KR100696050B1 - Attachment of a stiff heat spreader for fabricating a cavity down plastic chip carrier - Google Patents

Abstract

A rigid heat spreader element for producing a cavity down plastic chip carrier having the advantages of good heat dissipation properties, small weight, small thickness, small warpage and torsion is disclosed. The rigid heat spreader element is formed by bonding the heat spreader and the thermally conductive sheet using the first adhesive sheet. The first adhesive sheet is a prepreg or prepregs formed of fiber reinforced resin. The second adhesive sheet is used to bond the circuit board and the rigid heat spreader element. The second adhesive sheet is composed of a single adhesive layer or a laminated structure of adhesive layers. The adhesive layer is formed of an adhesive material, an adhesive material filled with flakes, an adhesive material filled with short fibers, or an adhesive material filled with particles. The second adhesive sheet is not formed of prepregs or prepregs. The circuit board has an opening for receiving the electronic chip.

Cavity Down Plastic Chip Carrier, Heat Spreader

Description

Attachment method of a stiff heat spreader for fabricating a cavity down plastic chip carrier

1 is a cross-sectional view of a cavity down chip carrier of the prior art in accordance with a wire bonding technique.

2 is a cross-sectional view of a cavity down chip carrier of the prior art with a built-in reinforcement.

3 is an exploded view showing the layers used to fabricate a cavity down chip carrier with a heat spreader element in accordance with one embodiment of the present invention.

4 is a cross-sectional view of a heat spreader element in accordance with one embodiment of the present invention.

5 is an exploded view showing the layers used to fabricate a cavity down chip carrier with embedded sharp connectors in accordance with one embodiment of the present invention.

6 is an exploded view showing the layers used to make a cavity down chip carrier with two second thermally conductive sheets in accordance with one embodiment of the present invention.

7 is an exploded view showing the layers for fabricating a multi-chip cavity down chip carrier with a heat spreader element.

<Explanation of symbols for the main parts of the drawings>

1,101,201: substrate 6,10: thermally conductive sheet                 

9,14,15: adhesion promoter layer 11: hole

DESCRIPTION OF REFERENCE NUMERALS 16 first adhesive sheet 17 rigid heat spreader element 19 second adhesive sheet 100 cavity down chip carrier 102 204 recess cavity 103 205 heat spreader

104: adhesive layer 105: side wall 106, 207: chip 107: bonding wire 109: external connection means 110: printed circuit board 202: copper layer 203,206: adhesive 209: conductive wire 211: solder ball

FIELD OF THE INVENTION The present invention generally relates to the manufacture of electronic packages comprising single chip packages and multiple chip packages, and more particularly to the manufacture of multiple cavity down chip packages with heat spreaders used as attached reinforcements.

As the semiconductor industry continues to advance, electronic circuitry and electronic packaging have typically been designed to use as small an area as feasible. Circuit space is generally a valuable asset for communication, and miniaturization of electronic circuits generally increases speed, reduces noise, and brings other performance benefits. Such miniaturization is desirable in electronics used in various devices such as aircraft, automobiles, mobile phones, portable computers, portable camcorders, and the like. However, as the number of transistors fabricated on a single semiconductor device increases, the total amount of heat generated in the semiconductor device also increases, so thermal density problems often arise as miniaturization increases.

One type of semiconductor chip package includes one or more semiconductor chips attached to a substrate, such as a ceramic substrate or a plastic substrate, where the ceramic substrate uses a ceramic material as an insulating layer and the plastic substrate insulates the plastic base material. Use as a layer. Such semiconductor chip packages, formerly termed chip carriers, are generally interconnected on a printed circuit card or printed circuit board. The chip can be attached to the substrate in several ways. Currently, the best known approach is wire bonding, where electrical connections are made by attaching very small wires from the device side of the chip to appropriate points on the substrate. Another method of attachment is to use small solder balls to physically attach the chip and form the desired electrical connection, which is called flip chip bonding.

