Table of Contents. iii

Transcription

1 Thermal Analysis

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3 Table of Contents Performing Thermal Analyses... 1 Overview... 1 Simplifying Assumptions... 2 Approach... 2 Common Analysis Parameters... 2 Specialized Parameters... 3 Modifying Set Up Parameters... 3 Prerequisites for Performing a Thermal Analysis... 3 Critical Analysis Parameters... 4 Part Data Tab... 4 Part Variable Data Tab... 4 Package Data Tab... 4 Modifying Part Placement... 5 Placing Parts... 7 Moving Parts... 7 UnPlacing Parts... 7 Zooming and UnZooming... 8 Using the Part Finder... 8 The Placement Statistics Panel... 9 Adding Setup Data Adjusting the Color Scale Setting Boundary Conditions Refining Boundary Conditions Editing Part Data Zooming and UnZooming Editing the Parameters Analyzing the Board The PWB Analysis Display Selecting Parts Selecting Displays Adjusting the Color Scale Zooming and UnZooming Exiting the Display Tool Index iii

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5 Performing Thermal Analyses Overview Thermal analysis is the process of determining the board temperature profile of a board, given the physical make up of the board and the power and placement of the parts feeding power into the board. From this temperature profile, the junction, case, and substrate temperatures are calculated. The substrate temperature is defined as the average temperature of the area on which the part is resting. The junction temperature only has meaning for semiconductor devices (both microcircuits and discrete semiconductors) which have junctions. Case temperature is the most widely applicable parameter and is used extensively by commercial methodologies of failure rate calculation, such as Bellcore. It is common during the early phases of development to assume that the applied power form all devices is some percentage of the rated power, or that the junction / case temperatures do not exceed a given value and develop a reliability estimate based these assumptions. The thermal analysis tools provide a rapid means of determining where these assumptions may lead to problems, and where added detail on actual component power dissipation may be needed. The tool also allows the user to conduct initial sensitivity analyses on component placement and to identify areas where active cooling may be needed. The tool included in ASENT is intended to be a high order tool, that is, it is intended to provide rapid approximate (plus or minus 5 degrees) answers consistent with the accuracy of the input data. This level of accuracy is sufficient to identify areas in need of further attention, either from a perspective of improving the accuracy of the applied power assumptions, or assemblies where detailed thermal analysis and trade analysis may be necessary. A specialist with more powerful and detailed thermal analysis tools (which also generally require more expertise to operate) would perform the detailed thermal study. The ASENT Thermal Analysis tool supports 5 different cooling methods: Conduction Primary cooling of the board is by conduction spreading in the board and conduction across the mounting hardware, typically card guides or clamps which conduct the heat from the card to a chassis or cold plate. Conduction with Natural Convection This method is only applicable if the card is mounted vertically, as shown on the screen. The heat transfer to the air, which rises as it becomes heated by the card, is taken into account in addition to the heat transfer by conduction in the card and across the card mounting hardware. Flowover The primary means of cooling is blowing air over the card, such as through a rack of cards. Forced Convection - The primary means of cooling is blowing air through a fin structure attached to the card. The fin structure may either be in the center portion of the card assembly, with additional layers and components on both card sides, 1

6 Thermal Analysis or may be on the back (bottom layer) of the card, in which case the card may only have parts on Side A Forced Convection with Natural Convection - This method is only applicable if the card is mounted vertically, as shown on the screen. The heat transfer through the heated air which rises along the face of the card is taken into account in addition to the heat transfer through the fin structure Simplifying Assumptions As a first order tool some assumptions were made to reduce the complexity of the calculations and increase the speed of the calculations. Some of the more significant of these assumptions are: Board Shape All boards are approximated by rectangles of their greater outer dimensions. Part Shape All parts are approximated by rectangles of their outer dimensions. For the Forced Convection and Flowover cooling method calculations, the parts are assumed to average 4 times as long as they are high. The density of air is constant, at the sea level typical density ( Kg/Cubic Meter). Approach The board is broken down into a three dimensional array of rectangular nodes, with each layer having a number of nodes determined by multiplying the number of Rows by the number of Columns. The analysis is termed a finite difference analysis where the heat flow is calculated on a node by node basis assuming the node has reached equilibrium, that is, the heat flowing out of the node is the same as that flowing in. This is an iterative approximation technique where a node temperature is estimated, the heat flow calculated, and another temperature is estimated until equilibrium is achieved. A conduction example of the breakdown is shown in the figure below. The ASENT Thermal Analysis tool is based on the algorithms and approach developed by the CALCE Electronic Packaging Research Center (EPRC) of the University of Maryland. Extensive validation studies and tests have been conducted which verified the validity of this approach. An explanation and validation guide is available. Common Analysis Parameters There are 5 basic parameters used by the analysis, independent of the choice of cooling method these are: Max Iterations This is the maximum number of times that the tool will calculate the board (runs) before the calculator will terminate. If the calculator gets to this number (initially 2000) the analysis is termed no not have converged, and any resulting temperatures are meaningless. Temperature data is not provided in this situation. Convergence Value This is the maximum temperature between runs (initially 0.5 degrees C) at which the analysis is considered complete. It is a measure (in addition to the number of rows and columns) of the accuracy of the analysis. The calculator will stop when the temperature difference between consecutive runs falls below this number. The resulting temperatures are considered valid and are written to the database. 2

