Lecture 10 - Electronics Cooling Basics——FloEFD的培训教程(三天)李中云.ppt

1、184,Lecture 10 Electronics Cooling Basics,Content Modelling Boards and Components Simple and more detailed (Overlapping parts) IDF Import Thermal vias EL-Module PCB generator 2R compact components Joule Heating Peltier Element For Flotherm Users: Operational differences between FT and EFD,185,EFD vs

2、. FLOTHERM,Fairly rectangular geometries Unrivaled fast calculation Manual & instantaneous meshing Semi-automatic or manual transformation of CAD-Import Specific Objects and parametric SmartParts No CAD experience necessary High productivity by attributes and Command Center Specialized for Electroni

3、cs Cooling Manual input of current on straight traces (only),General (curved) geometries 3-5 time longer CPU times and memory consumption Automatic meshing by algorithm Direct CAD import - Construction via and like CAD - General Fluid Dynamics with more physical modelling 3D electrical simulation wi

4、th Joule Heating,186,FOR FLOTHERM USERS ONLYOperational Differences Between EFD and FLOTHERM,Objects are not keypointed Remeshing after a change of the mesh connectivity is necessary even if geometry has not changed, but e.g. material assignments changed Geometrical copy does not copy physical prope

5、rties Overlapping of solids by order of material and not by hierarchy of parts Preprocessing not possible while solving 1st time opening of wizard can take hours for very extensive geometries No multiprocessing facilities Renaming of parts by save as and replace EFD has better 2D sources Changing of

6、 a power value gives a reaction in temperature much slowlier 2-resistor models need 2 bricks with correct area,187,Thermal Model Required,In principle, any CAD drawing can be used for electronics cooling calculations, however a mechanical drawing contains too much details is usually not a thermal mo

7、del ! Simplifications and enhancements/replacements are necessary Remove screws, legs, pins, sealings, etc. Close holes Replace fan blade geometries and extended perforations Create physical component and board models,188,Board Modelling,Dont use just Epoxy (k=0.2 W/m K) Level 0: k=10 W/m K Level 1:

8、 Orthotropic conductivity Level 2: More detailed with individual layers Level 4: All circuits (traces). Not possible,In-Plane Conductivity (W/mK),Normal Conductivity (W/mK),189,IDF Import,IDF is a almost standardized ASCII format to decribe board outlines and components. *brd,*bdf / *emn,*emp / *.bd

9、f,*.ldf / other There are dialects spoken Specification available on demand FLOTHERM is reading just the boundig boxes very quick Size and name filtering possible EFD.lab is reading all details very slow. no filtering IDF Components are just “images”,190,IDF Repair,Delete unnecessary small component

10、s Smear out their total power onto the whole board Deleting of legs and unnecessary details (holes) later Eventually replace bricks by a component model 2R detailed,191,PCB Generator(EL Module),Any plate can be defined as a board by manual input of k Extension by the PCB Generator Allows to obtain t

11、he bi-axial thermal conductivity values, with the normal (through plane) and in-plane thermal conductivities automatically derived from the PCB structure and the properties of the specified conductor and dielectric materials. The board can also be arbitrarily oriented with respect to the global coor

12、dinate system, i.e. angled PCBs can be modelled.,192,Modelling Advice: PCB shape must be a rectangular brick. In the case of an inclined PCB in contact with another non-inclined PCB, it is recommended that the inclined plate is either inserted directly into the non-inclined plate or the connector bl

13、ock and care is taken to refine the mesh in the connecting region. In the example shown, the region should be well resolved: the easiest way to achieve this is to apply local mesh settings on the edges of the two connectors & the edges of the two angled dimms and then set to refine all solid cells t

14、o an appropriate level of refinement.,193,Thermal Vias,Vias are modelled using one solid volume with an effective conductivity normal to the PCB Detailed knowledge about the layer stack is needed,194,Package Modelling,Content of a CAD Library usually is not a thermal model Transistor modelling Level

