CA1201817A - Self-positioning heat spreader - Google Patents
Self-positioning heat spreaderInfo
- Publication number
- CA1201817A CA1201817A CA000423966A CA423966A CA1201817A CA 1201817 A CA1201817 A CA 1201817A CA 000423966 A CA000423966 A CA 000423966A CA 423966 A CA423966 A CA 423966A CA 1201817 A CA1201817 A CA 1201817A
- Authority
- CA
- Canada
- Prior art keywords
- heat spreader
- lead frame
- heat
- notches
- capacitance
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
- H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having at least one potential-jump barrier or surface barrier, e.g. PN junction, depletion layer or carrier concentration layer
- H01L21/34—Manufacture or treatment of semiconductor devices or of parts thereof the devices having at least one potential-jump barrier or surface barrier, e.g. PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies not provided for in groups H01L21/0405, H01L21/0445, H01L21/06, H01L21/16 and H01L21/18 with or without impurities, e.g. doping materials
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L23/00—Details of semiconductor or other solid state devices
- H01L23/34—Arrangements for cooling, heating, ventilating or temperature compensation ; Temperature sensing arrangements
- H01L23/42—Fillings or auxiliary members in containers or encapsulations selected or arranged to facilitate heating or cooling
- H01L23/433—Auxiliary members in containers characterised by their shape, e.g. pistons
- H01L23/4334—Auxiliary members in encapsulations
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L23/00—Details of semiconductor or other solid state devices
- H01L23/34—Arrangements for cooling, heating, ventilating or temperature compensation ; Temperature sensing arrangements
- H01L23/36—Selection of materials, or shaping, to facilitate cooling or heating, e.g. heatsinks
- H01L23/367—Cooling facilitated by shape of device
- H01L23/3672—Foil-like cooling fins or heat sinks
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
- H01L2924/0001—Technical content checked by a classifier
- H01L2924/0002—Not covered by any one of groups H01L24/00, H01L24/00 and H01L2224/00
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
- H01L2924/30—Technical effects
- H01L2924/301—Electrical effects
- H01L2924/3011—Impedance
Abstract
A SELF-POSITIONING HEAT SPREADER
ABSTRACT
A heat spreader which is self-positioning into a mold cavity prior to encapsulation in plastic is provided. To minimize capacitance between the spreader and a metal lead frame having a semiconductor die mounted thereon, the heat spreader has a frame with notches in the opposite ends which define bifurcated limbs. Lateral standoffs extend from each of the sides thereof and feet extend from the bottom surface thereof. A central portion extends a predetermined distance from the top surface thereof for intimate positioning with the lead frame. The standoffs, limbs and feet are sized to firmly position the heat spreader upon insertion into the mold cavity. To maintain substantially constant capacitance between the spreader and the lead frame from part to part, each bifurcated limb has an inner edge which complements or conforms to the portion of the lead frame which will overlay the limb in the encapsulated plastic.
ABSTRACT
A heat spreader which is self-positioning into a mold cavity prior to encapsulation in plastic is provided. To minimize capacitance between the spreader and a metal lead frame having a semiconductor die mounted thereon, the heat spreader has a frame with notches in the opposite ends which define bifurcated limbs. Lateral standoffs extend from each of the sides thereof and feet extend from the bottom surface thereof. A central portion extends a predetermined distance from the top surface thereof for intimate positioning with the lead frame. The standoffs, limbs and feet are sized to firmly position the heat spreader upon insertion into the mold cavity. To maintain substantially constant capacitance between the spreader and the lead frame from part to part, each bifurcated limb has an inner edge which complements or conforms to the portion of the lead frame which will overlay the limb in the encapsulated plastic.
Description
iZC~ 317 A SELF-POSITIONING HE~T SPREADER
Technical Field This invention relates generally to heat spreaders and, more particularly, to a heat spreader adapted for insertion into a mold cavity prior to plastic encapsulation with a semiconductor device.
Background Art Metal heat spreaders o various shapes ancl designs have been commonly used to spread or conduct heat away from a ~netal lead fra~e which is electrically connected to an integrated circuit die. One application of such heat spreaders has been to physically attach the heat spreader to the metal lead frame wherein both the heat spreader and lead frame are encapsulated ln plastic. In such an application, a heat spreader is used to spread heat in a relatively uniform manner throughout plastic and is not used for contact to an external heat sink. When heat spreaders have an exposed surface, poor adhesion between plastic and metal may allow moisture to enter into the package. Exposed metal surfaces may also result in a fragile structure. A disadvantage with heat spreaders that are directly connected to a metal lead frame is that achieving the physical connection requires a separate manufacturing step. A further disadvantage with such heat spreaders is the fact that capacitance exists between the heat spreader which acts as one long conducting surEace or plate and the lead frame which acts as another conducting surface or plate. Since the lead frame has different voltages at various points during operation and the distance separating the two conducting surfaces is small, a large capacitance is created between the two surfaces.
