Abstract:
An apparatus for heatsink attachment. The apparatus includes a substrate, a semiconductor chip on top of and physically attached to the substrate, and a lid on top of the substrate. The lid includes a first thermally conductive material. The apparatus further includes a heatsink on top of the lid. The heatsink includes a second thermally conductive material. The semiconductor chip and the substrate share a common interface surface that defines a reference direction perpendicular to the common interface surface and pointing from the substrate towards the semiconductor chip. The lid is disposed between the substrate and the heatsink. The lid includes a first protruding member. The first protruding member of the lid is farther away from the substrate than a portion of the heatsink in the reference direction.

Description:
FIELD OF THE INVENTION 
   The present invention relates generally to semiconductor chips and more particularly to heatplates for heatsink attachment for semiconductor chips. 
   BACKGROUND OF THE INVENTION 
   In the prior art, after a semiconductor chip is attached to a printed circuit board, a heatsink is conventionally placed on top of the chip via a heatplate so as to absorb the heat generated from the chip during the chip operation. To hold the heatsink in place, clips are conventionally used to hold the heatsink to the printed circuit board. In other words, areas of the printed circuit board must be used for the clips to hold the heatsink in place. Therefore, there is a need for an apparatus (and a method for forming the same) in which the heatsink is held in place without utilizing areas of the printed circuit board. 
   SUMMARY OF THE INVENTION 
   The present invention provides a structure, comprising (a) a substrate; (b) a semiconductor chip on top of and physically attached to the substrate; (c) a lid on top of the substrate, wherein the lid comprises a first thermally conductive material; and (d) a heatsink on top of the lid, wherein the heatsink comprises a second thermally conductive material, wherein the semiconductor chip and the substrate share a common interface surface that defines a reference direction perpendicular to the common interface surface and pointing from the substrate towards the semiconductor chip, wherein the lid is disposed between the substrate and the heatsink, wherein the lid comprises a first protruding member, and wherein the first protruding member of the lid is farther away from the substrate than a portion of the heatsink in the reference direction. 
   The present invention also provides a structure formation method, comprising providing a structure which includes (a) a substrate;(b) a semiconductor chip on top of and physically attached to the substrate, wherein the semiconductor chip and the substrate share a common interface surface that defines a reference direction perpendicular to the common interface surface and pointing from the substrate towards the semiconductor chip; and (c) a lid on top of the substrate, wherein the lid comprises a first thermally conductive material; and placing a heatsink on top of the substrate, wherein the heatsink comprises a second thermally conductive material, wherein the lid is disposed between the substrate and the heatsink, wherein the lid comprises a first protruding member, and wherein the first protruding member of the lid is farther away from the substrate than a portion of the heatsink in the reference direction. 
   The present invention provides an apparatus (and a method for operating the same) in which the heatsink is held in place without utilizing areas of the printed circuit board. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1A  shows a cross-section view of a structure, in accordance with embodiments of the present invention. 
     FIG.  1 Ai shows a perspective view of the structure of  FIG. 1A  along a line  1 Ai- 1 Ai of  FIG. 1A . 
     FIGS.  1 B- 1 Biv illustrate a process for forming a lid of  FIG. 1A , in accordance with embodiments of the present invention. 
       FIG. 1C  shows a top-down view of the lid of FIG.  1 Biv. 
       FIG. 2A  shows a cross-section view of a structure, in accordance with embodiments of the present invention. 
       FIG. 2B  shows a top-down view of a lid of  FIG. 2A . 
       FIG. 3A  shows a cross-section view of a structure, in accordance with embodiments of the present invention. 
       FIGS. 3B-4  illustrates a process for forming a lid of  FIG. 3A , in accordance with embodiments of the present invention. 
       FIG. 5A  shows a cross-section view of a structure, in accordance with embodiments of the present invention. 
       FIG. 5B  shows a perspective view of the structure of  FIG. 5A  along a line  5 B- 5 B of  FIG. 5A . 
       FIG. 6  shows a cross-section view of a structure, in accordance with embodiments of the present invention. 
       FIG. 7  shows a cross-section view of a structure, in accordance with embodiments of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1A  shows a cross-section view of a structure  100 , in accordance with embodiments of the present invention. More specifically, in one embodiment, the structure  100  comprises an organic substrate  120  and a chip  140  which is attached to the organic substrate  120 . Illustratively, the chip  140  comprises solder balls  112  which electrically connect devices (not shown) of the chip  140  to substrate pads (not shown) of the organic substrate  120 . In one embodiment, the organic substrate  120  comprises substrate balls  110  which are electrically connected to the solder balls  112 . Illustratively, the structure  100  further comprises an underfill layer  114  which physically holds the chip  140  tightly to the organic substrate  120 . 
