HDI plate heat dissipation structure capable of improving surface flatness and HDI plate

Abstract

The utility model relates to the related technical field of circuit boards, and provides an HDI board heat dissipation structure capable of improving surface flatness and an HDI board, the HDI board heat dissipation structure comprises a first laser blind hole, a mechanical buried hole and a second laser blind hole which are sequentially arranged on the HDI board from the upper layer to the lower layer; the first laser blind hole, the mechanical buried hole and the second laser blind hole are sequentially connected through a heat conduction material. According to the utility model, a laser blind hole and mechanical buried hole mode is adopted to form a new heat dissipation structure, and the flatness of the surface of the printed circuit board is ensured while the heat dissipation effect is ensured.

Description

Technical Field

[0001] The utility model relates to the technical field of circuit boards, in particular to an HDI board heat dissipation structure and an HDI board for improving surface flatness. Background Art

[0002] The statements in this section merely provide background technical information related to the present invention and do not necessarily constitute prior art.

[0003] The COB light source area of ​​the optical module HDI board requires that the surface of the chip bonding area is flat, the height of the surface protrusions is generally required to be less than 10um, and the chip must be well cooled.

[0004] The inventors found in their research that the traditional heat dissipation structure is to lay copper as a thermal conductive material over a large area under the chip, and then arrange mechanical through holes to improve the longitudinal thermal conductivity of the printed circuit board (PCB board for short), and to export the heat of the chip to the back of the PCB board through the mechanical through holes, and then export the heat through thermal pads and other devices. In order to meet the requirements of the surface flatness of the circuit board, the copper filling process cannot be used for plugging due to aspect ratio and process limitations. Usually, the mechanical through holes are plugged with POFV. After POFV plugging, the resin will bulge by reducing copper, and then the resin will be ground flat by grinding the plate to control the flatness. There will be bulges or depressions at the plugging hole, and the process flow of the grinding plate process for flatness control is complicated. It is difficult to control the bulge height at the plugging hole within 10um, resulting in a reduced yield and an increase in the manufacturing cost of the PCB board. Utility Model Content

[0005] In order to solve the above problems, the utility model proposes an HDI board heat dissipation structure and an HDI board with improved surface flatness, and adopts a laser blind hole plus a mechanical buried hole method to form a new heat dissipation structure, which ensures the flatness of the surface of the printed circuit board while ensuring the heat dissipation effect.

[0006] In order to achieve the above purpose, the utility model adopts the following technical solutions:

[0007] One or more embodiments provide an HDI board heat dissipation structure with improved surface flatness, including a first laser blind hole, a mechanical buried hole, and a second laser blind hole arranged in sequence from the upper layer to the lower layer of the HDI board; the first laser blind hole, the mechanical buried hole, and the second laser blind hole are connected in sequence through a thermal conductive material.

[0008] An HDI board adopts the above-mentioned HDI board heat dissipation structure for improving surface flatness to set a heat dissipation area.

[0009] Compared with the prior art, the beneficial effects of the utility model are:

[0010] The utility model sets a set number of laser blind holes on both sides of the HDI board, sets mechanical buried holes on the middle layer, and connects the laser blind holes and the mechanical blind holes through heat-conducting materials, thus forming a heat transfer channel from the upper layer to the lower layer of the HDI board, and heat is transferred in sequence through the first laser blind hole, the heat-conducting material, the mechanical blind hole, the heat-conducting material, and the second laser blind hole. The laser blind holes are set on both sides of the HDI board. Compared with the mechanical through holes, the depressions and protrusions caused by the laser blind holes when plugging the holes are greatly reduced, which can greatly improve the flatness of the surface.

[0011] The advantages of the present invention and additional advantages will be described in detail in the following specific embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The illustrative embodiments of the present invention and their descriptions are used to explain the present invention, but do not constitute a limitation on the present invention.

