Source: http://www.google.com/patents?pg=PA7&zoom=4&dq=6272333&id=18YWAAAAEBAJ&output=text
Timestamp: 2013-12-06 13:56:59
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Matched Legal Cases: ['art 62', 'art 61', 'arts 13', 'art 14', 'art 13', 'arts 13', 'art 13', 'art 14', 'arts 13', 'art 42', 'art 41', 'arts 41', 'art 42', 'art 62', 'art 61', 'art 62', 'art 61', 'art 61', 'art 62', 'art 67', 'art 62']

Patent US5912803 - Heat dissipating box - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Advanced Patent Search | Page images | Sign inAdvanced Patent SearchPatentsThe present invention relates to a heat dissipating box for a printed board assembly (PBA) using natural convection for cooling. The PBA 64 is fastened between a first part 62 and a second part 61 and the joint is sealed with an elastic material 71. A back plane, which has an opening for a connector...http://www.google.com/patents/US5912803?utm_source=gb-gplus-sharePatent US5912803 - Heat dissipating boxHeat dissipating box Uno Dahl et alOverviewAbstractDrawingsDescriptionClaims Patent number: 5912803Filing date: Mar 6, 1998Issue date: Jun 15, 1999 Page imagesPDF
HEAT DISSIPATING BOX
A similar device is described in the U.S. Pat. No. 4,794, 487 by Maschek et al., where an electronic device is protected from heat radiation from the outside, for example solar rays. The purpose is to prevent the electronic device to be heated up inside the device using upper and lower ventilation slots and achieving natural convection by a chimney effect.
An enclosure for cooling electronic components is described in the U.S. Pat. No. 4,535,386 by Frey, Jr et al, where the cooling is performed utilising natural convection. The enclosure comprises an inner chimney where the heat dissipating components are mounted at the lower part of said chimney. The heated air rises from the components and is led to a heat exchanger and a natural turbulence is thereby created.
The present invention solves the problems by introducing 5 an improved box for heat dissipation with a high cooling efficiency, including means for conducting heat from the PBA to the inside of the box.
Most of the heat from a PBA originates from a few numbers of electronic components. The heat dissipating 10 property of the PBA, mounted inside a box, increases rapidly if the heat dissipating components are placed near or in contact with the box. A good thermally contact can be obtained by means of filling the distance between the heat dissipating components on the PBA and the box with for 15 example gap-fillers, which are thermally good conductors. An alternative way of creating means for a good thermal contact is to place bumps, for example supports or ridges, on the inside of the box, which are in close contact with the PBA.
The present invention has a major advantage in a high cooling efficiency when exposed to cooling by natural 35 convection even though the box is sealed.
40 A better understanding of the present invention can be obtained when the following detailed description of the preferred embodiments is considered in conjunction with the following drawings.
FIG. 1 is a perspective view of an assembly with an enclosure including several boxes according to the present invention with an open door. The assembly is cooled by using natural convection. 50 FIGS. 2a-2c are different views of a heat dissipating box according to the present invention.
FIG. 3 is a cross-sectional view of the heat dissipating box in FIG. 2b, section A—A.
FIG. 4 is a top view of a first part of the same heat 55 dissipating box as shown in FIG. 3.
FIG. 6 is a top view of a first part of the same heat dissipating box as shown in FIG. 5. 60 FIG. 7 is a cross-sectional view of a combined heat dissipating box, according to the invention.
65 PREFERRED EMBODIMENTS
FIG. 1 shows a complete assembly 1 comprising an enclosure 2 with an enclosure door 3. The enclosure has
several ventilation louvers 4 in the lower part of the enclosure and at least one ventilation slit 5 on the top of the enclosure. The angled top 6 of the enclosure is designed to prevent snow or falling leaves to block the ventilation slit and interrupt the natural convection cooling. The enclosure 5 is divided into two parts by means of a partition wall 9 on which main frame connectors 10 are mounted. Apertures for mounting of cables 7 are provided in the base 8 on the back side of the partition wall. The back of the partition wall is a sealed compartment and contains interconnections between the main frame connectors and incoming cables. Boxes 11 containing electronic devices, such as PBA's, are fastened to the main frame connectors 10 on the front side of the partition wall 9 and sealed to the partition wall by means of an elastic material, such as an O-ring.