The methods have been used to install integrated circuit chips in plastic packages for low cost packaging means compared to ceramic packages. Plastic packages are also known to provide some important advantages for chip operation compared to ceramic packages, including high current carrying capability, low dielectric constant for short operational delay time, with reduced inductance and capacitance. However, the low temperature stability of the plastic package is still a problem. This problem is highlighted in the development of current plastic packages. One solution to this problem is a cavity down chip package structure in which a heat slug or heat spreader is attached to the bottom of the package and the chip is installed in a recess cavity having an open side of the recess cavity towards the printed circuit card or printed circuit board. To employ.

1 illustrates a conventional cavity down chip carrier 100. It includes a plastic wiring board 101 having a recess cavity 102 and a heat slug or heat spreader 103 bonded to the substrate 101 by an adhesive layer 104. Sidewalls 105 may be formed of an electrically and / or thermally conductive layer to connect the wiring layer and heat spreader in the substrate 101 for further thermal or electrical performance. The chip 106 is installed on the heat spreader 103 inside the recess cavity 102. Conductive wires are used to interconnect the chip 106 to the substrate 101. After the wire bonding process, the cavity 102 is filled with a sealant 108 to cover and protect the bonding wire 107 and the chip 106 against environmental erosion. External connection means 109 for electrically connecting the substrate 101 to the printed circuit board 110 is attached to a suitable area on the top surface of the substrate 101. The external connection means 109 may be conductive pins or solder balls or pillars when used in plastic pin grid arrays (PPGA) or plastic ball grid arrays (PBGA) or plastic pole grid arrays (PCGA). As an alternative structure, additional heat absorbers may be attached to the backside of the heat spreader 103 if needed for further improved heat dissipation.

In order to solve the problem of bending or torsion in the manufacture of cavity down plastic chip carriers, reinforcements or multiple copper layers may sometimes be embedded. A conventional example is shown in FIG. The prior art cavity down plastic chip carrier, the so-called super ball grid array package, has a circuit board 201 having a first surface 201a and a second surface 201b against the first surface. ) And an inner copper layer 202 on the first surface 202a attached to the second surface 201b of the circuit board 201 by an adhesive 203. An opening is formed on each of the centers of the circuit board 201 and the copper layer 202 to form a recess cavity 204 penetrating the circuit board 201 and the copper layer 202. A heat spreader 205 is attached to the other surface 202b of the copper layer 202 using the adhesive 206 to improve heat dissipation characteristics. The chip 207 is installed on the heat spreader 205 inside the recess cavity 204 by an adhesive 28. Conductive wire 209 is used to interconnect chip 207 to substrate 201. After the wire bonding process, the cavity 204 is filled with a seal to cover and protect the bonding wire 209 and the chip 207 against environmental erosion. Solder balls 211 that electrically connect the substrate 201 to the printed circuit board 212 are attached to appropriate areas on the first surface 201a of the substrate 201. As an alternative structure, additional heat absorbers may be attached to the second surface 205b of the heat spreader 205 as needed for further improved heat dissipation.

U. S. Patent No. 6,034, 427 (by JJD Lan et al.) Describes the use of a reinforcement for plastic cavity down BGAs, where the reinforcement is first attached to the circuit board by prepreg and then the heat spreader using an adhesive film. It is attached to stiffeners. In this method, when the heat spreader is formed of a copper base material, for example, a copper or copper base alloy, which is well known as a relatively soft material, the cure shrinkage of the adhesive film is thermally compressed with the heat spreader together with the circuit board comprising the reinforcement. It can cause bending during the process.

U. S. Patent No. 6,060, 778 (by TSJeong et al.) Also discloses a similar process for producing plastic cavity down BGAs, wherein the BGA package is described as having good heat dissipation capacity, small weight, thin thickness and low manufacturing cost. have. The method includes using a first thermally conductive layer attached to a circuit board. A second thermally conductive layer (ie, a heat spreader) is attached to the circuit board that includes the first thermally conductive layer. However, this method is shown in FIG. 7 of the patent but is not included in the claims of the patent. This method has the same problem as described above in US Patent No. 6034427, that is, the warpage of the produced BGA is difficult to eliminate.

