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Accessory - Shoulder Screw


Shoulder Screw

The shoulder screw attachment method is a very common way to attach heat sinks of greater mass to the PCB.
The heat sink is mounted to the board with spring loaded shoulder screws. The compression load from the springs applies the appropriate mounting force to the heat sink and generates the necessary pressure on the thermal interface material. This compression force is preferable to the undesirable tension or shear forces that would be transmitted to the chip and solder balls if the heat sink was mechanically attached directly to the chip's package or substrate.

A large combination of standard screws and springs are available. Alpha can generate the complete assembly design, including springs, screws and thermal interface material. Shoulder screws and springs can also be purchased separately.

Related information : Spring Selection

Guideline for small size heat source(bare-chip)


Explanation of shoulder screws

Shoulder screw nomenclature

Shoulder screws consist of the "Head", the "Shoulder", and the "Thread" sections.

heatsink line E-RING

Within the shoulder section, an E-ring can be inserted into the groove, making the screw captive to the heat sink. Captive hardware allows the heat sink to be easily assembled and disassembled from the PCB without the inconvenience of loose hardware. Captive hardware also reduces the total number of components, simplifying the BOM.

The shoulder screws can be used with board mounted threaded inserts or standoffs. If the treaded inserts are on the backside of the PCB, the shoulder diameter needs to be larger than the hole in the PCB. When the shoulder screws are tightened, the shoulder will bottom on the PCB surface or the standoff. Once the shoulder makes contact, the heat sink is properly installed.

Mounting components for PCB attachment

As discussed above, there are several different hardware components that can be used to attach shoulder screw heat sinks to the PCB. Final heat sink design will depend on which mounting component is used. Please review the specification of each mounting component and how the component is used to attach the heat sink to the PCB.
Alpha's standard shoulder screw thread specification is M3. If you need additional information regarding these components, please contact Alpha sales.

Press-in or Soldered Inserts and Spacers * Nuts
PEM and MAC8
Common nuts
Stand-offs Backing Plate
Installed on PCB surface (component side).
Nut required on backside of PCB.

Backing Plate/Stiffener
Backing plate is installed on the backside of the PCB. It provides attachment hardware and additional stiffness, preventing excessive bowing of the PCB. Alpha supplies standard backing plates.

*Alpha does not provide these components as standard parts.

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Installing Procedure and other components

Guidance for installing procedure

1. Select heat sink

1. Heat sinks requires thru holes on the corners for shoulder screws.

2. Assemble shoulder screws and springs

2. Install shoulder screw and spring through hole.

3. Install E-rings

3. E-ring is inserted into the groove, making the shoulder screw and spring captive.

4. Complete pre-assembly of screws and springs

4. The heat sink is now pre-assembled with shoulder screws and springs.
Thermal interface material can be applied at this time to the heat sink base surface.

5. Install mounting components on the PCB

5. Install mounting components in the PCB.

6. Install heat sink from component side

6. Gently place the heat sink on top of chip from component side and line up screws with the thru holes/mounting components in the PCB.

7. Finish assembly

7. Tighten the screws in an alternating crisscross pattern.

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Alpha standard Shoulder Screw Attached Heat Sinks

Heat Sink with attachment holes

We have standard heat sinks designed to be used with Alpha standard shoulder screws and springs. The thru hole positions are fixed in the heat sinks. If the standard hole locations are not compatible with your PCB, semi-custom heat sinks with a compatible hole layout can easily be created. Standard heat sinks are highly recommended for shorter lead times and lower initial cost. The heat sinks and hardware can be purchased separately, or assemblies calling out specific heat sink, screw, and spring combinations can be quickly created.

Heat Sink with attachment holes

Related Information

Test Report (Shock and Vibration)
Design for Installation (Foolproof/Poka-yoke design options)
Guideline for small size heat source(bare-chip)
TIM: Thermal Interface Material Data

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