7 Performing Thermal Analyses Relaxation This is a factor that is used to speed the calculation. Typical values range from 0.5 to 1.75 (the initial value). While this factor can speed the calculation, under certain circumstances, values above one can prevent the analysis from converging. If you encounter a situation that does not converge, reducing the relaxation factor below one may allow the analysis to converge. Row and Columns These numbers will determine how many nodes the board is divided up into, and the granularity of the of the layer temperature display. Increasing the number of rows and columns will increase the precision of the part temperatures, particularly for small parts, but the calculation will take longer, as will the loading of the board images. Specialized Parameters All the cooling methods other than Conduction require some additional parameters which apply to the cooling method selected. Any specialized parameters will be presented in the central portion of the Parameters input panel of the PWB Thermal Setup tab when the cooling method is selected. The specialized parameters are: Ambient Temperature This is the temperature of the air surrounding the board. This is used by the cooling methods involving Natural Convection. Air Gap This is the distance between the board and the edge of the case or the adjacent card. It is assumed to be the same distance on both the top and bottom of the board. This is used by the cooling methods involving Natural Convection. Air Flow Rate This is the volume of air being delivered (in cubic feet or meters per minute) for cooling. This is used by the cooling methods involving Forced Convection. Air Pressure This is the pressure of the delivered cooling air at the inlet to the board. This is used by the cooling methods involving Forced Convection. Side A Channel - This is the distance between the top of the board and the edge of the case or the adjacent card. This is unique to the Flowover cooling method. Side B Channel - This is the distance between the bottom of the board and the edge of the case or the adjacent card. This is unique to the Flowover cooling method. Modifying Set Up Parameters Any time the Part Placement is modified, or the thermal setup parameters are changed the results of any previous thermal analysis are cleared out. In addition to the Layer Temperature profiles, this includes the Junction, Case and Substrate Temperature Rises. This assures you that the thermal data you are looking at is the result of an analysis using the displayed set up parameters and part placement. Prerequisites for Performing a Thermal Analysis In order to successfully conduct a Thermal Analysis and obtain meaningful data from the analysis the Board and its components must have sufficient definition to provide the information for the calculation tool. This includes: The board must have a PWB component. 3