[0013] Figure 1 This is a schematic diagram of a first heat dissipation structure using stacked holes in Example 1 of the utility model;

[0014] Figure 2 This is a schematic diagram of a second heat dissipation structure using staggered holes in Example 1 of the utility model;

[0015] Figure 3 This is a structural diagram of the first heat dissipation structure of Example 1 of the utility model and the traditional mechanical through hole being arranged simultaneously;

[0016] Figure 4 It is the utility model embodiment 1 Figure 1 AA section view;

[0017] Figure 5 It is the utility model embodiment 1 Figure 1 BB cross-sectional view;

[0018] Figure 6 is a schematic diagram of the cross-sectional structure of the mechanical through hole 13 of Embodiment 1 of the present utility model;

[0019] Figure 7 It is a schematic diagram of the cross-sectional structure of the laser blind via in Example 1 of the utility model;

[0020] Among them: 1. The first layer of heat dissipation copper skin, 2. The second layer of heat dissipation copper skin, 3. The third layer of heat dissipation copper skin, 4. The fourth layer of heat dissipation copper skin, 5. The fifth layer of heat dissipation copper skin, 6. The sixth layer of heat dissipation copper skin, 7. The seventh layer of heat dissipation copper skin, 8. The eighth layer of heat dissipation copper skin, 9. Circuit board, 10. The first laser blind hole, 11. Mechanical buried hole, 12. The second laser blind hole, 13. Mechanical through hole;

[0021] 10-1, surface hole plate, 10-2, laser hole;

[0022] 11-1, mechanical through hole plate, 11-2, hole copper, 11-3, via. DETAILED DESCRIPTION

[0023] The utility model is further described below in conjunction with the accompanying drawings and embodiments.

[0024] It should be noted that the following detailed descriptions are exemplary and are intended to provide further description of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0025] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the utility model. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0026] Technical term explanation:

[0027] HDI board: HDI is the abbreviation of High Density Interconnector. HDI board is a kind of printed circuit board, which uses micro blind buried hole technology and has a relatively high line distribution density.

[0028] POFV process, namely (Plating Over Filled Via), is a special process used on PCB. The process is to plate copper on the hole wall, plug the hole with epoxy resin, grind the surface, and finally plate copper on the surface.

[0029] In the technical solutions disclosed in one or more embodiments, Figures 1 to 7 As shown, the HDI board includes a multi-layer structure, a HDI board heat dissipation structure for improving surface flatness, which is arranged on the HDI board to achieve heat dissipation, including a first laser blind hole 10, a mechanical buried hole 11, and a second laser blind hole 12 arranged in sequence from the upper layer to the lower layer of the HDI board; the first laser blind hole 10, the mechanical buried hole 11, and the second laser blind hole 12 are connected in sequence through thermal conductive materials.

[0030] In this embodiment, laser blind holes are set through a set number of layers on both sides of the HDI board, and mechanical buried holes are set through the middle layer. The laser blind holes and the mechanical blind holes are connected by heat conductive materials, thus forming a heat transfer channel from the upper layer to the lower layer of the HDI board, and heat is transferred in sequence through the first laser blind hole 10, the heat conductive material, the mechanical buried hole 11, the heat conductive material, and the second laser blind hole 12. Laser blind holes are set on both sides of the HDI board. Compared with mechanical through holes, the depressions and protrusions caused by the laser blind holes when plugging the holes are greatly reduced, which can greatly improve the flatness of the surface.

[0031] In some embodiments, the number of layers set on both sides of the HDI board are used as blind hole layers, and the remaining layers in the middle are used as buried hole layers, forming a structure of a first blind hole layer, a buried hole layer, and a second blind hole layer; a first laser blind hole 10 is set through each layer in the first blind hole layer, a mechanical buried hole 11 is set through each layer in the buried hole layer, and a second laser blind hole 12 is set through each layer in the second blind hole layer.

[0032] Optionally, the set number of layers of the first blind hole layer and the second blind hole layer may be equal;

[0033] Furthermore, the number of the first blind hole layer and the second blind hole layer is set as required, and is at least two layers.

[0034] Specifically, the HDI board includes a multi-layer circuit board 9 for laying out circuits; each layer of the circuit board of the HDI board can be a PP board or a Core board; PP is a film, also known as a semi-cured sheet PREPREG (PP), which is mainly composed of resin and reinforcing materials. One or both sides of the PP sheet are covered with copper foil to form a core board, also known as a Core board, which are all non-conductive materials.

