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# Thermal resistance from Junction to board & junction to case required for HMC516LC5

Iam perfoming thermal analysis of PCB enclosed in enclosure, From datasheet of the component Thermal resistance(channel to die bottom) given is 76.9 °C/W. The value of which i considered is  Thermal resistance from junction to board

This consideration is because iam performing thermal analysis in Ansys  ICEPAK  in which IC is modelled as a two resistor network

Since these components have exposed pad technically resistance towards board will be less ..my question is my understanding of Resistance towards board is it correct & the how to find resistance towards top of the case

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• Hi Mohamed023,

The thermal resistance Teta Jc specified in the data sheet, 76.9 C/W, is from the channel to the exposed pad at the bottom of the package. The HMC516 is packaged in an air cavity package, the thermal resistance to case top will be very hgh compared to the thermal resistance to the exposed pad.

Regards,

Jim B

• Hi Jim

Thanks for your clarification, How to find thermal resistance junction to case top? which is required for thermal analysis

• Is there any way to calculate theoretically Channel to top case thermal resistance

• Hi Mohamed023,

Yes, you need to have a thermal analysis software package, create a thermal model and setup a thermal simulation.

Regards,

Jim B

PDF

• Or else can i refer the  ADI Thermal resistance table, considered Theta JA which is 44 for 32Pin  5x5 mm QFN Package (UH 32) as Resistance from junction to top case for my simulation purpose

Because for simulation, i need at least two resistance values

one is junction to top case, Which is unknown in these case

& other is  junction to board,

• Or else can i refer the  ADI Thermal resistance table, considered Theta JA which is 44 for 32Pin  5x5 mm QFN Package (UH 32) as Resistance from junction to top case for my simulation purpose

Because for simulation, i need at least two resistance values

one is junction to top case, Which is unknown in these case

& other is  junction to board,

• Hi Mohamed023,

The package you are referring to is not the correct package. The correct package is: LCC, 32-Lead LCC (4.9mm x 4.9mm), E-32-1. I do not believe it is in the table you have referenced.

Regards,
Jim B

• Hi Jim

Thanks .. I have refereed datasheet of HMC815B, Package detail is E-32-1, in this datasheet Theta JA is 46.4 which is less than Theta JC 76.9,  which contradicts

Actually for this since it is a expose pad Theta JC should be less than Theta JA

• Hi Jim

Thanks .. I have refereed datasheet of HMC815B, Package detail is E-32-1, in this datasheet Theta JA is 46.4 which is less than Theta JC 76.9,  which contradicts

Actually for this since it is a expose pad Theta JC should be less than Theta JA

• Hi Jim

Thanks .. I have refereed datasheet of HMC815B, Package detail is E-32-1, in this datasheet Theta JA is 46.4 which is less than Theta JC 76.9,  which contradicts

Actually for this since it is a expose pad Theta JC should be less than Theta JA

• Where is the ADI Thermal Resistance Table located? Can you provide a link?

• Hi Mohamed023,

First of all theHMC815B is a totally different chip with a different Pdiss and layout. So the theta numbers will be different. I also find it hard to believe that theta JA & theta JC for an air cavity package can be with in 0.3 degrees.

Die layout and the Pdiss of the device all affect the thermal resistance.

The interface from the channel to the ceramic lid is air. Air is not a very good thermal conductor. I would expect the Theta JC top for the HMC516LC5  as a rough estimate, to be double the theta JC to the exposed pad, ~153.8 C/W.

Regards,

Jim B

• Hi Mohamed023,

First of all theHMC815B is a totally different chip with a different Pdiss and layout. So the theta numbers will be different. I also find it hard to believe that theta JA & theta JC for an air cavity package can be with in 0.3 degrees.

Die layout and the Pdiss of the device all affect the thermal resistance.

The interface from the channel to the ceramic lid is air. Air is not a very good thermal conductor. I would expect the Theta JC top for the HMC516LC5  as a rough estimate, to be double the theta JC to the exposed pad, ~153.8 C/W.

Regards,

Jim B

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