阅读说明：本技术 一种高频pcb电路板高密精细化导热铜箔布局方法 (Layout method of high-density refined heat-conducting copper foil of high-frequency PCB ) 是由 李宝童 闫素娜 徐俊豪 刘宏磊 光宏昊 洪军 于 2020-06-08 设计创作，主要内容包括：一种高频PCB电路板高密精细化导热铜箔布局方法,先确定设计域内的载荷与边界条件,包括温度边界、产热区域、有效导热系数以及产热率的确定；然后进行rank-1微结构模型拓扑优化,采用最优导热微结构rank-1微结构模型为材料插值模型开展高频PCB电路板导热路径的拓扑优化；再进行高频PCB电路板优化结构的映射；最后进行适应性处理,获得导热铜箔最终布局；本发明方法设计得到的结果较之传统的拓扑优化结构热性能更优越,可用于高频PCB电路板高密精细化导热铜箔布局设计。(A high-density refined heat-conducting copper foil layout method for a high-frequency PCB circuit board comprises the steps of firstly determining load and boundary conditions in a design domain, wherein the conditions comprise a temperature boundary, a heat production region, an effective heat conductivity coefficient and a heat production rate; then carrying out topology optimization on the rank-1 microstructure model, and carrying out topology optimization on the heat conduction path of the high-frequency PCB by adopting the optimal heat conduction microstructure rank-1 microstructure model as a material interpolation model; mapping the optimized structure of the high-frequency PCB circuit board; finally, carrying out adaptive treatment to obtain the final layout of the heat-conducting copper foil; the result obtained by the design of the method is more excellent in thermal performance compared with the traditional topological optimization structure, and can be used for layout design of high-density refined heat-conducting copper foil of a high-frequency PCB circuit board.)

1. A layout method for high-density refined heat-conducting copper foil of a high-frequency PCB circuit board is characterized by comprising the following steps:

1) load and boundary condition determination:

the high-frequency PCB circuit board is composed of three layers of resin substrates, partial areas between the substrate layers and the upper and lower surfaces of the high-frequency PCB circuit board are plated with copper to serve as a heat conduction path of the circuit board, the plane size of the high-frequency PCB circuit board is a mm multiplied by a mm, and the heat conduction along the thickness direction is neglected;

in the working process of the high-frequency PCB, partial heat generated by the transistor and the inductor is conducted to the nut columns at four corners of the high-frequency PCB, and then is transmitted to an external device by the nut columns; meanwhile, under the action of natural convection or forced convection at the upper and lower surfaces of the high-frequency PCB, part of heat can be transferred to a cooling medium in a convection heat exchange mode;

the high-frequency PCB circuit board is formed by superposing three layers of resin substrates and four copper layers, and the effective heat conductivity coefficient of the material in a two-dimensional equivalent area is calculated when the topological distribution of the copper material in each copper layer is assumed to be the same and the heat conduction process in the high-frequency PCB circuit board is simplified into a two-dimensional problem; the effective thermal conductivity of the copper material coverage area is:

in the formula: k is a radical of_CuAnd k_minCopper and resin substrates, respectivelyThermal conductivity of (C), H_CuAnd H_baseTotal thickness of copper layer and resin substrate layer, respectively, H_tol＝H_Cu+H_baseThe total thickness of the high-frequency PCB is the total thickness of the high-frequency PCB; the effective thermal conductivity of the resin substrate region is still k_min；

2) And (3) topology optimization of the rank-1 microstructure model:

based on rank-1 microstructure model, the topological optimization formula of the heat conduction structure is written as:

in the formula: the heat conduction structure is omega, D_G(x) Is the material thermal conductivity tensor at any point x of the structure; q is the volumetric heat generation rate; n is a boundary_NA unit vector in the outer normal direction; the topological optimization target c is a structural heat conduction performance parameter, and comprises structural thermal flexibility, structural maximum temperature and difference between a structural temperature field and given temperature distribution; the inequality constraint represents the limit on the usage of the high heat conduction material, wherein f is the volume ratio of the maximum allowable high heat conduction material; the topological optimization variable field gamma (x) represents the volume ratio of the high heat conduction material at any point x, is called as material pseudo density, and can describe the material distribution in the structure omega; at any point x in the structure, gamma (x) ═ 1 indicates that the point is a high heat conduction material, and gamma (x) ═ 0 indicates that the point is a low heat conduction material;

