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Torque Standards for Power Packages

STMicroelectionics¹⁾ gives the following guidelines for various packages when using M3 hardware:

Package	Typical torque (N*m)	Maximum torque (N*m)
TO-220	0.55	0.70
TO-220SG	0.55	0.70
Pentawatt	0.55	0.70
Heptawatt	0.55	0.70
TO-220FP	0.55	0.70
ISOWATT220	0.55	0.70
TO-247	0.55	1.00
TO-218	0.55	1.00

The kind of insulator (mica, silicone, etc.) isn't specified for these data.

A different STMicroelectronics reference ²⁾ provides empiric data for a number of packages over a range of torques using mica insulators. The data show marginal to no improvement in thermal resistance above 50Nxcm, this corroborating the 0.55 N*m typical figure given in the table.

However, the maximum torque is slightly contradicted here (emphasis added):

Suggested maximum torques for M3 screws are _80Nxcm_ for TO220, PENTAWATT, HEPTAWATT, MULTIWATT and CLIPWATT 19 H packages. Particularly for FLEXIWATT package, clipping system is strongly recommended. While suggested maximum torque for M3 screws is 70 Nxcm for TO220SG (single gauge).

The data given in the table above is the more conservative and therefore preferred: 0.55 N*m nominal for all packages listed with a maximum 0.7 N*m for everything except TO-247 and TO-218, which can be squeezed up to 1 N*m.

Infineon³⁾.

TI⁴⁾.

¹⁾

TN1225: Mounting instructions for THD (through hole device) packages. STMicroelectronics. Accessed June 2, 2022

²⁾

ANAN260: Handling and mounting ICs in plastic power packages. STMicroelectronics. Accessed June 2, 2022

³⁾

TO-247-3 Advanced Isolation: AN2017-42. Infineon. Accessed June 2, 2022

⁴⁾

AN-1364 TO-247 Package: SNOA460. Texas Instruments. Accessed June 2, 2022