8 Thermal Analysis The parts should have their location on the PWB defined. (They should be placed ). Select the PWB Placement tab to review the part placement and any unplaced parts. The Cooling Type and Boundary Conditions must be defined. The remaining analysis parametrics are provided default values that will generally suffice for an initial run of the Thermal Calculator. This is performed in the PWB Thermal Setup tab. Critical Analysis Parameters Many of the parameters which are key to the temperatures calculated by the Thermal Calculator are the same as those which drive the Failure Rate Calculation, such as part type. Several other parameters figure prominently in the analysis which are not significant in Failure Rate Calculation, such as mounting height, pin length, number of thermal vias, case to substrate material. While these parameters are not generally used in the failure rate calculation, they will affect the Case or Junction Temperature, which, in turn, will drive the predicted failure rate. Part Data Tab The important parameters appearing on the Part Data Tab are: Case To Substrate Material this is typically Air but can be set to any defined material. The default/typical material for the board is set in the PWB Thermal Setup tab. Data only needs to be entered on the Part Data tab where the case to substrate material is different than the default/typical. Mounting Height this is the typical height between the bottom of the case and the board. Like the Case to Substrate material, the default/typical height for the board is set in the PWB Thermal Setup tab. Data only needs to be entered on the Part Data tab where the height is different than the default/typical. Number of Thermal Vias (# of Thermal Vias) If there are Thermal Vias under the part in addition to the Plated Through Holes, enter the number here. This will decrease the Case and Junction Temperatures. Placement Data (x_center, y_center, side, orientation) All of these can be set simultaneously using the Part Placement (see Modifying Part Placement) tab in a graphical manner, however data may be observed and refined directly on the Part Data tab if desired. Generally if any of these fields is blank, the part is unplaced. Part Variable Data Tab The Applied Power field is the only field on this tab which impacts the thermal analysis. If this parameter is not applicable to the part type (such as Capacitors, Connectors, Crystals, etc) the part will not impact the temperatures calculated by the Analysis. Such non-power parts may be left unplaced without any effect on the analysis results. Package Data Tab The Package Data tab contains many of the parameters that are central to the Thermal Analysis. These are: Pin Length this is distance from where the pin meets the body to the top of the board. This is only applicable to leaded parts. For unleaded surface mount parts (such as chip resistors, Leadless Chip Carriers, Ball Grid Arrays, etc) this is zero. The mounting height is used to approximate the distance of the solder joint thermal path to the board for leadless parts. Pin Cross Section (pin_x_section) this is the average cross sectional area of the lead for leaded parts, or the average horizontal cross section of the solder joints for leadless parts. Pin Material This is the material of the pins. The only material properties of significance to the Thermal Analysis are the x, y and z conductivities. For leadless parts, this should be set to the solder material used on the board. Pins per Package (pins_package) this is the number of leads on the package, regardless of whether they are electrically significant. This is the number of solder pads on leadless parts. 4

9 Performing Thermal Analyses Number of Plate Through Holes this should be equal to the number of pins per package for leaded parts, and zero for surface mount parts (leadless or leaded). Size (x_package, y_package, z_package) - this is the size of the body of the part and determines the contact area over which the power from the part is dissipated. All parts are approximated by a rectangle described by these dimensions, so shape does not affect analysis results. The package data is most easily checked (and corrected if necessary) in the Component Data Manager. Boards with lots of parts on them typically use a much smaller number of packages, usually only a dozen or so at most. A list of the packages of used on the board can be obtained quickly using the Package Count Report under the Reports Metrics menu. Modifying Part Placement The placement of parts on the board is one of the essential building blocks for the Physics of Failure related analyses such as Thermal Analysis and Vibrational Analysis. The Part placement display also provides a quick look at the physical appearance of the board, allowing you and the designer to validate that you are working on the current version of the design. To access the PWB Placement Tool: 1. Select the board of interest by clicking on it in the product tree display with the left mouse button. 2. Select the 'PWB Placement Data' tab in the Node Data area on the right side of the screen (This tab will only be presented if there is a PWB type component in the parts list of the chosen board). The PWB outline and the parts are shown in reduced scale on the data tab. The parts on the top side (side 'A') are shown in cyan while the parts shown as empty outlines are on the bottom (side 'B'). Part R3 is on the bottom of the board in the following figure. 3. To edit the placement data, press the 'Edit' button. The placement panel fills the entire screen and is comprised of four areas: 5

10 Thermal Analysis The toolbar (along the top) The Placement Area (in the middle of the screen) The Unplaced List & button (on the right side of the screen) The button panel with the Save and Cancel buttons (on the bottom of the screen). 4. Parts can be placed, unplaced, moved from one side of the board to another, rotated, or moved using this tool. In additon, two utilities, a part finder and a placement information summary are provided. In the lower left corner of the screen, the coordinates of the present cursor position are displayed (the lower left corner of the board is normally 0,0). 5. The Toolbar is described in the figure below. The Transparent Button shows the outline of the Parts on the other side of the Board. The Grid button turns the grid on or off. The grid is intended to assist you in placing parts. The 'Side' selector is used to display either Side 'A' or Side 'B' as the top of the board. The board is not rotated or flipped, the display of the parts is the primary effect of changing sides. 6. Leaving the cursor over a button for a few seconds will bring up the 'Hint' tag which will show the label (name) of the button. 6

