WO2014167143A1

WO2014167143A1 - Electronic device with built-in heat dissipation, electronic controller and static relay comprising same, and method for manufacturing said device

Info

Publication number: WO2014167143A1
Application number: PCT/ES2013/070233
Authority: WO
Inventors: Herminio Navalon Carretero; Camilo GOMEZ OUTEDA; Luis Felipe RODRIGUEZ IRIBARNE; Valentin PICAZO TOLEDO; Juan Diego NAVALON GARCIA; Alfredo PEREZ PELLICER
Original assignee: Nagares, S.A.
Priority date: 2013-04-12
Filing date: 2013-04-12
Publication date: 2014-10-16

Abstract

The invention discloses an electronic device with improved heat dissipation properties with respect to prior art devices. This electronic device is for use in electronic power controllers for PTC devices or static relays used in the field of motor vehicles, and comprises a base plate (1) supporting power elements (2), control elements, and metal terminals (3+, 3-) for connection to a power supply, the power elements (2) being mounted on an extension (4) of a metal connection terminal (3+, 3-) serving as heatsink.

Description

Electronic device with integrated thermal dissipation controller and static relay comprising it and manufacturing procedure of said device

DESCRIPTION

OBJECT OF THE INVENTION

The present invention belongs to the field of electronic devices based on semiconductors.

The object of the present invention is a novel electronic device that has improved thermal dissipation characteristics in relation to prior art devices. This electronic device can be applied, for example, to electronic power controllers for PTC devices

(Positive Temperature Coefficient) or static relays used in the automotive field.

The present invention also relates to the manufacturing process of said electronic device with integrated thermal dissipation.

BACKGROUND OF THE INVENTION

Currently, multiple applications of electronic power controllers comprising a power transistor are known, for example, for the control of motor vehicle heating devices. The use of a complementary electric heating in the installation of heating / air conditioning of a motor vehicle allows to cover the time interval during which it is not yet available for the heating of the heat that the motor yields. Complementary electric heaters reach operating temperature within a few seconds, so they can adequately heat the air inside the vehicle. In these complementary electric heaters used in the heating / air conditioning installations of motor vehicles, PTC heating elements that transform electricity into preference are preferably used. hot. The PTC heating elements have a conductive heat connection with radiator elements, so that the heat generated by the PTC heating elements is transferred to the circulating air inside the vehicle by means of the radiator elements. However, PTC elements can sometimes reach temperatures of up to 200 ^e C, so it is extremely important to maintain adequate control and regulation of their temperature.

To perform this control, it is increasingly common to use controllers based on semiconductor elements that regulate the electric current that passes to each PTC heating element depending on the required heating power. The semiconductor components, normally power transistors, can function as switches that connect or disconnect the power supply of the PTC heating elements. Another option that allows more precise dosing of the heating power is that the power supply to the PTC heating elements can be regulated by the semiconductor components so that it is continuous. The disadvantage of continuous regulation is that semiconductor elements must dissipate a large amount of energy in the form of heat, so overheating can occur.

When the electronic controller of a complementary heating of a motor vehicle is heated, the gases generated during the carbonization of the plastic materials can diffuse directly through the ventilation system of the motor vehicle and enter the cabin, immediately affecting the health of They are in the cabin. On the other hand, these gases form a fog that worsens the driver's vision to the outside, and even obstructs it completely.

Even when the temperature of the semiconductor element is controlled or there is another electronic control of the actual temperature to disconnect the electric current in time before an overheating occurs, the problem of the lack of reliability of such overheating protection carried out in this way remains. . A protection against electric overheating of the controller is also not a satisfactory solution, since in this case it is not achieved either Always the required reliability. On the other hand, the realization of a protection against electrical overheating for high current intensities entails a considerable increase in the mounting dimensions of the control unit.

The same heating problem can also occur in relation to static relays known as SSR (Solid State Relay), which are electronic switching devices that connect and disconnect loads. Its function is the same as that of electromechanical relays, but instead of using a coil or electromagnet, the static relay mainly has a control or input circuit and a power or output circuit, without understanding moving parts inside.