[0035] The first blind hole layer and the second blind hole layer penetrate at least two layers of the circuit board. The first blind hole layer and the second blind hole layer are connected to the mechanical buried holes set in the middle buried hole layer through connecting thermal conductive materials. Thermal conductive materials are set on the surface of the circuit board where the first blind hole layer and the second blind hole layer are connected, so as to conduct the heat of the chip on the surface of the circuit board.

[0036] Optionally, the heat-conducting material is laid on the surface of the area where the heat dissipation structure of the HDI board is arranged and between each circuit layer, and copper sheet, aluminum sheet, etc. can be selected; preferably, copper sheet is used;

[0037] The heat conductive material can be set to a circular shape, a square shape or an irregular shape, and can be electrically isolated from the circuit set on the circuit board, without affecting the circuit structure of the PCB circuit connection. Figure 4 and 5 The shaded part is the square heat dissipation copper sheet.

[0038] A specific example is provided in which an HDI board is provided with 8 layers of heat dissipation copper sheets as an example. The heat dissipation copper sheets include a first heat dissipation copper sheet 1, a second heat dissipation copper sheet 2, a third heat dissipation copper sheet 3, a fourth heat dissipation copper sheet 4, a fifth heat dissipation copper sheet 5, a sixth heat dissipation copper sheet 6, a seventh heat dissipation copper sheet 7 and an eighth heat dissipation copper sheet 8; between the heat dissipation copper sheets is a circuit board 9 of the HDI board.

[0039] Optionally, a first laser blind hole 10 can be set to connect the first heat dissipation copper skin 1 and the third heat dissipation copper skin 3, a mechanical buried hole 11 can be set through the third heat dissipation copper skin 3 to the sixth heat dissipation copper skin 6, and a second laser blind hole 12 can be set between the sixth heat dissipation copper skin 6 and the eighth heat dissipation copper skin 8, so as to form a stacked hole design of blind holes and buried holes. The specific structure is as follows Figure 1 shown.

[0040] In some embodiments, the number of laser blind vias and mechanical buried vias 11 on both sides is set according to a set multiple;

[0041] Specifically, the number of the first laser blind vias is set to N1 times the number of the mechanical buried vias 11; the number of the second laser blind vias is set to N2 times the number of the mechanical buried vias 11; preferably, N1=N2 is set, and N1 and N2 are not less than 1.27.

[0042] The larger the ratio of the total number of laser blind vias to the total number of mechanical buried vias 11 is, the better the heat dissipation effect is, and it far exceeds the heat dissipation effect of the mechanical through-holes 13 , and is applicable to printed circuit boards with n-order blind and buried vias.

[0043] The density of the laser blind vias is set on the HDI board according to the density of the mechanical buried vias 11. The density of the mechanical buried vias 11 gradually increases along the longitudinal direction, and the density of the laser blind vias also gradually increases.

[0044] In this embodiment, by controlling the number of laser blind holes, the heat dissipation effect of the HDI board provided with mechanical through holes 13 alone can be achieved or exceeded.

[0045] According to a further technical solution, the first laser blind via and the second laser blind via arranged on both sides of the HDI board are plugged by a copper filling process.

[0046] The first laser blind hole and the second laser blind hole can adopt an array structure of multiple rows and columns, such as Figure 4 As shown, Figure 1 In the AA view, the top and bottom surfaces of the HDI board are both provided with thermal conductive copper sheets, and the laser blind holes are set to 3 rows and 3 columns;

[0047] Optionally, the mechanical buried vias are arranged equidistantly at a hole center distance d=0.508 mm, and the setting of this distance can meet the size requirements of various mechanical through holes.

[0048] Specifically, the mechanical through holes may adopt an array structure of multiple rows and columns, such as Figure 5 As shown,

[0049] A feasible technical solution is that the first laser blind via 10, the second laser blind via 12 and the mechanical buried via 11 on both sides of the HDI board adopt a stacked hole structure so that some of the laser blind vias are connected to the holes of the mechanical buried vias, such as Figure 1 As shown, the number of the first laser blind vias 10 or the second laser blind vias 12 is greater than the number of the mechanical buried vias 11, and the extra first laser blind vias 10 or the second laser blind vias 12 are connected to the mechanical buried vias through the heat conductive material provided in the corresponding layer.