It is therefore an object of the present invention to provide a method of forming a low cost plastic cavity down chip carrier with good heat dissipation capability and small weight, and free of warpage and torsion. Briefly, the present invention provides a method of first bonding two or multiple thermally conductive sheets to form a rigid heat spreader element and then bonding the rigid heat spreader element to a circuit board (or so-called integrated circuit board). . This method is quite different from the methods provided by US Pat. Nos. 6,034,427 and 6,060,778, both conventional methods of adhering a first thermally conductive sheet to a circuit board and thereafter a circuit comprising the first thermally conductive sheet in advance. A second thermally conductive sheet is attached to the board. There is one more obvious difference here. That is, the method of the present invention proposes to use prepregs or prepregs as an adhesive layer for adhering thermally conductive sheets and to use a prepreg free material as an adhesive layer for adhering the thermally conductive sheet to a circuit board. The method proposed in patent 6,034,427 uses a prepreg free material as the adhesive layer for bonding the thermally conductive sheets and uses the prepreg to adhere the thermally conductive sheet to the circuit board. According to the present invention, the use of prepregs to bond thermally conductive sheets can form very stiff heat spreader elements. After the rigid heat spreader element is attached to the circuit board, the rigid heat spreader element can be used as a reinforcement for the resulting cavity down chip carrier, so that warpage and torsion of the resulting cavity down chip carrier can be greatly reduced.

Therefore, it is an object of the present invention to provide a rigid heat spreader element for producing cavity down plastic chip carriers having good heat dissipation properties, small weight, small thickness and small warpage and twist.

It is another object of the present invention to employ the first adhesive sheet to bond the first thermally conductive sheet and the second thermally conductive sheet to form a rigid first heat spreader element. The first adhesive sheet having any configuration is a prepreg or prepregs based on fiber reinforced resin. The second thermally conductive sheet has an opening for receiving the electronic chip and the electronic chip can be attached directly on the surface of the first thermally conductive sheet.

It is another object of the present invention to employ a plastic circuit board having an opening for receiving an electronic chip and a second adhesive sheet for bonding a rigid first heat spreader element. The second adhesive sheet having any configuration consists of a single adhesive layer or a laminated structure of a plurality of adhesive layers. The adhesive layer is formed of an adhesive material, a flake-filled adhesive material, a fiber-filed material or a particle-filled material. The adhesive layer is not a prepreg.

It is another object of the present invention to provide a rigid second heat spreader element formed by laminating a first thermally conductive sheet and two or more second thermally conductive sheets using the first adhesive sheet between the thermally conductive sheets. . The first adhesive sheet having any configuration is a prepreg or prepregs based on fiber reinforced resin. The second thermally conductive sheet has an opening for receiving the electronic chip and the electronic chip can be attached directly on the surface of the first thermally conductive sheet.

It is another object of the present invention to employ a second adhesive sheet for bonding a second heat spreader element with a plastic circuit board having an opening for receiving an electronic chip. The second adhesive sheet having any configuration consists of a single adhesive layer or a laminated structure of a plurality of adhesive layers. The adhesive layer consists of an adhesive material, an adhesive material filled with flakes, an adhesive material filled with fibers, or an adhesive material filled with particles. The adhesive layer is not prepregs or prepregs.

The present invention provides a rigid heat spreader that can also be used as a reinforcement to produce cavity down plastic chip carriers that are free of warpage and torsion. At the same time, the heat dissipation efficiency can be further increased.