based on the rank-1 microstructure model, the specific expression of the material thermal conductivity tensor is as follows:

in the formula: k is a radical of₀And k_minThe thermal conductivity coefficients of the high-structure and low-heat conduction materials are respectively;

topology optimization of high-frequency PCB heat conduction path by adopting rank-1 microstructure model as material interpolation modelThe method comprises the steps of optimizing pseudo density and characteristic direction angle variables of a microstructure in topology optimization based on a rank-1 microstructure model, solving a structure temperature field by using a finite element method, dividing the structure into n × n finite element grids in the topology optimization based on the rank-1 microstructure model, dividing a corresponding design variable field by using the same finite element grids, taking minimized structure thermal flexibility as an objective function, limiting the proportion of high thermal conductive materials in the optimized structure, considering that the optimization process is converged and limiting the maximum iteration times to be L when the maximum change of the topology variables of two adjacent optimization iterations is smaller than a set value_maxSecondly;

3) mapping of the optimized structure of the high-frequency PCB:

visualizing the optimization result based on the rank-1 material model by adopting a mapping method, taking a cosine function related to the direction and angle of the rank-1 microstructure as a mapping function, taking a cosine function related to the pseudo-density of the rank-1 microstructure as a mapping threshold, and mapping the topology optimization result to a four-node quadrilateral grid of 2n multiplied by 2n by utilizing a Heaviside step function to obtain a macroscopic structure only consisting of given high and low heat conduction materials;

4) adaptive processing: and rounding the layout of the heat-conducting copper foil according to the requirements of the production process so as to obtain the final layout of the heat-conducting copper foil.

2. The layout method of the high-density refined heat-conducting copper foil of the high-frequency PCB circuit board as claimed in claim 1, wherein in order to adapt to different design requirements and not to be limited to the constraint and optimization target, a designer can add thermal resistance evaluation and temperature uniformity evaluation and can also modify material proportion constraint; the evaluation method was obtained by finite element calculation.

Technical Field

The invention belongs to the technical field of thermal performance optimization design of structures, and particularly relates to a layout method of high-density refined heat-conducting copper foil of a high-frequency PCB.

Technical Field

The electronic unit in the high-frequency PCB circuit board is powered by the circulation of current, and the current can cause the heat dissipation and the temperature rise of the surrounding space; higher operating temperatures can degrade the performance of the electronic components and seriously affect their reliability and safety, with the failure rate being exponentially proportional to the operating temperature; also, high operating temperatures result in high thermal stresses at the joints of the electronic components attached to the circuit board, causing their failure; thus, the need for thermal control becomes critical in the design and operation of electronic devices;

the design of the layout of the heat transfer structure has an important influence on the heat dissipation performance of the heat transfer structure, the design of the structural layout form in the actual engineering depends on the experience and inspiration of designers, the effective design idea of a certain type of heat transfer structure is not necessarily suitable for other types of heat transfer structures, and the improvement of the heat dissipation performance of the structure obtained by using the traditional topological optimization method is very limited, so that the requirement of the interior of the current circuit board on heat control cannot be met.

Disclosure of Invention

In order to overcome the defects of the prior art, the invention aims to provide a high-density refined heat-conducting copper foil layout method for a high-frequency PCB, wherein topological optimization of a heat-conducting path of the high-frequency PCB is carried out by adopting a rank-1-based microstructure model, and then an optimization result based on the rank-1 microstructure model is visualized by adopting a mapping method, and a design result is more excellent than the thermal performance of a traditional topological optimization structure, so that scheme support can be directly provided for actual engineering design.