11 Performing Thermal Analyses Placing Parts Parts which are imported from the Layout tools will already be placed. Parts you add to a board in the Reliability Manager or import through IGS will not be placed and will show up in the unplaced list on the right side of the board. Placement data may also be added through the User Defined Import. To Place a part: 1. Highlight the part to be placed by clicking on the part reference designator in the Unplaced Parts List. 2. Click on the 'Place' button. 3. The part appears in the middle of the board and the 'Select' button on the toolbar is pressed. 4. Click on the part with the left mouse button and drag it to the desired location. 5. Release the mouse button. The part is now placed. Moving Parts Parts can be moved through the Drag-n-Drop method or through the use of an input panel. The Drag-n-Drop method is more adaptable to quick trade studies and alternative investigations. The input panel is most useful if you are placing parts from a list of coordinates. In either case, the first step is to assure that the 'Select' the left mouse button to press it. To use the Drag-n-Drop method: button is pressed on the toolbar. If not, click on it with 1. Click on the part with the left mouse button and drag it to the desired location. 2. Release the mouse button. The part is now moved to the new location. To use the Input panel method: 1. Double Click on the part of interest with the left mouse button. 2. The 'Refine Placement' input panel is displayed. The reference designator of the part you are working on is shown in the title bar of this panel. 3. Enter the new coordinates of the part center. 4. Use the 'Side' pull down menu to select the side of the board the part will be on. 5. Use the 'Orientation' pull down menu to select the part orientation. 6. Press the 'Ok' button. The part moves to the prescribed location. UnPlacing Parts Parts are removed from the board using the 'Delete' button. To delete a part: 7

12 Thermal Analysis 1. Press the 'Delete' key using the left mouse button. 2. Select the part to be unplaced by clicking on it with the left mouse button. A confirmation panel is displayed. 3. Click on 'Yes' with the left mouse button. 4. The part is removed from the board and the reference designator appears in the 'Unplaced Parts List' on the right side of the board. 5. Continue selecting parts and responding 'Yes' until all the parts of interest are unplaced. 6. Click on the 'Select' button to return to the Select/Move mode. Zooming and UnZooming The part reference designators are shown on the part outlines where room permits. It is quite often that there are a number of parts on the board that are too small for the reference designator label to fit, and it is thus difficult to find the part of interest. The 'Zoom' feature provides a solution to the problem by allowing you to specify an area which will be expanded to fill the entire screen, magnifying the part dimensions to a point where the reference designators can be displayed. To Zoom in on a location: 1. Click on the 'Zoom' button. 2. Place the mouse in the placement area and press and hold the left mouse button. 3. 'Drag' a rectangle over the parts of interest. 4. Release the Mouse button. After a brief pause, the display fills with the area you outlined. You can Zoom again, further increasing the magnification until you achieve the desired level of detail. To Unzoom (or Zoom Out) just press the 'Unzoom' is once again displayed. button. It steps back through the zooming process until the entire board Using the Part Finder Perhaps the fastest way to find that ONE part of interest is to use the 'Part Finder' button opens a list of the parts on the board. button on the toolbar. Pressing the 8

13 Performing Thermal Analyses Highlight the part on the list and press the 'Find' button. The part outline appears in red. Double clicking on the part will verify that the desired component was found and will present the placement information for the part. The Placement Statistics Panel 9

14 Thermal Analysis The 'Show Placement Information' button will display a summary of the board and placement information. Clicking on the button brings up a display panel with the summary. Click on the 'Ok' button to close the panel. Adding Setup Data The 'PWB Thermal Setup' tab provides the capability to graphically establish the boundary conditions for the thermal analysis. In this tab you may also establish the typical / default values for mounting height and case to substrate material. Selecting this tab will also inititialize the PTH and VIA tabs and populate them with default data. The tab also provides a placement display to provide a quick look at the physical appearance of the board, allowing you and the designer to validate that you are working on the current version of the design. The Themal Setup Tool will also allow you adjust the part parameters of Applied Power, Mounting Layer and Mounting Height, as well as the case to substrate material on a part by part basis. To access the 'PWB Analysis Results' Tool: 1. Select the board of interest by clicking on it in the product tree display with the left mouse button. 2. Select the 'PWB Thermal Setup' tab in the Node Data area on the right side of the screen (This tab will only be presented if there is a PWB type component in the parts list of the chosen board). The PWB outline and the parts are shown in reduced scale on the data tab. Existing boundary conditions are shown in the color of the temperature scale for the board. 10

