Method for simulating temperature on or in circuit board of electrical circuit

Abstract

The invention relates to a method for calculating a temperature on or in a printed circuit board of an electrical circuit, in which a model of a circuit carrier is formed and cells (Zi, j) of the circuit carrier adjacent to each other are delimited in the model, and in order to calculate the temperature of the cells, a power balance is continuously calculated for each cell (Zi, j), in order to balance:-detecting or estimating the thermal power (Pti, j-1, Pti, j + 1, Pti-1, j, Pti + 1, j) provided from and dissipated into an adjacent cell by thermal conduction from known operating parameters,-detecting or estimating the thermal power (Pti, j-1, Pti, j + 1, j) provided by thermal conduction from the adjacent cell (Zi, j-1, Pti, j + 1, j) arranged in said cell (Zi, j-1, j-1, Pti, j + 1, j) to the adjacent cell (Zi, j-1, j, Pti + 1, j) by thermal conduction from known operating parameters. The thermal power (Pthi, j) generated and introduced into the circuit carrier and / or converted in the unit (Zi, j) by a structural element on the unit (Zi, j), and / or the thermal power (Pki, j) dissipated from the unit (Zi, j) by heat conduction to a heat sink arranged on the unit (Zi, j) or by convection or radiation is detected or estimated on the basis of known operating parameters.

Description

Technical Field

[0001] The invention relates to a method for calculating the temperature on or in a printed circuit board of an electrical circuit. Background Art

[0002] The temperature of electronic components during operation of electrical circuits has always been an important issue in circuit design. Almost all components from which circuits are built have properties that are related to the temperature of the components. Thus, ohmic resistance, capacitance or inductance change depending on the temperature. The properties of semiconductor components also change. Thus, for example, light-emitting diodes may change their light color or brightness depending on the temperature. During the operation of the circuit, the temperature is not static, but changes dynamically, for example depending on the circuits connected, the power conversion of the components through which the current flows, and the heat transferred from the circuit, for example, by convection and / or radiation.

[0003] The temperature distribution in electronics is not uniform. The temperature profile changes dynamically depending on the load state, internal structure and external influences. It is important to know or estimate relatively accurately the current component temperature on the printed circuit board or in the electronic control unit in order to achieve optimized temperature protection, overload protection or even temperature compensation of optoelectronic components.

[0004] For example, document DE 10 2021 113 177 A1 discloses providing a temperature sensor to determine the temperature of a component. The greater the number of components whose temperature is particularly important for the function of the circuit, the greater the effort for temperature detection. This is where the present invention comes into play. Summary of the invention

[0005] The object of the present invention is to find a simple possibility of taking into account the temperature of components of an electrical circuit even if and precisely when the electrical circuit has a large number of components whose temperature is important for the functioning of the circuit.

[0006] This object is achieved according to the invention by a method according to claim 1 .

[0007] According to claim 1, a model of the printed circuit board is formed for the method. In this model, cells are separated from one another, which together form the model of the printed circuit board. The temperature of each such cell is calculated, thereby simulating the temperature of a real printed circuit board. In order to calculate the temperature of the cells, a power balance is calculated continuously and preferably in real time for each cell. The basis for the method is a thermal finite element model. In order to balance:

[0008] - according to the invention, the thermal power provided by thermal conduction from and dissipated into the adjacent cells is detected or estimated from known operating parameters,

[0009] - according to the invention, the thermal power generated by the components arranged on the unit and introduced into the circuit carrier by heat conduction is detected or estimated on the basis of known operating parameters,

[0010] - detecting or estimating the thermal power converted in the unit based on known operating parameters, and / or

[0011] According to the invention, the thermal power dissipated from the unit by heat conduction into a cooling body arranged on the unit or by convection or by radiation is detected or estimated based on known operating parameters.

[0012] Preferably, for each unit under consideration, the change in temperature is calculated from the product of the power balance of the unit under consideration, the thermal capacity of the unit and the time that has passed since the last calculation of the temperature change. For each unit under consideration, the calculated temperature change can be added to the last calculated temperature to calculate the temperature. Other calculation formulas are also possible. The temperature is preferably calculated in cycles, so that the time that has passed between two consecutive calculation time points is always the same. This time, which is also called the step width, can be, for example, 2.5 milliseconds, which means that the temperature is then recalculated in practice every 2.5 milliseconds.

[0013] In the method according to the invention, the thermal power provided by heat conduction from one of the adjacent cells and dissipated into the adjacent cell can be detected by calculation. To this end, the product of the difference between the last calculated temperature of the cell and the last calculated temperature of the adjacent cell on the one hand and the heat transfer coefficient between the cell and the adjacent cell on the other hand can be formed. The heat transfer coefficient between the cell and the adjacent cell is related to the material from which the printed circuit board is formed. The heat transfer coefficient can be determined from the material properties of the electrically insulating material used for the printed circuit board and the electrically conductive material used and the proportion of these materials at the boundary between the cell and the adjacent cell. To this end, the area at the boundary between the cells can be determined and the area proportion of the different materials can be determined.

