Printed circuit boards (PCBs) form the foundation of electronics hardware, providing the platform to mount and interconnect components. But bare PCBs themselves need to be securely mounted inside enclosures and chassis to survive in end-use environments. A variety of techniques exist for fixing PCBs, one of which involves small metal spring clips.
These PCB mounting clips offer a quick, reusable method of securing circuit boards. In this comprehensive guide, we’ll explore what PCB clips are, the different types and materials available, their installation and usage best practices, and the advantages over other PCB mounting methods.
Choosing suitable PCB mounting clips helps streamline manufacturing while allowing serviceability, vibration resistance, and reliable board retention over time and environmental stresses. Read on to learn more about this indispensable PCB mounting hardware.
What Are PCB Mounting Clips?
PCB mounting clips are small spring-loaded metal fasteners that secure a printed circuit board to a device enclosure or chassis panel. They eliminates the need for separate board retention hardware like screws or standoffs.
The basic design uses spring properties to clamp onto the edge of the inserted PCB and provide downward holding force. The clip’s frame or base is simultaneously fixed to the enclosure interior surface. This effectively sandwiches the board securely between the clip and chassis wall.
Clips are typically made from stainless steel or beryllium copper alloy for good spring properties. They represent a reusable, zero-hardware approach to PCB mounting. Just pop in the board and the clips hold it firmly in place; no tools required.
PCB mounting clips hold boards by clamping onto their edges
Functions of PCB Mounting Clips
What core functions do PCB mounting clips serve?
Secures the PCB
The spring force of the bent metal clip grasps the edge of the inserted PCB to hold it stationary and prevent detachment.
Allows Quick Installation & Removal
No screws or standoffs needed to install or remove the board – just press it into the clips. This enables easy assembly and servicing.
Absorbs Vibration & Shock
The springiness of the clips dampens vibrations that would otherwise transmit to solder joints and cause failure. This cushions the PCB from shocks and impacts.
Compensates for Tolerances
The clips’ flexibility and range of motion accommodates variance in PCB size as well as thermal expansion.
Requires No Board Modification
Clips mount only to the board edge, avoiding modifications like drilling holes that could weaken the PCB.
Provides Electrical Isolation
Most clips have an insulating plastic lining to prevent shorting between PCB and chassis.
PCB clips simplify mounting while offering considerable functionality in an compact package.
Types of PCB Mounting Clips
Several variety of mounting clip designs exist, differing in aspects like retention method, position of the clip on the PCB, and specificity to board thickness.
Rail Mount Clips
- Clips fasten horizontally along a chassis mounting rail
- Allow sliding PCB insertion into the channel
- Most accommodate range of PCB thicknesses
Wall Mount Clips
- Affix vertically to enclosure walls or panels
- PCB presses straight down into clips
- Can be open frame or closed bodied
Open Top Clips
- Clip grabs top edge of PCB
- Allows vertical top-down insertion
- Provides access to PCB bottom
Closed Top Clips
- Clips over top side of PCB
- Grasps both top and bottom edge
- Restricts component height on bottom
Single Board Thickness
- Tight fidelity for specific PCB thickness
- Maximum holding strength
- Requires closely matching clip to board
Multiple Board Thickness
- Flexible spring accommodates a range of PCBs
- Looser grip but avoids mismatch issues
Consider the enclosure design, board dimensions, accessibility needed, and desired versatility when selecting clip configuration.
PCB Clip Materials
Material choice determines clip properties like springiness, durability, corrosion resistance, and cost:
Stainless Steel
- Most common – combines good strength and corrosion resistance
- Types 303, 304, 316 used for clips
- Can fatigue or fracture from excessive flexing
Beryllium Copper Alloy
- Copper alloy with 2-3% beryllium
- Excellent elasticity and fatigue lifetime
- Much costlier than steel
Phosphor Bronze
- Copper alloy with around 5% tin and 0.5% phosphorus
- Very robust elasticity
- Comparable cost to steel
Plastic
- Engineering plastics like acetal resin or PTFE
- Avoid metal corrosion and conductance
- Limitations in temperature and strength
Matching material performance to design needs and environment allows optimizing clip longevity and reliability.
Key Properties of PCB Clips
To select suitable mounting clips, consider these key mechanical properties:
- Young’s Modulus – The elasticity as measured by stiffness. Affects spring characteristics.
- Yield Strength – Stress point at which material transitions from elastic to plastic behavior, causing permanent deformation.
- Fatigue Strength – Resistance to failure under cyclical stresses from vibration. Important for resilience.
- Corrosion Resistance – Material durability when exposed to humidity, contaminants, cleaning agents. Stainless steel excels here.
- Electrical Conductivity – Performance tradeoff between conductance and isolation. Metals conduct while plastics insulate.
- Operating Temperature – Clips must maintain integrity across electronics’ temperature range.
- Flammability Rating – Materials should meet minimum flammability standards for safety compliance.
Consider target levels for each factor based on the application and environment.