Static relays are normally used for applications in environments prone to inflammations, since they do not produce sparks when closing their contacts, as well as in machinery that does not require continuous maintenance or in environments with presence of dirt such as dust or oil. In automotive, static relays are often used for the activation of light loads, such as water supply devices, regulation of headlights and lights, horn, etc. DESCRIPTION OF THE INVENTION

Both the above-mentioned controllers and the static relays conventionally comprise control elements that act on power transistors, both of which are arranged on a substrate that can be made of glass or ceramic fiber, such as a printed circuit, either directly or by means of the interposition of a layer of conductive material, such as a laminate or a coating. However, as mentioned, said electronic components must not exceed a maximum temperature at which the heat generated must be efficiently dissipated into the outside environment. However, the substrates used as the basis for the printed circuits on which the power transistors are conventionally mounted are not good conductors of heat, so it is difficult to evacuate the heat generated in the power elements. To solve this problem, the present invention proposes to fix the power transistors, or in general the power elements, to the extension of one of the connection terminals to the corresponding supply means. In fact, in fields such as automotive and others, the elements that use power transistors that must dissipate energy receive the power supply from the outside, usually from batteries, and therefore have a pair of metal terminals for connection to those batteries. These terminals, being metallic, are good conductors of heat, and an increase in their temperature hardly affects their function as electrical contact. The present invention takes advantage of this fact to fix the power elements to an extension of one of the battery connection terminals, thus obtaining a considerable improvement in the heat dissipation capacity of the device.

In this document, the term "power element" refers in general to any type of electronic power element that may require considerable heat dissipation, including not only transistors, but also other semiconductor switching elements.

In this document, the term "control element" refers in general to any electrical or electronic element that is used for the control of the described power elements, and whose normal operation does not imply dissipation of considerable amounts of heat.

In this document, the term "power medium" refers not only to batteries, but in general to any type of power supply to the device of the invention, such as the power grid or a DC converter.

In this document, the term "base plate" refers to the electrical and thermally insulating plate that constitutes the mechanical support on which the control elements, power, connection, as well as the rest of the elements are arranged, directly or indirectly. which constitutes the device of the invention, and which may possibly present elements that help heat dissipation, such as fins or similar structures. A first aspect of the invention relates to an electronic device with integrated thermal dissipation, which comprises a base plate that supports power elements, control elements, and metal terminals connecting to a supply means, where the elements of power are fixed on an extension of a metallic connection terminal that acts as a heat sink.

It is understood that the metallic terminal of connection to whose extension the power elements are fixed can be any, positive or negative, although in a preferred embodiment of the invention the positive terminal is used.

This novel configuration has several advantages. On the one hand, as mentioned above, the thermal dissipation capacity of the device is improved. In addition, since the power elements and the control elements are fixed to different parts, the probability that the control elements are damaged by the heat generated by the power elements during operation of the device is minimized. Thirdly, it allows the fixing of the power elements to be extended to the extension of the metal connection terminal, fixing techniques that could otherwise damage the control elements, such as reflow welding or even by means of a sintering process to improve the connection between the power elements and the extension of the metal terminal. Another advantage of the invention is that the need to provide the base plate with a radiator or similar elements for the evacuation of the heat generated by the power elements is avoided, which makes it possible to decrease its size, and the plate itself can act base as radiator.

To further improve the heat dissipation capacity of the device, in a preferred embodiment of the invention the extension of the metal terminal comprises fins like fins. These projections can protrude on a lower face of the device, thus keeping the upper face essentially flat to facilitate its integration with other elements.

As for the materials, the extension of the metal connection terminal can be made in principle of any metal conventionally used for the manufacture of terminals and electrical contacts, since all of them are good conductors of heat. In a preferred embodiment of the invention the extension of the metal connection terminal is made of tinned copper, tinned brass or aluminum.

Preferably, the extension of the metal connection terminal is fixed to the base plate. In addition, the possibility is contemplated that to improve the rigidity of the fixation and the heat transfer capacity from the extension of the metal terminal of connection to the base plate, and to facilitate a correct placement of said extension of the terminal on the plate base, the extension of the metal terminal is embedded in the base plate. That is, the base plate can have a recess in which the extension of the metal connection terminal is adjusted.