"
~24~
For some applications the capacitance does not present a significant problem. ~lowever, in many hiqh speed circuits, such as a microprocessor, the capacitance can be a severe problem. Another pro~lem is t:he variation in capacitance from part to part which results from variation in the position oE the heat spreader with respect to the lead frame. As a result of the variation oE capacitance from part to part, a heat spreader configuration may ~e acceptable for some parts but ~e unacceptable for other parts having different lead frame configurations.
Brief Su~mary of the Invention Accorclingly, an object of the present invention is to provide an improved heat spreader which is selE-positionin~ in a mold cavity prior to plastic encapsulation.
~nother object of the present invention is to provide an improved heat spreader having a configuration in which capacitance between the heat spreader and a lead frame is minimized.
Another object of the present invention is to provide an improved heat spreader having substantially the same amount of capacitance between itself and a lead frame from part to part.
~ further object of the present invention is to provide an improved heat spreader which is anodized and self-positioning in a mold cavity prior to plastic encapsulation.
Yet another object of the present invention is to provide an improved heat spreader for use in a semiconductor package havinq a low thermal impedance.
In carrying out the above and other objects oE the present invention, there is provided, in one form, a self-positionin~ heat spreader adapted Eor insertion into a 81~7 mold cavity prior to encapsulation with an encapsulant such as plastic. ~he heat spreader is placed into the mold cavity and is parallel to a first surface of a metal lead frame which has a semiconductor die connected to a second surface. The heat spreader has a frame with notches at opposite ends to reduce capacitance and which define bifurcated limbs which are sized to extend to within a predetermined tolerance of the end walls of the mold cavity. In order to ma}se capacitance substantially uniform from unit to unit, the inner edges of each limb complement the portion of the lead frame which overlays the limb. A pair of spaced-apart lateral standoffs extend from each side of the heat spreader to within a predetermined tolerance of the side walls of the mold cavity. At least a pair of feet extend A predetermined distance below the lead frame, and a central portion extends to within a predetermined tolerance of the bottom surface of the lead Erame. ~t leas-t one surface of the heat spreader is covered with an insulation such as anodization to prevent electrical contact between the heat spreader and the lead frame.
Brief Description of the Drawings FIG. 1 illustrates a top plan view of a self-positioning heat spreader constructed in accordance with the preferred embodiment of the present invention;
FIG. 2 illustrates a side elevational view of the heat spreader of FIG. 1; and FIG. 3 illustrates a cross sectional view of a heat spreader accordin~ to this invention taken substantially on line 3-3 of FIG. 1.
Detailed Description of the Preferred Embodiment Shown in FIG. 1 is a heat spreader 10 constructed in ,. -accordance with -the preferred embodiment. Heat spreader 10 may be inserted into either a lower or an upper half of a mold cavity (not shown). Although a lower thermal impedance may be obtained when heat spreader 10 is utilized in an upper half of a mold cavity, heat spreader 10 is typically utilized in a lower half of a mold cavity.
In such a conventional fabrication of an encapsulated integrated circuit, an upper half of a mold cavity containing a lead frame ~not shown) which is connected to a semiconductor die is positioned within the lower half of the mold cavity. The semiconductor die has electrical wires extending therefrom to the lead frame. Both halves of the mold cavity are Eilled with an encapsulant, such as molten plastic, to form an encapsulated semiconductor device.
In a preferred form, heat spreader 10 comprises an elongated heat conductive frame 12 which is metal, such as aluminum, and is complete]y anodized or insulated.
Although heat spreader 10 is preferably metal, heat spreader 10 may be fabricated from any other material which has a greater heat conductivity than the encapsulant. While it will be understood that heat conductive frame 12 is preferably elongated, a substantially s~uare frame may also be used. At the two ends of frame 12 is a notch 14 and and a notch 16, respectively. A pair of bifurcated limbs 18 and 20 surround notch 14 and a pair of bifurcated limbs 22 and 24 surround notch 16. Limbs 18 and 20 terminate with an end edge 26 and an end edge 28, respectively. Limbs 22 and 24 terminate with an end edge 30 and an end edge 32, respectively. Limbs 18 and 20 have an inner ed~e 34 and an inner edge 36, respectively, and limbs 22 and 24 have an inner edqe 38 and an inner edqe 40, respectively.
Lateral standoffs 42, 44, 46 and 48 extend Erom the outer sides of limbs 18, 20, 22 and 24, respectively. Extending a predetermined distance from the lower surface of heat spreader 1~ are feet 50l 52, 54 and 56. A central portion 58 extends from the top surface of heat spreader 10 to within a predetermined tolerance of the bottom 6urface of S a lead frame (not shown).