[0014] It is also possible to calculate the thermal power dissipated from the unit by heat conduction into a cooling body arranged on the unit. This heat conduction can be calculated similarly to the heat conduction into adjacent units.

[0015] The model can be selected such that a cell corresponds to an area of ​​the printed circuit board in the form of a cuboid. The area can have square surfaces as top and bottom sides. The model can be simplified to a two-dimensional model, thereby saving computing power and memory. The cell is then not a cuboid, but a rectangle, in particular a square.

[0016] The power converted in a cell may be determined based on known, measured, calculated or estimated electrical quantities such as current and voltage.

[0017] The considerations based on the method according to the invention for calculating the temperature or the method according to the invention can also be used to determine the temperature of a circuit component. This can be the junction temperature of a semiconductor component, which is a component of a circuit with a printed circuit board, whose temperature is calculated. The junction temperature can be determined as follows:

[0018] - based on the determined temperature of the unit on which the semiconductor component is attached to the printed circuit board,

[0019] - according to the electrical power of the semiconductor structure, and

[0020] -Based on the heat transfer coefficient.

[0021] One or more methods according to the invention can be implemented in a control device for controlling at least one component, wherein the component comprises an electrical circuit with a printed circuit board and, if necessary, components whose temperature is determined. The component and the control device assigned to the component can be part of a motor vehicle. For example, it can be a control device for controlling a vehicle light source. The component, i.e., for example, the light source, can have an electrical circuit with a printed circuit board, on which components of the circuit are arranged. The control device and one or more components can be parts of a device.

[0022] From the model, the surface temperature profile of the printed circuit board can be calculated continuously and in real time based on known operating parameters, such as operating voltage, known current and power, and power loss of relevant components of the circuit.

[0023] In addition, one or more temperature sensors can be mounted on the printed circuit board in order to compare the results of the temperature simulation with actual measurements and to adjust the model. In this case, the measured temperature and the temperature calculated with the aid of the model can be compared repeatedly and thus high deviations between the calculations made with the aid of the model and the actual values ​​can be prevented. In this way, internal and external convection of the electrical device in which the printed circuit board is arranged can be taken into account, which is difficult to take into account and model in the model.

[0024] By knowing the current, position-dependent temperature profile, the control software can take appropriate measures, which include, for example:

[0025] - a position- and temperature-dependent correction of the luminous flux by varying the drive current in the optoelectronic element, which is important, for example, when driving particularly temperature-sensitive RGB light-emitting diodes, and / or

[0026] - A time-dependent reduction in the output power when the temperature is too high. In this case, short, temporarily higher power peaks can be tolerated, since the temperature is estimated in real time, taking into account the thermal capacity of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The invention is explained in more detail with the aid of the accompanying drawings. In the drawings:

[0028] Figure 1 A simple model for calculation according to the method of the present invention is shown,

[0029] Figure 2 Show according to Figure 1 A diagram of a unit in the model and a schematic diagram of the heat power referenced to that unit. DETAILED DESCRIPTION

[0030] The thermal finite element model of the printed circuit board of the electronic assembly to be monitored is defined once. Then, calculations are performed in real time during the continuous operation of the assembly.

[0031] The simple case shown is a surface model. More complex models can also be used, in which cooling bodies or also ventilation conditions are taken into account.

[0032] Using this model, a grid is imaginarily placed on the printed circuit board, thereby forming cells, each of which represents an area of ​​the printed circuit board. Each cell Z in the grid 1,1, …Z m,n Represented by indices i and j, where 1≤i≤m, 1≤j≤n.

[0033] For each single unit Z i,j Establishing power balance Pb i,j ( Figure 2 ).

[0034] Pb i,j =Pth i,j -Pk i,j -Pt i,j-1 -Pt i,j+1 -Pt i-1,j -Pt i+1,j

[0035] Unit Z i,j The power balance Pb i,j Basically from unit Z i,j Specifically, the following powers flow into the power balance:

[0036] -Pth i,j : The thermal power provided by the conversion in the unit or in the structural elements on the unit

[0037] -Pk i,j : Power dissipated by convection, radiation or a cooling body on the unit,

[0038] -Pt i,j-1 : The thermal power transferred between units (i,j) and (i,j-1),

[0039] -Pt i,j+1 : The thermal power transferred between cells (i,j) and (i,j+1),

[0040] -Pt i-1,j : The heat power transferred between units (i,j) and (i-1,j),

[0041] -Pt i+1,j : The heat power transferred between cells (i,j) and (i+1,j),

[0042] This balance is calculated at discrete time points with an interval dt. This balance can be used to calculate the unit Z i,j Temperature change dT i,j , and determine the temperature change between two calculation time points.

