The junction temperature Tvj doesn’t increase immediately when power losses are generated on a semiconductor chip. There is a time delay due to thermal capacity of materials composing the IGBT module. The equation in the data sheet shows the relationship of the transient thermal resistance to the pulse width tw when a single square wave pulse (power loss) is applied. Transient temperature rise of the junction ΔT(j-c) can be obtained from the transient thermal resistance.
FAQ Categories: Thermal Design
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How do I use the equation and table that are attached to the transient thermal resistance curve in the data sheet?
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Where is a NTC mounted in a module?
Please contact Fuji Electric Corp. of America or your local sales representative or distributor to answer your question.
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How works a stencil mask to apply thermal compound and can I purchase it from Fuji?
A stencil mask is a 200 μm-thick, metal plate with multiple holes punched in the compound application area. A compound can be applied with a uniform thickness of 100 μm when clamping the stencil to a heat sink after application. We do not sell stencil masks but we can provide a mask drawing that corresponds to the relevant package.
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Can I get a drawing of the internal chip layout to measure the case temperature TC?
Please contact Fuji Electric Corp. of America or your local sales representative or distributor to answer your question.
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What factors determine the value of thermal resistance Rth(j-c)?
The thermal resistance value may differ even in the same rating, when comparing different families of products made by Fuji Electric or other companies. A low thermal resistance in a certain product may be due to a larger semiconductor chip size, or the use of a ceramic insulating substrate with good thermal conductivity.
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How do I mount a module?
Refer to IGBT module’s Application Manual Chapter 6-3 or Mounting Instruction.
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How do I calculate the power cycle in cases where there are multiple temperature rise peaks?
In cases where the temperature increases n-times per device operation cycle, we assign a power cycle life expectance count as PC(k=1, 2, 3, …, n). PC(k) is the power cycle life for the k-th temperature rise. A combined power cycle life expectancy count can be expressed by the formula below.
For details, refer to Application Manual Chapter 11.
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What is the temperature difference between Tj and NTC temperature?
Please contact Fuji Electric Corp. of America or your local sales representative or distributor to answer your question.
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Is the temperature Tj represented by the NTC temperature?
They are not the same. When incorporating it in an IGBT module, NTC is positioned far from the chip to ensure insulation. This produces a temperature gap between them although NTC’s temperature will follow that of chip’s Tj.
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What range is used for heat sink flatness as a reference?
Guides to flatness values for a heat sink are 50 μm or less for 100 mm between screw mounting locations, and 10 μm or less for surface roughness. An excessive convex warp will cause an insulation breakdown, leading to a critical incident. An excessive concave warp will reduce heat radiation by creating a gap between the product and heat sink, which may lead to thermal destruction.
