阅读说明：本技术 表面安装式热缓冲器 (Surface-mounted thermal buffer ) 是由 雅克·赫尔斯特罗姆 于 2019-10-03 设计创作，主要内容包括：一种用于消散由发热电气部件(16)产生的热量的组件(110),该发热电气部件在表面安装过程中被表面安装在电路板(11)上。该组件包括热缓冲器(120),该热缓冲器由导热且导电的材料制成,并且被表面安装在电路板(11)上以便焊接至发热电气部件(16)的热标记件(18)上。该组件进一步包括与该热缓冲器热接触的散热器(12)、以及在该热缓冲器与该散热器之间的电流分隔件(13)。在进一步将热量消散到以电流方式分隔的散热器之前,热缓冲器的热容可以吸收电气部件的散热的短时增加。这样可以极大地改善表面安装式部件的性能。(An assembly (110) for dissipating heat generated by a heat-generating electrical component (16) that is surface mounted on a circuit board (11) during a surface mounting process. The assembly includes a heat buffer (120) made of a thermally and electrically conductive material and surface mounted on the circuit board (11) for soldering to a heat flag (18) of the heat generating electrical component (16). The assembly further comprises a heat sink (12) in thermal contact with the heat buffer, and a current partition (13) between the heat buffer and the heat sink. The heat capacity of the heat buffer may absorb a brief increase in the heat dissipation of the electrical components before further dissipating the heat to the galvanically separated heat sink. This can greatly improve the performance of the surface-mounted component.)

1. An assembly (10; 110) for dissipating heat generated by a heat-generating electrical component (16) that is surface-mounted on a circuit board (11) during a surface-mounting process, the assembly comprising:

a heat buffer (20; 120) made of a thermally and electrically conductive material, said heat buffer being surface-mounted on the circuit board (11) for soldering to a heat marker (18) of the heat-generating electrical component (16),

a heat sink (12) in thermal contact with the heat buffer, and

a current divider (13) between the heat buffer and the heat sink.

2. The assembly according to claim 1, wherein the heat buffer (120) is mounted in a corresponding opening (21) formed in the circuit board (11), and during the surface mounting the heat marker (18) is soldered on an upper surface (121a) of the substantially flat receiving portion (121) of the heat buffer (120).

3. The assembly of claim 2, wherein the protruding portion (123) of the heat buffer (120) is surface mounted to a pad (114a) that is thermally connected to the heat spreader (12) by a plurality of vias (115) extending through the circuit board (11).

4. The assembly according to claim 1, wherein the heat buffer (20) is surface mounted in the vicinity of the electrical component and is soldered to an end portion (18a) of the heat marker (18) accessible from above (16) during the surface mounting.

5. The assembly of claim 3, wherein the component (16) and the heat buffer (20) are both surface mounted to a pad (14a) that is thermally connected to the heat spreader (12) by a plurality of vias (15) extending through the circuit board (11).

6. Assembly according to claim 4, wherein the upper surface (121a) of the receiving portion (121) is flush with the surrounding circuit board (11).

7. Assembly according to claim 4 or 5, wherein the thickness of the receiving portion (121) is in the range of 90-110% of the thickness of the circuit board (11).

8. An assembly according to any one of the preceding claims, wherein the electrical component (16) and the heat buffer (20; 120) are surface mounted on the same side (11a) of the circuit board (11), while the heat sink (12) is arranged on the opposite side (11) of the circuit board.

9. The assembly according to any one of the preceding claims, wherein the thermal marker (18) serves as a terminal of the electrical component (16) and the thermal buffer (20; 120) is provided with contact points for facilitating electrical connection of the terminal.

10. The assembly of claim 8, wherein the contact point is a threaded hole for receiving a screw (23).

11. Assembly according to any one of the preceding claims, wherein the heat buffer (20; 120) has a constant cross-section in one direction (A), allowing manufacturing by extrusion.

