Mounting with Plastic and Metal Clips

Plastic Clips

Plastic clips offer a low cost mounting option for ICs. The clips are held in place with a screw and work by applying pressure to the front of the package. In some applications, the temperature of the heatsink may get as high as 125 °C; the softening temperature of the clip should be >150 °C. Detailed information about plastic clips can be found in the Supporting Documents area of this section.

Mounting Guidelines for Plastic Clips (Screw Mount)

Hole Size: Designed for standard TO-220 heatsinks (3.2 mm typical)
Screw Size: 3 mm (M3) pan head screw
Maximum Torque: The screw torque recommendation is 1.8 to 2.3 lbf • in or 0.20 to 0.26 Nm maximum.

• To avoid the need for a washer between the screw head and the surface of the clip, the screw head should be flat. Excessive unevenness, the use of a smaller screw, or larger heat sink hole can cause the clip to crack. As with the TO-220 package, the use of lock nuts, spring washer, and thread lock is permissible.
• Self-tapping screws are not recommended due to the variability in the force they apply to the clip and therefore the package. Rivets should not be used under any circumstances.
• The heatsink mounting surface must be flat and without burrs to prevent damage to the IC. Finally, the IC should be mounted to the heat sink before soldering the assembly to the PCB. Soldering the IC and heat sink to the PCB and then mounting the clip will put unacceptable mechanical stress on the IC package.
• The use of thermal grease or a thermally conductive pad is recommended to reduce the thermal impedance between the rear of the package and the heatsink.

Supporting Documents – Plastic Clip
Clip Drawing

Supporting Documents – Plastic Mini Clip
Mini Clip Drawing
Material Safety Data Sheet (MSDS)
Material Specifications - English
Material Specifications - Chinese
RoHS Test Report

Supporting Documents – Extended Plastic Clip
Extended Plastic Clip
Single Screw Extended Plastic Clip
RoHS Test Report

Supporting Documents – EZ Clip
EZ Clip Drawing

Stainless Steel Clips

The stainless steel clip provides a metal option to the plastic clip. This strip is held in place with a screw and works by applying pressure to the front of the package. Detailed information about the stainless steel clip can be found in the supporting documents table of this section.

Mounting Guidelines for Stainless Steel Clip with Screw

Hole Size: Designed for standard TO-220 heatsinks (3.2 mm typical)
Screw Size: 3 mm (M3) pan head screw
Maximum Torque: The screw torque recommendation 0.26 Nm (2.3 lbf · in).

• Due to the robustness of the metal material, the torque used to fix the metal clip to the heatsink is less critical than for plastic types (no risk of cracking). Provided the mounting point is firmly attached to the heatsink, the force applied to the package is a function of the clip design and material used.
• Self-tapping screws may be used, but threaded screws are recommended due to their repeatability and robustness against shock. Rivets should not be used due to the shock that the part experiences during the riveting process. As with the TO-220 package, the use of lock nuts, spring washer, and thread lock is permissible.
• The heatsink mounting surface must be flat and without burrs to prevent damage to the IC. Finally, the IC should be mounted to the heat sink before soldering the assembly to the PCB. Soldering the IC and heat sink to the PCB and then mounting the clip will put unacceptable mechanical stress on the IC package.
• The use of thermal grease or a thermally conductive pad is recommended to reduce the thermal impedance between the rear of the package and the heatsink.

Supporting Documents – Stainless Steel Clip
Steel Clip Drawing
RoHS Inspection Certificate
RoHS Test Report

Stainless Steel U-Clips

Another option of mounting is to use a U-Clip. The U-Clip fits over the side of the heatsink and the front of the package and holds the package firmly to the heatsink (see Figure 10). A variety of U-Clips are commonly available.

The U-Clip is a common mounting option in many of today's high volume designs. Below are two photographs showing the U-Clip being used in high-volume inkjet printer power supplies. Figure 11 shows the U-Clip securing a bridge rectifier to a heatsink. Figure 12 shows a TO-220 held in place by the U-Clip.

Mounting Guidelines for Stainless Steel U-clip

• It is recommended that the IC is attached to the heatsink using the U-clip to form a sub-assembly.
• This sub-assembly is then assembled into the printed circuit board before soldering. This is to ensure that co-planarity is maintained between the IC and heatsink surface.
• Soldering the IC first, then attaching the heatsink is not recommended as typically the IC will not make good contact with the heatsink, thereby increasing thermal impedance.
• In a production environment, a jig may be used to ensure alignment of the part and heatsink while the clip is inserted.

Vibration Resistance

To demonstrate the ability of the U-Clip to stay securely in place during vibration and mechanical shock, an test board, using the CLP212SG, CLP212G and CL212TG clips from Aavid Thermalloy, was submitted for testing to ensure that they were able to meet the IEC-60068 standard. All three of the U-Clips studied passed the shock and vibration test. The full test report can be downloaded here.

Metal and Plastic Clip Vendor Information

Vendor	Contact Information	Type	Part Number	Recommended Heatsink Height (without notching)
Kang Yang Hardware Enterprises Co., Ltd	Nancy Lin +886-2-2647-6930 nancy@kangyang.com.tw	Mini	PH-3	20 mm
		Metal Plastic	TRK-24 TC-24NNHA	20 mm
Thermshield	Thermshield, LLC PO Box 1641 Laconia, NH 03247 +1 603 524-3714 +1 603 524-6602 (FAX) sales@thermshield.com http://www.thermshield.com	Plastic	TS-11042-CY	24 mm

U-Clip Vendor Information

Vendor	Contact Information	Type	Part Number	Recommended Heatsink Height (without notching)	Recommended Heatsink Wall Thickness
Aavid Thermalloy	www.aavidthermalloy.com	U-Clip	CLP212SG	15.5 mm	2.25 mm
			CLP212G	24 mm	6.2 mm
			CLP212TG	20 mm	4.8 mm