In order to achieve the aim, the invention adopts the technical scheme that:

a layout method of high-density refined heat-conducting copper foil of a high-frequency PCB circuit board comprises the following steps:

1) load and boundary condition determination:

the high-frequency PCB circuit board is composed of three layers of resin substrates, partial areas between the substrate layers and the upper and lower surfaces of the high-frequency PCB circuit board are plated with copper to serve as a heat conduction path of the circuit board, the plane size of the high-frequency PCB circuit board is a mm multiplied by a mm, and the heat conduction along the thickness direction is neglected;

in the working process of the high-frequency PCB, partial heat generated by the transistor and the inductor is conducted to the nut columns at four corners of the high-frequency PCB, and then is transmitted to an external device by the nut columns; meanwhile, under the action of natural convection or forced convection at the upper and lower surfaces of the high-frequency PCB, part of heat can be transferred to a cooling medium in a convection heat exchange mode;

the high-frequency PCB circuit board is formed by superposing three layers of resin substrates and four copper layers, and the effective heat conductivity coefficient of the material in a two-dimensional equivalent area is calculated when the topological distribution of the copper material in each copper layer is assumed to be the same and the heat conduction process in the high-frequency PCB circuit board is simplified into a two-dimensional problem; the effective thermal conductivity of the copper material coverage area is:

in the formula: k is a radical of_CuAnd k_minThermal conductivity coefficients of copper and resin substrates, H_CuAnd H_baseTotal thickness of copper layer and resin substrate layer, respectively, H_tol＝H_Cu+H_baseThe total thickness of the high-frequency PCB is the total thickness of the high-frequency PCB; the effective thermal conductivity of the resin substrate region is still k_min；

2) And (3) topology optimization of the rank-1 microstructure model:

based on rank-1 microstructure model, the topological optimization formula of the heat conduction structure is written as:

in the formula: the heat conduction structure is omega, D_G(x) Is the material thermal conductivity tensor at any point x of the structure; q is the volumetric heat generation rate; n is a boundary_NA unit vector in the outer normal direction; topological optimization objective c is structural heat conductionPerformance parameters including structural thermal compliance, structural maximum temperature, and difference in structural temperature field from a given temperature profile; the inequality constraint represents the limit on the usage of the high heat conduction material, wherein f is the volume ratio of the maximum allowable high heat conduction material; the topological optimization variable field gamma (x) represents the volume ratio of the high heat conduction material at any point x, is called as material pseudo density, and can describe the material distribution in the structure omega; at any point x in the structure, gamma (x) ═ 1 indicates that the point is a high heat conduction material, and gamma (x) ═ 0 indicates that the point is a low heat conduction material;

based on the rank-1 microstructure model, the specific expression of the material thermal conductivity tensor is as follows:

in the formula: k is a radical of₀And k_minThe thermal conductivity coefficients of the high-structure and low-heat conduction materials are respectively;is the characteristic direction angle of rank-1 microstructure;

the method comprises the steps of adopting a rank-1 microstructure model as a material interpolation model to carry out topological optimization of a heat conduction path of the high-frequency PCB, simultaneously optimizing pseudo density and characteristic direction angle variables of a microstructure in topological optimization based on the rank-1 microstructure model, solving a structural temperature field by using a finite element method, dividing a structure into n × n finite element grids in the rank-1 microstructure model, dividing a corresponding design variable field by using the same finite element grids, taking minimized structural thermal flexibility as a target function, limiting the proportion of high heat conduction materials in the optimized structure, and considering that the optimization process is converged and limiting the maximum iteration times to be L when the maximum change of topological variables of two adjacent optimization iterations is smaller than a set value_maxSecondly;

3) mapping of the optimized structure of the high-frequency PCB:

visualizing the optimization result based on the rank-1 material model by adopting a mapping method, taking a cosine function related to the direction and angle of the rank-1 microstructure as a mapping function, taking a cosine function related to the pseudo-density of the rank-1 microstructure as a mapping threshold, and mapping the topology optimization result to a four-node quadrilateral grid of 2n multiplied by 2n by utilizing a Heaviside step function to obtain a macroscopic structure only consisting of given high and low heat conduction materials;

4) adaptive processing: and rounding the layout of the heat-conducting copper foil according to the requirements of the production process so as to obtain the final layout of the heat-conducting copper foil.

In order to adapt to different design requirements, the thermal resistance evaluation and the temperature uniformity evaluation can be added by a designer without being limited to the constraint and the optimization target, and the material proportion constraint can be modified; the evaluation method was obtained by finite element calculation.