The boxes 11 are cooled, when they dissipate heat, by a 15 flow of air in through the ventilation louvers 4, upwards between the boxes 11 and out through the top slit 5. This assembly is designed to be placed outdoors which means exposure to solar rays, rain and other types of weather conditions. This requires that the connections and the elec- 20 tronic devices in the boxes must be protected from the outside environment.
FIGS. 2a-2c show views of a first preferred embodiment. This box 11 is designed for high cooling performance and the surface area of the box is enlarged with cooling fins 12. 25 The box comprises at least two main parts 13 and 14 and a separate back plane 19. A PBA is squeezed between the two main parts that are fastened together with some type of fastening devices, preferable screws 15 but other fastening means can be used, for example glue or rivets. The front 30 plane 16 of the box can be equipped with apertures for connectors 17, for example test ports and indicators 18 if so is desired. The back plane 19 of the box is equipped with at least one opening for a connector 20 from the PBA, called PBA-connector. The PBA-connector is plugged in to the 35 main frame connector 10 during normal operation of the assembly and the back plane is sealed to the partition wall using an elastic material, for example an O-ring.
The design of the heat dissipating box 11 can be adjusted for low heat dissipating PBA's, where the need to enlarge 40 the surface area is less. This type of box comprises at least two plain main parts, without the cooling fins, that are fastened together in a similar way as described in FIGS. 2a-2c and the same type of back plane for the PBAconnectors. The box can also be equipped with the same 45 apertures for test ports and indicators on the front plane.
FIG. 3 shows a cross-sectional view of a heat dissipating box 11, section A—A FIG. 2b. A first part 14 and a second part 13 forms a cavity 21, where a PBA 22 is mounted. The edge of the PBA is placed in a niche 33, see FIG. 4, created 50 by the main parts 13 and 14 and the height hi of the niche must be greater than the thickness h2 of the PBA's printed circuit board. The joint between the main parts are sealed with an elastic material 23, which protects the cavity 21 and the PBA 22 from the outside environment. 55
The first and second parts are fastened together by screws 15, where each screw is placed through a drilled hole 24 in the second part 13, through an aperture in the PBA and fastened in a threaded hole 25 in the first part 14. The holes 24 and 25 are drilled through second supports 30 and into 60 first supports 31, where the hole is threaded. The first and second supports prevents the PBA from deforming when the screws are tightened. A close contact between the supports 30 and 31 and the PBA enhances the possibility to conduct heat from the PBA's circuit board. This can be difficult to 65 obtain due to variations in manufacture of the main parts 13 and 14.
FIG. 5 shows a cross-sectional view of a second preferred embodiment of a heat dissipating box 40. A first part 42 and a second part 41 forms a cavity 43, where a PBA is mounted, not shown in the figure. The edge of the PBA is placed in a niche 44 created by the main parts 41 and 42 and the height hi of the niche must be greater than the thickness of the PBA's printed circuit board. The joint between the main parts is sealed with an elastic material 45, which protects the cavity 43 and the PBA from the outside environment.
There are at least three rows of first ridges 46 placed on the first surface 43a of the cavity 43 with an intermediate distance dl in a third direction parallel to the direction of the back plane. The second surface 43b of the cavity has at least two rows of second ridges 47 with an intermediate distance d2 in the third direction. The first and second ridges must be dislocated a distance d3 in the third direction when the first and second parts are positioned on top of each other. The distance d2 is preferable equal to:
d2=dl,
and the distance d3 is preferable equal to: d3=d2/2.
h5>minimum thickness-d3/200. A lesser distance can cause the PBA to be damaged from the pressure of the ridges.