Feet 50, 52, 54 and 56 help position and support heat spreader 10 from the floor of the mold cavity. A primary purpose of feet 50, 52, 54 and 56 is to elevate elongated frarne 12 from the bottom surface of the mold cavity. As a result, heat spreader 10 does not have an exposed surface as a heat sink would and is essentially totally encapsulated. Complete encapsulation is important since plastic does not always strongly adhere to metal. When a metal surface of heat spreader 10 is exposed/ moisture can often enter the metal-plastic interface. Further, heat spreader 10 may be inadvertently pulled out or just come out of the plastic if exposed. Feet 50, 52, 54 and 56 therefore extend below heat spreader lO a predetermined distance to insure that the lower surface of heat spreader 10 is totally encapsulated in plastic. Although four ` distinct feet have been shown in a preferred form, either ` as few as two or more than four feet may be used. When - only two feet are used, both feet are positioned toward the opposite end of heat spreader 10 from the end in which the encapsulant enters. The flow of encapsulant allows the end having no feet to be sligthly raised from the mold cavity.
The purpose of central portion 58 i5 to put only a portion of metal heat spreader 10 in close proximity to the lead frame. The reason for putting only a portion of heat spreader 10 in close proximity to the lead frame is to minimize the capacitance which exists between the two conducting surfaces. Such capacitance increases as the the distance or thickness of the plastic dielectric between the surfaces decreases. However, the lead frame and heat spreader 10 can not he separated by a large distance without seriously reducinq the heat spreading ability of heat s~reader 10. Central portion 58 may be placed virt~lally ad~acent the lead frame because heat spreader 10 is anodized to have an electrically insulatin~
skin. As a result, even if no plastic separates heat spreader 10 and a lead frame, heat spreader 10 will not electrically contact an electronic circuit which is attached to the lead frame.
Lateral standoffs 42, 44t 46 and 48 are essential for heat spreader 10 to be self-positioning into the mold cavity. Lateral standoffs extend into within a first predetermined tolerance of the side walls oE the cavity so that when heat spreader 10 is dropped into the cavity, heat spreader 10 i5 substantially parallel to the lead frame. Furtherr when plastic is Elowing through the mold cavity, heat spreader 10 will not be able to move sideways. Ends 26, 28, 30 and 32 are also sized to extend to within a second predetermined tolearance of the end walls of the mold cavity. Similarly, when plastic flows into the mold cavity, heat spreader 10 will not he able to move lengthwise since limbs 18, 20, 22 and 24 are firmly wedged against the end walls of the mold cavity.
Notches 14 and 16 serve a two-fold purpose. Firstly, by reducing the a~ount of metal associated with frame 12, the amount of unwanted capacitance between frame 12 and the lead frame is reduced. In some applications, the inte~rated circuit which is used with the lead frame is very capacitance sensitive. Therefore, a reduction in conducting surface area is often essential to minimi~e capacitance between heat spreader 10 and the lead frame.
Secondly, notches 1g and 16 are very helpful in allowing plastic to freely flow into the mold cavity at either end.
If metal extended all the way across ends 26 and 28 and '7 ends 30 and 32, plastic flow would be obstructed when entering the mold cavity and flow problems could resul-t.
Another important feature of heat spreader 10 is the design oE inner edges 34, 36, 38 and 40 which are made to complement or conform to the portion of the lead frame which overlays limbs 18, 20, 22 and 24, respectively. The lead frame has a particular design and contour and oEten has a radial design from a centrally located integrated circuit die. By making heat spreader 10 follow the same contour, the variation in heat spreader-lead frame capacitance from unit to unit is substantially reduced.
Furthermore, inner edges 34, 36, 38 and 40 are centered between two adjacent leads of a lead Erame design. As a result, the heat spreader-lead frame capacitance variation is further reduced. Thus, all semiconductor devices utilizing a particular lead frame design will have substantially the same heat spreader-lead frame capacitance.
A further feature of heat spreader 10 is the ; 20 utilization of tapered edges 59, 60, 62 and 64 from end edges 26, ~8 30 and 32, respectively. The purpose of tapering end edges 26, 28, 30 and 32 is to allow more plastic to exist around the corners of the integrated circuit package and have a more durable part. Because integrated circuits can receive physical abuse during handling, this feature tends to increase the integrity of the package.
An additional feature of heat spreader 10 is the utilization of ribs 66 and 68 extendin~ from the upper surface of heat spreader 10 to within a predetermined tolerance of the bottom surface of the lead frame.
Although in the preferred form two ribs are shown, one o~
more ribs may be used. Further, the positionin~ of ribs &6 and 68 is not critical and ribs 66 and 68 may be located at any distance from notches 14 and lG and central - lZ~ 17 portion 58. Ribs 66 and 68 function to keep the plastic which is flowing in the mold cavity from twisting or moving limbs 18, 20~ 22 and 24 up agAinSt the lead frame.