[0043] dT i,j =c i,j *Pb i,j *dt

[0044] Here, c i,j It is unit Z i,j The heat capacity of the unit Z i,j Temperature change dT i,j and at the previous calculation time point unit Z i,j The known temperature T i,j , so we can calculate the unit Z at the current calculation time point i,j Temperature Tn i,j :

[0045] Tn i,j =T i,j +dT i,j

[0046] By adjusting the parameter Pk i,j Proper modeling allows for different cooling body connections for each unit

[0047] The junction temperature of the semiconductor component can be determined based on the solder point temperature T i,j , semiconductor power and heat transfer coefficient.

[0048] Reference numerals list

[0049] Zi,j Model Unit

[0050] Pth i,j Thermal power provided by conversion in the unit or structural elements on the unit

[0051] P i,j : Power dissipated by convection, radiation or a cooling body on the unit

[0052] Pt i,j-1 : The heat power transferred between units (i,j) and (i,j-1)

[0053] Pt i,j+1 : The heat power transferred between cells (i,j) and (i,j+1)

[0054] Pt i-1,j : The heat power transferred between units (i,j) and (i-1,j)

[0055] Pt i+1,j : The heat power transferred between cells (i,j) and (i+1,j)

Claims

1. A method for calculating the temperature on or in a printed circuit board of an electrical circuit, wherein: A model of the circuit carrier is formed and mutually adjacent cells (Z) of the circuit carrier are delimited in the model. i,j ), and in order to calculate the temperature of the unit, for each unit (Z i,j ) continuously calculates the power balance, where, in order to balance - Detecting or estimating from known operating parameters the thermal power (Pt) provided by thermal conduction from and dissipated into adjacent cells i,j-1 ,Pt i,j+1 ,Pt i-1,j ,Pt i+1,j ), - detect or estimate based on known operating parameters by heat conduction arranged in the unit (Z i,j ) and introduced into the circuit carrier and / or in the unit (Z i,j ) is the thermal power converted (Pth) i,j ), and / or - detect or estimate from known operating parameters the i,j ) is conducted to the unit (Z i,j ) or dissipated by convection or radiation (Pk i,j ).

2. The method according to claim 1, characterized in that For each unit considered (Z i,j ), the temperature change is from the considered unit (Z i,j ), the thermal capacity of the unit and the time elapsed since the last temperature change was calculated.

3. The method according to claim 2, characterized in that For each unit considered (Z i,j ), in order to calculate the temperature, the calculated temperature change is added to the last calculated temperature.

4. The method according to any one of claims 1 to 3, characterized in that The thermal power provided by thermal conduction from one of the neighboring cells and dissipated into the neighboring cell is detected by calculation, i.e. by calculating the last calculated temperature of the cell on the one hand and the temperature of the neighboring cell (Z i,j ) and on the other hand the difference between the cell and the adjacent cell (Z i,j ) is the product of the heat transfer coefficients between them.

5. The method according to claim 4, characterized in that The heat transfer coefficient is obtained from the material properties of the electrical insulating material and the conductive material used for the printed circuit board and the material in the unit (Z i,j ) is determined by the ratio of the boundary with the adjacent cells.

6. The method according to any one of claims 1 to 5, characterized in that Calculate from the unit (Z i,j ) is conducted to the unit (Z i,j ) and dissipated in the cooling body on it.

7. The method according to any one of claims 1 to 6, characterized in that The unit (Z i，j ) corresponds to an area of ​​a printed circuit board in the form of a cuboid having rectangular, in particular square, surfaces on the top and bottom as boundary surfaces.

8. Method for calculating the junction temperature of a semiconductor component, the semiconductor component being a component of an electric circuit having a printed circuit board, the temperature of which is calculated according to one of claims 1 to 7, characterized in that The junction temperature is determined according to the unit (Z) of the printed circuit board to which the semiconductor structure is attached. i,j ) is determined according to one of claims 1 to 7 as a function of the electrical power of the semiconductor component and as a function of the heat transfer coefficient.

9. A control device for controlling at least one component, in particular a component in a motor vehicle, for example for controlling a light source of the vehicle, wherein: The assembly comprises an electrical circuit having a printed circuit board on which components of the circuit are arranged, characterized in that the control device is suitable and designed to calculate the temperature of the printed circuit board by means of a method according to one of claims 1 to 7.

10. The control device according to claim 9, characterized in that: The control device is suitable and designed to calculate the temperature of one or more semiconductor components by means of the method according to claim 8 .

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