[sdiy] Need a TO220 thermo pad that can withstand 130vdc without arcing..

[Ben Stuyts]

"Yes, Kapton (polyimide) tape can work as an insulator for your TO-220 package, but there are a few considerations:

Pros of Kapton Tape
✔ High Breakdown Voltage
    • Kapton tapes typically have a dielectric strength of >6 kV per mil (25.4 µm thickness), making them well-suited for 130VDC insulation.
✔ Thin & Flexible
    • A 25µm (1 mil) Kapton layer can withstand thousands of volts while keeping thermal resistance low.
✔ No Need for Thermal Compound
    • If properly applied, it provides good thermal contact without requiring grease or paste.
✔ Temperature Resistance
    • Works in temperatures up to 400°C, much higher than silicone pads.

Cons / Considerations
⚠ Higher Thermal Resistance
    • Kapton is not designed for optimal thermal conductivity.
    • Thermal conductivity: ~0.12 W/m-K (vs. 0.9-3.0 W/m-K for thermal pads).
    • If your TO-220 dissipates significant heat, Kapton will be less effective than a dedicated thermal pad.
⚠ Pressure & Application Matters
    • The quality of contact depends on how well it is applied.
    • Air gaps or poor adhesion may increase thermal resistance.
⚠ Single Layer vs. Multi-Layer
    • A single layer of Kapton should be enough for 130VDC.
    • If concerned, two layers will provide extra safety.

Verdict✅ Kapton tape can work electrically for 130VDC insulation, but its thermal performance is inferior to silicone pads.
If your TO-220 generates significant heat, a high-quality silicone thermal pad (like Sil-Pad 400 or Keratherm Red T-441) is a better choice. If heat dissipation is minor, Kapton is a valid option.”

Are those specs for Kapton correct?

"Apologies for any confusion caused by earlier information. Upon reviewing the specifications for Kapton tape, here are the accurate details:
    • Dielectric Strength: Kapton films have a dielectric strength of approximately 154 kV/mm (3,900 V/mil) for a 125 µm (5 mil) thickness. mu2e.phy.duke.edu
    • Thermal Conductivity: Standard Kapton HN films exhibit a thermal conductivity of about 0.12 W/m-K. matweb.com

Given your requirement for a thermal pad that can withstand 130 VDC without arcing, Kapton tape's dielectric strength is more than sufficient. However, its thermal conductivity is relatively low compared to specialized thermal interface materials. If your application involves significant heat dissipation, you might want to consider materials specifically designed for thermal management, such as thermally conductive silicone pads.”

I wonder why ChatGPT can’t give a correct answer the first time.

Ben


> On 29 Jan 2025, at 22:00, Chromatest J. Pantsmaker <chromatest at chromatest.net> wrote:
> 
> Will Kapton tape work?
> 
> On Wed, Jan 29, 2025, 1:57 PM Ben Stuyts via Synth-diy <synth-diy at synth-diy.org> wrote:
> And upon checking the Sil-Pad and pointing out that the specs were in error:
> 
> "Apologies for any confusion in my earlier response. Upon reviewing the specifications for Bergquist Sil-Pad 400, here are the accurate details:
> 
> Breakdown Voltage:
> 0.007-inch thickness: 3,500 VAC
> 0.009-inch thickness: 4,500 VAC
> Thermal Conductivity: 0.9 W/m-K
> Operating Temperature Range: -60°C to +180°C
> Given your requirement for a thermal pad that can withstand 130 VDC without arcing, the Sil-Pad 400's breakdown voltage ratings are more than sufficient. For instance, the 0.007-inch version can handle up to 3,500 VAC, which is significantly higher than 130 VDC. Additionally, this silicone-based pad does not require any thermal compound, aligning well with your preferences.
> 
> Therefore, Bergquist Sil-Pad 400 should be a suitable choice for your application.”
> 
> Sigh…
> 
> Ben
> 
> 
>> On 29 Jan 2025, at 21:51, Ben Stuyts <ben at stuyts.nl> wrote:
>> 
>> I’m having fun asking these kind of things on ChatGPT 4o, so beware, the following is unverified :-)
>> 
>> “For a TO-220 package that needs to withstand 130VDC without arcing and without using mica or thermal compound, silicone-based thermal pads are an excellent choice. These pads provide electrical insulation while maintaining good thermal conductivity.
>> 
>> ### Recommended Options:
>> 1. **Bergquist Sil-Pad 400**
>>    - Breakdown Voltage: >4kV
>>    - Thermal Conductivity: 1.1 W/m-K
>>    - Operating Temperature: -60°C to +180°C
>>    - No additional compound required
>> 
>> 2. **3M 5590H**
>>    - Breakdown Voltage: >5kV
>>    - Thermal Conductivity: 3.0 W/m-K
>>    - Operating Temperature: -60°C to +150°C
>>    - Self-adhesive and no compound needed
>> 
>> 3. **Keratherm Red T-441**
>>    - Breakdown Voltage: >6kV
>>    - Thermal Conductivity: 1.8 W/m-K
>>    - Operating Temperature: -40°C to +200°C
>>    - High electrical insulation and no compound required
>> 
>> These materials are widely available from electronics distributors like Digi-Key, Mouser, or RS Components. When choosing a thermal pad, ensure that it meets your thermal dissipation needs in addition to the voltage requirements.”
>> 
>> Ben
>> 
>> 
>>> On 29 Jan 2025, at 19:58, Jean-Pierre Desrochers via Synth-diy <synth-diy at synth-diy.org> wrote:
>>> 
>>> Need a TO220 thermo pad that can withstand 130vdc without arcing..
>>> I sillicon made type that does not need any compound would do best.
>>> No mica/compound stuff.
>>> I searched on Digikey and they have a lot available but nothing stated
>>> about their voltage breakdown..
>>>  Any idea ?
>>>  ________________________________________________________
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>> 
>> 
> 
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