Power Electronics Integration, Packaging and Thermal Management
Best Practices Overview for Electronics Thermal...
Transcript of Best Practices Overview for Electronics Thermal...
Best Practices Overview for
Electronics Thermal
Simulations
Geometry Preparation
Mesh
Materials
Conditions
Solution
Results
STAR-CCM+ Simulation Process
http://www.cd-adapco.com/webcasts (Industry = Electronics)
STAR-CCM+ Electronics Thermal Seminars
Natural convection series
– Best practices
– Small internal air gaps
– Radiation
Forced convection series
– Best practices, part 1
– Best practices, part 2
– Complex heat sinks
– Geometry preparation
• Assumes 3D-CAD → Parts → Regions
• Composite parts Geometry
• Pre-defined parts-based mesh (PBM) operations Mesh
• Air (ideal gas or Boussinesq)
• Solids (common in electronics) Materials
• Pre-defined boundaries
• Forced & natural convection
• Field functions for ambient temperature & altitude Conditions
• Segregated flow & energy with under-relaxation
• Gravity & radiation (natural convection)
• Stopping criteria Solution
• Temperature report
• Geometry & mesh scenes
• Temperatures with velocity vectors on section planes Results
STAR-CCM+ Template Simulation File
Solids
– Eliminate mechanical connectors
(screws, rivets, springs, etc.)
– Fill holes
– Simplify individual parts
– Sheet metal modifications
– Eliminate interferences
– Fill undesired gaps
Best Practices: Geometry Preparation
Air
– Internal: Fill the empty space
– External
• Natural: Sphere or hemisphere
• Forced: Short inlet, extended outlet
– Tools (3D-CAD): Extract Internal / External Volume, Boolean
Best Practices: Geometry Preparation
Best Practices: Geometry Preparation
Best Practices: Geometry Preparation
Ideally: Conformal polyhedral
mesh
– Strongly recommended for natural
convection (because of radiation)
– Good for forced convection
Option: Polyhedral (conformal)
air, trimmed (non-conformal)
solids
– Suitable for forced convection
Part-Based vs Regions-Based
– Preference
– Conformal thin mesh not yet
available with PBM
Typical mesh: 500,000 –
5,000,000 cells
Best Practices: Meshing
Best Practices: Meshing
Air
– Ideal gas with temperature-
varying properties always suitable
– Boussinesq sufficient for natural
convection
Solids
– Isotropic solids
– Orthotropic solids (e.g. PCBs)
• Separate continua
• Properties in the region
• Typical PCB: kplanar ~ 10 W/m-K,
kthrough plane ~ 0.5 W/m-K
– Components
• Can use contact resistances on
interface to model as 2-resistor.
• Otherwise aluminum oxide (k ~ 25
W/m-K) common.
Best Practices: Materials
Heat sources
– Temperature on all inlets & outlets
– If no air surrounding the enclosure in the model (common in forced
convection), to model heat loss to the ambient add convection on boundary:
• External natural convection: h ~ 5 – 10 W/m2-K
• External forced convection: h > 20 W/m2-K
– Heat power on all dissipating components*
Best Practices: Conditions
Heat Electrical
power supplied
Component
(e.g. IC, IGBT,
MOSFET,
LED,…)
Electrical power
delivered
RF energy,
visible light
• “Wall power”
• Max power (power budget)
• Measured power?
• Duty-cycled?
• What is the efficiency?
FORCED
CONVECTION Flow inlet Flow outlet
Flow “pushed”
into the system
• Specified positive flow speed
velocity), positive pressure,
positive mass flow rate, or
fan pressure jump
• Ambient temperature
• Pressure outlet (0 Pa)
• Ambient temperature (for any
reverse flow)
Flow “pulled”
through the
system
• Stagnation inlet (0 Pa)
• Ambient temperature
• Specified negative flow speed
velocity), negative pressure,
negative mass flow rate, or
fan pressure jump
• Ambient temperature (for any
reverse flow)
Fan inside the
system:
Internal
Interface fan +
• Stagnation inlet (0 Pa)
• Ambient temperature
• Pressure outlet (0 Pa)
• Ambient temperature (for any
reverse flow)
Best Practices: Conditions
Internal Interface Fan
– Only the circular or annular faces used as boundaries in fan definition
– Flow direction: From Boundary-0 to Boundary-1 (Swap Boundaries on the
interface as needed)
– Fan curve
• Define in the fan interface as a polynomial, OR
• Input fan curve to Tools > Tables & then select the curve.
Best Practices: Conditions
Natural Convection: Conditions on the exterior air boundary
– Convection
• Stagnation Inlet (0 Pa)
• Total temperature = Ambient temperature
– Radiation
• Boundary transparency = 1.0
• Radiation temperature is specified in the air continua
– Inside a room: Radiation temperature = wall temperature
– Outdoors: Turn on solar if device exposed to the sun during the day, at night Radiation Temperature = sky radiation temperature
Best Practices: Conditions
Solvers > Segregated Energy
– Fluid Under-Relaxation = 0.99
(default is 0.9)
– Solid Under-Relaxation = 0.9999
(default is 0.99)
Best Practices: Solution
Stopping Criteria
– Often convergence in 300 – 500
iterations.
– Observed residuals (non-
normalized)
• Energy residual < 1E-5
• Momentum residuals < 1E-8
– Convergence requires more
iterations for a finer mesh.
Scalability
– For typical size scales well to ~8
cores.
– I typically run with 2 or 4 cores.
Best Practices: Results
Best Practices: Results
Rthermal = (Tcenter of base – Tambient)
Heat power
Report (expression) from field functions:
($ThermocoupletemperatureReport -
$Tambient_K)/$Heat_power
Natural Convection
– Best practices: http://www.cd-adapco.com/webinar/electronics-best-practices-session-1-
simulating-natural-convective-airflow-electronic
– Small gaps: http://www.cd-adapco.com/webinar/electronics-best-practices-session-2-natural-
convection-analyses-thin-air-gaps
– Radiation: http://www.cd-adapco.com/webinar/electronics-best-practices-session-3-natural-
convection-analyses-thermal-radiation
Forced Convection
– Best practices, part 1: http://www.cd-adapco.com/webinar/best-practices-forced-convection-
simulations-series-1-part-1
– Best practices, part 2: http://www.cd-adapco.com/webinar/best-practices-forced-convection-
simulations-series-1-part-2
– Modeling complex heat sinks: http://www.cd-adapco.com/webinar/efficient-modeling-
complex-heat-sinks-series-2-part-1
– Geometry preparation: http://www.cd-adapco.com/webinar/geometry-preparation-electronics-
thermal-simulations-series-2-part-2
More Information: Web Seminar Recordings
Thank you!
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