The invention has the beneficial effects that:

compared with the traditional optimization method, the method provided by the invention has the advantages that the thermal performance such as the highest temperature and the like of the optimization design scheme is obviously improved, the proportion of high-heat-conduction materials is ensured, and the high-density refined heat-conduction copper foil layout design of the high-frequency PCB is realized.

Drawings

Fig. 1 is a topological optimization algorithm example of a heat conduction path of a high frequency PCB, wherein (a) is a "topological variable-material property" model, (b) is load and boundary conditions, and (c) is a setting of a design area.

Fig. 2 is a calculation of the equivalent thermal conductivity of the circuit board, wherein (a) is a schematic cross-sectional view of the circuit board, and (b) is the distribution of the material in the two-dimensional equivalent area.

FIG. 3 is an optimized structure of a circuit board, wherein (a) is an optimized structure based on a rank-1 micro-structural model and (b) is a macro-map of the optimized structure;

fig. 4 is an optimized structure and temperature cloud obtained based on rank-1 microstructure model.

Detailed Description

The present invention will be described in detail below with reference to the accompanying drawings.

A layout method of high-density refined heat-conducting copper foil of a high-frequency PCB circuit board comprises the following steps:

(1) load and boundary condition determination:

the high-frequency PCB circuit board is composed of three layers of resin substrates, the thickness of each substrate is 0.305mm,0.711mm and 0.305mm respectively, copper with the thickness of 70 mu m is plated between the substrate layers and in partial areas of the upper surface and the lower surface of the high-frequency PCB circuit board to be used as a heat conduction path of the high-frequency PCB circuit board, and the plane size of the high-frequency PCB circuit board is 65mm multiplied by 65 mm; because the thickness of the high-frequency PCB circuit board is far smaller than the plane size of the high-frequency PCB circuit board, the heat conduction along the thickness direction can be ignored, and the high-frequency PCB circuit board is taken as an engineering object to carry out topological optimization research on the heat conduction path of the high-frequency PCB circuit board, as shown in figure 1;

in the working process of the high-frequency PCB, partial heat generated by the transistor and the inductor is conducted to the nut columns at four corners of the high-frequency PCB, and then is transmitted to an external device by the nut columns; meanwhile, under the action of natural convection or forced convection at the upper and lower surfaces of the high-frequency PCB, part of heat can be transferred to a cooling medium in a convection heat exchange mode; the heat generated by the transistor in the high-frequency PCB is about twice that of the inductor, and when the temperature of the stud is fixed to 10 ℃, about 22.4 percent of the total heat is dissipated to the surrounding environment through natural convection heat exchange, so that in the topological optimization of a heat conduction path, the area where the transistor and the inductor are arranged is provided with uniformly distributed constant heat sources, and the heat generation amounts are respectively 2Q₀And Q₀The temperature of four corners of the high-frequency PCB is constant to be T₀Applying a constant heat flux q ″, throughout the region, 10 ℃_convSo as to simulate the influence of the heat convection outside the circuit board surface.

The high-frequency PCB circuit board is formed by overlapping three layers of resin substrates and four copper layers, and the effective heat conductivity coefficient of the material in a two-dimensional equivalent area is calculated as shown in FIG. 2 when the topological distribution of the copper material in each copper layer is assumed to be the same and the heat conduction process in the high-frequency PCB circuit board is simplified into a two-dimensional problem; the effective thermal conductivity of the copper material coverage area is:

in the formula: k is a radical of_CuAnd k_minThe specific value is k which is the heat conductivity coefficient of the copper substrate and the resin substrate respectively_Cu＝400W/(m·K)，k_min＝0.3W/(m·K)；H_CuAnd H_baseThe total thickness of the copper layer and the resin substrate layer is respectively H_Cu＝0.28mm，H_base＝1.321mm；H_tol＝H_Cu+H_baseThe effective thermal conductivity coefficient of the resin substrate region is still k for the total thickness of the high-frequency PCB_min；