For example: One type of standard PBA has a length of 265 mm and for that kind of PBA the intermediate distance d2 between the ridges is selected to be 75 mm and the
intermediate distance d3 between the first and second rows of ridges is selected to be 75 mm/2=37.5 mm. If the minimum thickness of the PBA's printed circuit board is 1.8 mm the distance h5 between the tops of the ridges is equal to: h5=1.6125. 5
No apertures are needed in the PBAfor fastening the PBA inside the cavity, but there is a need to design a component layout on the circuit board in a way that permits the ridges in the cavity to be in contact with the PBA. A close contact between the ridges and the PBA enhances the possibility to conduct heat from the PBA's circuit board without using any kind of gap-fillers and an even better conductivity can be obtained if the ridges are in contact with the conductive pattern and connected to for example earth potential.
FIG. 6 shows a top view of the first part 42 together with a cross-sectional view of a mounted back plane 19 of the 15 heat dissipating box in FIG. 5. The ridges 46 are placed in parallel rows on the first surface 43a of the cavity in the first direction perpendicular to the back plane 19 of the box. The total length (L1+L2) of the ridges in a row must be equal to or exceed 50% of the inside distance L3 of the cavity in the 20 same direction. The first part also include at least four threaded holes 50 to fasten the first and second part of the box with screws or a similar fastening device.
An elastic material 45 is placed around three sides of the cavity in a groove and is adjusted to seal apertures for 25 eventual test ports 17 and indicators 18 using for example elastic o-rings 37. The fourth side is sealed with an elastic material 35 when the back plane 19 is mounted. Small gaps 38 will appear between the elastic material 45 around the cavity and the elastic material in the back plane 35. These 30 gaps are used to lead humidity created inside the cavity out to the ambient area. The PBA39 with the PBA-connector 20 is outlined in the figure, with the dashed lines.
FIG. 7 shows a cross-sectional view of a third preferred embodiment of a heat dissipating box 60. A first part 62 and 35 a second part 61 forms a cavity 63, where a PBA 64 is mounted. This embodiment is a combination of the two previous described embodiments.
The first part 62 has at least three rows of a first type of bumps 65 and at least two rows of a second type of bumps 40 66. The first type of bumps, described in the second embodiment, comprises at least one ridge 65. The second type of bumps, described in the first embodiment, comprises at least three first supports 66, which contains a threaded hole 67. The rows are all parallel and the rows with the first 45 supports 66 are placed between the rows of the ridges 65 extending in a first direction perpendicular to the direction of the back plane and on the cavity's first surface 63a.
The second part 61 has at least two rows comprising at least three second supports 68 containing a drilled hole 69, 50 described in the first embodiment. A difference from the previously described first embodiment is that the second supports have a larger top area compared to the first supports top area, and the tops of the supports coincide when the second part 61 and first part 62 are fastened together. Screws 55 70 are mounted through the hole 69 in the second part and fastened in the threaded part 67 in the first part.
The PBA 64 is placed between the rows of bumps 65 and 66 and in a niche 49. The PBA's printed circuit board is squeezed in the same way as described in the second 60 preferred embodiment, where the ridges on the second surface are replaced with the first and second supports with an intermediate distance h6 calculated the same way as for the intermediate distance h5 in the second preferred embodiment. 65
FIG. 8 shows a top view of the first part 62 together with a cross-sectional view of a mounted back plane 19 of the
heat dissipating box in FIG. 7. The ridges 65 are placed in parallel rows inside the cavity 63 in the first direction perpendicular to the back plane 19 of the box. The total length of the ridges in a row must be equal to or exceed 50% of the inside distance of the cavity in the same direction as previously described in FIG. 6.
1. A heat dissipating box for at least one printed board assembly (PBA), where the heat dissipating box comprises at least two main parts, a first part and a second part, creating a cavity, in which the PBA is mounted and where a joint between said parts is sealed by using an elastic material and a back plane mounted to the two main parts sealing the cavity by using an elastic material between said main parts and the back plane, characterised in that surfaces of the cavity (21,43,63), created by said first part (14,42,62), the first surface (43a, 63a), and said second part (13,41,61), the second surface (27,43fc,63fc), has bumps (30,31,46,47,65,66, 68) to achieve a good thermal contact between the mounted PBA (22,39,64) in the box (11,40,60) and the surfaces of the cavity (21,43,63) inside the box.