Here is a snapshot of some ongoing work – Andreas Berggren’s thermal  model of MIST. The goal is to be able to model individual printed circuit boards.And he is getting there, it seems!

## 2 thoughts on “Thermal analysis started”

1. Freddy says:

Great work! How did you model those PCB’s and the connection between them and the satellite structure?

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In order to model the PCBs it is important to understand what they are made of and how they are designed. There are several different designs a PCB can take but in general they are made of a four layer material called FR-4. FR-4 is the primary backbone upon which the majority of PCBs are produced. A thin layer of Copper foil is laminated to either one or both of the sides of the FR-4 glass epoxy panel. The Copper foil thickness is in general either 34.1, 68.2 or 102.3 micrometer. For the thermal model the value of 68.2 micrometer is used and it is assumed that there are Copper foil on both sides of the PCB.

Furthermore, thermal coupling was defined between the front and backside mesh of the PCBs with a total conductance given by:

G_tot = 1/(1/G_1 + 1/G_2)

where

G_i = (K*A_cross section)/dx

where K is the conductance of the material and A_cross section is the cross section area between the front and backside of the PCBs and dx is the distance the heat will travel, in this case the thickness of the PCB (from the top mesh to the bottom mesh). The conductance of Copper is 387 W/mK and FR-4 has an conductance of 0.25 W/mK.

For the connection between the PCBs and the satellite structure a thermal coupling was defined in the same way as for the PCBs but now between the PCB (the Copper layers) and the railings seen in the photo. In this case the area in contact between the PCB and the railings is the area of the screws that will be in contact with the PCB. Consider a screw head, if using the CubeSat kit PCB Specification the diameter of the screw head is 6.35 mm and the diameter of the hole in the PCB that the screw will go into is 3.18 mm. This means that the contact area between the screw and the PCB is the area of the screw head minus the area of the hole.

/Andreas

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