Deep Dive into Thermal Contact Fixation Solutions for Power Semiconductors and Cooling Blocks

2026-04-03

In high-performance power electronic systems, the heat dissipation efficiency of semiconductor devices (such as TO-220 and TO-247 packages) depends not only on the material of the cooling block but also on the quality of the thermal interface pressure between the device and the contact surface. To ensure that the Thermal Interface Material (TIM) fully fills voids and maintains long-term stability, selecting the appropriate pressure-fixation mechanism is critical.

The following is a detailed comparative analysis of the four mainstream fixation solutions used in the industry and their technical characteristics.

1. Spring Clips —— Pursuit of Balance and Efficiency

For compact packages like TO-220 and TO-247, spring clips are recognized as the preferred solution.

Technical Advantages:

Uniform Pressure Distribution: The clip typically acts on the geometric center of the package, effectively counteracting the “single-sided stress” caused by traditional screw fixation. This ensures a uniform TIM thickness, thereby reducing thermal resistance.

Dynamic Stress Compensation: The elastic modulus of the clip allows it to absorb the expansion and contraction stresses of the semiconductor during cyclic thermal loading, preventing contact failure caused by thermo-mechanical fatigue.

High Production Consistency: Assembly requires only a simple snap-fit, avoiding quality fluctuations caused by inconsistent manual tightening torque.

Limitations:

Structural Dependency: The cooling block usually requires pre-machined slots or steps to accommodate the clips, increasing the machining complexity of the baseplate.

Fixed Pressure Specifications: The clamping force is determined by the material and geometry of the clip, offering little room for adjustment later.

2. Bolt with Belleville Washers —— Pursuit of Ultimate Stability

Fixation is achieved by passing a bolt through the package mounting hole and using a Belleville washer to maintain pressure.

Technical Advantages:

Powerful Pressure Output: By adjusting the torque or selecting different washer specifications, extremely high contact pressure can be achieved, suitable for high-power applications with stringent thermal resistance requirements.

Superior Shock Resistance: The combination of mechanical thread locking and spring pre-loading provides the highest mechanical reliability in environments with heavy vibration or impact, such as transportation.

Limitations:

Risk of Stress Concentration: Pressure is concentrated around the mounting hole, which can cause a slight “warping” at the far end of the device, creating air gaps.

Complex Assembly Process: Involves multiple loose components (bolts, washers, insulating bushings, etc.) and requires high precision in torque control.

3. Clamping Bars / Leaf Springs —— Pursuit of Array Integration

A long metal clamping bar is used to simultaneously press down a row or group of semiconductor devices.

Technical Advantages:

High Integration: A minimalist structure can fix multiple devices simultaneously, significantly saving space on the cooling baseplate.

Broad Contact Area: The bar can span the entire surface of the devices, providing a flatter pressure distribution.

Limitations:

Height Sensitivity: If there are minor height tolerances between multiple devices, the bar may exert insufficient pressure on some. This typically requires adding flexible materials, such as thermal conductive pads, for compensation.

4. Constant Force Springs —— Pursuit of Top-tier Performance

Usually applied to press-pack power modules or precision equipment extremely sensitive to thermal drift.

Technical Advantages:

Highly Constant Pressure: Provides a nearly unchanged load over a wide range of displacement, completely ignoring displacement fluctuations caused by thermal expansion.

Minimized Thermal Resistance: This is the most reliable solution for achieving ultra-low interface thermal resistance.

Limitations:

High Cost: Involves precision molds and complex mechanical support frames; typically reserved for high-end fields like HVDC transmission and rail transit.

Conclusion and Recommendations

When selecting a solution, if your application focuses on mass production reliability and thermal distribution uniformity, Spring Clips are recommended. If the application environment involves strong vibrations or requires extreme contact pressure, a combination of Bolts and Belleville Washers should be chosen.

Dongguan Haocheng Hardware & Spring Co., Ltd. boasts over two decades of extensive experience in custom manufacturing, having accumulated a wealth of practical case studies and design solutions specifically within the field of semiconductor thermal interface mounting. Beyond offering standardized products, we are dedicated to providing you with comprehensive, one-stop technical support—ranging from pressure calculations to structural optimization. We welcome your inquiries for quotations or the opportunity to discuss design details; we look forward to crafting highly reliable thermal connection solutions tailored to your needs.

Contact: Jordan Liu
Email: jordanliu@hcmetal.cn
WhatsApp: +86 18219271011