12. A method for mounting a heat buffer of thermally and electrically conductive material on a circuit board to dissipate heat from a heat-generating component, the method comprising surface mounting the component and the heat buffer on the circuit board by:

pads (14, 14 a; 114a) are printed (step S1; step S11) on the circuit board (11),

arranging (steps S2, S4; steps S12, S14) the heat buffer (20; 120) and the component (16) on the circuit board such that the heat buffer is placed in electrical contact with a heat marker (18) of the component (16) and such that the heat buffer and selected terminals of the component are in electrical contact with at least one pad (14, 14 a; 114a),

the circuit board on which the component and the heat buffer are arranged is heated (step S5; step S15) so that the component is soldered to the heat buffer, and both the component and the heat buffer are soldered to at least one pad.

13. The method of claim 12, wherein the step of disposing the heat buffer (120) and the component (16) on the circuit board comprises:

the heat buffer (120) is placed (step S12) in the corresponding opening (21) formed in the circuit board (11),

arranging solder on an upper surface (121a) of the substantially flat receiving portion (121) of the heat buffer (120) (step S13), and

placing (step S14) the component (16) on the solder,

thus, in the heating step, the thermal marker (18) of the component is welded to the upper surface (121a) of the receiving portion (121).

14. The method of claim 13, wherein a portion of the heat buffer (20) is disposed on the pad (114a) that is thermally connected to an opposite side of the circuit board (11) by a plurality of vias (15) extending through the circuit board.

15. The method according to claim 12 or 13, further comprising placing the circuit board on a support (124), against which the underside of the receiving portion can rest during the step of heating the circuit board.

16. The method of claim 11, wherein the step of disposing the heat buffer (120) and the component (16) on the circuit board comprises:

placing (step S2) the component (16) on a pad (14a) on the circuit board so that an end portion (18a) of the thermal marker (18) is accessible from above (16),

solder is arranged on the end portion (18a) (step S3),

placing (step S4) the heat buffer (20) in the vicinity of the electrical component so that the heat buffer rests at least partially on the end portion (18a),

thus, in the heating step, the heat buffer (20) is welded to the end portion (18a) of the heat marker (18).

17. The method of claim 16, wherein the heat buffer (20) is disposed on the pad (114a) that is thermally connected to the opposite side of the circuit board (11) by a plurality of vias (15) extending through the circuit board.

Technical Field

The present invention relates to a component for dissipating heat from a surface mounted electrical component, also known as a Surface Mounted Device (SMD).

Background

Many electrical components, particularly semiconductor components such as solid state transistors, solid state power switches, and integrated circuits, generate heat during operation. Some of the most important examples include MOSFETs (metal oxide semiconductor field effect transistors) and IGBTs (insulated gate bipolar transistors). In many cases, the ability of these components to dissipate the heat generated can degrade their performance. Moreover, it is desirable to dissipate this heat to avoid thermal degradation or complete failure. Some components are able to satisfactorily dissipate the generated heat, while others require additional cooling elements such as heat sinks to dissipate the heat.

In recent years, Surface Mount Technology (SMT) in which components are mounted on the surface of a Printed Circuit Board (PCB) rather than in holes is often used to produce electronic circuits. When SMT is used, pads are printed (e.g. screen printed) on the circuit board, components are placed on the circuit board in contact with the pads, and the circuit board and components are heated in an oven to melt the solder. Components adapted for this type of mounting are often referred to as surface mounted devices, i.e. SMDs. Surface mounting is often the preferred mounting method for automated and semi-automated production processes. However, surface mounting presents challenges in the cooling of components.

The most common method of cooling surface mounted components is to dissipate heat through the circuit board to a heat sink disposed on the other side. The component typically has a thermal "pad" or thermal "flag that is soldered to a thermal pad on the circuit board. The pads of the various components are typically thermally connected to the heat spreader by vias (i.e., metal-filled through holes in the circuit board). In case the thermal marker is also used as a terminal of a component (e.g. a drain/collector of a power transistor), a current separator is required between the thermal marker and the via of the component, and this is usually provided by an electrically insulating but thermally conductive layer (e.g. alumina) or by forming a "blind" via (i.e. a via that does not penetrate completely through the circuit board).

Another approach is to mount the heat sink separately on top of the electrical component and make thermal contact with the component. For example, some microprocessors are provided with such "top-mounted" heat sinks, typically strapped to the processor and thermally connected to the exterior of the package using a suitable thermal glue.