   In one embodiment, the structure  100  further comprises a stiffener  130 , a lid (also called heatplate)  180 , and a heatsink  190 . Illustratively, the stiffener  130  and the lid  180  comprise nickel plated copper. In one embodiment, the heatsink  190  comprises aluminum. Illustratively, the stiffener  130  is attached to the organic substrate  120  by an adhesive layer  122 . In one embodiment, the lid  180  is attached to the bottom surface  142  of the chip  140  by a thermal adhesive layer  150 . Illustratively, the thermal adhesive layer  150  comprises a thermally conductive material. In one embodiment, the lid  180  is also attached to the stiffener  130  by an adhesive layer  160 . Illustratively, the heatsink  190  is pressed down by holders  185   a  and  185   b  of the lid  180  against a top surface  182  of the lid  180  via a thermal grease layer  170 . In one embodiment, the thermal grease layer  170  comprises a thermally conductive material. Illustratively, the structure  100  of  FIG. 1A  can be electrically coupled to a circuit board (not shown) using the substrate balls  110 . 
   In one embodiment, with reference to  FIG. 1A , the structure  100  can be formed as follows. Illustratively, after being fabricated, the chip  140  is flipped up side down and then is attached to the organic substrate  120  using the solder balls  112  of the chip  140  and the underfill layer  114 . Next, in one embodiment, the stiffener  130  is physically attached to the organic substrate  120  using the adhesive layer  122 . Next, in one embodiment, the lid  180  is (i) physically attached to the stiffener  130  using the adhesive layer  160  and (ii) thermally and physically coupled to the bottom  142  of the chip  140  via the thermal adhesive layer  150 . Then, in one embodiment, the thermal grease layer  170  is applied to the top surface  182  of the lid  180 . Next, in one embodiment, the heatsink  190  is slid into place in a direction perpendicular to the page. In one embodiment, the heatsink  190  is held in place by the holders  185   a  and  185   b  that press the heatsink  190  down against the top surface  182  of the lid  180 . 
   FIG.  1 Ai shows a perspective view of the structure  100  along a line  1 Ai- 1 Ai of  FIG. 1A . 
   FIGS.  1 B- 1 Biv illustrate a process for forming the lid  180  of  FIG. 1A , in accordance with embodiments of the present invention. More specifically, in one embodiment, the process for forming the lid  180  starts with the lid  180  of  FIG. 1B  (top-down view). FIG.  1 Bi shows a cross-section view of the lid  180  of  FIG. 1B  along a line  1 Bi- 1 Bi. 
   Next, in one embodiment, with reference to FIGS.  1 B and  1 Bi, the lid  180  is bent in directions  182   a ′ and  182   b ′ along lines  182   a  and  182   b , respectively, resulting in the lid  180  of FIG.  1 Bii. Next, in one embodiment, the lid  180  of FIG.  1 Bii is bent in directions  184   a ′ and  184   b ′ along lines  184   a  and  184   b , respectively, resulting in the lid  180  of FIG.  1 Biii. Then, in one embodiment, the lid  180  of FIG.  3 Biii is bent in directions  186   a ′ and  186   b ′ along lines  186   a  and  186   b , respectively, resulting in the lid  180  of FIG.  1 Biv. 
     FIG. 1C  shows a top-down view of the lid  180  of FIG.  1 Biv. 
     FIG. 2A  shows a cross-section view of a structure  200 , in accordance with embodiments of the present invention. More specifically, in one embodiment, the structure  200  is similar to the structure  100  of  FIG. 1A  except that the structure  200  does not have the stiffener  130  and that a lid  280  of the structure  200  is different from the lid  180  of the structure  100  ( FIG. 1A ). More specifically, in one embodiment, the lid  280  is similar to the lid  180  of  FIG. 1A  except that the lid  280  has an opening  282  (not shown in  FIG. 2A  but shown in  FIG. 2B ) that allows for closer thermal contact of the heatsink  190  to the bottom surface  142  of the chip  140  via the thermal grease layer  170  ( FIG. 2A ). Illustratively, the lid  280  is attached to the organic substrate  120  by an adhesive layer  260 , whereas the heatsink  190  is pressed down against the bottom surface  142  of the chip  140  by the holders  185   a  and  185   b  of the lid  280  via the thermal grease layer  170 . 