Therefore, the use of a rib would be more significant if positioned on the end o the mold cavity where plastic is entering. However, i-f the manufacture of central portion 58 is within the specified predetermined tolerance, rihs 66 and 68 are not essential to heat spreader 10.
Shown in FIG. 2 is a side elevational view of heat spreader 10. As previously noted, the positioning of ribs 66 and 68 and feet 52 and 56 with respect to central portion 58 is not critical. However, in the preferred form, all ribs, feet, limbs and standoffs are substantially symmetrical with central portion 58.
Shown in FIG. 3 is a cross sectional view of heat spreader 10 taken substantially on line 3-3 of ~IG. 1. An additional feature of heat spreader 10 now made apparent is a channel 70 which exists under central portion 58 and extends through notch 1~ and notch 16. Inner inclined edges 72 and 74 elevate an inner section 76 of elongated frame 12 to within a predetermined tolerance of the bottom surface of the metal lead frame so that inner section 76 is higher than sides 78 and 80. Side 78 is the side which includes limbs 20 and 24, and side 80 is the side which ` 25 includes limbs 18 and 22. The purpose for elevating inner section 76 is to place a substantial amount of metal heat spreader 10 as close as possible to a lead frame to further reduce the thermal impedance. ~lso, by elevating inner section 76, plastic may flow into the mold cavity more freely. By now it should be apparent that the features of heat spreader 10 have been optimized to provide a low thermal impedance, free plastic flow and a low and substantially consistent heat spreader-lead frame capacitance. The features discussed also provide a heat spreader which may be easily loaded into a mold cavity ...
L8~17 since the spreader is self-positioning.
While the invention has been described in the context of a preferred embodiment, it will be apparent to thos2 skilled in the art that the present invention may be S modiEied in numerous ways and may assume many emboditnents other than that specifically set out and described above.
Accordin~ly, it is intended by the appended claims to cover all modifications of the invention which fall within the true spirit and scope oE the invention.
. .
Technical Field This invention relates generally to heat spreaders and, more particularly, to a heat spreader adapted for insertion into a mold cavity prior to plastic encapsulation with a semiconductor device.
Background Art Metal heat spreaders o various shapes ancl designs have been commonly used to spread or conduct heat away from a ~netal lead fra~e which is electrically connected to an integrated circuit die. One application of such heat spreaders has been to physically attach the heat spreader to the metal lead frame wherein both the heat spreader and lead frame are encapsulated ln plastic. In such an application, a heat spreader is used to spread heat in a relatively uniform manner throughout plastic and is not used for contact to an external heat sink. When heat spreaders have an exposed surface, poor adhesion between plastic and metal may allow moisture to enter into the package. Exposed metal surfaces may also result in a fragile structure. A disadvantage with heat spreaders that are directly connected to a metal lead frame is that achieving the physical connection requires a separate manufacturing step. A further disadvantage with such heat spreaders is the fact that capacitance exists between the heat spreader which acts as one long conducting surEace or plate and the lead frame which acts as another conducting surface or plate. Since the lead frame has different voltages at various points during operation and the distance separating the two conducting surfaces is small, a large capacitance is created between the two surfaces.
"
~24~
For some applications the capacitance does not present a significant problem. ~lowever, in many hiqh speed circuits, such as a microprocessor, the capacitance can be a severe problem. Another pro~lem is t:he variation in capacitance from part to part which results from variation in the position oE the heat spreader with respect to the lead frame. As a result of the variation oE capacitance from part to part, a heat spreader configuration may ~e acceptable for some parts but ~e unacceptable for other parts having different lead frame configurations.
Brief Su~mary of the Invention Accorclingly, an object of the present invention is to provide an improved heat spreader which is selE-positionin~ in a mold cavity prior to plastic encapsulation.
~nother object of the present invention is to provide an improved heat spreader having a configuration in which capacitance between the heat spreader and a lead frame is minimized.
Another object of the present invention is to provide an improved heat spreader having substantially the same amount of capacitance between itself and a lead frame from part to part.
~ further object of the present invention is to provide an improved heat spreader which is anodized and self-positioning in a mold cavity prior to plastic encapsulation.
Yet another object of the present invention is to provide an improved heat spreader for use in a semiconductor package havinq a low thermal impedance.
In carrying out the above and other objects oE the present invention, there is provided, in one form, a self-positionin~ heat spreader adapted Eor insertion into a 81~7 mold cavity prior to encapsulation with an encapsulant such as plastic. ~he heat spreader is placed into the mold cavity and is parallel to a first surface of a metal lead frame which has a semiconductor die connected to a second surface. The heat spreader has a frame with notches at opposite ends to reduce capacitance and which define bifurcated limbs which are sized to extend to within a predetermined tolerance of the end walls of the mold cavity. In order to ma}se capacitance substantially uniform from unit to unit, the inner edges of each limb complement the portion of the lead frame which overlays the limb. A pair of spaced-apart lateral standoffs extend from each side of the heat spreader to within a predetermined tolerance of the side walls of the mold cavity. At least a pair of feet extend A predetermined distance below the lead frame, and a central portion extends to within a predetermined tolerance of the bottom surface of the lead Erame. ~t leas-t one surface of the heat spreader is covered with an insulation such as anodization to prevent electrical contact between the heat spreader and the lead frame.