Yet another example, shown for example in US 5,930,114, is to surface mount a heat sink attachment to a circuit board in thermal connection with solder pads onto which surface mounted components are soldered. The heat may then dissipate over the surface of the pad to the heat sink attachment and further to the heat sink attached thereto.

The challenge with the conventional approach is that the thermal resistance between the component and the heat sink is too large. Thermal resistance is defined as the heat gain per power consumption measured in units of K/W (kelvin per watt). Thus, thermal resistance defines how the temperature of a component will rise for a given power consumption. It is noted that even if the heat sink has sufficient heat capacity to dissipate heat dissipated by the componentsAveragePower-derived heat, thermal resistance also prevents sufficiently rapid dissipation of the generated heat associated with the power spike. For many components, such as solid state power switches in power converters, the peak power may be several times greater than the average power consumption.

By way of example, the thermal resistance between a silicon junction and a component housing (e.g., a TO-263 package) is typically in the range of 0.5-2K/W, the thermal resistance across the circuit board is typically in the range of 1-5K/W, and the thermal resistance through the alumina layer is typically in the range of 0.5-3K/W. Therefore, conservatively, a total of about 5K/W. If the temperature of the heat sink is 80 c and the junction can withstand 175 c, the temperature rise achievable is 95 c. When the thermal resistance is 5K/W, the maximum allowable power consumption (loss) in the part is 19W. Power losses directly affect the total power available to the system and therefore have significant advantages in reducing thermal resistance.

Document DE 19654353 discloses a mounting arrangement for semiconductor components on a printed circuit board. The heat sink is disposed between the component and the circuit board. The heat sink is electrically isolated from the circuit board by an isolation layer.

There is therefore a need for an improved solution to obtain a satisfactory heat dissipation of surface mounted components.

Disclosure of Invention

It is an object of the present invention to overcome this challenge and provide improved dissipation of heat from heat-generating electrical components surface mounted on a circuit board.

According to a first aspect of the invention, this and other objects are achieved by an assembly for dissipating heat generated by a heat-generating electrical component, the heat-generating electrical component being surface-mounted on a circuit board, the assembly comprising a heat buffer made of a thermally and electrically conductive material, said buffer being surface-mounted on the circuit board for soldering to a thermal marker of the heat-generating electrical component, a heat sink in thermal contact with the heat buffer, and a current partition between the heat buffer and the heat sink.

Therefore, the thermal marker of the heat generating component is soldered to the heat buffer during surface mounting, so that the thermal capacity of the heat buffer can absorb a short-term increase in heat dissipation of the electrical component, as compared to conventional solutions. Thus, the heat buffer acts as an intermediate reservoir of heat before further dissipating the heat to the galvanically separated heat sink. For many electrical components, such a thermal buffer will be able to handle high power consumption peaks, thereby greatly improving the performance of surface mounted components.

As an example, the thermal impedance of the thermal buffer may be less than 0.5K/W over a time span of 1-3 s. Typical materials suitable for the heat buffer are copper, brass and the like.

A suitable mass of heat buffer made of copper or brass may be on the order of ten grams. This can be compared TO the amount of copper in a typical power transistor package (e.g., TO-263) on the order of one gram. Thus, the heat capacity increases by ten times, indicating that the component can withstand a given power consumption (loss) for ten times longer.

Furthermore, in many applications, the present invention also enables thermal resistance to be reduced by the circuit board and galvanic isolation from the heat sink. In conventional solutions, this thermal resistance depends to a large extent on the welding area of the thermal markers of the component. According to the invention, in which the heat marker is also soldered to the heat buffer, which in turn is also surface mounted (soldered) to the circuit board, is the heat markerAndthe combined solder areas of the heat buffer may be used to provide a thermal interface through the circuit board, thereby reducing thermal resistance.

Again, for the TO-263 package, the thermal label has a surface area of 75 square millimeters. If the surface mount area of the surface mount bumper soldered to the flag is 150 mm square, the thermal resistance to the heat sink may be reduced to one third (three times as large as the total surface area).

