as a different LED selection or, where appropriate, a different operating current.
Key Takeaway
Mounting holes, connectors and housing restrictions do not necessarily consume large areas of an LED PCB.
Their importance is often where they are located.
Even a small mechanical feature can conflict with an ideal LED position, interrupt otherwise uniform LED spacing, affect PCB routing or interfere with another component.
When this happens, the solution depends on which requirements can still change.
If the housing is still flexible, a mounting position may sometimes be adjusted. If the housing has already been tooled, changing the PCB layout is often more practical.
A good custom LED PCB layout is therefore not simply the most uniform LED pattern—it is the most practical balance between LED placement, electrical routing and the mechanical requirements of the finished product.
If you are developing an OEM product, you do not need to finalize every PCB detail before discussing the LED module.
If your housing is already designed, you can provide the available dimensions, mounting-hole locations and mechanical drawings.
If the housing has not yet been finalized, NKT can develop a preliminary LED arrangement and PCB configuration based on your LED quantity, output and product requirements, then provide the proposed design for confirmation.
Learn more about LED Module Development and PCB Design Support, or discuss a new project through Request a Quote.