[0050] like Figure 4 As shown in the figure, the AA section is used to show the positional relationship between the first heat dissipation copper sheet 1 and the first laser blind hole 10. The shaded part in the figure is the set heat conductive material. Taking the square heat conductive sheet as an example, the heat conductive sheet of the same size and shape is set at the same position on the surface of the HDI circuit board and between each layer. The first laser blind hole 10 and the second laser blind hole 12 are set in 3 rows and 3 columns as an example. Figure 5 In the figure, the mechanical buried vias 11 are arranged at the positions of the laser blind vias at the four corners to form a stacked via structure. The BB section view is used to show the positional relationship between the third layer of heat dissipation copper sheet 3 and the mechanical buried vias 11 .

[0051] Another technical solution that can be implemented is that the first laser blind hole 10, the second laser blind hole 12 and the mechanical buried hole 11 adopt a staggered hole structure, the first laser blind hole 10, the second laser blind hole 12 and the mechanical buried hole 11 are staggered by a set distance, and the laser blind hole is connected to the mechanical buried hole 11 through a heat conductive material set in a corresponding layer. The specific structure is as follows Figure 2 shown.

[0052] The heat dissipation effect of the above heat dissipation structure is described as follows:

[0053] The stacked hole structure of the optical module HDI board is as follows Figure 3 As shown, the figure shows the design of the second-order blind buried via stacking holes. The mechanical buried via 11 and the traditional mechanical through hole 13 have the same size and adopt the POFV plugging method with the same hole structure. Then the mechanical buried via 11 in the figure and the traditional mechanical through hole 13 have the same longitudinal heat dissipation effect between the third layer of heat dissipation copper skin 3 to the sixth layer of heat dissipation copper skin 6, that is, the thermal resistance of the mechanical buried via 11 is the same as the thermal resistance of the part using the mechanical through hole 13 at this thickness, and the thermal resistances are connected in series in the longitudinal direction. It is only necessary to calculate the thermal resistance relationship between the laser blind hole and the through hole part under the blind hole layer thickness d1 to determine the heat dissipation effect.

[0054] According to Fourier's law of heat conduction, the following formula is obtained:

[0055]

[0056] Where R is thermal resistance, in ℃ / W; d is material thickness, in m; λ is thermal conductivity, in W / (m℃); A is cross-sectional area, in m²;

[0057] The thermal resistance of the laser blind hole and the mechanical buried hole 11 at the corresponding thickness can be calculated. According to the conventional design of the optical module, the aperture of the laser hole is usually 0.1mm, and the aperture φ of the mechanical buried hole 11 is usually 0.15mm, 0.2mm, and 0.25mm according to the space. Here, the aperture φ=0.15mm of the mechanical buried hole 11 is taken as an example for calculation.

[0058] The thickness of the blind hole layer where the laser blind hole is located is: d1;

[0059] The radius r1 of the mechanical buried hole 11: r1=φ / 2=0.075mm;

[0060] The single-side thickness of the copper hole of the mechanical buried hole is 0.025mm;

[0061] Via radius r2: r2=r1-single-side thickness of hole copper=0.075mm-0.025mm=0.05mm;

[0062] Laser blind hole radius r3: r3=0.1mm / 2=0.05mm;

[0063] The thermal conductivity λ of different materials is shown in Table 1 below, where K can be replaced by ℃;

[0064] Table 1

[0065]

[0066] The pofv plug structure of the conventional mechanical through hole 13 is as follows Figure 6 As shown, it includes: a via hole 11-3, in which a resin plug is filled; a circle of hole copper 11-2; and a surface layer of a mechanical through hole plate 11-1.

