Liquid cooled dissipator for electronic components equipped with selectively arranged dissipation fins.

Abstract: This invention concerns a liquid cooled dissipator for electronic components (C) characterised by selectively arranged dissipation fins (2), namely fins (2) positioned only in proximity of the areas against which the electric components (C) to cool are mounted.

Description: This invention concerns a liquid cooled dissipator having selectively arranged fins for electronic power components. It is common knowledge that all electronic components, especially power components, produce a considerable amount of heat during operation which must be dispersed in order to avoid compromising the proper operation of the same. For some time heat dissipators have been available on the market on which the electronic components are fitted in order to considerably reduce their operating temperature. The first class of dissipators is the so called air dissipator in which most of the heat is dispersed by the production of forced air. It should be noted however that in the case of electronic power components with particularly high operating temperatures, heat dissipators cooled by flows of high pressure refrigerated liquids have been designed. In particular this last type of dissipator generally consists of a metal plate provided over the full extension of its internal face, with a closely fitting regular series of dissipation fins; this plate is sealed at the bottom by a hermetic lid which forms an internal sealed duct in which the cooling liquid circulates. In this compartment of the dissipator - in which the above dissipation fins on the internal face of the plate are fitted - the forced circulation of the cooling liquid takes place. This forced circulation cools the dissipating fins and by conduction also cools the entire surface of the supporting plate; considering therefore that the electronic components to cool are mounted externally to said finned plate, it is evident that cooling of the plate effectively ensures the required heat dissipation to the advantage of the electronic components. Although these traditional liquid cooled dissipators are undoubtedly practical, it is possible to improve them from both an operational and structural point of view. In particular, with reference to said traditional liquid dissipators, the dissipation fins on the internal face are too numerous. It has been ascertained in fact that of the numerous fins on the internal face of a dissipator of this kind, those which ensure major heat dispersion are those positioned precisely at the points corresponding to the position of the electronic components to cool mounted outside the dissipator itself. The fins arranged in the areas around those where the electronic components are mounted are not only negligible in terms of heat dispersion but also significantly hinder the load loss in terms of the forced circulation of the cooling liquid. In particular, the significant resistance produced by this closely fitting and uniform series of fins has forced designers of traditional liquid dissipators to carefully develop the characteristics of the relevant water systems both in terms of dimensions and power absorption. The liquid dissipator according to the invention has been designed taking into account this very problem. It consists of a traditional structure composed of the finned plate closed at the bottom by means of the sealed lid but is also characterised by the use of dissipation fins arranged selectively, namely only at the points where the electronic components to cool are mounted on the external surface. On one hand this solution eliminates most of the dissipation fins on the internal surface of this dissipator giving an obvious saving in terms of costs, structure and design without however compromising in any way the heat dispersion capacity of the dissipator itself. On the other hand the liquid dissipator according to the invention makes it possible to realise in proximity of the finless areas, a number of preferential ducts for the circulation of the cooling liquid, which considerably reduce the resistance encountered by the liquid in the dissipator giving obvious design and technical - operational advantages. Another important characteristic of the new dissipator in question is that the new finned plate is produced from a single block of metal processed by the removal of shavings with NC machines or moulded; the dissipation fins are produced from the full block by the removal of shavings. Although this process implies long technical times it does however ensure considerable advantages: the first of which is the operational flexibility which translates above all into the possibility of varying at any time - simply by modifying the job programme of the NC machine - the number and position of fins and the shape of the cooling liquid ducts on the internal surface of the dissipator according to the invention. The fact that the new dissipator according to the invention is produced from a single block of uniform material moreover permits obtaining a minimum thermal resistance in that the same is due exclusively to the arrangement and shape of the fins and the liquid flow, without mentioning the high interface thermal resistances when the dissipator is not obtained from a single block. Thanks to the fact that the dissipator in question is designed from a single block, the surface on which the components to cool are mounted, is extremely flat with an excellent finish; this also gives an extremely important technical - operational advantage in that the components to cool are often fitted on a copper or aluminium plate which is in turn abutted directly against the dissipator in question and which transfers the thermal flow to the latter. It is therefore evident that a better finish of the external surface of the dissipator leads to major adhesion between the copper or aluminium supporting plate of the electronic components and the dissipator itself. The uniformity of the material of the new dissipator in question is also particularly important for the prevention of corrosion and electro-corrosion. Another important characteristic of the dissipator according to the invention is the use of a special type of dissipation fins; the geometry and centre to centre distances, namely the two most important parameters to optimise the performance of the fins from a thermal and fluid mechanics point of view, have been carefully designed. For major clarity the description of the invention continues with reference to the enclosed drawings which are intended for purposes of illustration and not in a limiting sense, where: figure 1 illustrates the dissipator in question with a view of the side on which the components to cool are mounted; a part of the supporting plate is removed from the drawing in order to illustrate the internal structure of the dissipator; figure 2 illustrates the dissipator in question with a view of the opposite side; a part of the lid has also been removed from this drawing; figure 3 is an axonometric view of one of the dissipation fins; figure 4 is a view of a section of the supporting plate on which the two electronic components are mounted; figure 5 is a cross-section of figure 4 on plane V-V; figure 6 is a view of a finned section of the dissipator in question; figure 7 is a cross-section of figure 6 on plane VII-VII. With reference to the above drawings, the dissipator in question consists of a metal plate (1) provided on its internal surface with a series of selectively arranged dissipation fins (2). The bottom of said plate (1) is sealed by means of a sealed lid (3) which - thanks to the presence of several longitudinal baffles (4) - creates a number of internal ducts (1a) in which the cooling liquid circulates. In particular the cooling liquid circulating in said ducts (1a) flows into the dissipator in question through an inlet (1b) and flows out of the dissipator through an outlet (1c). As mentioned previously, the characteristic of the dissipator according to the invention lies in the fact that the dissipation fins (2) are arranged in "bunches" on the internal surface of plate (1) only at the points where the electronic components (C) to cool are mounted on the external surface. In other words, for each area on which the electronic components to cool are mounted, a corresponding finned area or finning is provided on plate (1) in which the fins (2) are provided in a number proportional to the thermal flow to eliminate. Another important feature of the device in question is the particular configuration of each of the finned areas. With reference to figures 1 and 6, each of these finned areas consists of a series of fins (2) - which are pins to all effects and purposes - staggered on several parallel rows having an orthogonal direction with respect to the ducting (1 a). With reference to figures 4, 5, 6 and 7, it should be noted that: letter A refers to the area of the average section, defined as the ratio between the volume of the pin (2) and the height (H) of the pin; letter P refers to the perimeter of section A; letter D refers to the corresponding diameter of the section A, defined as the ratio 3xA/P; letter H refers to the height of the pin (2); code HD refers to the non dimensional height of the pin (2) defined as H/D; code ST refers to the transverse pitch between the fins, measured in an orthogonal direction to that (indicated by arrow F) of the cooling liquid flow; code SL refers to the longitudinal pitch between the fins measured in a direction parallel to that of the cooling liquid flow; code STD refers to the transverse non dimensional pitch defined as the ratio ST/D; code SLD refers to the longitudinal non dimensional pitch defined as ratio SL/D. The following table refers to the three non dimensional parameters, defined above, which indicates a field of optimal values for each in terms of the operation of the dissipator according to the invention; 1.50 HD 3.00 1.10 STD 2.00 1.08 SLD 2.50 Finally it is pointed out that the use of these preferential values for the three non dimensional parameters is valid and efficacious regardless of whether the pin (2) is circular or otherwise.

