Patent Publication Number: US-2023137239-A1

Title: Cooling of an electronic device

Description:
BACKGROUND 
     Technical Field 
     The present disclosure generally concerns electronic systems and devices, and their protection and cooling means. The present disclosure in some embodiments applies to means for cooling an electronic device protected by a package. 
     Description of the Related Art 
     Many techniques for cooling electronic systems and devices protected by a package are known. It is for example known to use packages adapted to dissipating the heat generated by the components and circuits of the electronic device or system. 
     It is desirable to be able to at least partly improve means for cooling the electronic devices protected by a package. 
     BRIEF SUMMARY 
     An embodiment overcomes all or part of the disadvantages of known electronic device cooling means. 
     An embodiment provides an electronic device comprising: 
     an electronic chip comprising an active area on a first surface, and a second surface opposite to the first surface; 
     a substrate, the first surface of said chip being mounted on a third surface of said substrate; and 
     a thermally-conductive cover comprising a transverse portion extending at least above the second surface of said electronic chip, wherein the electronic device further comprises at least one thermally-conductive pillar coupling the second surface of the electronic chip to said transverse portion of said thermally-conductive cover. 
     According to an embodiment, said at least one thermally-conductive pillar is a metal pillar. 
     According to an embodiment, said at least one thermally-conductive pillar comprises a first copper portion. 
     According to an embodiment, said at least one thermally-conductive pillar comprises at least a second portion made of a metal solder alloy. 
     According to an embodiment, said at least one thermally-conductive pillar is surrounded by a first layer made of a first thermally-conductive material extending from said second surface of the electronic chip to said transverse portion of said thermally-conductive cover. 
     According to an embodiment, said first layer further covers at least a fourth lateral surface of said electronic chip. 
     According to an embodiment, said transverse portion of said cover having a first portion having a first thickness extending above the second surface of said electronic chip, and at least a second portion having a second thickness greater than the first thickness extending at the periphery of said electronic chip. 
     According to an embodiment, the second portion extends all the way to the level of the first surface of said electronic chip. 
     According to an embodiment, said second portion is coupled to said third surface of said substrate by at least one first thermally-conductive bar. 
     According to an embodiment, the cover further comprises at least one lateral portion surrounding the electronic chip, and at least one extension extending from the lateral portion of the cover to said fourth lateral surface of said electronic chip. 
     According to an embodiment, the space between said transverse portion of said cover and said at least one extension is filled with a second thermally-conductive material. 
     According to an embodiment, said extension is coupled to said third surface of said substrate by at least a second thermally-conductive bar. 
     According to an embodiment, the thermally-conductive cover is a metal cover. 
     According to an embodiment, said at least one extension comprises on its upper surface at least one groove. 
     An embodiment provides a method of manufacturing an electronic device comprising an electronic chip having an active area on a first surface, and a second surface opposite to the first surface, the method comprising the successive steps of:
         forming at least one thermally-conductive pillar on said second surface of said electronic chip;   mounting said electronic chip on a third surface of a substrate, the first surface of the chip being on the side of the third surface of said substrate; and   arranging a thermally-conductive cover comprising a transverse portion extending above the first surface of said electronic chip, said transverse portion being in contact with said at least one thermally-conductive pillar.       

     According to an embodiment, said at least one thermally-conductive pillar comprises a first copper portion and at least a second portion made of a metal solder alloy. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The foregoing features and advantages, as well as others, will be described in detail in the following description of specific embodiments given by way of illustration and not limitation with reference to the accompanying drawings, in which: 
         FIG.  1    comprises a side cross-section view and a top cross-section view of an embodiment of an electronic device; 
         FIG.  2    comprises six side cross-section views illustrating steps of an implementation mode of the method of manufacturing the embodiment of  FIG.  1   ; 
         FIG.  3    comprises a side cross-section view and a top cross-section view of another embodiment of an electronic device; 
         FIG.  4    shows a side cross-section view of another embodiment of an electronic device; 
         FIG.  5    shows a side cross-section view of another embodiment of an electronic device; 
         FIG.  6    shows a side cross-section view of another embodiment of an electronic device; 
         FIG.  7    shows a side cross-section view of another embodiment of an electronic device; 
         FIG.  8    shows a side cross-section view of another embodiment of an electronic device; 
         FIG.  9    shows a side cross-section view of another embodiment of an electronic device; 
         FIG.  10    shows a side cross-section view of an embodiment of an electronic device according to another aspect; 
         FIG.  11    shows a side cross-section view of another embodiment of an electronic device; and 
         FIG.  12    comprises three side cross-section views illustrating steps of an implementation mode of the method of manufacturing the embodiment of  FIG.  10   . 