[0067] (1) Calculate the thermal resistance of a single through-hole PofV plug with a thickness of d1;

[0068] The longitudinal thermal resistance of the mechanical through hole 13 is divided into two parts, the hole copper thermal resistance and the through hole pofv resin plug thermal resistance, and the two parts are in parallel relationship;

[0069] The area formula of a circle is: S=πr²;

[0070] Mechanical through hole 13 cross-sectional area S1:

[0071] S1=πr1²=3.1415*0.075mm*0.075mm=177*10 -10 (m²);

[0072] Via cross-sectional area S2:

[0073] S2=πr2²=3.1415*0.05mm*0.05mm=79*10 -10 (m²);

[0074] Hole copper 11-2 cross-sectional area S3:

[0075] S3=S1-S2=98*10 -10 (m²);

[0076] Single through-hole copper thermal resistance:

[0077] R 孔铜 = d1 / λS3= d1 / 388*98*10 -10 =0.26*10 6 d1 (℃ / W);

[0078] Thermal resistance of single via pofv resin plug:

[0079] R 树脂 = d1 / λS2=d1 / 2.4*79 *10 -10 =53*10 6 d1 (℃ / W);

[0080] The thermal resistance of a single mechanical through hole 13 using a pofv resin plug is the parallel thermal resistance of the hole copper and the thermal resistance of the through hole pofv resin plug, and the calculation formula is:

[0081] R 通孔 =R 孔铜 *R 树脂 / (R 孔铜 +R 树脂 )=0.26*10 6 d1 (℃ / W);

[0082] Calculate the thermal resistance of n laser blind vias filled with copper, where the thickness is d1:

[0083] (2) Laser blind hole copper filling plugging structure, such as Figure 7 As shown, it includes: a laser hole 10-2 and a surface hole plate 10-1, and the laser hole is filled with copper plating;

[0084] The longitudinal thermal resistance of the laser blind hole is the thermal resistance of the laser blind hole filled with copper, which is calculated as follows:

[0085] Laser blind hole cross-sectional area S4:

[0086] S4=πr3²=3.1415*0.05mm*0.05mm=79*10 -10 m²

[0087] Thermal resistance of a single laser blind via with copper filling:

[0088] R 激光盲孔填铜 =d1 / (λS4)=d1 / (388*79*10 -10 m²)=0.33*10 6 d1 (℃ / W);

[0089] The thermal resistance of n laser blind vias filled with copper is in parallel and is calculated as follows:

[0090] R n个激光盲孔填铜 = R 激光盲孔填铜 / n=0.33*10 6 d1 / n (℃ / W)

[0091] The size and plugging method of the mechanical buried via 11 and the traditional mechanical through hole 13 are set to be the same, and the heat dissipation of the buried via layer in the middle is equivalent to the heat dissipation of the traditional mechanical through hole 13; for the blind hole layer, this embodiment makes the thermal resistance of n laser blind holes filled with copper plug holes equivalent to the thermal resistance of a single mechanical through hole 13pofv plug hole, and the multiple relationship of the number of laser blind holes and mechanical buried holes 11 can be calculated, that is, the multiple relationship of the number of laser blind holes and mechanical buried holes is calculated as follows:

[0092] 0.33*10 6 d1 / n=0.26*10 6 d1

[0093] n=1.27

[0094] That is, the number of 0.1mm laser blind holes is ≥1.27 times the number of 0.15mm mechanical buried holes. The heat dissipation effect can reach or exceed the heat dissipation effect of through holes under the same area.

[0095] The same method can be used to calculate the heat dissipation equivalent multiples of 0.1 mm laser blind holes and mechanical buried holes 11 of different sizes. If the multiples exceed the following values, the heat dissipation effect exceeds, see Table 2 below.

[0096] Table 2

[0097]

[0098] According to the above calculation method, it can be concluded that the heat dissipation effect of the laser blind hole plus the mechanical buried hole 11 replacing the mechanical through hole 13 has nothing to do with the order thickness of the blind buried hole, but is positively correlated with the number of laser blind holes arranged. Under the premise that the mechanical through hole 13 can meet the heat dissipation requirements of the product, the more the number of laser blind holes arranged under the same area, the better the heat dissipation effect. Therefore, the heat dissipation hole design scheme proposed in this embodiment adopts the method of laser blind hole plus mechanical buried hole stacking, which can replace the design of mechanical through hole 13, and the number of laser blind holes arranged is the largest, and the heat dissipation effect is the best.