Brief Description of the Drawings FIG. 1 illustrates a top plan view of a self-positioning heat spreader constructed in accordance with the preferred embodiment of the present invention;
FIG. 2 illustrates a side elevational view of the heat spreader of FIG. 1; and FIG. 3 illustrates a cross sectional view of a heat spreader accordin~ to this invention taken substantially on line 3-3 of FIG. 1.
Detailed Description of the Preferred Embodiment Shown in FIG. 1 is a heat spreader 10 constructed in ,. -accordance with -the preferred embodiment. Heat spreader 10 may be inserted into either a lower or an upper half of a mold cavity (not shown). Although a lower thermal impedance may be obtained when heat spreader 10 is utilized in an upper half of a mold cavity, heat spreader 10 is typically utilized in a lower half of a mold cavity.
In such a conventional fabrication of an encapsulated integrated circuit, an upper half of a mold cavity containing a lead frame ~not shown) which is connected to a semiconductor die is positioned within the lower half of the mold cavity. The semiconductor die has electrical wires extending therefrom to the lead frame. Both halves of the mold cavity are Eilled with an encapsulant, such as molten plastic, to form an encapsulated semiconductor device.
In a preferred form, heat spreader 10 comprises an elongated heat conductive frame 12 which is metal, such as aluminum, and is complete]y anodized or insulated.
Although heat spreader 10 is preferably metal, heat spreader 10 may be fabricated from any other material which has a greater heat conductivity than the encapsulant. While it will be understood that heat conductive frame 12 is preferably elongated, a substantially s~uare frame may also be used. At the two ends of frame 12 is a notch 14 and and a notch 16, respectively. A pair of bifurcated limbs 18 and 20 surround notch 14 and a pair of bifurcated limbs 22 and 24 surround notch 16. Limbs 18 and 20 terminate with an end edge 26 and an end edge 28, respectively. Limbs 22 and 24 terminate with an end edge 30 and an end edge 32, respectively. Limbs 18 and 20 have an inner ed~e 34 and an inner edge 36, respectively, and limbs 22 and 24 have an inner edqe 38 and an inner edqe 40, respectively.
Lateral standoffs 42, 44, 46 and 48 extend Erom the outer sides of limbs 18, 20, 22 and 24, respectively. Extending a predetermined distance from the lower surface of heat spreader 1~ are feet 50l 52, 54 and 56. A central portion 58 extends from the top surface of heat spreader 10 to within a predetermined tolerance of the bottom 6urface of S a lead frame (not shown).
Feet 50, 52, 54 and 56 help position and support heat spreader 10 from the floor of the mold cavity. A primary purpose of feet 50, 52, 54 and 56 is to elevate elongated frarne 12 from the bottom surface of the mold cavity. As a result, heat spreader 10 does not have an exposed surface as a heat sink would and is essentially totally encapsulated. Complete encapsulation is important since plastic does not always strongly adhere to metal. When a metal surface of heat spreader 10 is exposed/ moisture can often enter the metal-plastic interface. Further, heat spreader 10 may be inadvertently pulled out or just come out of the plastic if exposed. Feet 50, 52, 54 and 56 therefore extend below heat spreader lO a predetermined distance to insure that the lower surface of heat spreader 10 is totally encapsulated in plastic. Although four ` distinct feet have been shown in a preferred form, either ` as few as two or more than four feet may be used. When - only two feet are used, both feet are positioned toward the opposite end of heat spreader 10 from the end in which the encapsulant enters. The flow of encapsulant allows the end having no feet to be sligthly raised from the mold cavity.
The purpose of central portion 58 i5 to put only a portion of metal heat spreader 10 in close proximity to the lead frame. The reason for putting only a portion of heat spreader 10 in close proximity to the lead frame is to minimize the capacitance which exists between the two conducting surfaces. Such capacitance increases as the the distance or thickness of the plastic dielectric between the surfaces decreases. However, the lead frame and heat spreader 10 can not he separated by a large distance without seriously reducinq the heat spreading ability of heat s~reader 10. Central portion 58 may be placed virt~lally ad~acent the lead frame because heat spreader 10 is anodized to have an electrically insulatin~
skin. As a result, even if no plastic separates heat spreader 10 and a lead frame, heat spreader 10 will not electrically contact an electronic circuit which is attached to the lead frame.