     
    
    
     DETAILED DESCRIPTION 
     Like features have been designated by like references in the various figures. In particular, the structural and/or functional features that are common among the various embodiments may have the same references and may dispose identical structural, dimensional and material properties. 
     For the sake of clarity, only the steps and elements that are useful for an understanding of the embodiments described herein have been illustrated and described in detail. 
     Unless indicated otherwise, when reference is made to two elements connected together, this signifies a direct connection without any intermediate elements other than conductors, and when reference is made to two elements coupled together, this signifies that these two elements can be connected or they can be coupled via one or more other elements. 
     In the following disclosure, unless otherwise specified, when reference is made to absolute positional qualifiers, such as the terms “front,”, “back,” “top,” “bottom,” “left,” “right,” etc., or to relative positional qualifiers, such as the terms “above,” “below,” “upper,” “lower,” etc., or to qualifiers of orientation, such as “horizontal,” “vertical,” etc., reference is made to the orientation shown in the figures. 
     Unless specified otherwise, the expressions “around,” “approximately,” “substantially” and “in the order of” signify within 10%, and in some embodiments within 5%. 
       FIG.  1    comprises two cross-section views (A) and (B) illustrating an embodiment of an electronic device  100 . View (A) is in some embodiments a side cross-section view of device  100  along the axis AA shown in view (B). View (B) is, in some embodiments, a top cross-section view of device  100  along the axis BB shown in view (A). 
     Electronic device  100  comprises an electronic chip  101  comprising one or a plurality of components (not shown in  FIG.  1   ) formed inside and/or on top of a substrate plate, for example, a silicon substrate. Chip  101  comprises a surface  103  and a surface  105  opposite to surface  103 . Chip  101  for example has a cuboid shape. On the side of surface  103  is the active area  107  of chip  101 , shown by hatchings in  FIG.  1   . Here call active layer of an electronic chip the portion of the electronic chip having most of the electronic components of the chip and the electric contacts which enable the chip to be used formed therein. Chip  101  further comprises lateral surfaces  109 . 
     Electronic device  100  further comprises a substrate  111  having chip  101  mounted thereon. Substrate  111  is for example a printed circuit board, a succession of conductive layers and of insulating layers forming metallization levels, a plate crossed by electrically-conductive vias, etc. More precisely, surface  103  of chip  101  is mounted on a surface  113  of substrate  111  via electric connectors  115  coupling electronic contacts of the active area  107  of chip  101  to electric contacts formed at the level of surface  113  of substrate  111 . The contacts of active area  107  and of surface  113  are not shown in  FIG.  1    for simplicity. Electric connectors  115  are, for example conductive balls or conductive bumps, for example solder balls. Electric connectors  115  are embedded in a filling material  117  enabling to protect them. This filling material  117  is an electrically-insulating material. These may for example be materials known under trade name XS8410-302SNS8AG or U8410-399F (Namics). Further, the substrate  111  may comprise contacts (not shown in  FIG.  1   ) on its other surfaces, e.g., surface  114  that is opposite to surface  113 , to allow the connection of electronic device  100  to other electronic devices. These contacts may be electrically coupled to other contacts via solder balls, not shown in  FIG.  1   . 
     Electronic device  100  further comprises a cover  119  made of a thermally-conductive material. According to an example, cover  119  is a metal cover, in some embodiments, made of copper. Cover  119  comprises a transverse portion  121  extending substantially parallel to the surfaces  103  and  105  of chip  101  and to surface  113  of substrate  111 , and lateral portions  123  extending substantially parallel to surfaces  109  of chip  101 . According to an example, transverse portion  121  and lateral portions  123  each are plates of substantially constant thickness, for example, having a thickness in the range from 0.3 mm to 1 mm, inclusive, for example, in the order of 0.5 mm. According to an example, cover  119  is made of one piece and comprises portions  121  and  123 . according to an embodiment, portions  121  and  123  may be parts attached to one another to form cover  119 , for example, attached together by gluing. 
