Application Note

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Rectifiers
Application Note
Mounting Considerations for the TO-220FP (FULL-PAK)
By Antonio Mini
DEVICE MOUNTING CONSIDERATIONS
Failure (body cracks) caused by mechanical stress during device mounting are common in plastic semiconductor packages,
such as the TO-220, TO-220FP, and TO-247.
The aim of this document is to suggest a few good practices for the mounting of TO-220FP packages. It is important to minimize
any mechanical stress effects to the device by applying the optimum screw mounting torque.
Vishay TO-220FP devices are intended to be mounted by screws and flat washers, as shown in the following picture.
M3 screw
Flat washer
TO-220FP
Thermal conductive compound
Heatsink
Spring lock washer
Nut
The recommended mounting torque - using the assembly above - is provided in a component’s datasheet.
Revision: 10-May-16
Document Number: 95651
For technical questions within your region: [email protected], [email protected], [email protected]
THIS DOCUMENT IS SUBJECT TO CHANGE WITHOUT NOTICE. THE PRODUCTS DESCRIBED HEREIN AND THIS DOCUMENT
ARE SUBJECT TO SPECIFIC DISCLAIMERS, SET FORTH AT www.vishay.com/doc?91000
APPLICATION NOTE
Fig. 1
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Mounting Considerations for the TO-220FP (FULL-PAK)
Following are the minimum precautions necessary to avoid inducing stress and damage to the device:
• Fasten the device to the heatsink before soldering the leads to avoid stress to the leads.
• A flat washer for spreading the pressure must be used. The M3 screw head must not press directly onto the device’s body.
Ensure that the washer does not damage the plastic body of the package during the mounting process.
• To avoid stress to the device and poor contact between the device and heatsink, care must be taken with the mounting hole.
Punched mounting holes must be avoided, because they may not guarantee proper surface flatness and may lead to device
deformation and consequent body cracks when mounting torque is applied.
• When drilled mounting holes are used, surface clean up to remove burrs is essential. To prevent body deformation, a large
countersink must be avoided or reduced to the smallest size possible (see Fig. 2).
The recommended maximum mounting hole diameter (including countersink) is not to exceed 3.6 mm.
See detail
Deformed body
Fig. 2
• Make sure the contact surfaces of the heatsink and washer are free of burrs, flat, and clean.
• Use thermal conductive compound (thermal paste) between the contact surfaces to eliminate any air gaps and improve the
contact.
HEATSINK RECOMMENDED SPECIFICATION
• The heat sink mounting surface must be clean, with no corrosion or oxides surface. It is very important to keep the mounting
surface free from particles, scratches, and burrs.
Revision: 10-May-16
Document Number: 95651
2
For technical questions within your region: [email protected], [email protected], [email protected]
THIS DOCUMENT IS SUBJECT TO CHANGE WITHOUT NOTICE. THE PRODUCTS DESCRIBED HEREIN AND THIS DOCUMENT
ARE SUBJECT TO SPECIFIC DISCLAIMERS, SET FORTH AT www.vishay.com/doc?91000
APPLICATION NOTE
• The contact surface of the heatsink must be flat, with a recommended tolerance of 16 μm (reference length 0.8") and a surface
roughness of < 0.02 mm (< 0.79 mil).
Application Note
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Mounting Considerations for the TO-220FP (FULL-PAK)
BENDING AND CUTTING LEADS
Leads bending must be done carefully.
Following are the minimum precaution to be taken to avoid to induce stresses and damages to the device:
1. Never clamp the plastic package but the leads only.
Clamp
tool
2. When clamping the leads they must be clamped between the device body and the bending point (Fig. 3)
Lead forming
tool
Clamp
tool
Plastic body
Spaced
Fig. 3
3. Leads should be bent at a minimum distance of 4.0 mm from the diode body (Fig. 4)
4 mm min.
Corrrect
Incorrect
Fig. 4
4. To avoid breaking / fractures of the leads never bend the leads more than 90° and L with a radius smaller than terminal
thickness (Fig. 5)
R>L
L
Fig. 5
Revision: 10-May-16
Document Number: 95651
3
For technical questions within your region: [email protected], [email protected], [email protected]
THIS DOCUMENT IS SUBJECT TO CHANGE WITHOUT NOTICE. THE PRODUCTS DESCRIBED HEREIN AND THIS DOCUMENT
ARE SUBJECT TO SPECIFIC DISCLAIMERS, SET FORTH AT www.vishay.com/doc?91000
APPLICATION NOTE
Plastic body
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Mounting Considerations for the TO-220FP (FULL-PAK)
5. Lateral bending of terminal is not allowed (Fig. 6)
Incorrect
Fig. 6
6. Leads should never be bent more than once.
It is important to minimize the strain during the leads bending.
If the package / lead interface is strained, the resistance to humidity could be compromised and mechanical stress could be
induced to the silicon chip. Any damage may affect the reliability of the devices.
APPLICATION NOTE
Revision: 10-May-16
Document Number: 95651
4
For technical questions within your region: [email protected], [email protected], [email protected]
THIS DOCUMENT IS SUBJECT TO CHANGE WITHOUT NOTICE. THE PRODUCTS DESCRIBED HEREIN AND THIS DOCUMENT
ARE SUBJECT TO SPECIFIC DISCLAIMERS, SET FORTH AT www.vishay.com/doc?91000
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