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Jmar_12
New Contributor

In a question I posted on 4/21/2021 (Thermal resistance values for CY7C) it was stated " As per our packaging team we have simulated Theta JB which is 13.45 C/W using an 8-Layer (101.5 x 114.4 x 1.6mm) PCB."

However, this value is greater than the  data sheet Theta JA (12.23 °C/W) which does not make too much sense. For a typical FBGA package without an exposed heat sink or heat spreader, majority of the heat is removed from the base of the package. 

Can you provide some insite on this?

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1 Solution
PradiptaB_11
Moderator
Moderator

Hi,

I think there was a typo from our side in the previous post. Please refer to the below values that we have with us both from simulation and measurements. A device soldered on the PCB should observe a lower Theta JB value. We believe the PCB in the data below plays a bigger role in the lower value than the socket.

Type

Simulation

Measurement

Board Mount

Soldered

Socketed

test Condition

102x114x1.6mm, 8-layer PCB

170x220×2.35mm, 8-layer PCB

Theta JA

16.11⁰C/W

12.23⁰C/W

Theta JB

11.72⁰C/W

9.34⁰C/W

Theta JC

2.1⁰C/W

2.1⁰C/W

 

Thanks,

Pradipta.

View solution in original post

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4 Replies
PradiptaB_11
Moderator
Moderator

Hi,

We will need to check this with our team internally. Will keep you updated on this. 

Thanks,

Pradipta.

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PradiptaB_11
Moderator
Moderator

Hi,

I think there was a typo from our side in the previous post. Please refer to the below values that we have with us both from simulation and measurements. A device soldered on the PCB should observe a lower Theta JB value. We believe the PCB in the data below plays a bigger role in the lower value than the socket.

Type

Simulation

Measurement

Board Mount

Soldered

Socketed

test Condition

102x114x1.6mm, 8-layer PCB

170x220×2.35mm, 8-layer PCB

Theta JA

16.11⁰C/W

12.23⁰C/W

Theta JB

11.72⁰C/W

9.34⁰C/W

Theta JC

2.1⁰C/W

2.1⁰C/W

 

Thanks,

Pradipta.

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Jmar_12
New Contributor

Pradipta, 

Thanks for the response. You stated "A device soldered on the PCB should observe a lower Theta JB value. We believe the PCB in the data below plays a bigger role in the lower value than the socket." I agree with your statement, but the soldered value you have listed (11.72C/W) is higher than the socket value (9.34C/W) which contradicts what you said above. Can you clarify? 

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PradiptaB_11
Moderator
Moderator

Hi

Yes, even though both PCBs are 8 layer, the socketed PCB is much larger and thicker, which is why we believe the Theta JB value is lower on the socketed PCB. So, we should not consider this  as a contradiction. 

Thanks,

Pradipta.

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