According to one embodiment, the heat buffer is surface-mounted near the electrical component and is welded to the end portion of the heat marker that is accessible from above.

In addition, both the component and the heat buffer may be surface mounted to a pad that is thermally connected to the heat spreader by a plurality of vias extending through the circuit board. It is to be noted that in this case the pad does not have to be a single continuous pad, but may be formed by two or more discrete pads.

For many components, such as power transistors, the surface of the actual semiconductor junction (where heat is generated) is significantly smaller than the surface of the thermal marker. Thus, the heat dissipation process involves spreading the generated heat laterally over the thermal indicia. This lateral heat diffusion contributes to the thermal resistance since the thermal marker is not particularly thick (typically about 1 mm).

According to another embodiment that solves this particular problem, the heat buffer is therefore mounted in a corresponding opening formed in the circuit board, and the heat marker is soldered on top of the substantially flat receiving portion of the heat buffer during surface mounting. To enable surface mounting, the upper surface of the receiving portion is preferably flush with the rest of the circuit board.

It is to be noted that the heat buffer in this embodiment is not strictly a surface mounted device SMD, since it is actually mounted in an opening in the circuit board. However, it is still mounted using surface mount technology, and therefore, for the purposes of the present invention, the heat buffer will also be referred to in this embodiment as being surface mounted.

The thickness of the receiving portion is preferably similar to the thickness of the circuit board, e.g. 1.4-1.5mm, and thus the heat from the semiconductor junction can be dissipated more efficiently and the thermal resistance between the component and the heat sink can be reduced even further. Preferably, the thickness of the receiving portion is in the range of 90% -110% of the thickness of the circuit board.

In some embodiments, the thickness of the receiving portion is slightly larger than the circuit board, in which case the gap between the bottom side of the circuit board and the heat sink may be bridged by the resilient layer.

In other embodiments, the thickness of the receiving portion is slightly smaller than the circuit board, in which case the gap between the bottom side of the heat buffer and the heat sink may be bridged by a thermally conductive layer, such as a gap pad or gap filler.

When the heat buffer is mounted in an opening in a circuit board, the protruding portion of the heat buffer (protruding outside the opening for placement on the surface of the circuit board) is preferably surface mounted to a solder pad on the circuit board, which is preferably thermally connected to the heat sink, for example, by a plurality of vias extending through the circuit board.

If the thermal flag is used as a terminal of an electrical component (e.g., a drain/collector of a power transistor), the buffer may be provided with a contact point to facilitate electrical connection of the terminal. For example, the bumper may be provided with a threaded hole.

Drawings

The present invention will be described in more detail with reference to the appended drawings, in which currently preferred embodiments of the invention are shown.

Fig. 1a-1b show perspective views of an assembly according to a first embodiment of the invention.

Fig. 2a-2b show perspective views of an assembly according to a second embodiment of the invention.

Fig. 3a-3c show three examples of how the bumper of fig. 2a-2b can be supported during surface mounting.

Fig. 4 shows an assembly according to another embodiment of the invention.

Fig. 5 is a flow chart illustrating a surface mounting process of the assembly in fig. 1a-1 b.

Fig. 6 is a flow chart illustrating a surface mounting process of the components in fig. 2a-2 b.

Detailed Description

Fig. 1a (exploded view) and 1b (installed view) show a first embodiment of the invention. The assembly 10 here comprises a Printed Circuit Board (PCB)11, a heat sink 12 and a current isolation layer 13. The heat sink is made of a thermally conductive material such as aluminum and may be formed with a flange (not shown) to increase convection with the ambient air. The galvanic isolation layer is intended to galvanically isolate the heat sink from the circuit board while providing a satisfactory thermal connection. The layer may be alumina. A set of solder pads 14 is printed onto the upper surface 11a of the PCB using, for example, a screen printing method. The solder material is typically a SAC (Sn/Ag/Cu) alloy.

At least one of these pads is referred to as a thermal pad 14a and is placed in thermal connection with the heat spreader 12 via a set of vias 15 (see fig. 1 b). Each via 15 may be a metal filled hole extending through the circuit board 11. Vias 15 provide thermal connection through the circuit board, while layer 13 provides galvanic isolation of heat spreader 12.