     Cover  119  is arranged over chip  101  to protect the surfaces  105  and  109  of chip  101 . Cover  119  is attached to surface  113  of substrate  111  through bonding, for example, via a glue layer  125  arranged between the end of the lateral portions  123  of cover  119  and surface  113  of substrate  111 . 
     Electronic device  100  further comprises one or a plurality of, in some embodiments, a plurality of, thermally-conductive pillars  127  extending from surface  105  of chip  101  to the transverse portion  121  of cover  119 . According to an embodiment, a first end  128  of each pillar  127  is in direct contact with surface  105 , and a second end  129 , opposite to the first end, is in direct contact with the transverse portion  121  of cover  119 . 
     Pillars  127  are distributed on surface  105  of chip  101  (see view (B)). According to an embodiment, pillars  127  are concentrated in the areas of chip  101  generating the most heat. 
     According to an embodiment, pillar(s)  127  are metal pillars. According to an embodiment, pillar(s)  127  comprise at least one portion made of a first metal, for example, copper or an alloy comprising copper, and at least a second portion made of a second metal, for example, a metal alloy, for example, a metal alloy intended for soldering. According to an example, the first end  128  corresponding to the first portion of pillar  127 , and the second end  129  corresponds to the second portion of pillar  127 . A device  100  may comprise pillars  127  of different shapes. Pillars  127  may have a tubular shape with an oblong or even round cross-section (see view (B) of  FIG.  1   ). 
     Substrate  111 , cover  119 , and pillar(s)  127  form the protection package of chip  101  in electronic device  100 . 
     According to an example of embodiment, electronic device  100  has a length and a width in the range from 13 mm to 55 mm, inclusive, for example a length in the order of 45 mm and a width in the order of 45 mm, and a thickness in the range from 1.5 mm to 4 mm, inclusive, for example, in the order of 2.5 mm. For such an electronic device, chip  101  may have a length and a width in the range from 10 mm to 20 mm, inclusive, for example, a length in the order of 15 mm and a width in the order of 15 mm, and a thickness in the range from 150 mm to 400 mm, inclusive, for example, in the order of 300 mm. In this case, pillars  127  may have a width in the range from 30 to 100 μm, inclusive, for example in the order of 60 or 80 μm, and a height in the range from 50 to 120 μm, inclusive. An advantage of this embodiment is that it enables to efficiently remove the heat generated by chip  101  during its operation. In other words, the package formed by substrate  111 , cover  119  and pillar(s)  127  enables to extract the heat from chip  101 . Indeed, during its operation, chip  101  may generate heat, pillars  127  being thermally-conductive, they enable to guide the heat generated by chip  101  towards cover  119 , which is itself thermally-conductive, to remove as much heat as possible to the outside of the electronic package. 
     Another advantage of this embodiment is that the pillar concentration may be increase at the level of hot spots of chip  101 , that is, the areas of surface  103  generating the most heat. This is not true for a uniform layer made of a thermally-conductive material. 
       FIG.  2    comprises six cross-section views (A), (B), (C), (D), (E), and (F), each illustrating a step of an implementation mode of a method of manufacturing the device  100  described in relation with  FIG.  1   . 
     The steps illustrated in  FIG.  2    are performed while the chips are still in a wafer. For simplification, only one chip  201  is shown in  FIG.  2   . 
     At the step of view (A), the different chips  201  comprise an active area  203  arranged on the side of a surface  205 , opposite to a surface  207 , at the wafer scale. 
     At the step of view (B), connectors  209  of the type of the connectors  115  of  FIG.  1    are formed at the level of contacts of the active area  203  of chip  201 . The wafer is then flipped so that its surface  207  is accessible. The wafer is then thinned so that its thickness is at a desired thickness. 
     At the step of view (C), wafer  201  is bonded to a temporary support  211  via a temporary bonding layer  213  arranged at the level of connectors  209 . 
