HPC/AI Servers: Torque and Material Selection for Thermal Modules and Fasteners
Executive Summary
A heatsink compression screw is not tightened by simply tightening it harder; it must compress evenly, stay loose-free, leak-free and be serviceable. Based on the YF Zhichengjia HPC/AI-server handbook, this article explains heatsink compression torque, pre-applied adhesive and IP68 sealing, UQD quick connectors, and captive panel screws.
Table of Contents
Special Requirements of Thermal Modules on Fasteners
The heat density of AI compute chips rises year by year, and fastening of heatsinks, heat-pipe modules and cold plates has evolved from "just press the heatsink down" into an independent engineering topic. According to the YF Zhichengjia HPC/AI-server handbook, the thermal-side joint must simultaneously satisfy four things: sufficient and even compression (to keep the thermal interface material, TIM, in contact with the chip), long-term anti-loosening (fan vibration never stops), sealing when needed (liquid cooling must not leak), and serviceability (fasteners must not be lost when panels are removed in the field).
Heatsink Compression: How to Set Torque and Clamping Force
The core of heatsink mounting screws is not "tightening" but "even compression." If the clamping force of the several screws around one chip scatters, the TIM layer thickness varies and local hot spots trigger frequency throttling. Following the logic of GB/T 16823.2 General Rules for Tightening of Threaded Fasteners and GB/T 16823.3 Torque-Clamp-Force Testing, thermal simulation first determines the required clamping-force range, which is then converted into assembly torque. The torque coefficient K is unavoidable here: because surface state differs within a screw batch, K fluctuation directly amplifies clamping-force scatter.
| Thermal Joint Position | Fastener Solution | Control Point |
|---|---|---|
| Heatsink compressing chip | Anti-loosening coated screws (TORX) | Diagonal multi-pass tightening, even clamping |
| Heat pipe / vapor chamber fixing | Short-thread stainless screws | Control insertion depth, avoid piercing heat pipe |
| Liquid cold-plate mounting | Sealing screws / sealed self-clinching studs | Stable O-ring compression, up to IP68 |
| Cold plate to piping | UQD quick connector | Zero drip, high flow, blind mate |
| Serviceable panel cover | Captive screws | Screw stays after removal, no loss |
Anti-Loosening and Sealing: Pre-Applied Adhesive, O-Rings and IP68
The handbook's anti-loosening path uses dual principles in parallel: the bolt achieves anti-loosening through combined washers and pre-applied thread-locking adhesive (chemical plus physical). The chemical means is a micro-encapsulated nylon layer that breaks and cures on insertion; the physical means is the friction locking of the combined washer. At waterproof positions, adhesive can be pre-applied under the head or on the threads, or an O-ring added, reaching IP68. This is especially critical for liquid-cooled cabinets—the sealed self-clinching studs, pre-applied rivet nuts and pre-applied rivets in the handbook are prepared for sheet-metal cabinet joints needing water protection, achieving IP68 sealing.
Liquid-Cooling Joints: UQD Quick Connectors
Cold-plate liquid cooling is spreading rapidly across AI servers, and the piping-to-cold-plate connection is therefore standardized. The UQD connector described in the handbook offers three features—zero drip, high flow and quick coupling—and is used in AI-server liquid-cooling systems for quick sealed connection between cold plates and piping, guaranteeing efficient cooling and convenient maintenance. Its value is that when servicing personnel pull piping in the field, drip is controlled to a minimal range and the whole loop need not be drained—the prerequisite for scaled liquid-cooling O&M.
Material and Surface-Finish Selection
Thermal-side screws sit long-term in a temperature-cycling environment, so material choice must balance heat-transfer concerns against corrosion: common practice is stainless screws with aluminum/copper heatsinks (adding isolation coating when avoiding dissimilar-metal galvanic corrosion), and zinc-nickel plating or stainless passivation at salt-spray-sensitive positions. The handbook also mentions self-clinching grounding terminals for sheet-metal grounding—fan shielding and cabinet equipotential bonding both rely on this low-resistance ground path; if a grounding terminal loosens, EMC problems become very hard to trace.
Selection Recommendations
- Heatsink compression screws: calibrate the torque-clamp-force relation per GB/T 16823.3, tighten diagonally in passes, pre-applied adhesive for anti-loosening.
- Liquid cold plates: sealing screws / sealed self-clinching studs; put O-ring compression into drawing tolerance, target IP68.
- Cold plate to piping: UQD zero-drip quick connectors, blind mate.
- Service panels: captive screws; after panel removal the screw does not fall or hit boards.
- Grounding path: design self-clinching ground terminals separately; do not share clamping points with thermal screws.
The acceptance standard for thermal fastening is "ten years no leak, ten years no loosen, and every maintenance step is convenient." Locking torque calibration, anti-loosening sealing and quick-connect O&M together at the drawing stage prevents liquid-cooled server thermal joints from repeatedly catching fire during mass production.
Conclusion
Thermal-module fastening is where "tight is good" becomes actively dangerous. A heatsink screw that is over-tightened bows the board, cracks the die attach, or squeezes the thermal interface material too thin; one that is under-tightened leaves an air gap that doubles thermal resistance. This is why compression screws are specified as a matched set with even torque sequencing, and why clamping force—not torque—is the true design target, with torque used only as the process control. Anti-loosening around thermal modules is driven by fan vibration and by the cyclic pump-out of the thermal interface, so pre-applied adhesive or spring washers are added even at static positions. Liquid-cooled joints add a sealing dimension: O-rings and UQD quick connectors depend on controlled bolt preload to maintain a leak-free face seal over temperature swings, and IP68 is specified for the coolant manifold. Material and finish are chosen for corrosion and conductivity—aluminum cold plates with compatible fasteners, and copper busbar hardware plated for stable contact resistance. The takeaway is that thermal fasteners must be co-designed with the heatsink, the gasket, and the board stack-up; a screw chosen in isolation will always compromise thermal performance somewhere downstream.
In short, treat thermal fasteners as part of the thermal path: torque, gasket, and preload are co-designed with the cold plate, and validated across temperature cycling rather than once at room temperature.
Thermal-module fastener selection for AI servers has evolved from a single screw into a combined system of "compression screws + anti-loosening coating + O-rings + UQD quick connect + captive panels." YF Zhichengjia, founded in Shenzhen in 2005, is a fastener manufacturer serving the HPC/AI-server industry with anti-loosening, sealing, captive screws and UQD connectors. For design and selection material see the technical document library; thermal connection solutions can be jointly developed by contacting our technical engineers.
