Vol.006 - Spring Screw vs. Push Pins with Compression Springs: What Really Impacts Thermal Performance?

A Selection Guide to Thermal Module Retention Solutions

Spring Screw vs. Spring-Loaded Push Pin (Push Pin with Compression Springs)

1. Introduction: How Mounting Methods Affect Thermal Performance

Following the previous issue’s discussion on thermal structures and thermal interface materials (TIMs), this article further examines how retention mechanism design influences thermal performance.

In thermal module design, the contact quality between the heat source and the heatsink directly affects overall heat transfer efficiency. One of the key factors behind that contact quality is contact pressure.

Common thermal module mounting methods include screw mounting, spring screw, push pin, clip, and adhesive mounting such as thermal tape or adhesive.

Each mounting method differs in pressure control capability, assembly efficiency, and suitable application scenarios. This article focuses on two of the most representative solutions currently used in thermal module design: spring screws and spring-loaded push pins. It further explores the differences between the two in terms of contact pressure, TIM compatibility, and practical application.

2. Overview of Retention Mechanism Design

2.1 Spring Screw

A spring screw structure consists of a screw, its threaded shaft structure, and a compression spring, which together generate preload during the fastening process.

Contact pressure is primarily provided by the compression spring. Its magnitude depends on the spring characteristics, such as spring rate and deflection, and can be adjusted through fastening torque. When used together with a backplate design, it can also reduce the risk of PCB deformation.

Key features

·       Contact pressure can be accurately designed and adjusted.

·       Pressure stability and consistency are high.

·       Suitable for high-power and high-reliability applications.

·       Rework and maintenance are easier because the structure supports repeated assembly and disassembly.

2.2 Spring-Loaded Push Pin

A spring-loaded push pin is a structure that combines a plastic fastener with a spring. It is secured by inserting the pin into the PCB, while the spring provides preload.

Compared with conventional non-spring push-pin fasteners, it already offers a basic level of contact pressure while retaining the advantage of fast assembly.

Key features

·       Fast, tool-free installation.

·       Provides a certain level of preload.

·       More cost-competitive.

·       Pressure control capability is limited by the spring and structural design.

3. Comparison of Mounting Methods

Item	Spring Screw	Spring-Loaded Push Pin
Pressure Control Capability	Stable & Adjustable Preload	Limited Preload
Contact Stability	High	Medium
Thermal Performance	High	Medium
Assembly Efficiency	Medium	High
Cost	Higher	Medium
Maintainability	High	Medium
Suitable Application	High heat flux density / High reliability-asked applications.	Low-to-medium heat flux density / Assembly efficiency-oriented applications.

 

4. Matching Mounting Methods with TIM Applications

Mounting methods and TIMs should be designed together, because different interface materials have significantly different requirements for pressure and compression conditions.

4.1 TIM Pressure Requirements

TIM Type	Pressure Dependence	Design Focus
Thermal Paste	Medium	Requires sufficient and uniform pressure so the material can spread into a thin and continuous thermal interface.
PCM	Medium	Requires both pressure and temperature to activate filling.
Thermal Pad	Medium to high	Requires compression and must achieve the target compression defined by the material specification.
Thermal Tape	Low	Primarily used for adhesion and gap filling.

 

4.2 Recommended Pairings

1. Spring Screw

Spring screws are suitable for TIMs that require stable, uniform, or controllable pressure.

·       Thermal Paste: It requires sufficient and uniform pressure to spread and form an extremely thin and continuous thermal interface layer, while excess material is squeezed out toward the edge area. Spring screws provide stable preload control and are therefore suitable for applications with stricter thermal resistance requirements or long-duration operation.

·       PCM: Once heated, PCM softens and fills the interface, but stable pressure is still required to maintain contact.

·       High-compression thermal pads / gap fillers: For example, materials that require more than 50% compression, depending on thickness and pressure conditions, need adequate pressure and controlled compression travel to ensure the target compression is achieved.

·       This makes spring screws suitable for high-power and high heat-flux-density applications.

2. Spring-Loaded Push Pin 

Because spring-loaded push pins provide a certain level of preload, they can be used with some TIMs under appropriate conditions.

·       Thermal Paste: It may be used in medium- to low-power applications or where thermal resistance requirements are less stringent, but the spring force provided by the push pin must still be sufficient to spread the paste evenly.

·       Thermal Tape: Its pressure requirement is low, making it suitable for lightweight designs and fast assembly.

·       Low-compression or thin thermal pads: These are only suitable when the material can perform effectively under low-pressure conditions and after verification against the material specification.

4.3 Key Principle

The mounting method determines the range of pressure that can be applied, while the TIM determines the heat transfer efficiency achievable under that pressure condition.

5. Relationship Between Contact Pressure and Thermal Resistance

There is a clear relationship between thermal performance and contact pressure:

·       Low pressure leads to poor contact and high thermal resistance.

·       Medium pressure improves contact quality, and thermal resistance drops rapidly.

·       At high pressure, the benefit gradually approaches saturation.

In addition, spring-loaded push pins provide only a limited pressure range, while spring screws can enter the optimal pressure range.

For high-power applications, the choice of mounting method directly affects the upper limit of achievable thermal performance.

6. Application Recommendations

The selection of a mounting method should be evaluated based on the system’s thermal design conditions and mechanical requirements, rather than being classified only by product type.

Recommended: Spring Screw

Spring screws are recommended under the following conditions:

·       High-power or high heat-flux-density applications.

·       Applications using thermal paste or PCM.

·       Designs requiring precise contact pressure control to reduce thermal resistance.

·       Long-duration operation or applications with high reliability requirements.

Common Use Cases

Server systems, AI platforms, high-performance IPC, mobile CPUs, and high-power embedded platforms.

Recommended: Spring-Loaded Push Pin

Spring-loaded push pins are recommended under the following conditions:

·       Medium- to low-power applications.

·       Applications using low-compression or thin TIMs.

·       Designs with lower requirements for contact pressure control.

·       Situations where assembly efficiency and cost are priorities.

·       Space-constrained designs or applications requiring tool-free installation.

Common Use Cases

Certain embedded and networking modules, peripheral IC cooling, and low-power systems.

7. Conclusion

Spring screws and spring-loaded push pins are not interchangeable replacements for one another. Rather, they are retention solutions designed for different application conditions.

At its core, choosing a mounting method is a matter of balancing three factors: pressure control capability, thermal performance, and cost and assembly efficiency.

With proper mechanical design and TIM selection, thermal module performance can be improved effectively while ensuring long-term system stability.