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--- electronics:torque_standards_for_power_packages [2022/06/17 18:47] – [Torque Standards for Power Packages] mithat
+++ electronics:torque_standards_for_power_packages [2024/01/18 02:50] (current) – [onsemi] mithat
@@ Line 3: / Line 3: @@
 <WRAP center round info 60%>
 The recommendations below are based on current data. As more sources are found, these recommendations may change.
-</WRAP>
-<WRAP center round important 60%>
-This just in: [[https://www.onsemi.com/pub/Collateral/AN1040-D.PDF|https://www.onsemi.com/pub/Collateral/AN1040-D.PDF]]. Details from this have yet to be integrated into the content below.
 </WRAP>
 ===== Recommendations =====
-The best data appears to be that provided in STMicroelectronics' TN1225(([[https://www.st.com/resource/en/technical_note/dm00238320-mounting-instructions-for-thd-through-hole-device-packages-stmicroelectronics.pdf|TN1225: Mounting instructions for THD (through hole device) packages]]. STMicroelectronics. Accessed June 2, 2022.)). Their data is reproduced verbatim below:
+==== STMicroelectionics ====
+Comprehensive data and test results for various packages is provided in STMicroelectronics' TN1225(([[https://www.st.com/resource/en/technical_note/dm00238320-mounting-instructions-for-thd-through-hole-device-packages-stmicroelectronics.pdf|TN1225: Mounting instructions for THD (through hole device) packages]]. STMicroelectronics. Accessed January 17, 2022.)). Their data is reproduced verbatim below:
 ^ 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                 |
+|TO-247-4      | 0.55                       | 1.00                 |
+|TO-3P         | 0.55                       | 1.00                 |
+|TO-3PF        | 0.55                       | 1.00                 |
-Use of M3 screws is assumed in the data above. However, using #4-40 screws (about 5% thinner than M3) with proper washers shouldn't change things significantly.
+The kind of insulator (mica, silicone, etc.) isn't specified. M3 hardware was used in this note, and I don't expect using #4-40 screws (about 5% thinner than M3) with proper washers to change things significantly. Details of the hardware stackup are shown below.
+{{:electronics:stmicroelectronics-tn1225-hardware-stackup.png|}}
-===== Discussion of data from sources =====
+STMicroelectronics' AN260 reference provides empiric data for a number of packages not covered above, over a range of torques and using mica insulators.(([[https://www.st.com/resource/en/application_note/cd00003783-handling-and-mounting-ics-in-plastic-power-packages-stmicroelectronics.pdf|ANAN260: Handling and mounting ICs in plastic power packages]]. STMicroelectronics. Accessed January 17, 2022.)) These data show marginal to no improvement in thermal resistance above 50Nxcm, which corroborates the 0.55 N*m typical figure given in the previous table.
-==== STMicroelectionics ====
+However, the maximum torque is slightly contradicted here (emphasis added):
-STMicroelectionics gives the following guidelines for various packages when using M3 hardware(([[https://www.st.com/resource/en/technical_note/dm00238320-mounting-instructions-for-thd-through-hole-device-packages-stmicroelectronics.pdf|TN1225: Mounting instructions for THD (through hole device) packages]]. STMicroelectronics. Accessed June 2, 2022.)):
+> 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).
+This leads to the following table for packages covered by this note.
 ^ 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                 |
+|TO-220        | 0.55                       | 0.80                 |
-|Heptawatt     | 0.55                       | 0.70                 |
+|Pentawatt     | 0.55                       | 0.80                 |
-|TO-220FP      | 0.55                       | 0.70                 |
+|Heptawatt     | 0.55                       | 0.80                 |
-|ISOWATT220    | 0.55                       | 0.70                 |
+|Multiwatt     | 0.55                       | 0.80                 |
-|TO-247        | 0.55                       | 1.00                 |
+|Clipwatt      | 0.55                       | 0.80                 |
-|TO-218        | 0.55                       | 1.00                 |
+|FLEXIWATT     | use clip                   | use clip             |
-The kind of insulator (mica, silicone, etc.) isn't specified for these data.
+The hardware stackup shows only a screw entering the device tab through an optional washer and a bolt on the heatsink side:
-A different STMicroelectronics reference provides empiric data for a number of packages over a range of torques using mica insulators.(([[https://www.st.com/resource/en/application_note/cd00003783-handling-and-mounting-ics-in-plastic-power-packages-stmicroelectronics.pdf|ANAN260: Handling and mounting ICs in plastic power packages]]. STMicroelectronics. Accessed June 2, 2022.)) The data show marginal to no improvement in thermal resistance above 50Nxcm, which corroborates the 0.55 N*m typical figure given in the previous table.
+{{:electronics:stmicroelectronics-an260-fig8.png|}}
+===== Data from other sources =====
-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.
 ==== Infineon ====
@@ Line 59: / Line 52: @@
 TI mentions 50N-cm as the recommended maximum for their multi-lead TO-247 packages.(([[https://www.ti.com/lit/an/snoa460/snoa460.pdf|SNOA460: AN-1364 TO-247 Package]]. Texas Instruments. Accessed June 2, 2022.)) How well this translates to other packages is unknown, but it does put the figure in the same ballpark as STMicroelectronics' recommendations.
+==== onsemi ====
+onsemi's AN1040/D(([[https://www.onsemi.com/pub/Collateral/AN1040-D.PDF|AN1040/D: Mounting Considerations
+For Power Semiconductors]]. onsemi. Accessed Jan 17, 2024.)) advocates the use of conical "Belleville" washers for mounting devices:
+{{:electronics:onsemi-an1040-d-fig20.png|}}
+However, the text implies that torque cannot be used to set the device pressure with conical washers because, "The assembler applies torque until the washer depresses to half its original height. (Tests should be run prior to setting up the assembly line to determine the proper torque for the fastener used to achieve 50% deflection." Thus, it appears the washer determines the pressure on the device rather than torque on the screw, because torque on the screw is determined by the amount needed to compress the washer just right.
+Perhaps not surprisingly then, specific torque ratings are difficult to derive from this note. However, it shows for TO-220 packages remarkable consistent thermal resistances for greased mica mounting with unspecified hardware over 2 to 6 in-lbs (0.23 to 0.68 N*m). One table shows a torque of 8 in-lbs (0.90 N*m) used with a TO−220AB device.