Claims: A liquid cooled dissipator for electronic power components of the type consisting of a metal plate (1) provided with internal dissipation fins (2) and a duct (1a) in which the cooling liquid that flows in through an inlet (1b) and flows out through an outlet (1c), circulates, characterised in that the above dissipation fins (2) are provided only at the points of the internal surface of plate (1) corresponding to the areas of the external surface of the plate (1) where the electronic components to cool are mounted. A liquid cooled dissipator for electronic power components according to claim 1, characterised in that each finned area consists of a series of fins or pins (2) which are staggered on several parallel rows having orthogonal direction with respect to duct (1a). A liquid cooled dissipator for electronic power components according to the previous claims characterised in that three non dimensional parameters (HD, STD, SLD), namely the non dimensional height (HD) of the pin (2) defined as H/D; the transverse non dimensional pitch (STD) defined as the ratio ST/D, and the longitudinal non dimensional pitch (SLD) defined as ratio SUD have the following values: 1.50<HD< 3.00 1.10< STD< 2.00 1.08< SLD< 2.50 wherein H refers to the height of the pin (2); D refers to the corresponding diameter of the section A, defined as the ratio 3xA/P and A refers to the area of the average section, defined as the ratio between the volume of the pin (2) and the height (H) of the pin; P refers to the perimeter of section A; ST refers to the transverse pitch between the fins, measured in an orthogonal direction to that of the cooling liquid flow, and SL refers to the longitudinal pitch between the fins measured in a direction parallel to that of the cooling liquid flow.

Inventors: FUMI EUGENIO, FUMI, EUGENIO
Applicants: ITELCO S P A, ITELCO - S.P.A.
Application year: 1997
Main classification: H05K7
IPC codes: H01L23, H05K7