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Shoulder Screw

Shoulder Screw

Shoulder Screw Shoulder Screws are an extremely reliable attachment method.
Several standard screws are available, while springs generate the appropriate mounting force/pressure. Alpha can design and produce the entire assembly, including the heat sink, shoulder screws, springs, and thermal interface material.

1. Shoulder Screw Specification
Model   A
Screw size C
Download Availability /
Price / Order
 Data Sheet Other
SS diagram

SS-13.2 13.20 4.20 M3 4.20 catalog




SS-19-4.2-M3-4.2 19.00 catalog
SS-22 22.00 4.00 catalog
SS-10-4.8-M3-5 10.00 4.78 5.00 catalog
SS-12-4.8-M3-4 12.00 4.00 catalog
SS-13-4.8-M3-3.5 13.00 3.50 catalog
SS-13-4.8-M3-5 5.00 catalog
SS-13.7-4.8-M3-5.8 13.72 5.84 catalog
SS-16-4.8-M3-7 16.00 7.00 catalog
SS-16.5-4.8-M3-5.8 16.51 5.84 catalog
SS-19-4.8-M3-7 19.00 7.00 catalog
SS-19.3-4.8-M3-5 19.30 5.00 catalog

2. Features & Explanation of shoulder screws

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

Features of shoulder screws

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.

Stable & Robust

Shoulder screws offer the most reliable and rugged attachment method possible. Passed all shock and vibration testing.

Safe & Simple

Captive hardware and simple installation minimizes possibility of error and damage.

Prevent Board Warpage

A standard or custom backing plate is an option for high attachment forces.

Flexible Design

Hole location and attachment forces can be customized for each specific application.

Attachment Force

Appropriate attachment force/pressure can be consistently generated through screw/spring selection.

High Performance

High performance interface materials including phase change and thermal grease can be used instead of tape or epoxy.

3. Spring Selection

Please visit Spring Selection page.

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 *



PEM and MAC8


Common nuts


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's standard backing plates.

*Alpha does not provide these components as standard parts.

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.

Shoulder Screw Alpha offers the following standard shoulder screw attached heat sinks:

Typical attachment methods
Test Report (Shock and Vibration)

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