     At the step of view (D), one or a plurality of, in some embodiments a plurality of, thermally-conductive pillars  215  are formed at the level of the surface  207  of the different chips  201  in the wafer. According to an embodiment, a metal portion  217  is formed first, after which a second metal portion  219  is formed on top. For example, the pillars are formed by electrolytic deposition. 
     At the step of view (E), the temporary support is removed. The manufacturing of unit chips  201  is for example ended by a singulation step. 
     At the step of view (F), chip  201  is attached to a substrate  221  of the type of the substrate  111  of  FIG.  1    via connectors  209 . A filling material  223  is then arranged between the active area of chip  201  and a surface  225  of substrate  221 . 
     Then, a cover  227  of the type of the cover  119  of  FIG.  1    is arranged on chip  201 . For this purpose, lateral portions of cover  227  are bonded, for example by gluing, to the surface  225  of substrate  221 . The gluing is for example performed by deposition of a glue layer  229 . According to an example, if cover  227  is formed of a plurality of parts glued together, cover  227  may be assembled around chip  201 . 
       FIG.  3    comprises two cross-section views (A) and (B) illustrating an embodiment of an electronic device  300 . View (A) is in some embodiments a side cross-section view of device  300  along the axis AA shown in view (B). View (B) is, in some embodiments, a top cross-section view of device  300  along the axis BB shown in view (A). 
     Further, electronic device  300  has elements common with the electronic device  100  described in relation with  FIG.  1   . These common elements are not described again in detail herein, and only the differences between devices  100  and  300  are highlighted. 
     Electronic device  300  differs from device  100  in that a layer  301  made of a thermally-conductive material is formed around pillar(s)  127 . Layer  301  extends along the entire height of pillar(s)  127 , that is, from the layer  105  of chip  101  all the way to the transverse portion  121  of cover  119 . According to an embodiment, a lower surface of layer  301  is in direct contact with surface  105 , and an upper surface, opposite to the lower surface, is in direct contact with the transverse portion  121  of cover  119 . 
     According to an embodiment, layer  301  may extend over one or a plurality of portions (see view (B) of  FIG.  3   ) of the surface  105  of chip  101  but may, according to a variant, extend over the entire surface  105  of chip  101 . According to an example, layer  301  is formed at the level of one or a plurality of hot spots of chip  101 . 
     As previously mentioned, layer  301  is made of a thermally-conductive material. According to an example, this material is selected by the group comprising: the material bearing reference SE4450 commercialized by Dow Corning, and the material bearing reference TC304 commercialized by Dow Corning. 
     An advantage of this embodiment is that layer  301  enables to improve the heat transfer from the chip to the outside of the package. 
     Device  300  further has the same advantages as those of the device  100  described in relation with  FIG.  1   . 
       FIG.  4    is a side cross-section view illustrating an embodiment of an electronic device  400 . 
     Electronic device  400  has elements common with the electronic device  300  described in relation with  FIG.  3   . These common elements are not described again in detail herein, and only the differences between devices  400  and  300  are highlighted. 
     Electronic device  400  differs from device  300  in that layer  301  is replaced with a layer  401  made of a thermally-conductive material formed around pillar(s)  127 . Like layer  301 , layer  401  extends all along the height of pillar(s)  127 , that is, from the layer  105  of chip  101  to a transverse portion  403  of cover  119 . Further, according to an embodiment, layer  401  further covers all or part of the lateral surfaces  109  of chip  101 . 
     Further, like layer  301 , layer  401  may extend over one or a plurality of portions (see view (B) of  FIG.  5   ) of the surfaces  105  and  109  of chip  101  but may, according to a variant, extend all over surface  105  of chip  101  and over all the surfaces  109  of chip  101 . According to an example, layer  401  is formed at the level of hot spots of chip  101 . 
     As previously mentioned, layer  401  is made of a thermally-conductive material. According to an example, this material is selected from the group comprising: the material bearing reference SE4450 commercialized by Dow Corning, and the material bearing reference TC3040 commercialized by Dow Corning. 
     Electronic device  400  further differs from device  300  in that cover  119  comprises a transverse portion  403  different from the transverse portion  121  described in relation with  FIG.  1   . Transverse portion  403  comprises portions of different thicknesses, in some embodiments, transverse portion  403  comprises:
         a portion  405  of thickness P1 extending above chip  101 ; and   at least a portion  407  of a thickness P2 extending around, that is, at the periphery of, chip  101 .       