Lateral standoffs 42, 44t 46 and 48 are essential for heat spreader 10 to be self-positioning into the mold cavity. Lateral standoffs extend into within a first predetermined tolerance of the side walls oE the cavity so that when heat spreader 10 is dropped into the cavity, heat spreader 10 i5 substantially parallel to the lead frame. Furtherr when plastic is Elowing through the mold cavity, heat spreader 10 will not be able to move sideways. Ends 26, 28, 30 and 32 are also sized to extend to within a second predetermined tolearance of the end walls of the mold cavity. Similarly, when plastic flows into the mold cavity, heat spreader 10 will not he able to move lengthwise since limbs 18, 20, 22 and 24 are firmly wedged against the end walls of the mold cavity.
Notches 14 and 16 serve a two-fold purpose. Firstly, by reducing the a~ount of metal associated with frame 12, the amount of unwanted capacitance between frame 12 and the lead frame is reduced. In some applications, the inte~rated circuit which is used with the lead frame is very capacitance sensitive. Therefore, a reduction in conducting surface area is often essential to minimi~e capacitance between heat spreader 10 and the lead frame.
Secondly, notches 1g and 16 are very helpful in allowing plastic to freely flow into the mold cavity at either end.
If metal extended all the way across ends 26 and 28 and '7 ends 30 and 32, plastic flow would be obstructed when entering the mold cavity and flow problems could resul-t.
Another important feature of heat spreader 10 is the design oE inner edges 34, 36, 38 and 40 which are made to complement or conform to the portion of the lead frame which overlays limbs 18, 20, 22 and 24, respectively. The lead frame has a particular design and contour and oEten has a radial design from a centrally located integrated circuit die. By making heat spreader 10 follow the same contour, the variation in heat spreader-lead frame capacitance from unit to unit is substantially reduced.
Furthermore, inner edges 34, 36, 38 and 40 are centered between two adjacent leads of a lead Erame design. As a result, the heat spreader-lead frame capacitance variation is further reduced. Thus, all semiconductor devices utilizing a particular lead frame design will have substantially the same heat spreader-lead frame capacitance.
A further feature of heat spreader 10 is the ; 20 utilization of tapered edges 59, 60, 62 and 64 from end edges 26, ~8 30 and 32, respectively. The purpose of tapering end edges 26, 28, 30 and 32 is to allow more plastic to exist around the corners of the integrated circuit package and have a more durable part. Because integrated circuits can receive physical abuse during handling, this feature tends to increase the integrity of the package.
An additional feature of heat spreader 10 is the utilization of ribs 66 and 68 extendin~ from the upper surface of heat spreader 10 to within a predetermined tolerance of the bottom surface of the lead frame.
Although in the preferred form two ribs are shown, one o~
more ribs may be used. Further, the positionin~ of ribs &6 and 68 is not critical and ribs 66 and 68 may be located at any distance from notches 14 and lG and central - lZ~ 17 portion 58. Ribs 66 and 68 function to keep the plastic which is flowing in the mold cavity from twisting or moving limbs 18, 20~ 22 and 24 up agAinSt the lead frame.
Therefore, the use of a rib would be more significant if positioned on the end o the mold cavity where plastic is entering. However, i-f the manufacture of central portion 58 is within the specified predetermined tolerance, rihs 66 and 68 are not essential to heat spreader 10.
Shown in FIG. 2 is a side elevational view of heat spreader 10. As previously noted, the positioning of ribs 66 and 68 and feet 52 and 56 with respect to central portion 58 is not critical. However, in the preferred form, all ribs, feet, limbs and standoffs are substantially symmetrical with central portion 58.
Shown in FIG. 3 is a cross sectional view of heat spreader 10 taken substantially on line 3-3 of ~IG. 1. An additional feature of heat spreader 10 now made apparent is a channel 70 which exists under central portion 58 and extends through notch 1~ and notch 16. Inner inclined edges 72 and 74 elevate an inner section 76 of elongated frame 12 to within a predetermined tolerance of the bottom surface of the metal lead frame so that inner section 76 is higher than sides 78 and 80. Side 78 is the side which includes limbs 20 and 24, and side 80 is the side which ` 25 includes limbs 18 and 22. The purpose for elevating inner section 76 is to place a substantial amount of metal heat spreader 10 as close as possible to a lead frame to further reduce the thermal impedance. ~lso, by elevating inner section 76, plastic may flow into the mold cavity more freely. By now it should be apparent that the features of heat spreader 10 have been optimized to provide a low thermal impedance, free plastic flow and a low and substantially consistent heat spreader-lead frame capacitance. The features discussed also provide a heat spreader which may be easily loaded into a mold cavity ...
L8~17 since the spreader is self-positioning.
While the invention has been described in the context of a preferred embodiment, it will be apparent to thos2 skilled in the art that the present invention may be S modiEied in numerous ways and may assume many emboditnents other than that specifically set out and described above.
Accordin~ly, it is intended by the appended claims to cover all modifications of the invention which fall within the true spirit and scope oE the invention.
. .