Referring now to FIG. 3, according to a preferred embodiment of the invention, a plastic chip carrier substrate 1 having an opening 2 and several tires 3 is first provided. The substrate 1 comprises a wiring circuit layer separated by an organic insulating layer, through holes, conductive through holes, vias in the substrate 1, a protective layer on the surface of the tire 3, and electrodes (or so-called adhesion). Fingers), electrodes (or so-called landing pads), protective coatings and dams on the surface 4, and protective coatings and electrodes on the second surface 5, all of which are related Known in the art. For example, the first thermally conductive sheet 6 (or so-called heat) formed of copper, copper alloy, aluminum, aluminum alloy, graphite fiber-reinforced copper or copper alloy, copper or copper alloy filled with silicon carbide particles, or the like The diffuser) may have both surfaces thereof, i.e., the surfaces of which the first surface 7 and the second surface 8 are chemically or physically roughened. On the first surface 7, an adhesion promoter layer 9, for example an oxide layer or a binder, is deposited to improve the adhesion properties. The binder may include a silane binder, a titanium binder, a zirconium binder, an aluminum binder, or the like. For example, a second thermally conductive sheet 10 (or so-called internal heat) having holes 11 through the sheet 10 formed of copper, copper alloys, copper or copper alloys filled with silane carbide particles, or the like. The conductive sheet) may have both surfaces thereof, that is, the surfaces on which the first surface 12 and the second surface 13 are chemically or physically roughened. On the surfaces 12 and 13, adhesion promoter layers 14 and 15 are also deposited respectively to improve the adhesion properties. However, according to the invention, the adhesion promoter is not limited to oxides or binders. The first surface 7 of the heat spreader 6 is preferably formed of a first thermally conductive sheet 10 by a first adhesive sheet 16 which is, for example, a fiber reinforced resin which is a prepreg or prepregs. 1 is laminated on the surface. After thermocompression, the rigid heat spreader element 17 is completed comprising the heat spreader 6 and the internal thermally conductive sheet 10 together with the first adhesive sheet. The rigid heat spreader element 17 is a rigid sandwich structure because the first adhesive sheet 16, for example the prepreg, becomes relatively hard after thermal compression. The first thermally conductive sheet 6 and the second thermally conductive sheet 10 preferably have the same thickness, and their symmetrical sandwich structure will provide optimum mechanical properties to prevent the occurrence of bending and torsion problems. It should be noted that Thermal or electrically conductive layers 18 may also be deposited to thermally connect the heat spreader 6 to the internal thermally conductive sheet 10 to further improve heat dissipation.

As an alternative method, according to a preferred embodiment of the invention, a thermal or electrically conductive layer 18a, for example a thin copper layer, is deposited on the surface of the rigid heat spreader element 17 as shown in FIG. Can be. Naturally, it is preferable to acid wash or plasma wash the surface prior to the deposition of the layer 18 or 18a. On the second surface 8 of the heat spreader 6 a protective coating, for example of epoxy resin, diamond, carbon-based diamond, etc., filled with nickel, gold, thermally conductive particles, may also be formed. . Normally, the second surface 8 may be a surface that has been chemically or physically roughened prior to the deposition of the protective coating. The second adhesive sheet 19 is placed between the second surface 5 of the substrate 1 and the first surface 12 of the internal thermally conductive sheet 10. By compression, the heat spreader element 17 is adhered to the second surface 5 of the substrate 1 after the second adhesive sheet 19 has been cured by means such as heat or radiation. However, the first and second adhesive sheets 16 and 19 are not limited to any form or configuration. After the sidewall plating, die attach, wire bonding, seal fill and external terminal attach processes, which are well known in the art, the cavity down chip carrier 200 shown in FIG. 2 may be fabricated.

A particular shape as shown in FIG. 4, that is, a thin thermally conductive layer 18a is deposited to thermally connect the first thermally conductive sheet 6 and the second thermally conductive sheet 10, resulting in a cavity down. Better thermal performance for the chip carrier is obtained. However, this advantageous result with better thermal performance cannot be obtained through the method presented in US Pat. No. 6,060,778, because the present invention in which the thermally conductive sheets are first adhered to form a heat spreader element prior to attachment of the circuit board. Unlike the method presented by, the conventional method is because the thermally conductive sheet is first adhered to the circuit board.