     According to an embodiment, thickness P1 is smaller than thickness P2. In practice, thickness P2 is large enough for portion  407  to extend at least all the way to the level of surface  103  of chip  101 . Thereby, lateral surfaces  109 , and more precisely the portions of layer  401  covering them, are in contact with portion  407  of the transverse portion  403  of cover  119 . Thus, according to an embodiment, an upper surface of layer  401  is in direct contact with surface  105  and surfaces  109 , and a lower surface, opposite to the upper surface, is in direct contact with the transverse portion  403  of cover  119 . 
     An advantage of this embodiment is that layer  401  and portion  407  of the transverse portion  403  of cover  119  enable to remove the heat emitted from the lateral surfaces  109  of chip  101 . 
     Device  400  further has the same advantages as those of the device  300  described in relation with  FIG.  3   . 
       FIG.  5    is a side cross-section view illustrating an embodiment of an electronic device  500 . 
     Further, electronic device  500  has elements common with the electronic device  400  described in relation with  FIG.  4   . These common elements are not described again in detail herein, and only the differences between devices  400  and  500  are highlighted. 
     Electronic device  500  differs from device  400  in that device  500  comprises one or a plurality of, in some embodiments, a plurality of, thermally-conductive bars  501  arranged between portion  407  of the transverse portion  403  of cover  119  and surface  113  of substrate  111 . In some embodiments, according to an embodiment, bar(s)  501  are in direct contact with portion  407  of the transverse portion  121  of cover  119  and with surface  113  of substrate  111 . 
     According to an embodiment, thermally-conductive bar(s)  501  extend over all or part of surface  113 . Bar(s)  501  have a width in the range from 50 μm to 100 μm, for example, in the order of 80 μm. 
     According to an embodiment, thermally-conductive bar(s)  501  are metal bars, for example, bars made of copper or of a metal alloy comprising copper. 
     An advantage of this embodiment is that bar(s)  501  enable to remove part of the heat released by chip  101  in substrate  111 . 
     Device  500  further has the same advantages as those of the device  400  described in relation with  FIG.  4   . 
       FIG.  6    is a side cross-section view illustrating an embodiment of an electronic device  600 . 
     Further, electronic device  600  has elements common with the electronic device  100  described in relation with  FIG.  1   . These common elements are not described again in detail herein, and only the differences between devices  100  and  600  are highlighted. 
     Electronic device  600  differs from device  100  in that device  600  comprises layer  401  made of a thermally-conductive material described in relation with  FIG.  4   . 
     Electronic device  600  differs from device  100  in that device  600  further comprises one or a plurality of, in some embodiments a plurality of, extensions  601  at the level of the lateral portions  123  of cover  119 . In some embodiments, extensions  601  extend from the lateral portions  123  of cover  119  to the lateral surfaces  109  of chip  101 , and more precisely to the portions of layer  401  covering them. According to an example, extensions  601  have a thickness in the order of the thickness of chip  101 . Extensions  601  may have a thickness greater than that of the chip. They may also have a smaller thickness but to the detriment of the heat dissipation effect. 
     According to an embodiment, extensions  601  are made of the same material as cover  119 . Further, as described in relation with  FIG.  1   , cover  119  may be made of a single part comprising portions  121  and  123 , and extensions  601 , but according to a variant, portions  121  and  123  and extensions  601  may be parts attached to one another to form cover  119 . These parts may be attached together by gluing, that is, for example, via one or a plurality of glue layers  603 . It will be within the abilities of those skilled in the art to imagine a plurality of combinations of parts enabling to obtain the cover  119  of device  600 . 
     An advantage of this embodiment is that the extensions  601  of cover  119  enable to remove the heat emitted from the lateral surfaces  109  of chip  101 . 
     Device  600  further has the same advantages as those of the devices  100  described in relation with  FIG.  1   . 
       FIG.  7    is a side cross-section view illustrating an embodiment of an electronic device  700 . 
     Further, electronic device  700  has elements common with the electronic device  600  described in relation with  FIG.  6   . These common elements are not described again in detail herein, and only the differences between devices  600  and  700  are highlighted. 