The heat-generating electrical component 16 has been surface mounted (i.e., SMT mounted using surface mount technology) to the pad 14. Thus, the component 16 may be referred to as a surface mounted device SMD. The surface mounting process typically involves placing SMDs on the associated pads using a pick and place machine (robot) and then heating the circuit board and the SMDs disposed thereon in an oven.

By way of example, the component 16 is a semiconductor device, for example a power transistor, such as a MOSFET or an IGBT, having one or more pn junctions in the semiconductor crystal. The semiconductor may be made of silicon. For surface mounting, semiconductor components, such as power transistors, can be arranged inside the SMD package 17, encapsulating the component 16. In this case, examples of related known SMD packages include TO-262, TO-263, and TO-268.

The component 16, here an SMD package 17, has thermal markers 18 and terminal pins 19 soldered to the pads 14a, 14, respectively, during surface mounting. The purpose of the thermal marker 18 is to ensure a satisfactory thermal connection of the component 16 to the heat sink 12, so that heat generated by the component 16 (e.g. by a pn-junction in the component) can be dissipated.

The thermal marker 18 typically (but not necessarily) serves as one of the terminals of the component 16. For example, if the component is a power transistor, the thermal marker is typically the drain/collector of the transistor.

The assembly further includes a heat buffer 20 made of an electrically and thermally conductive material such as copper or brass. In the same surface mounting process, the heat buffer 20 is also surface-mounted to the circuit board, and is also soldered to the flag 18.

The mass of the heat buffer may be on the order of 10 grams, for example in the range of 5-25 grams, and will therefore significantly increase the heat capacity of the component 16. For example, an SMD package such as TO-263 contains only about 1 gram of copper. Thus, a copper buffer with a mass of 10 grams will increase the heat capacity by a factor of 10.

Referring to fig. 5, a surface mounting process of the component 16 and the heat buffer 20 will be briefly described. First, in step S1, each pad including the pad 14a is printed on the PCB 11. Then, in step S2, the component 16 (and other SMDs) are placed on the pads 14a, for example, using a pick and place machine, and in step S3, solder paste is applied to the portion 18a of the marker 18 that extends outside the side of the component 16/package 17 so as to be accessible from above. Solder may be applied, for example, using a solder paste application nozzle or by using a pick and place machine to place the solder material of the platelet on the portion 18 a. Then, in step S4, the heat buffer 20 is placed near the component 16 (or package 17) so that the recess 20a rests on the portion 18 a. Finally, in step S5, the circuit board 11 and the SMDs placed thereon are heated in an oven to complete surface mounting.

Turning now to fig. 2a-2b, a second embodiment of the present invention is shown. Again, the assembly 110 comprises a circuit board 11, a heat sink 12, a galvanic isolation layer 13 and an electrical component 16, which is here surrounded by a package 17 having thermal pads 18 and terminal pins 19. These elements will not be described again.

In this embodiment, the heat buffer 120 is formed with a substantially flat receiving portion 121 extending from a main body 122 of the heat buffer 120. Further, the circuit board 11 is formed with an opening 21 corresponding to the shape of the heat buffer 120 so that the heat buffer 120 can be mounted in the opening.

A pad 114a smaller than pad 14a in fig. 2a is printed next to the opening and the protruding portion 123 of the heat buffer is soldered to this pad. Alternatively, as illustrated in fig. 3b, the solder pad 114a may be thermally connected to the heat spreader 12 by a via 115.

In the illustrated example, the thickness of the receiving portion corresponds to the thickness of the circuit board, in a typical example 1.4 mm. Further, the upper surface 121a of the receiving portion 121 is flush with the upper surface of the circuit board, so that the thermal marker 18 of the component can be soldered to the upper surface 121a while the legs of the component are soldered to the corresponding pads 14 on the circuit board.