As for the control elements of the device, these are preferably fixed on a printed circuit board fixed on the base plate. Thus, the control elements and the power elements are fixed to different parts (metal or printed circuit board and extension of the connection terminal, respectively), between which the base plate is interposed, which is not a good transmitter of the hot. Therefore, in the device of the invention it is more difficult for the high temperatures that the power elements can reach to damage the control elements.

Preferably, the base plate is made of liquid crystal polymer (LCP Liquid Crystal Polymer), polyether ether ketone (PEEK Polyether ether ketone) or phenylene polysulfide (PPS Polyphenylene sulfide) can be used. The melting temperatures of these materials are higher than necessary for the process of welding by refusion or sintering process of the power elements on the extension of the connection terminal. In addition, its coefficients of thermal expansion between 1 and 5 um / (m ^e C) are low to maintain the geometry during the aforementioned refusion welding process or sintering process.

Regarding the fixing of the power elements to the extension of the terminals of connection, this can be done in different ways as long as the fixation is firm enough and allows a good heat transmission from said power elements towards the extension of the connection terminals. In a preferred embodiment of the invention, the technique of refusion welding is used, since it allows both control and power elements to be welded simultaneously, reducing the thermal stress of welding separately from the two elements that would force a final resolution of the whole.

Refusion welding, or reflow, is a process in which a solder paste is used to attach one or more electronic components to their contact pads on a printed circuit board by applying heat or infrared radiation through stages of different intensity which can be programmed in manufacturing machinery. To improve the thermal transmission, between the connected elements, both the refusion process and the sintering process can be carried out in a vacuum atmosphere reducing the air bubbles that could be trapped under the power transistors.

As indicated, it is possible to use the sintering technique instead of refusion welding to fix the power elements to the extension of the connection terminals, in order to optimize the thermal transmission between those parts. The sintering process consists of the combined application of pressure and temperature to a paste of silver compounds located between the power components and the extension of the metal connection terminal, so that the electrical and thermal conduction between both components is optimized.

Additionally, various means can be used to facilitate a correct positioning of the power elements on the extension of the connection terminals. For example, the base plate may comprise ribs for centering the power elements on the extension of the metal connection terminal. Another option is that the power elements are embedded in the extension of the metal connection terminal, that is, that the extension of the terminal has recessed areas adjusted to the dimensions of the elements of power, which fit inside.

Finally, it is necessary to emphasize that the use of this new device is not restricted to devices or equipment used in the automotive field, but can be used in general for any type of device or equipment.

In addition, it should be understood that an apparatus or equipment that includes the device described herein may further comprise other additional elements that are not mentioned in this application. By way of example, two devices can be mentioned specifically comprising an electronic device with integrated thermal dissipation such as the one described herein: an electronic power controller for PTC devices of the type used in automotive for temperature control of heating, and a static relay of the type used in automotive for the activation of light loads, such as water supply devices, regulation of headlights and lights, horn.

A second aspect of the invention is directed to a method of manufacturing an electronic device with integrated thermal dissipation as described above, where before the step of welding by refusion of the power elements on the extension of the metal connection terminal acting as Heatsink is carried out a prior fixation of said power elements.

Preferably, said prior fixation is carried out using at least one of the following methods: fixation by point adhesive, fixation by perimetral adhesive with solder paste inside, and fixation by screen printing or pad printing of welding mask.

In summary, the device described in the present invention fundamentally presents the present advantages in relation to the prior art:

- Allows the removal of the ceramic or glass fiber intermediate substrate under the power elements, thus eliminating the main restrictions on the transfer of heat to the outside, with a direct connection of the power elements with the metal extension that generates a transfer Direct thermal, with lower voltage drops, greater efficiency and thermal conduction and without additional losses.

- For medium powers, it is possible to suppress the heatsink that the base plate usually has (for example, a radiator, as shown in the figures), because the battery voltage supply busbar can dissipate heat very effectively by conduction towards the power bums, besides dissipating by convection and radiation.

- For high powers, where a heatsink is necessary, it offers a surface of very high thermal conductivity to perform the physical union with the heatsink, approximately, between 15 and more than 1000 times the thermal conductivity offered by other methods and substrates.

- Comparing with other mounting methods, where the power elements are connected to a printed circuit, either on the basis of fiberglass or on a ceramic base, the heat generation by Joule effect on the tracks of the power elements is around 30 times lower than in printed circuits of 35 microns of copper and 15 times less than in printed circuits with tracks of 70 microns of copper. In addition, the thermal resistance to dissipation by conduction towards the external wiring improves in equal proportion.