     Electronic device  700  differs from device  600  in that device  700  comprises one or a plurality of, in some embodiments a plurality of, thermally-conductive bars  501  as described in relation with  FIG.  5   . In device  700 , bar(s)  501  are arranged between the extension(s)  601  of cover  119  and the surface  113  of substrate  111 . In some embodiments, according to an embodiment, bar(s)  501  are in direct contact with the extension(s)  601  of cover  119  and with the surface  113  of substrate  111 . 
     Device  700  has the same advantages as those of the devices  500  and  600  described in relation with  FIGS.  5  and  6   . 
       FIG.  8    is a side cross-section view illustrating an embodiment of an electronic device  800 . 
     Further, electronic device  800  has elements common with the electronic device  600  described in relation with  FIG.  6   . These common elements are not described in detail again herein, and only the differences between devices  600  and  800  are highlighted. 
     Electronic device  800  differs from device  600  in that the space, or cavity,  802  formed between extensions  601  and the transverse portion  121  of cover  119  is filled with a thermally-conductive material  801 . In some embodiments, material  801  is a material having a thermal conductivity greater than 2 W/mK, or even 3 W/mK. Material  801  is for example selected from the group comprising: the material known under trade name SE4450 of Dow Corning, and the material known under trade name TC3040 of Dow Corning. The use of materials known under trade name TIM is also possible. 
     According to an example of embodiment, material  801  is injected into space  802  via a cavity  803  formed through the transverse portion  121  of cover  119 . 
     An advantage of this embodiment is that the presence of material  801  enables to improve the heat removal in cover  119 . 
     Device  800  further has the same advantages as those of the device  600  described in relation with  FIG.  6   . 
       FIG.  9    is a side cross-section view illustrating an embodiment of an electronic device  900 . 
     Further, electronic device  900  has elements common with the electronic device  800  described in relation with  FIG.  8   . These common elements are not described in detail again herein, and only the differences between devices  800  and  900  are highlighted. 
     Device  900  differs from device  800  in that device  900  comprises one or a plurality of, in some embodiments a plurality of, thermally-conductive bars  501  as described in relation with  FIG.  5   . In device  900 , bar(s)  501  are arranged between the extension(s)  601  of cover  119  and the surface  113  of substrate  111 . In some embodiments, according to an embodiment, bar(s)  501  are in direct contact with the extension(s)  601  of cover  119  and with the surface  113  of substrate  111 . 
     Device  900  has the same advantages as those of the devices  500  and  800  described in relation with  FIGS.  5  and  8   . 
       FIG.  10    is a side cross-section view illustrating an embodiment of an electronic device  1000  according to another aspect. 
     Electronic device  1000  has elements common with the electronic device  600  described in relation with  FIG.  6   . These common elements are not described again herein, and only the differences between devices  1000  and  600  are highlighted. 
     Device  1000  differs from device  600  in that device  100  comprises no thermally-conductive pillar  127  between the surface  105  of chip  101  and the transverse portion of metal cover  119 . 
     Instead, device  1000  comprises a layer  1001  made of a thermally-conductive material. Layer  1001  extends from the surface  105  of chip  101  to the transverse portion  121  of cover  119 . In some embodiments, according to an embodiment, a lower surface of layer  1001  is in direct contact with surface  105 , and an upper surface, opposite to the lower surface, is in direct contact with the transverse portion  121  of cover  119 . According to an embodiment, layer  1001  may extend over the entire surface  105  or over one or a plurality of portions of the surface  105  of chip  101 , as described for layer  301  in relation with  FIG.  3   . According to an example, layer  1001  is formed at the level of one or a plurality of hot spots of chip  101 . Further, like the layer  401  described in relation with  FIG.  4   , layer  1001  may further cover all or part of the lateral surfaces  109  of chip  101 . According to an example, layer  1001  is made of a material selected from the group comprising: the material bearing reference SE4450 commercialized by Dow Corning, and the material bearing reference TC3040 commercialized by Dow Corning. 