Referring to fig. 6, a surface mounting process of the component 16 and the heat buffer 120 will be briefly described. First, in step S11, each pad including the pad 114a is printed on the PCB 11. Then, in step S12, the heat buffer 120 is placed in the opening 21 (e.g., using a pick-and-place machine), after which, in step S13, solder is applied on the surface 121a (e.g., using a solder dispensing nozzle or by placing a solder sheet). In step S14, the component 16 is placed on the surface 121 a. Finally, in step S15, the circuit board 11 and the SMDs placed thereon are then heated in an oven to complete surface mounting. Note that although the heat buffer 120 is arranged in the opening 21, it is surface-mounted to the pad 114 a.

It is noted that the circuit board 11 is typically handled during surface mounting in a manner that does not have underlying support. Here, however, the heat buffer 120 needs to be supported in the opening 21 throughout the surface mounting process. A number of different examples of how this can be achieved are shown in figures 3a-3 c.

In fig. 3a, the circuit board 11 and all things arranged thereon are placed on the carrier 124 during surface mounting. The carrier 124 may be made of a ceramic material such as alumina, for example. After the surface mounting process, the circuit board 11 may be separated from the (ceramic) carrier 124, after which the circuit board 11 is mounted to the heat sink 12 provided with the current separation layer 13. Alternatively, the ceramic support layer is permanently attached to the circuit board and is configured to form part of the current separation layer 13.

In fig. 3b, the front end of the receiving portion 121 is provided with protruding "fingers" 125 which rest against the upper side of the circuit board 11.

Finally, in fig. 3c, the front side 21a of the opening 21 is tapered and the front side 126 of the receiving portion 121 of the heat buffer 120 has a corresponding taper, so that the circuit board 11 will support the heat buffer.

When the method in fig. 3b and 3c is used and the heat buffer rests on the upper side of the circuit board 11 instead of on a support below the circuit board, there may be slight variations in the vertical position of the bottom side of the heat buffer 120. To compensate for this variation, it may be preferable to use "gap pads" called "gap fillers" instead of alumina as the spacer layer 13.

In the illustrated embodiment, in addition to fig. 3b, it is noted that the heat buffer 20, 120 is shaped with a constant cross section in direction a. This makes it possible to manufacture the heat buffer by extrusion, thereby significantly reducing the cost. If extrusion is not possible or preferred, the heat buffer 20, 120 may be formed, for example, by molding, stamping the heated blank, or other suitable metal working technique.

Further, in the illustrated example, the heat buffer 20, 120 is provided with threaded holes 24 for receiving screws 23. Such screws thus provide a convenient electrical connection point, for example for the drain/collector of a power transistor, in the case where the thermal marker 18 is used as a terminal of the component 16.

If the bumper 120 is supported by the carrier 124 in surface mounting, as illustrated in fig. 3a, threaded holes 24 may extend through the bumper 120 so that the bumper 120 may be secured to the carrier 124 using screws 23. The thickness of the receiving portion 121 may then preferably be slightly greater than the thickness of the circuit board 11 (e.g., on the order of 0.1mm thick). By placing an elastomeric material (not shown) between the carrier 124 and the circuit board 11, the circuit board 11 will remain stationary during surface mounting while ensuring that the bottom sides of all of the bumpers 120 lie in the same plane. When the circuit board is then mounted to the heat sink 12 via the isolation layer 13, an elastic layer (again not shown) may again be used to compensate for the level difference.

Fig. 4 very schematically shows an embodiment in which the heat buffer 220 is mounted in the opening 21 from the opposite side of the circuit board 11 with respect to the component 16.

In this case, first, a pad (not shown) is printed on the opposite side 11b of the circuit board 11, and the heat buffer 220 is placed in the opening 21 and surface-mounted to the circuit board. The PCB 11 is then flipped over and pads are printed on the first surface 11a (including on the flat upper surface 221a of the receiving portion 221 of the heat buffer 220). The component 16 is then placed on the surface 221a and surface-mounted by heating.

In this case, the heat buffer 220 will create a separation between the PCB 11 and the heat sink 12, which separation needs to be filled with a suitable filler 222.

The person skilled in the art realizes that the present invention by no means is limited to the preferred embodiments described above. On the contrary, many modifications and variations are possible within the scope of the appended claims. For example, the shape of the heat buffer may be different from the illustrated example and instead adapted to the particular application. Further, the details of the heat sink, its attachment to the circuit board, and the current dividers are not important to the invention and may vary.