- In the application of the device for electronic power controllers for PTC devices, as the heat generated can be conducted and dissipated by convection until the air flow that is intended to be heated with the PTC system, having a lower thermal resistance achieves greater efficiency in the use of electrical energy for heat generation. As a result, energy consumption is reduced to obtain the same thermal increase in the heating flow and the efficiency of the heating system improves.

BRIEF DESCRIPTION OF THE FIGURES

Figures 1 a and 1 b show an example of an electronic power controller for PTC devices used in automotive in accordance with the prior art. Figures 2a and 2b show an example of an electronic power controller for PTC devices incorporating a device according to the present invention where the control elements are fixed to a printed circuit board.

Figures 3a and 3b show a second example of an electronic power controller for PCT devices comprising a device according to the present invention where the control elements are replaced by a metal plate that activates the power transistors.

Figures 4a-4c show details corresponding to different ways of presetting and centering the power elements to the extension of the connection terminal.

Figures 5a-5b show two representative graphs in which the reliability improvement is quantified respectively in a controller for PTC according to the prior art and in a controller for PTC according to the invention.

Figure 6 shows an example of a static relay incorporating a device according to the present invention.

PREFERRED EMBODIMENT OF THE INVENTION

Some particular embodiments of the invention are described below with reference to the attached figures. In general, similar reference numbers have been used to designate similar parts in the different figures

Figs. 1 a and 1 b show two views of an electronic power controller (100) for PTC devices of the type used for heating control in the automotive field according to the prior art. This electronic power controller (100) has a base plate (101) that constitutes the mechanical support on which the rest of the elements are arranged. In this example, on a printed substrate (107), usually of ceramic material, The power elements (102), in this example transistors, and also the control elements are fixed to the base plate (101). The device is powered by a pair of terminals (103+, 103-) that are connected to a battery. The terminals (109) constitute the output of the controller (100).

Fig. 1b shows the path through which heat evacuation is carried out in this controller (100). The power elements (102) generate heat, which passes through the ceramic material substrate to which said power elements (102) are fixed towards the base plate (101). Finally, the heat is eliminated through the bottom of the base plate (101), which for that purpose has a radiator-shaped structure (1 15).

Figs. 2a and 2b, on the other hand, show two views of an electronic power controller (10) for PTC devices according to the present invention. This controller (10) is formed by a base plate (1) that provides a mechanical support to the rest of the elements, in particular a pair of terminals (3+, 3-) connecting to the power supply, in this example batteries (not shown), a printed circuit board (7) on which the control elements (not shown) are arranged, and the extension (4) of the metal connection terminal (3+) on which the elements are fixed ( 2) power. In this example, the extension (4) is embedded in the base plate (1), that is, it is fixed to the base plate (1) within a recessed area, such that its upper surface is approximately flush with the upper surface of the base plate (1) and flush with the upper surface of the printed circuit (7). It would also be possible for the fixing to be such that the lower face of the extension (4) of the terminal (3+) was exposed by the lower part of the controller (10), thus facilitating the evacuation of heat by convection. In Figs. 2a and 2b have also shown the output terminals (9) of the controller (10) that emerge from the base plate itself (1) on one of its larger sides parallel to it.

Thus, being the power elements (2) located on the metal extension (4) and the control elements (not shown) located on the circuit printed (7), it is more difficult for the high temperature that the former can reach to affect the latter. In addition, the metal extension (4) allows heat to be evacuated more efficiently than through the printed substrate (107) that was used in the prior art.

Fig. 2b shows the path followed by the heat generated by the power elements. In the first place, this heat passes to the metal extension (4) of the terminal (3+), and is transmitted quickly throughout the terminal due to the good thermal conduction properties of the metal from which it is made. The heat is then evacuated in two ways: a first convection path through the lower part of said extension (4), after crossing the base plate (1); and a second route by conduction through the terminal (3+).

In addition, although it is not represented in Figs. 2a and 2b, the controller (10) can be provided with mechanical rigidity by adding an encapsulant, with the option of adding to the same thermoconductive load, such as silica powder to improve the technical characteristics.