15 Performing Thermal Analyses 3. Click on the 'Edit' button. The display tool becomes a full screen tool. The PWB Display panel fills the entire screen and is comprised of four areas: The toolbar (along the top) The Display Area (in the middle of the screen) The Color Scale (on the right side of the screen) The button panel with the 'Save' and Cancel buttons (on the bottom of the screen). A close up of the toolbar is shown in the figure below. The UnZoom button steps back through the zooming process until the entire board is displayed. The Transparent Button shows the outline of the Parts on the other side of the Board. The Adjust the Color Grid button provides the capability to specify the colors scale for temperatures. The Reset button removes all boundary conditions. The Parameters button brings up a panel where the analysis parameters, as well as the default / typical values for munting height and case to substrate material are established and maintained. 11

16 Thermal Analysis The 'Side' selector is used to display either Side 'A' or Side 'B' as the top of the board. The button only affects the presentation if the Transparent button is not pressed, in which case only the parts on the select side are shown. 4. Leaving the cursor over a button for a few seconds will bring up the 'Hint' tag that will show the label (name) of the button. Adjusting the Color Scale The color scale provides an easy way to set the temperature of the inlet air, for forced convection type cooling, or card edges for conduction type cooling. The color scale may be easily adjusted to reflect the temperatures that the user will use to set the boundary conditions. To adjust the color scale: 1. Press the Adjust Color Scale button. 2. The Adjust Color Grid input panel is presented. 3. Enter the values for the minimum value and the temperature increment between colors. There are 10 colors available in addition to black for Insulated. The values may be either typed directly in, or the up and down arrows may be used to toggle the values up or down. Temperatures are accepted in whole degrees and any fraction entered will be rounded to the nearest whole degrees. (Remember this is a first order tool!) 4. Press Apply. The input panel is closed and, after a brief pause, the color scale is redisplayed with the new values. Setting Boundary Conditions Boundary conditions are set by painting blocks (nodes) with the color that represents the desired temperature. For forced convection type cooling methods, this is a single vertical line (column) of nodes which represent the location of the inlet air, typically on the left side of the board. For conduction type cooling the board edge temperatures are the ring of nodes just outside the outline of the board. To set boundary conditions: 1. Click on the Set button. 2. Click on the color of the color scale that reflects the temperature you want. The temperature number turns from gray to white when it is selected. 12

17 Performing Thermal Analyses In this case, 41 degrees is selected. 3. Select a node and click on it with the left mouse button. It will be painted in the selected color. If you click on it with the right mouse button it will be reset, or cleared. 4. Consecutive blocks may be painted by clicking on them individually or by holding down the left mouse button and dragging the cursor over them. Refining Boundary Conditions The Setup tool provides the capability to set boundary conditions of individual to temperatures not shown on the color grid. This is done through the Refine button. To set or change a node temperature to a value not show on the color grid: 1. Select the Refine button on the toolbar. 2. Select the node to be set. An input panel is presented. 3. Enter the temperature for the node. The temperature may be either typed directly in, or the up and down arrows may be used to toggle the temperature up or down. Temperatures are accepted in whole degrees and any fraction entered will be rounded to the nearest whole degrees. (Remember this is a first order tool!) 4. Press the Apply button. 5. The node is presented in a crosshatch of the next highest temperature on the color grid. Editing Part Data As part of the set up for thermal analysis, the part data important to the analysis may be fine tuned from within the PWB Thermal Setup tab. To modify the part data: 1. Select the Edit Part button on the toolbar. 2. Double Click with the left mouse button on the part to be edited. An input panel is presented. 13