   In one embodiment, with reference to  FIG. 2A , the structure  200  can be formed as follows. Illustratively, after being fabricated, the chip  140  is flipped up side down and then is attached to the organic substrate  120  using the solder balls  112  of the chip  140  and the underfill layer  114 . Next, in one embodiment, the lid  280  is physically attached to the organic substrate  120  using the adhesive layer  260  such that the chip  140  fits in the opening  282  ( FIG. 2B ). Then, in one embodiment, the thermal grease layer  170  is applied to the bottom surface  142  of the chip  140 . Next, in one embodiment, the heatsink  190  is slid into place in a direction perpendicular to the page. In one embodiment, the heatsink  190  is held in place by the holders  185   a  and  185   b  that press the heatsink  190  down against the bottom surface  142  of the chip  140  via the thermal grease layer  170 . 
     FIG. 2B  shows a top-down view of the lid  280  of  FIG. 2A . As can be seen in  FIG. 2B , the lid  280  is similar to the lid  180  of  FIG. 1C  except that the lid  280  has an opening  282 . In one embodiment, the formation of the lid  280  is similar to the formation of the lid  180  of FIG.  1 Biv. 
     FIG. 3A  shows a cross-section view of a structure  300 , in accordance with embodiments of the present invention. More specifically, in one embodiment, the structure  300  is similar to the structure  100  of  FIG. 1A  except that the structure  300  does not have the stiffener  130  and that a lid  380  of the structure  300  is different from the lid  180  of the structure  100 . More specifically, the lid  380  is similar to the lid  180  of  FIG. 1A  except that a bottom member  381  of the lid  380  concaves up to create space for the chip  140 . In one embodiment, the lid  380  is attached to the organic substrate  120  by an adhesive layer  360 . 
   In one embodiment, with reference to  FIG. 3A , the structure  300  can be formed as follows. Illustratively, after being fabricated, the chip  140  is flipped up side down and then is attached to the organic substrate  120  using the solder balls  112  of the chip  140  and the underfill layer  114 . Next, in one embodiment, the lid  380  is (i) physically attached to the organic substrate  120  using the adhesive layer  360  and (ii) thermally and physically coupled to the bottom  142  of the chip  140  via the thermal adhesive layer  150 . Then, in one embodiment, the thermal grease layer  170  is applied to the top surface  382  of the lid  380 . Next, in one embodiment, the heatsink  190  is slid into place in a direction perpendicular to the page. In one embodiment, the heatsink  190  is held in place by the holders  185   a  and  185   b  that press the heatsink  190  down against the top surface  382  of the lid  380  via the thermal grease  170 . 
     FIGS. 3B-4  illustrates a process for forming the lid  380  of  FIG. 3A , in accordance with embodiments of the present invention. More specifically, in one embodiment, the process for forming the lid  380  starts with the lid  380  of  FIG. 3B  (top-down view). FIG.  3 Bi shows a cross-section view of the lid  380  of  FIG. 3B  along a line  3 Bi- 3 Bi. 
   Next, in one embodiment, with reference to FIG.  3 Bi, the lid  380  is bent along lines  382   a  and  382   b  and then is bent along lines  384   a  and  384   b  resulting in the lid  380  of FIG.  3 Bii. Next, in one embodiment, with reference to FIG.  3 Bii, the lid  380  (i) is bent along lines  386   a  and  386   b , then (ii) is bent along lines  388   a  and  388   b , and then (iii) is bent along lines  390   a  and  390   b  resulting in the lid  380  of  FIG. 4 . 
   In summary, with reference to  FIGS. 1A ,  2 A, and  3 A, the holders  185   a  and  185   b  help hold the heatsink  190  in place by pressing the heatsink  190  down against the top surface  182  of the lid  180  ( FIG. 1A ), or the bottom surface  142  of the chip  140  ( FIG. 2A ), or the top surface  382  of the lid  380  ( FIG. 3A ). 
     FIG. 5A  shows a cross-section view of a structure  500 , in accordance with embodiments of the present invention. More specifically, in one embodiment, the structure  500  is similar to the structure  100  of  FIG. 1A  except that the structure  500  comprises springs  510   a  and  510   b  and that a lid  580  of the structure  500  is different from the lid  180  of  FIG. 1A . Illustratively, the springs  510   a  and  510   b  are elastic structures. An elastic structure is a structure that tends to change its shape when being applied a force and tends to change back to its original shape when the force is removed. In one embodiment, the springs  510   a  and  510   b  can have any size and shape provided that the springs  510   a  and  510   b  maintain pressure against overhangs  584   a  and  584   b  of the lid  580  and horizontal members  192   a  and  192   b  of the heatsink  190 , respectively. Illustratively, the lid  580  is similar to the lid  180  ( FIG. 1A ) except that the lid  50  does not have holders (like the holders  185   a  and  185   b  of  FIG. 1A ). Instead, the overhangs  584   a  and  584   b  keep the springs  510   a  and  510   b  pressing the horizontal members  192   a  and  192   b  down, respectively, resulting in the heatsink  190  being pressed down against the top surface  582  of the lid  580  via the thermal grease layer  170 . 