Figs. 3a and 3b show a second embodiment of an electronic power controller (10) for PTC devices according to the invention where the power elements (2) are transistors with their internally incorporated control elements. These elements are known as IPS (Intelligent Power Switch) or SPS (Smart Power Switch), and for the activation of them only a signal that is sent through a metal plate (8) is used that is used instead of a printed circuit (7). In addition, in this second embodiment the extension (4) of the metal connection terminal (3+) has fins (5) protruding from the base plate (1) by the lower face of the controller (10), as well as the terminals (9) of output of the controller and the projections as fins comprising the metal terminal (3-), the lower face being understood as the face opposite to that on which the power elements (2) and the elements of control. These fins (5) help dissipate the heat generated by said power elements (2) by convection. In addition, in Fig. 3b it can be seen how in this example the extension (4) of the metal connection terminal (3+) is fixed inside a hole of the base plate (1), its lower surface remaining exposed by the underside of the controller (10). In this way, heat is evacuated by convection through the lower surface itself of the extension (4), unlike what happens in the embodiment shown in Figs. 2a and 2b, where the extension (4) is fixed on the base plate (1).

Note that, although in the example shown in Figures 3a and 3b the fins (5) protrude from the underside of the controller (10), it would be possible for both said fins (5) and terminals (9) and the projections as of fins of the metal terminal (3-), protruding from the upper face of the base plate (1). In either situation, all of them must stand out on the same side of the plate

(1) basic.

Figs. 4a-4c show different ways of performing a fixation and / or centering of the power elements (2) to the extension (4) prior to the definitive fixation using the refusion welding technique. Specifically, the leftmost power element (2) in Fig. 4a is pre-fixed by means of a pair of adhesive points (16) and the power element (2) located in the center of Fig. 4a is preset by means of a line (17) of perimeter adhesive with solder paste inside. Fig. 4c shows a third way of centering the power elements (2) in the extension (4) by means of screen printing or welding mask pad printing (18).

As for the centering of the power elements (2) on the extension (4), note that in this document the term "centered" refers not only strictly to the centering of the power element (2) on the extension (4), but in general to a proper positioning depending on the size of said extension (4), number of power elements (2) used, etc.

The power element (2) located more to the right in Fig. 4a is centered in its position thanks to ribs (6) of the base plate (1). Another way of facilitating the centering of the power elements (2) which consists of embedding them in the extension (4). This is shown in Fig. 4b, where the extension (4) has a recess of the size of the power element (2) to which it is fixed. Figs. 5a and 5b show comparative graphical paths in which it is observed that the proposed invention has greater reliability than the prior art due to superior integration. The parameter with which the reliability improvement is quantified is the average time in continuous operation until failure (MTTF). For the purpose of the invention the MTTF is 136.99 years versus 1.26 years of the prior art.

In Figs. 5a and 5b the MTTF value can be observed in hours depending on the temperature in ^e C and in the table shown below, the indicated values and improvements obtained are collected, indicating the operating conditions in which each value has been obtained . The conditions are equivalent for the prior art and the proposed invention.

It is defined as a calculation hypothesis for both assemblies, that the surfaces by which the heat generated by any of the mechanisms of dissipation is dissipated Heat transfer are isotherms.

Under the same environmental and operating conditions, the object of the patent shows an improvement in the thermal resistance of the order of 60%, in particular, 0.18 ^e C / W versus 0.45 ^e C / W of the prior art , which implies that before the same power dissipated, it undergoes less self-heating.

For a common power of 24W, compared to the prior art that reaches an increase of 10.8 ^e C, the object of the patent only increases its temperature 4.32 ^e C.

Inherent in a lower heating of the object of the patent, two technological improvements arise, the first of which is the ability to control greater power for the same heating.

For the same operating conditions, the following thermal resistances have been obtained as a function of the controlled power, 0.01 1898 ^e C / W for the prior art versus 0.006576 ^e C / W of the object of the patent. This means that, under the same working conditions and the same operating temperature limit, the prior art can control 4202.4W compared to 7603.4W for the purpose of the patent. This represents an improvement of 44.7%.

The second is that, for equal operating conditions, the reliability of the proposed system is increased 160 times due to the lower self-heating, this improvement is accumulated to the improvement of reliability by integration.