18 Thermal Analysis 3. The title bar of the input panel displays the Reference Designator of the selected part. 4. Enter the applied power of the component, either as an absolute value (one watt in the figure above) or check the % box to have the number interpreted as a percent or the rated power (the 1 would become one percent). This field is not presented if the part type is not one of those for which Applied Power is not an applicable field (such as Capacitors). 5. You may select the mounting layer from the list of board layers by clicking on the down arrow at the right of the Mounting Layer input field and selecting an element from the selection list presented. Parts with the Mounting Layer blank are assumed by the calculator to be mounted on the outside layer for their assigned side. (Layer 1 for side A the highest number layer for side B ). 6. The mounting height may be specified by entering a value in the third field of the input panel. This is in whole units (typically mils or thousanths of an inch). Parts with the Mounting Height field blank are assumed by the calculator to be mounted at the default mounting height (specified in the Parameters input panel.) 7. You may select the case to substrate material from the list of materials by clicking on the down arrow at the right of the Case To Substrate Material input field and selecting an element from the selection list presented. Parts with the Case To Substrate Material blank are assumed by the calculator to have the default material(specified in the Parameters input panel.). 8. When the desired modifications are made, press the Ok button. The modified data will also show up in the Part Data tab and the Part Variable Data (for the Power field). Zooming and UnZooming The part reference designators are shown on the part outlines where room permits. It is quite often that there are a number of parts on the board that are too small for the reference designator label to fit, and it is thus difficult to find the part of interest. The 'Zoom' feature provides a solution to the problem by allowing you to specify an area that will be expanded to fill the entire screen, magnifying the part dimensions to point where the reference designators can be displayed. To Zoom in on a location: 1. Click on the 'Zoom' button. 2. Place the mouse in the placement area and press and hold the left mouse button. 3. 'Drag' a rectangle over the parts of interest. 4. Release the Mouse button. After a brief pause, the display fills with the area you outlined. You can Zoom again, further increasing the magnification until you achieve the desired level of detail. To Unzoom (or Zoom Out) just press the 'Unzoom' is once again displayed. Editing the Parameters button. It steps back through the zooming process until the entire board The selection of the cooling method, as well as the default mounting height and case to substrate material are specified in the Parameters input panel of the Thermal Setup tab. To edit the parameters: 1. Click on the Parameters button on the toolbar. 14

19 Performing Thermal Analyses 2. The Parameters input panel is presented. 3. Select the Cooling Method by clicking on the arrow on the right side of the input field and selecting a type from the selection list presented. Many of the other parameters on the panel are dependent on the cooling type, and are not presented until the associated cooling type is selected. The 7 items shown in the lower portion of the figure above apply to all cooling methods. Note: A fin structure is required for either of the cooling methods involving Forced Convection. 4. Enter data for the input fields presented. 5. Select the default case to substrate material by clicking on the down arrow at the right of the Case To Substrate Material input field and selecting an element from the selection list presented. 6. Click on the Ok button. If you changed the Rows or the Columns field, the board display is redrawn with the new grid. Analyzing the Board The calculation of board temperatures is invoked from the Calculate menu item on the Baord pop-up menu, selecting the Thermal menu item from the submenu. The thermal calculator is then activated and begins the data integrity checks. The first check is for unplaced parts. If there are unplaced parts on the board, the user is presented with the list of unplaced parts and asked whether to continue. 15

20 Thermal Analysis If the parts listed are the part types for which Applied Power is not an applicable parameter (such as the Capacitors in the above figure) then the user can proceed with the analysis without compromising the accuracy of the results. The calculator then loads the parts, materials, layers and regions thd checks the data to assure it is complete. If there is a problem, the user is notified, the calculation aborted and the diagnostic file presented. The error panel below was generated by selecting the Forced Convection cooling type on a board which did not have a fin layer. Following successful completion of the data completeness checks, the calculator starts the iterative calculation of the nodes on the board. During this process, the status panel presents the number of the current iteration, the specified and the calculated temperature difference value (Convergence). The calculation will continue until either the calculated temperature difference value is less that the value specified or until the specified maximum iterations has been completed. Upon completion of the calculation, the diagnostics file is presented using Notepad. This file provides the capability to save and print the conditions, assumptions (defaults) which were used to provide the data being displayed in the PWB Analysis Display tab. 16