     Device  1000  further differs from device  600  in that the extension(s)  601  of cover  119  of device  1000  comprise at least one groove  1003 , or trench  1003 , surrounding chip  101 . In some embodiments, groove  10003  is formed from an upper surface of extension  601 , for example, a surface of the extension directed towards the transverse portion of cover  119 . Groove  1003  is for example placed at a distance from chip  101  in the range from 500 μm to 2 mm, for example, in the order of 1 mm. According to an example, the groove has a depth in the range from 30 μm to 150 μm, for example, in the order of 70 μm, and a width in the range from 500 μm to 1.5 μm, for example in the order of 1 mm. 
     According to an alternative embodiment, extensions  601  may comprise more than one groove  1003 , for example grooves  1003  parallel and/or concentric to one another. 
     An advantage of this embodiment is that said groove enables to slow down, or even to prevent, the migration of layer  1001  during the chip operation. 
       FIG.  11    is a side cross-section view illustrating an embodiment of an electronic device  1100  according to another aspect. 
     Further, electronic device  1100  has elements common with the electronic device  1000  described in relation with  FIG.  10   . These common elements are not described in detail again herein, and only the differences between devices  1100  and  1000  are highlighted. 
     Device  1100  differs from device  1000  in that device  1100  does not comprise layer  1001  but the layer  401  described in relation with  FIG.  4    and the pillars  127  described in relation with  FIG.  1   . 
     Device  1100  has the same advantages as those of the devices  600  and  1000  described in relation with  FIGS.  6  and  10   . 
       FIG.  12    comprises three cross-section views (A), (B), and (C) each illustrating a step of an implementation mode of a method of manufacturing the device  1000  described in relation with  FIG.  10   . An implementation mode of a method of manufacturing the device  1100  described in relation with  FIG.  11    will be deduced from the combination of the manufacturing method described in relation with  FIG.  2    and of the manufacturing method described hereafter. 
     At the step of view (A), a chip  1201  has been mounted on a substrate  1203 . For this purpose, connectors  1204  have been formed on a surface  1205  corresponding to the active area of chip  1201 . Connectors  1204  have been embedded in a filling material  1209  at the upper surface  1207  of substrate  1203 . 
     At the step of view (A), a first portion of a thermally-conductive cover of the type of the cover  119  described in relation with  FIG.  10    is arranged around chip  1201 . The portion of the cover comprises lateral portions  1211  of the cover, of the type of the portions  123  described in relation with  FIG.  1   , and extensions  1213 , of the type of the extensions  601  described in relation with  FIG.  6   . Like extensions  601 , extensions  1213  comprise one or a plurality of grooves  1215  formed from an upper surface of extensions  1213 . According to an example, grooves  1215  are formed in extensions  1215  at the step of view (A) or are preformed. According to an example, this portion of the cover is made of a single block. According to an embodiment, this portion of the cover is made of a plurality of portions assembled together, for example, by gluing. 
     The portion of the cover is attached to the upper portion  1207  of substrate  1203 , for example, via a glue layer  1217 . 
     At the step of view (B), a layer  1219  made of a thermally-conductive material is formed on all or part of a surface  1221  of chip  1201 , opposite to surface  1205 . Layer  1219  is deposited all the way to the groove  1215  of extensions  1213 . Layer  1219  may for example cover all or part of the lateral surfaces  1223  of chip  1201 . Layer  1219  is for example made of a material selected from the group comprising: the material bearing reference SE4450 commercialized by Dow Corning, and the material bearing reference TC3040 commercialized by Dow Corning. 
     At the step of view (C), the last portion of the cover is formed on chip  1201 . According to the example illustrated in view (C), the last portion of the cover is a lateral portion  1225  of the type of the lateral portion  121  described in relation with  FIG.  1   . Portion  1225  is for example a plate of material bonded on layer  1219  via a glue layer  1227  at the previously-attached lateral portions  1211  of the cover. According to an example, layer  1219  and glue layer  1227  have a substantially equal thickness. 
     Various embodiments and variants have been described. Those skilled in the art will understand that certain features of these various embodiments and variants may be combined, and other variants will occur to those skilled in the art. 
     Finally, the practical implementation of the described embodiments and variations is within the abilities of those skilled in the art based on the functional indications given hereabove. 