Finally, Fig. 6 shows a static relay (1 1) provided with a device as described in the present invention. The base plate (1), which in this case has a different shape, constitutes the mechanical support to which the rest of the elements are fixed: the terminals (3+, 3-), the printed circuit board (7) on the that the control elements (not shown), the metal extension (4) of the terminal (3+) on which the power element (2), and the output terminal (9) are fixed are fixed. The operation of this static relay is similar to that described in relation to the two controller examples (10) above. The heat dissipated by the power element (2) passes directly to the terminal (3+) and from there it is dissipated by convection to the outside air and by conduction along said extension (4) and said terminal (3+). In addition, although not shown in Fig. 6, the static relay (1 1) may be provided with mechanical rigidity by adding an encapsulant, with the option of adding to the same thermoconductive load to improve thermal characteristics.

Claims

one . Electronic device with integrated thermal dissipation, comprising a base plate (1) that supports power elements (2), control elements, and metal terminals (3+, 3-) connecting to a power supply, characterized in that the power elements (2) are fixed on an extension (4) of a metal terminal (3+, 3-) that acts as a heat sink.

2. Electronic device according to claim 1, wherein the power elements (2) are embedded in the extension (4) of the metal terminal (3+, 3-) that acts as a heat sink.

3. Device according to any of the preceding claims, wherein the metallic terminal (3+) that acts as a heat sink to whose extension (4) the power elements (2) are fixed is the positive terminal.

4. Electronic device according to any of the preceding claims, wherein the extension (4) of the metal terminal (3+, 3-) that acts as a heat sink comprises projections (5) as fins.

5. Electronic device according to claim 4, wherein the projections (5) as fins protrude from a lower face of the device.

6. Electronic device according to any of the preceding claims, wherein the extension (4) of the metal terminal (3+, 3-) that acts as a heat sink is made of tinned copper, tinned brass or aluminum.

7. Electronic device according to any of the preceding claims, wherein the extension (4) of the metal terminal (3+, 3-) that acts as a heat sink is fixed to the base plate (1).

8. Electronic device according to claim 7, wherein the extension (4) of the metal terminal (3+, 3-) that acts as a heat sink is fixed in a hole in the base plate (1) in such a way that its lower surface is exposed by the lower face of the device.

9. Electronic device according to claim 7, wherein the extension (4) of the metal terminal (3+, 3-) that acts as a heat sink is embedded in the base plate (1).

10. Electronic device according to any of the preceding claims, wherein the base plate (1) also comprises ribs (6) for centering the power elements (2) on the extension (4) of the terminal (3+) , 3-) metallic connection.

eleven . Electronic device according to any of the preceding claims, wherein the base plate (1) is made of liquid crystal polymer, polyether ether ketone or phenylene polysulfide.

12. Electronic device according to any of the preceding claims, wherein the control elements are fixed on a printed circuit board (7) fixed on the base plate (1).

13. Electronic device according to any one of claims 1 - 1, wherein the control elements are internally incorporated in the power elements (2), said power elements (2) being connected for activation to a plate (8) ) metal fixed on the base plate (1).

14. Electronic device according to any of the preceding claims, wherein the power elements (2) are fixed on the extension (4) of the metal connection terminal (3+, 3) that acts as a heatsink by refusion welding or by sintering process.

15. Electronic power controller (10) for PTC devices comprising an electronic device with integrated thermal dissipation according to any one of claims 1-14.

16. Static relay (1 1) comprising an electronic device with integrated thermal dissipation according to any one of claims 1-14.

17. Method of manufacturing the electronic device with integrated thermal dissipation of claim 14, characterized in that before the step of welding by refusion of the power elements (2) on the extension (4) of the metal terminal (3+, 3-) of connection that acts as a heat sink, a previous fixation of said power elements (2) is carried out.

18. Manufacturing method according to claim 17, wherein said pre-fixation is carried out using at least one of the methods of the following list: fixation by point adhesive (16), fixation by perimeter adhesive (17) with solder paste inside, and fixation by serigraphy or pad printing of soldering mask (18).

19. Manufacturing process according to any of claims 17-18, wherein refusion welding is performed under a vacuum atmosphere reducing air bubbles that could be trapped under the power elements (2).