21 Performing Thermal Analyses The PWB Analysis Display The 'PWB Analysis Results' tab provides the capability to graphically present the the results of analyses performed on the board, including the Physics of Failure related analyses such as Thermal Analysis and Vibrational Analysis. The tab also provides a placement display to provide a quick look at the physical appearance of the board, allowing you and the designer to validate that you are working on the current version of the design. To access the 'PWB Analysis Results' Tool: 1. Select the board of interest by clicking on it in the product tree display with the left mouse button. 2. Select the 'PWB Analysis Results' tab in the Node Data area on the right side of the screen (This tab will only be presented if there is a PWB type component in the parts list of the chosen board). The PWB outline and the parts are shown in reduced scale on the data tab. The initial display of the tab is the 'Power' display. The parts which have 'applied power' are shown in a color reflecting their power dissipation, while the parts for which this parameter is not applicable or no data is available are shown as empty outlines. The 'J0001' (a connector) on the left side of the figure below is an example of the power parameter not being applicable. 3. Click on the 'View' button. The display tool becomes a full screen tool. The PWB Display panel fills the entire screen and is comprised of four areas: The toolbar (along the top) The Display Area (in the middle of the screen) The Color Scale (on the right side of the screen) The button panel with the 'Ok' button (on the bottom of the screen). A close up of the toolbar is shown in the figure below. The 'Side' selector is used to display either Side 'A' or Side 'B' as the top of the board. The board is not rotated or flipped, the display of the parts is the primary effect of changing sides. 17

22 Thermal Analysis 4. Leaving the cursor over a button for a few seconds will bring up the 'Hint' tag which will show the label (name) of the button. Selecting Parts The 'Select' button provides the capability to check the exact numerical values of critical result values, should there be any question about the graphical display. To check the numerical values of a part: 1. Click on the 'Select' button with the left mouse button. 2. Double-click on a component with the left mouse button. A display panel of parameters appears. 3. Click on the 'Ok' button when you have finished reviewing the data. Selecting Displays Selecting the arrow in the 'View' field opens the drop down menu of available displays. In addition to Power, Failure Rate, Stress Ratios, Junction Temperature, Case Temperature, and Substrate Temperature, a 'Layer Temperature' entry is generated for each defined layer in the PWB part (these are defined in the Component Data Manager). Selecting the desired display and pressing 'Enter' (or the left mouse button) closes the pull down menu and repaints the display. The following figure is a typical 'Layer Temperature' display when layer themal data is available. 18

23 Performing Thermal Analyses Adjusting the Color Scale The graphical displays have historically been one of the most successful methods of communicating the overall status of a design, as well as any areas of concern, in a design review. The color scale used in the display tool may be customized to help you improve the clarity of the message delivered by the graphic display. The scale is divided into 10 bands. The default range is established by scanning the maximum and minimum values on the board. For Temperature, the increments will always be in whole degrees as the ASENT Thermal Tool is intended as a first order (initial approximation) tool, and the data provided to the tool does not consistantly have the precision to provide temperatures of greater accuracy. For all other items (power, failure rate, etc), three digits of precision are offered for the color scale. To modify the Color scale: 1. Press the 'Adjust Color Grid' button. 2. A dialog panel is presented. 19

24 Thermal Analysis 3. Enter the Minimum value and the Step using the up and down spin arrows next to the input windows. Pressing an arrow and holding down the button will cause the number to continue 'spinning' in the direction of the arrow. 4. Press 'Apply'. The color scale is redisplayed, and the display area is redrawn using the colors specified by the revised scale. 5. Alternately, you can revert to the default settings by pressing the 'Auto-Scale' button. This will recalculate the scale and redraw the display. Zooming and UnZooming The part reference designators are shown on the part outlines where room permits. It is quite often that there are a number of parts on the board that are too small for the reference designator label to fit, and it is thus difficult to find the part of interest. The 'Zoom' feature provides a solution to the problem by allowing you to specify an area which will be expanded to fill the entire screen, magnifying the part dimensions to point where the reference designators can be displayed. To Zoom in on a location: 1. Click on the 'Zoom' button. 2. Place the mouse in the placement area and press and hold the left mouse button. 3. 'Drag' a rectangle over the parts of interest. 4. Release the Mouse button. After a brief pause, the display fills with the area you outlined. You can Zoom again, further increasing the magnification until you achieve the desired level of detail. 20

25 Performing Thermal Analyses To Unzoom (or Zoom Out) just press the 'Unzoom' is once again displayed. button. It steps back through the zooming process until the entire board Exiting the Display Tool Pressing the 'Ok' button on the bottom panel exits the tool and returns to the data tab view. 21

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27 Index A Adding Setup Data Analyzing the Board C Critical Analysis Parameters... 4 M Modifying Part Placement... 5 O Overview... 1 P Prerequisites for Performing a Thermal Analysis... 3 T The PWB Analysis Display