     Electronic device ( 100 ;  300 ;  400 ;  500 ;  600 ;  700 ;  800 ;  900 ) may be summarized as including an electronic chip ( 101 ) including an active area ( 107 ) on a first surface ( 103 ) and a second surface ( 105 ) opposite to the first surface ( 103 ); a substrate ( 111 ), the first surface ( 103 ) of said chip ( 101 ) being mounted on a third surface ( 113 ) of said substrate ( 111 ); and a thermally-conductive cover ( 119 ) including a transverse portion ( 121 ;  403 ) extending at least above the second surface ( 105 ) of said electronic chip ( 101 ), wherein the electronic device ( 100 ;  300 ;  400 ;  500 ;  600 ;  700 ;  800 ;  900 ) further includes at least one thermally-conductive pillar ( 127 ) coupling the second surface ( 105 ) of the electronic chip ( 101 ) to said transverse portion ( 121 ;  403 ) of said thermally-conductive cover ( 119 ). 
     Said at least one thermally-conductive pillar ( 127 ) may be a metal pillar. 
     Said at least one thermally-conductive pillar ( 127 ) may include a first copper portion. 
     Said at least one thermally-conductive pillar ( 127 ) may include at least a second portion made of a metal solder alloy. 
     Said at least one thermally-conductive pillar ( 127 ) may be surrounded by a first layer ( 301 ;  401 ) made of a first thermally-conductive material extending from said second surface ( 105 ) of the electronic chip ( 101 ) to said transverse portion ( 121 ;  403 ) of said thermally-conductive cover ( 119 ). 
     Said first layer ( 401 ) may further cover at least a fourth lateral surface ( 109 ) of said electronic chip ( 101 ). 
     Said transverse portion ( 403 ) of said cover ( 119 ) may have a first portion ( 405 ) having a first thickness (P1) extending above the second surface ( 105 ) of said electronic chip ( 101 ), and at least a second portion ( 407 ) having a second thickness (P2) greater than the first thickness (P1) extending at the periphery of said electronic chip ( 101 ). 
     The second portion ( 407 ) may extend all the way to the level of the first surface ( 103 ) of said electronic chip ( 101 ). 
     Said second portion ( 407 ) may be coupled to said third surface ( 113 ) of said substrate ( 111 ) by at least one first thermally-conductive bar ( 501 ). 
     The cover ( 119 ) may further include at least one lateral portion ( 123 ) surrounding the electronic chip ( 101 ), and at least one extension ( 601 ) extending from the lateral portion ( 123 ) of the cover ( 119 ) to said fourth lateral surface ( 109 ) of said electronic chip ( 101 ). 
     The space ( 802 ) between said transverse portion ( 121 ) of said cover ( 119 ) and said at least one extension ( 601 ) may be filled with a second thermally-conductive material ( 801 ). 
     Said extension ( 801 ) may be coupled to said third surface ( 113 ) of said substrate ( 111 ) by at least a second thermally-conductive bar ( 501 ). 
     The thermally-conductive cover ( 119 ) may be a metal cover. 
     Said at least one extension ( 601 ) may include on its upper surface at least one groove ( 1003 ). 
     Method of manufacturing an electronic device may be summarized as including an electronic chip ( 201 ) having an active area ( 203 ) on a first surface ( 205 ), and a second surface ( 207 ) opposite to the first surface ( 205 ), the method including the successive steps of forming at least one thermally-conductive pillar ( 215 ) on said second surface ( 207 ) of said electronic chip ( 201 ); mounting said electronic chip ( 201 ) on a third surface ( 225 ) of a substrate ( 221 ), the first surface ( 205 ) of the chip ( 201 ) being on the side of the third surface ( 225 ) of said substrate ( 221 ); and arranging a thermally-conductive cover ( 227 ) including a transverse portion extending above the second surface ( 207 ) of said electronic chip ( 201 ), said transverse portion being in contact with said at least one thermally-conductive pillar ( 127 ). 
     Said at least one thermally-conductive pillar ( 215 ) may include a first copper portion and at least a second portion made of a metal solder alloy. 
     The various embodiments described above can be combined to provide further embodiments. Aspects of the embodiments can be modified, if necessary to employ concepts of the various embodiments to provide yet further embodiments. 
     These and other changes can be made to the embodiments in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the disclosure.