   In one embodiment, with reference to  FIG. 5A , the structure  500  can be formed as follows. Illustratively, after being fabricated, the chip  140  is flipped up side down and then is attached to the organic substrate  120  using the solder balls  112  of the chip  140  and the underfill layer  114 . Next, in one embodiment, the stiffener  130  is physically attached to the organic substrate  120  using the adhesive layer  122 . Next, in one embodiment, the lid  580  is (i) physically attached to the stiffener  130  using the adhesive layer  160  and (ii) thermally and physically coupled to the bottom  142  of the chip  140  via the thermal adhesive layer  150 . Then, in one embodiment, the thermal grease layer  170  is applied to the top surface  582  of the lid  580 . Next, in one embodiment, the heatsink  190  is slid into place in a direction perpendicular to the page. 
   Next, in one embodiment, the spring  510   a  is slid into place between the overhang  584   a  and the horizontal member  192   a  of the heatsink  190 . Similarly, the spring  510   b  is slid into place between the overhang  584   b  and the horizontal member  192   b  of the heatsink  190 . As a result, the heatsink  190  is held in place by the springs  510   a  and  510   b  that press the heatsink  190  down against the top surface  582  of the lid  580  via the thermal grease layer  170 . 
     FIG. 5B  shows a perspective view of the structure  500  along a line  5 B- 5 B of  FIG. 5A . It should be noted that a spring  510   b ′ of  FIG. 5B  is an alternative embodiment of the spring  510   b  of  FIG. 5A . 
     FIG. 6  shows a cross-section view of a structure  600 , in accordance with embodiments of the present invention. More specifically, in one embodiment, the structure  600  is similar to the structure  200  of  FIG. 2A  except that the structure  600  comprises the springs  510   a  and  510   b  and that a lid  680  of the structure  600  is different from the lid  280  of  FIG. 2A . Illustratively, the lid  680  is similar to the lid  280  ( FIG. 2A ) except that the lid  680  does not have holders (like the holders  185   a  and  185   b  of  FIG. 2A ). Instead, overhangs  684   a  and  684   b  keep the springs  510   a  and  510   b  pressing the horizontal members  192   a  and  192   b  down, respectively, resulting in the heatsink  190  being pressed down against the bottom surface  142  of the chip  140  via the thermal grease layer  170 . 
     FIG. 7  shows a cross-section view of a structure  700 , in accordance with embodiments of the present invention. More specifically, in one embodiment, the structure  700  is similar to the structure  300  of  FIG. 3A  except that the structure  700  comprises the springs  510   a  and  510   b  and that a lid  780  of the structure  700  is different from the lid  380  of  FIG. 3A . Illustratively, the lid  780  is similar to the lid  380  ( FIG. 3A ) except that the lid  780  does not have holders (like the holders  185   a  and  185   b  of  FIG. 3A ). Instead, overhangs  784   a  and  784   b  keep the springs  510   a  and  510   b  pressing the horizontal members  192   a  and  192   b  down, respectively, resulting in the heatsink  190  being pressed down against the top surface  782  of the lid  780  via the thermal grease layer  170 . 
   In summary, with reference to  FIGS. 5A ,  6 , and  7 , the springs  510   a  and  510   b  help hold the heatsink  190  in place by pressing the heatsink  190  down against the top surface  582  of the lid  580  ( FIG. 5A ), or the bottom surface  142  of the chip  140  ( FIG. 6 ), or the top surface  782  of the lid  780  ( FIG. 7 ). 
   With reference to  FIGS. 1A and 5A , in one embodiment, the lids  180  and  580  comprise protruding members. More specifically, the lid  180  comprises protruding members  189   a  and  189   b  and the lid  580  comprises protruding members  589   a  and  589   b . In one embodiment, the protruding members  189   a  and  189   b  comprise overhangs  187   a  and  187   b , respectively, and the protruding members  589   a  and  589   b  comprise the overhangs  584   a  and  584   b , respectively. Illustratively, the overhangs  187   a  and  187   b  comprise the holders  185   a  and  185   b , respectively. It should be noted that the protruding members  189   a  and  189   b  apply forces using the holders  185   a  and  185   b  to the heatsink  190  resulting in the heatsink  190  being pressed towards the substrate  120 . It should also be noted that the protruding members  589   a  and  589   b  apply forces via the springs  510   a  and  510   b  to the heatsink  190  resulting in the heatsink  190  being pressed towards the substrate  120 . 
   While particular embodiments of the present invention have been described herein for purposes of illustration, many modifications and changes will become apparent to those skilled in the art. Accordingly, the appended claims are intended to encompass all such modifications and changes as fall within the true spirit and scope of this invention.