The plastic chip carrier substrate 1 may be a single layer or a multi-layered substrate having a plurality of different layers superimposed of a dielectric material (ie, a material for forming an insulating layer) and a conductive material, wherein the organic dielectric material is For example, organic materials or fiber reinforced organic materials or particle reinforced organic materials, such as epoxy resins, polyimides, bismeleimide triazines, cyanate esters, polybenzocyclobutane or glass fiber composites thereof. The plastic chip carrier substrate 1 is preferably formed before adhering to the device, and conductive through holes that completely pass through the substrate may be made to form the cavity down chip carrier 200. In such a case, the cure shrinkage that occurs during the formation of the substrate 1 will not cause warpage or torsion when the substrate 1 is bonded to the heat spreader element.

Referring to FIG. 1, the heat spreader 103 is generally formed of copper or a copper base alloy. Copper sheets are known to soften when the actual operating temperature approaches about 300-400 ° C. In practical experience, if the heat spreader made of copper is too thin, for example 0.5 millimeters or less, the heat spreader 103 may be removed during the manufacturing process of forming the plastic chip carrier 100 because the heat spreader 103 is easy to deform. It becomes very difficult to handle. Therefore, the thickness of the heat spreader 103 made of copper is preferably larger than 0.5 milliliters. However, if a thinner heat spreader 103 of 0.5 millimeters or less is desired, the copper base alloy used to form the heat spreader 103 with higher mechanical strength is preferred. The content of the alloy component of the copper base alloy is preferably 5 wt% or less (weight percent relative to the total weight of the copper base alloy), for example, C194 or C305 copper alloy, preferably 0.5 wt% or less, for example The C151 copper alloy is preferred because the higher the content of the added copper component, the lower the thermal conductivity of the copper base alloy. It should be noted that copper in the present invention means copper alloys having an incidental alloying component content of 0.1 wt% or less.

However, the limitation on the thickness of the heat spreader 103 formed of copper larger than 0.5 millimeters can be lifted when the sandwich element 17 is used. For example, a copper heat spreader 6 having a thickness of 0.254 millimeters laminated to an internal thermally conductive copper sheet 10 having a thickness of 0.254 millimeters using prepregs may be used to fabricate the cavity down chip carrier 200. It is possible to form a sufficiently hard and thick element 17 that is easily adapted to the manufacturing process for the same. If higher mechanical strength of the element 17 is required to solve the resulting chip carrier warpage problem, then the first adhesive sheet 16 between the heat spreader 6 and the internal thermally conductive sheet 10 may also be It may be dog or multiple prepregs. It is preferred that the first and second thermally conductive sheets also have the same thickness, which has been found to provide optimum results resulting in improvement of the warpage problem.

In order to more fully protect the device 17 from environmental erosion, the sidewalls of the device 17 may also be covered with a protective layer 17a, for example nickel, gold, epoxy resin or the like. When a metal coating is deposited on the sidewalls, heat dissipation is also increased at the same time because the surface area for heat dissipation is increased.

According to a preferred embodiment of the present invention, the second adhesive sheet 19 is composed of one adhesive layer or a laminated structure of a plurality of adhesive layers. The adhesive layer is composed of an adhesive material, an adhesive material filled with short fibers, an adhesive material filled with flakes, or an adhesive material filled with particles. Since the fabric fibers are not filled in the adhesive material, the adhesive layer may not be a prepreg in the present invention. Examples of the adhesive material include, for example, resins such as epoxy resins, polyimide resins, polyurethanes and acrylic resins, and copolymers such as epoxy acrylic resins, epoxy butadiene resins and epoxy urethane resins, for example epoxy Polymer mixtures such as resin / halogenated polyhydroxystyrene mixtures and epoxy resin / phenol resin mixtures. The organic material may also be modified by silicon, halogen or phosphite or the like. Short fibers formed of metal, organic or inorganic materials such as tungsten short fibers, aramid short fibers, glass short fibers, and the like may be filled in the organic material to increase the mechanical strength or reduce the coefficient of thermal expansion of the second adhesive sheet. The flakes or particles may also be filled in the organic material for the same purpose. Examples of the flakes may be silver flakes or graphite flakes, and examples of the particles may be silica particles, barium sulfate particles, clay, calcium carbonate particles, melamine particles, polystyrene particles, copper particles or silver particles and the like. The adhesive material may include several other additives such as chemical catalysts, antioxidants, rheological agents, binders and colorants.