Claims (7)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A heat spreader adapted for insertion into a mold cavity prior to encapsulation thereof for conducting heat away from a metal lead frame and configured to minimize capacitance between the heat spreader and the lead frame, said heat spreader being substantially parallel to a first surface of the metal lead frame having a semiconductor die mounted on a first portion of the lead frame and connected to a second surface of the lead frame the heat spreader comprising:
a heat conductive frame having first and second notches formed in opposite ends thereof to define bifurcated limbs sized to extend into within a first predetermined tolerance of first and second end walls of said cavity, with inner edges of each such limb tapering to a predeter-mined one of the end walls and complementing a second portion of the lead frame which will overlay the limb when encapsulated to minimize said capacitance, at least a pair of spaced-apart lateral standoffs extending from each of first and second sides into within a second predetermined tolerance of first and second side walls of said cavity, at least a pair of spaced-apart feet extending a predetermined distance from a lower surface thereof; and a solid central portion adjacent said notches and extending to within a third predetermined tolerance of the first surface of the portion of said lead frame on which said die is mounted when encapsulated, whereby said first, second and third predetermined tolerances are selected so that said heat spreader is self-positioning with respect to said mold cavity and said lead frame.
a heat conductive frame having first and second notches formed in opposite ends thereof to define bifurcated limbs sized to extend into within a first predetermined tolerance of first and second end walls of said cavity, with inner edges of each such limb tapering to a predeter-mined one of the end walls and complementing a second portion of the lead frame which will overlay the limb when encapsulated to minimize said capacitance, at least a pair of spaced-apart lateral standoffs extending from each of first and second sides into within a second predetermined tolerance of first and second side walls of said cavity, at least a pair of spaced-apart feet extending a predetermined distance from a lower surface thereof; and a solid central portion adjacent said notches and extending to within a third predetermined tolerance of the first surface of the portion of said lead frame on which said die is mounted when encapsulated, whereby said first, second and third predetermined tolerances are selected so that said heat spreader is self-positioning with respect to said mold cavity and said lead frame.
2. The heat spreader of claim 1 wherein said heat spreader is made of an anodized metal.
3. The heat spreader of claim 1 further comprising at least one rib extending from an upper surface thereof to within a fourth predetermined tolerance of the first surface of said lead frame.
4. The heat spreader of claim 1 wherein said heat conductive frame comprises an elevated inner section extend-ing substantially from the first and second notches formed in the opposite ends of the lead frame and to within a fifth predetermined tolerance of the first surface of said lead frame.
5. The heat spreader of claim 1 wherein said bifur-cated limbs are tapered from the first and second sides of said heat spreader to the opposite ends of said heat conductive frame.
6. A self-positioning heat spreader adapted for insertion into a mold cavity prior to encapsulation in plas-tic substantially parallel to a first surface of a metal lead frame having a semiconductor die mounted on and connected to a second surface of the lead frame, the heat spreader min-imizing capacitance between said heat spreader and lead frame and providing a substantially uniform capacitance between the heat spreader and the lead frame for multiple encapsulated units, comprising:
a heat conductive frame having a solid central portion with tapered notches formed in opposite ends thereof immedi-ately adjacent said solid central portion to define bifur-cated limbs sized to extend into within a first predetermined tolerance of first and second end walls of said cavity with first and second inner edges of each such limb tapering to a predetermined one of the end walls, said tapered end notches complementing a plurality of leads of the metal lead frame which overlay each limb when encapsulated to minimize said capacitance.
a heat conductive frame having a solid central portion with tapered notches formed in opposite ends thereof immedi-ately adjacent said solid central portion to define bifur-cated limbs sized to extend into within a first predetermined tolerance of first and second end walls of said cavity with first and second inner edges of each such limb tapering to a predetermined one of the end walls, said tapered end notches complementing a plurality of leads of the metal lead frame which overlay each limb when encapsulated to minimize said capacitance.
7. A semiconductor device having a lead frame, a semiconductor die, and a heat spreader which minimizes capacitance between the lead frame and the heat spreader, the heat spreader comprising:
a notch formed in at least each end of the heat spreader to define bifurcated limbs with first and second inner edges of each such limb tapering to a distal end of each limb and complementing a portion of the lead frame which will overlay the limb when encapsulated;
at least a pair of spaced-apart lateral standoffs extending from each side of the heat spreader;
at least a pair of spaced-apart feet extending from a first surface of the heat spreader;
a channel formed along the first surface and extending from one of the notches to another one of the notches;
a heat conductive frame having a solid central portion and notches in opposite ends thereof immediately adjacent said solid central portion, said notches extending from each end of the heat conductive frame so that a substantial portion of each lead of the lead frame overlays one of said notches to minimize said capacitance; and a raised portion on a second surface of the heat spreader to be placed in close proximity to the semiconductor die, and the second surface has an insulating film to prevent electrically conductive contact between the heat spreader and the lead frame.