15、 0: Take just the copper flag as heat source and delete the auxiliary equipment (legs, encaps) Level 1: Add a silicon die and copper inside a plastic block Nesting of parts (see Day 3) Level 2: Construct a thermal model with legs, die, adhesive etc.,195,Other (logic) packages Level 0: brick with lum

16、ped conductivity k=5 to 20 W/m K Indicator for case temperature Level 1: 2-Resistor Compact Models If you like to believe datasheets Caution: the concept of a 2R model is only valid if there is a dominant heat flow either towards the board or towards top“ (case“). In fifty-fifty situations always be

17、 in doubt.,196,2R- Component Compact Model(EL Module),This is the simplest possible network compact model, and consists of a defined junction-to-case resistance (Rjc) and a junction-to-board (Rjb) resistance. In EFD, this data is applied to the defined package geometry consisting of two flat solid b

18、odies representing the junction and case. In-built library of two-resistor models of standard JEDEC package outlines.,197,Modelling Advice: The top face of a case body should be resolved so that to minimize the total area of cells cut off by the edges of the top face (blue cells on the image opposit

19、e). To achieve this you can set control planes slightly shifted from each edge toward the center of the face, or highly refine the top face with the local mesh. Bad resolution: the total area of cut off cells (blue cells) is substantial. Good resolution (four control planes are specified): the total

20、 area of cut off cells (blue cells) is negligible.,198,EFD: EL-Module Functionality List,EDB = Engineering Database,199,EFD: Electronics Feature Access,Flow Analysis Menu Update New Toolbar Entries Engineering Database Update,200,Perforated Plate(EL Module),This compact model object can be used to r

21、epresent a thin plate with multiple holes. No meshing overhead, associated with explicit representation of the hole features. Can be added as an additional condition to the opening with the Environment pressure boundary condition or a Fan already specified. The perforated plates are defined by the F

22、ree Area Ratio, and the shape (can be round, rectangular or regular polygon) and dimensions of the holes. Pressure drop coefficient is automatically calculated.,201,Electrical Conditions “Joule Heating”(EL Module),Steady-state direct electric current in electro-conductive solids. The corresponding s

23、pecific Joule heating effect R*I is automatically calculated and included in heat transfer calculations. The specific electrical resistivity of the material may be isotropic, anisotropic or temperature dependent. The calculations of electric potential and current are performed only in conductive sol

24、ids, i.e. metals and metal-containing composite materials. Dielectric solids, semiconductors, fluid and void areas do not participate in the calculation.,These pictures will be replaced,202,Joule Heating (EL Module),Modelling Advice It is recommended to well resolve thin elements not aligned to the

25、global coordinate system, e.g. thin curved wires. Good accuracy for a thin curved wire is achieved when you have 5 cells per thickness. It is not necessary to refine thin element if it is aligned with respect to the global coordinate system planes (no curving, no bending, not angled to the mesh). It

26、 is recommended to provide higher mesh resolution for components with higher electrical resistivity values. The area of contact should also be well resolved by the computational mesh.,203,Heat Pipe Compact Model(EL Module),Compact representation for the heat pipe requiring to specify the overall eff

27、ective thermal resistance of the heat pipe, based on its performance for the system being designed, along with selection of a part and two faces to define the heat flux direction. The performance of a heat pipe depends on many factors, such as inclination, orientation, length, etc. The user can simu

28、late different conditions by specifying different Effective Thermal Resistances for the part. Avoids the need to model the complex two-phase physics within these devices.,204,Engineering Database Library Update(EL Module),Features A broad range of new Solids, Fans, Thermoelectric Coolers, and Two-Re

29、sistor Components has been added to the Engineering Database. A library of interface materials has been added. A library of solids representing typical IC Packages has been added providing the possibility to simulate an IC Package as a one-piece solid with effective density, specific heat and therma

30、l conductivity.,Benefits User has immediate access to pre-defined and validated attributes associated with the electronics parts he is working with in design. They are presented to the user in a manufacturer centric way, that makes selection of the appropriate data fast and easy. The libraries can be further extended by the user with their own attribute datasets or if they wish to add another supplier dataset not currently available.,205,EDB: Fan Manufacturer Libraries (EL Module),206,EDB: