This page calculates the heat transfer coefficient and temperature of a PCB board with components. Components are assume to be isothermal blocks. Temperatures at each row of components is calculated for the specified conditions.

Define the PC board properties, component properties, and air flow properties. This page will calculate a heat transfer coefficient based on the flow conditions, calculate the resistance between the components and the air, as well as the component temperature.

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PC Board Properties

Description Symbol Value Units
Width of PCB (Lateral to Flow) Wb Meters
Height of flow channel above PCB HF Meters
Are their card guides at leading edges of PCB ? G None
Conductivity of the board (no copper) kb W/m-oC
Thickness of the board t Meters
Volume of copper per area of PCB (Lateral to Flow) phi1 m3/m2
Volume of copper per area of PCB (Parallel to Flow) phi2 m3/m2
Conductivity of the PCB copper kc W/m-oC

Component Properties

Description Symbol Value Units
Number of components (Parallel to Flow) N None
Length (Parallel to Flow) b Meters
Pitch (Parallel to Flow) d Meters
Number of components (Lateral to Flow) M None
Width (Lateral to Flow) S Meters
Pitch (Lateral to Flow) w Meters
Height (Protruding into Flow) e Meters
Heat Load per Component q W
Air gap between PCB and component del Meters
Number of leads per component n None
Length of leads L Meters
Cross-sectional area of one lead Al m2
Thermal conductivity of leads kl W/m-oC

Air Flow Properties

Description Symbol Value Units
Ambient temperature (at entrance) Ta oC
Average flow velocity in free flow area between boards um m/s
Thermal conductivity of air ka W/m-oC
Specific heat of air Cp J/kg-oC
Air density rho kg/m3

Results for PC Board

Equations Used Symbol Value Units
Value of G for heat transfer coefficient calculation G None
Flow area per PCB = Wb * HF - (M * S * e) a m2
Flow rate = um * a F m3/s
Lateral conductance of the board = (kb * t) + (kc * phi1) C1 W/oC
Streamwise conductance of the board = (kb * t) + (kc * phi2) C2 W/oC
Resistance across air gap = del / (ka * S * b) rc oC/W
Resistance across the leads = L / (kl * n * Al) rl oC/W
Interface resistance = 1 / ( (1/rc) + (1/rl) ) Ri oC/W
Exposed surface area = S * b + 2e (S + b) A1 m2
Equations Used Symbol Units
Heat transfer coefficient = h W/m2-oC
Effective area = A2 m2
Overall thermal resistance= 1 / (h x A1 + 1 / ( Ri + 1/ (A2 x h) ) ) R oC/W
Local air temperature = (q*M*(N-1)) / (F*rho*Cp) Tl oC
Component temperature = Tl + q * R Tc oC
N h Units A2 Units R Units Tc Units
1 W/m2-oC m2 oC/W oC
2 W/m2-oC m2 oC/W oC
3 W/m2-oC m2 oC/W oC
4 W/m2-oC m2 oC/W oC
5 W/m2-oC m2 oC/W oC
6 W/m2-oC m2 oC/W oC
7 W/m2-oC m2 oC/W oC
8 W/m2-oC m2 oC/W oC
9 W/m2-oC m2 oC/W oC
10 W/m2-oC m2 oC/W oC

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