Differences

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--- electronics:torque_standards_for_power_packages [2024/01/17 23:57] – mithat
+++ electronics:torque_standards_for_power_packages [2024/01/18 02:50] (current) – [onsemi] mithat
@@ Line 26: / Line 26: @@
 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). This leads to the following table for packages covered by this note.
+> 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) ^
@@ Line 37: / Line 39: @@
 |FLEXIWATT     | use clip                   | use clip             |
-The hardware stackup shows a screw entering the device tab through an optional washer and a bolt on the heatsink side.
+The hardware stackup shows only a screw entering the device tab through an optional washer and a bolt on the heatsink side:
+{{:electronics:stmicroelectronics-an260-fig8.png|}}
 ===== Data from other sources =====
@@ Line 51: / Line 54: @@
 ==== 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.)) introduces the use of conical "Belleville" washers for mounting devices:
+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 exact target torques cannot be set using 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.
+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.
-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 (N*m). One table shows a torque of 8 in-lbs (N*m) used with a TO−220AB device.
+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.