[0099] For the HDI board design of the optical module, the heat dissipation hole design method provided in this embodiment can completely replace the heat dissipation solution of the mechanical through holes 13 arranged in more than 2 columns and 2 rows. Under the same heat sink area, the heat dissipation effect is optimized, far exceeding the heat dissipation effect of the mechanical through holes 13, and the flatness of the laser blind hole can be controlled within the range of 5um by adjusting the electroplating parameters. The flatness process control is simple and the flatness control effect is better. For space-intensive PCB boards, the heat dissipation hole structure of this embodiment can also save board space by reducing the heat dissipation area to achieve the heat dissipation effect.

[0100] Example 2

[0101] Based on Example 1, this embodiment provides an HDI board, and adopts the HDI board heat dissipation structure for improving surface flatness described in Example 1 to set a heat dissipation area.

[0102] Specifically, the HDI board includes a multi-layer circuit board 9 for laying out circuits; each layer of the circuit board of the HDI board can be a PP board or a Core board; PP is a film, also known as a semi-cured sheet PREPREG (PP), which is mainly composed of resin and reinforcing materials. One or both sides of the PP sheet are covered with copper foil to form a core board, also known as a Core board, which are all non-conductive materials.

[0103] The above description is only the preferred embodiment of the utility model, and is not intended to limit the utility model. For those skilled in the art, the utility model can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the utility model shall be included in the protection scope of the utility model.

[0104] Although the above describes the specific implementation methods of the utility model in combination with the accompanying drawings, it is not intended to limit the scope of protection of the utility model. Technical personnel in the relevant field should understand that on the basis of the technical solution of the utility model, various modifications or deformations that can be made by technical personnel in this field without creative work are still within the scope of protection of the utility model.

Claims

1. An HDI board heat dissipation structure for improving surface flatness, characterized by: The method comprises a first laser blind hole, a mechanical buried hole and a second laser blind hole which are sequentially arranged on the HDI board from the upper layer to the lower layer; the first laser blind hole, the mechanical buried hole and the second laser blind hole are sequentially connected by heat conducting materials.

2. The HDI board heat dissipation structure for improving surface flatness according to claim 1, wherein: The set number of layers on both sides of the HDI board are used as blind hole layers, and the remaining layers in the middle are used as buried hole layers, forming a structure of the first blind hole layer, the buried hole layer, and the second blind hole layer; A first laser blind hole is set in the first blind hole layer through each layer, a mechanical buried hole is set in the buried hole layer through each layer, and a second laser blind hole is set in the second blind hole layer through each layer.

3. The HDI board heat dissipation structure for improving surface flatness according to claim 2, wherein: The set number of layers of the first blind hole layer and the second blind hole layer is equal.

4. The HDI board heat dissipation structure for improving surface flatness according to claim 1, wherein: The thermal conductive material is laid on the surface of the HDI board where the heat dissipation structure is arranged and between each circuit layer.

5. The HDI board heat dissipation structure for improving surface flatness according to claim 1, wherein: The number of laser blind vias and mechanical buried vias is set according to the set multiples. The number of the first laser blind vias is set to N1 times the number of the mechanical buried vias; the number of the second laser blind vias is set to N2 times the number of the mechanical buried vias, and N1 and N2 are not less than 1.

27.

6. The HDI board heat dissipation structure for improving surface flatness according to claim 1, wherein: The first laser blind via and the second laser blind via arranged on both sides of the HDI board are plugged by using a copper filling process.

7. The HDI board heat dissipation structure for improving surface flatness according to claim 1, wherein: The first laser blind via and the second laser blind via adopt an array structure with multiple rows and columns; Alternatively or alternatively, the mechanical buried vias may adopt an array structure of multiple rows and columns.

8. The HDI board heat dissipation structure for improving surface flatness according to claim 1, wherein: The first laser blind vias, the second laser blind vias and the mechanical buried vias on both sides of the HDI board adopt a stacked hole structure, so that some of the laser blind vias are connected to the holes of the mechanical buried vias.

9. The HDI board heat dissipation structure for improving surface flatness according to claim 1, wherein: The first laser blind via, the second laser blind via and the mechanical buried via adopt a staggered hole structure, and the first laser blind via, the second laser blind via and the mechanical buried via are staggered by a set distance.

10. An HDI board, characterized in that: A heat dissipation area is set using the HDI board heat dissipation structure with improved surface flatness as described in any one of claims 1 to 9.

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