(2) And (3) topology optimization of the rank-1 microstructure model:

based on rank-1 microstructure model, the topological optimization formula of the heat conduction structure can be written as:

in the formula: the heat conduction structure is omega, D_G(x) Is the material thermal conductivity tensor at any point x of the structure; q is the volumetric heat generation rate; n is a boundary_NA unit vector in the outer normal direction; the topological optimization target c is structural heat conduction performance parameters, such as structural thermal flexibility, structural maximum temperature, difference between a structural temperature field and given temperature distribution and the like; the inequality constraint represents the limit on the usage of the high heat conduction material, wherein f is the volume ratio of the maximum allowable high heat conduction material; the topological optimization variable field gamma (x) represents the volume ratio of the high heat conduction material at any point x, is called material pseudo density, and can describe the material distribution in the structure omega; at any point x in the structure, gamma (x) ═ 1 indicates that the point is a high heat conduction material, and gamma (x) ═ 0 indicates that the point is a low heat conduction material;

based on the rank-1 microstructure model, the specific expression of the material thermal conductivity tensor is as follows,

in the formula: k is a radical of₀And k_minThe thermal conductivity coefficients of the high-structure and low-heat conduction materials are respectively;is the characteristic direction angle of rank-1 microstructure;

carrying out topology optimization of a heat conduction path of the high-frequency PCB by using a rank-1 microstructure model as a material interpolation model, and simultaneously optimizing the pseudo density and characteristic direction angle variables of a microstructure in the topology optimization based on the rank-1 microstructure model; solving a structural temperature field by using a finite element method, dividing a structure into 400 multiplied by 400 finite element grids in a rank-1-based microstructure model, and dividing a corresponding design variable field by using the same finite element grids;

adopting density filtering to avoid checkerboard phenomenon in the optimized result, wherein the filtering radius is R_min1.5L/100, wherein L is the side length of the high-frequency PCB; the thermal flexibility of the minimized structure is taken as an objective function, and the proportion of high heat conduction materials in the optimized structure is limited to be not more than 50% of the whole area; maximum change of topological variable when two adjacent optimization iterations<When 0.001, the optimization process is considered to be converged, and the maximum iteration number is limited to 500 times; the optimized structure obtained based on the rank-1 microstructure model is shown in fig. 3 (a);

(3) mapping of the optimized structure of the high-frequency PCB:

the globally optimal 'volume-point' structure based on the rank-1 material model is composed of periodic rank-1 microstructures with different pseudo densities and characteristic directions, so that the topological configuration characteristics of the structure cannot be grasped and processed and manufactured; in order to obtain the macroscopic topological distribution of the heat conduction paths in the optimized structure, a mapping method is adopted to visualize the optimized result based on a rank-1 material model, a cosine function related to the direction and angle of a rank-1 microstructure is taken as a mapping function, a cosine function value related to the pseudo density of the rank-1 microstructure is taken as a mapping threshold, and the topological optimized result is mapped to a four-node quadrilateral mesh of 800 × 800 by using a Heaviside step function to obtain the macroscopic structure only consisting of given high and low heat conduction materials, as shown in fig. 3(b), so that the minimum size of the obtained heat conduction copper foil is L/800 ═ 65mm/800 ≈ 81 μm;

in the macroscopic heat conduction path distribution obtained by taking the pseudo density and the characteristic angle of the rank-1 microstructure as optimization variables, a high-temperature area and a low-temperature area in the lower side structure of the high-frequency PCB are directly connected through uniformly distributed needle-shaped heat conduction paths, so that the effective transfer of heat is ensured; a small number of needle-shaped finned columns are arranged in the left side area and the right side area of the high-frequency PCB, so that convection heat transfer is facilitated, and the structure temperature is further reduced; the internal temperature cloud chart of the high-frequency PCB circuit board after the layout optimization of the heat-conducting copper foil is shown in FIG. 4;

4) adaptive processing: and rounding the layout of the heat-conducting copper foil according to the requirements of the production process so as to obtain the final layout of the heat-conducting copper foil.

In order to adapt to different design requirements, the method is not limited to the constraint and optimization target, a designer can add thermal resistance evaluation, temperature uniformity evaluation and the like, and can modify the constraints such as material proportion and the like; the evaluation method was obtained by finite element calculation.