Size Considerations for PCB Clips
Clips must be sized appropriately for the PCB dimensions:
Clip Opening
The initial unsprung gap should be slightly larger than the PCB thickness to allow easy insertion.
Clip Length
Sufficient to grasp adequate PCB edge length for security. Typically 0.4 to 1 inch long.
Clip Height
Should match distance between installed PCB and case surface. Around 0.1 to 0.4 inches.
Clip Spring Force
Selected based on PCB weight to provide suitable retention without excessive force.
Clip Placement
Spaced evenly around board periphery, avoiding interference with components especially on bottom side.
Careful sizing during design prevents issues like inadequate grip, obstructed components, or excessive PCB bowing.
Installation Best Practices
Follow these guidelines for proper PCB clip implementation:
1. Match Clip to Board Thickness
Select clip with unsprung opening slightly larger than PCB thickness.
2. Position Clips Properly
Space clips evenly around board edges, avoiding component interference.
3. Clean Contact Surfaces
Remove any grease or debris for best clip adhesion and isolation.
4. Install Mounting Hardware
Securely anchor clips to chassis according to manufacturer instructions.
5. Insert PCB Smoothly
Press board into clips evenly without tilting or misaligning.
6. Inspect Mounting
Verify all clips have properly grasped board and anchored it securely.
Proper clip selection, positioning and installation prevents loose PCBs or altered circuit performance from shorting.
Benefits of Using PCB Clips
PCB clips offer notable advantages over traditional fastener methods:
Quick, Simple Installation – Just press fit the board without tools for fast assembly.
Easy Removal and Servicing – No unscrewing required to remove board from clips.
Reusable – Clips retain spring properties after repeated PCB insertions and removals.
Compensates for Tolerances – Flexibility accommodates variance in PCB dimensions.
No Board Modification – Avoid drilling mounting holes that risk damaging PCB laminate and traces.
Absorbs Vibration and Shock – Cushions PCB from environmental stresses that could break solder joints.
Lightweight – Important for weight-sensitive mobile and aerospace applications.
Low Cost – Simple bent metal design makes clips an affordable mounting option.
For applications requiring occasional PCB access or serviceability, clips eliminate the need to unfasten screws and provide tool-less convenience.
PCB Clip Design Considerations
Several factors go into engineering clips for optimal functionality:
- Avoid Plastic Deformation – Clip stresses should remain in elastic region to prevent permanent bends.
- Minimize Fatigue – Dynamic stress cycling can work-harden and prematurely fracture metals. Build in high fatigue resistance.
- Control Corrosion – Many options exist for corrosion-inhibiting platings and coatings on clips.
- Prevent Conductive Contact – Insulate clip contact regions with plastic sleeves, edge tape or conformal coatings on PCB.
- Accommodate Tolerances – Design spring geometry for flexibility to account for size variations in PCBs and enclosures.
- Ease Lead-In – Shape clip opening to guide PCB insertion without snagging.
- Supply Sufficient Force – Balance clip grip strength with avoiding excessive PCB bowing or deformation.
Detailed engineering of clip materials, mechanical design and installation practices is key to reliability.
PCB Clips – FQA
Here are answers to some frequently asked questions about PCB clips:
How many PCB mounting clips should be used?
As a general rule, use one clip adjacent each corner of the board, for a total of four clips. Very small boards may only need two clips while larger boards over 12 inches may require six clips or more. Space clips evenly around the PCB periphery for stability. Too few clips risks the board dislodging while too many impedes natural PCB expansion/contraction.
Can PCB clips be used in high vibration environments?
While clips can withstand mild vibration, their grip may loosen under sustained heavy vibration like in automotive or industrial equipment. Supplemental corner screw-downs or adhesives help strengthen retention in high vibration. Solid fastener mounts like standoffs provide maximum vibration resistance.
Do PCB clips allow stacking boards vertically?
Yes, elongated versions of PCB clips are available that can secure a vertical stack of multiple PCBs in alignment. The extended height clips span the entire stack while allowing insertion/removal of each board. Light pressure is maintained between boards to prevent rattling while avoiding bowing.
What prevents PCB clips from shorting the board to the chassis?
Clips either have an insulating plastic lining or are used with insulating washers and spacers to prevent the metal clip from electrically contacting the PCB or chassis surfaces. Insulating tape along the PCB edge provides additional protection.
Can PCB clips withstand high temperatures like SMT reflow?
While some specialty high-temp PCB clips exist, most standard clips are designed for hand assembly and lower temperature operation. Metal clip Solders would melt and plastics degrade at reflow temperatures. Fixturing or masking may be required during reflow to avoid damaging clips.
Conclusion
PCB mounting clips offer a quick, secure and reusable method of attaching printed circuit boards to enclosures and chassis. Their metal spring design provides sufficient retention while absorbing shock and vibration that could otherwise damage fragile solder joints. With careful attention to material selection, mechanical engineering and installation best practices, clips can simplify PCB mounting compared to screw fasteners. The availability of various clip configurations and custom designs ensures a mounting solution tailored for your specific application needs.