a notch formed in at least each end of the heat spreader to define bifurcated limbs with first and second inner edges of each such limb tapering to a distal end of each limb and complementing a portion of the lead frame which will overlay the limb when encapsulated;
at least a pair of spaced-apart lateral standoffs extending from each side of the heat spreader;
at least a pair of spaced-apart feet extending from a first surface of the heat spreader;
a channel formed along the first surface and extending from one of the notches to another one of the notches;
a heat conductive frame having a solid central portion and notches in opposite ends thereof immediately adjacent said solid central portion, said notches extending from each end of the heat conductive frame so that a substantial portion of each lead of the lead frame overlays one of said notches to minimize said capacitance; and a raised portion on a second surface of the heat spreader to be placed in close proximity to the semiconductor die, and the second surface has an insulating film to prevent electrically conductive contact between the heat spreader and the lead frame.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US36511482A | 1982-03-30 | 1982-03-30 | |
| US365,114 | 1982-04-05 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1201817A true CA1201817A (en) | 1986-03-11 |
Family
ID=23437521
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000423966A Expired CA1201817A (en) | 1982-04-05 | 1983-03-18 | Self-positioning heat spreader |
Country Status (6)
| Country | Link |
|---|---|
| EP (1) | EP0104231A4 (en) |
| JP (1) | JPS59500541A (en) |
| KR (1) | KR840004828A (en) |
| CA (1) | CA1201817A (en) |
| IT (1) | IT1164597B (en) |
| WO (1) | WO1983003712A1 (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2597261B1 (en) * | 1986-04-11 | 1988-10-14 | Aix Les Bains Composants | ENCAPSULATION BOX OF INTEGRATED CIRCUITS WITH IMPROVED THERMAL DISSIPATION, AND MANUFACTURING METHOD |
| JP3322429B2 (en) * | 1992-06-04 | 2002-09-09 | 新光電気工業株式会社 | Semiconductor device |
Family Cites Families (13)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| NL6901240A (en) * | 1968-01-26 | 1969-07-29 | ||
| DE2004768C3 (en) * | 1968-07-30 | 1979-09-06 | N.V. Philips' Gloeilampenfabrieken, Eindhoven (Niederlande) | Semiconductor component |
| GB1239634A (en) * | 1968-10-02 | 1971-07-21 | ||
| US3585272A (en) * | 1969-10-01 | 1971-06-15 | Fairchild Camera Instr Co | Semiconductor package of alumina and aluminum |
| US3868725A (en) * | 1971-10-14 | 1975-02-25 | Philips Corp | Integrated circuit lead structure |
| US3930114A (en) * | 1975-03-17 | 1975-12-30 | Nat Semiconductor Corp | Integrated circuit package utilizing novel heat sink structure |
| US4054901A (en) * | 1975-10-14 | 1977-10-18 | Thermalloy, Inc. | Index mounting unitary heat sink apparatus with apertured base |
| JPS53126275A (en) * | 1977-04-11 | 1978-11-04 | Hitachi Ltd | Semiconductor device |
| JPS53132975A (en) * | 1977-04-26 | 1978-11-20 | Toshiba Corp | Semiconductor device |
| US4132856A (en) * | 1977-11-28 | 1979-01-02 | Burroughs Corporation | Process of forming a plastic encapsulated molded film carrier CML package and the package formed thereby |
| JPS55134951A (en) * | 1979-04-10 | 1980-10-21 | Toshiba Corp | Semiconductor device |
| JPS6050346B2 (en) * | 1980-04-16 | 1985-11-08 | 日本電気株式会社 | Manufacturing method of semiconductor device |
| FR2488445A1 (en) * | 1980-08-06 | 1982-02-12 | Efcis | PLASTIC CASE FOR INTEGRATED CIRCUITS |
-
1983
- 1983-03-11 WO PCT/US1983/000351 patent/WO1983003712A1/en not_active Application Discontinuation
- 1983-03-11 EP EP19830901297 patent/EP0104231A4/en not_active Withdrawn
- 1983-03-11 JP JP58501368A patent/JPS59500541A/en active Pending
- 1983-03-18 CA CA000423966A patent/CA1201817A/en not_active Expired
- 1983-03-29 IT IT48015/83A patent/IT1164597B/en active
- 1983-04-04 KR KR1019830001389A patent/KR840004828A/en not_active Application Discontinuation
Also Published As
| Publication number | Publication date |
|---|---|
| WO1983003712A1 (en) | 1983-10-27 |
| IT1164597B (en) | 1987-04-15 |
| KR840004828A (en) | 1984-10-24 |
| EP0104231A4 (en) | 1985-10-30 |
| IT8348015A0 (en) | 1983-03-29 |
| JPS59500541A (en) | 1984-03-29 |
| EP0104231A1 (en) | 1984-04-04 |
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| MKEX | Expiry |