The choice of adhesive layer is essential to reduce warping and torsion of the cavity down chip carrier. In the modern industrial field, adhesive materials formed on the basis of thermosetting resins have been mainstream. Such conventional thermosetting resins are generally cured at high temperatures and cooled at room temperature. Therefore, it is desirable for this adhesive material to be sufficiently softened (ie having a low mechanical modulus) to compensate for the cure shrinkage occurring in the curing step. Normally, partially curing the thermosetting resin prior to adhesion and lowering the CTE and mechanical modulus of the adhesive material aids in good adhesion without bending. Practical experience shows that prepregs, which themselves have high mechanical modulus, are difficult to obtain good adhesion without bending to the cavity down chip carrier. To achieve good adhesion without warping, too much filler loading providing higher modulus or too little filler loading providing high CTE is undesirable. Moreover, it is preferable that CTE of an adhesive layer is 150 ppm / degrees C or less, It is more preferable that it is 100 ppm / degrees C or less, It is most preferable that it is 50 ppm / degrees C or less.

According to a preferred embodiment of the present invention, the rigid heat spreader element may have a sharp connector projecting out of the rigid heat spreader element. As shown in FIG. 5, a sharp connector 20 is formed on the first surface 12 of the inner thermally conductive sheet 10. Adhesion promoters 14, such as, for example, oxide layers or binders, are also formed on the same surface 12. Using pressure and heat, the inserted element 17 is bonded to the circuit board 1 by the second adhesive sheet 19. At the same time, the sharp connector 20 penetrates the adhesive sheet 19 and contacts the pre-aligned contact pads on the second surface 5 of the circuit board 1. Naturally, holes may be formed by laser or mechanical drilling at a predetermined connection position before bonding so that the connector 20 can easily pass through the adhesive sheet 19. The electrically conductive or thermally conductive sharp connector 20 can be of any shape and configuration. This kind of connection provides a thermal conduction path for the sandwich element 17 to act as a ground potential, especially when electrically connected to the ground plane (s), and to conduct heat generated by the transistor to the sandwich element 17, It further improves the electrical and thermal performance of the resulting plastic cavity down chip carrier.

According to a preferred embodiment of the invention, the rigid heat spreader element can be formed using two or more second thermally conductive sheets. As shown in FIG. 6, the second thermally conductive sheet 23 is bonded to the first thermally conductive sheet 22 using the first adhesive sheet 25, and the additional second thermally conductive sheet 22 is An additional first adhesive sheet 26 is used to bond to the second thermally conductive sheet 23. In addition, the two second thermally conductive sheets 23 and 24 have holes 27 passing through the sheets 23 and 24 to accommodate the electronic chip. An adhesion promoter layer 29, for example an oxide layer or a binder layer, may be formed on the surfaces of the first and second thermally conductive sheets, respectively, to improve the adhesion properties. Therefore, a rigid heat spreader element 28 having two second thermally conductive sheets 23 and 24 is formed. In this step, the rigid heat spreader element 28 can be bonded to the plastic circuit board 30 using a second adhesive sheet 31 to make the cavity down plastic chip carrier. As described above, the first adhesive sheets 23 and 24 are prepregs, while the second adhesive sheets 31 are adhesive materials not formed of prepregs or prepregs.

According to a preferred embodiment of the present invention, the chip carrier is not limited to a single chip package but also includes a multichip package. A typical example of a multichip package is shown in FIG. The circuit board 32 has two openings 33 and 34 that can each accommodate a semiconductor chip. Using pressure and heat, a heat spreader sandwich element 35 can be attached to the circuit board 32 by an adhesive sheet 36 and used to make a two chip chip carrier.

According to a preferred embodiment of the present invention, the chip carrier can be formed by attaching a sandwich element panel to a circuit board panel by an adhesive sheet for industrial mass production. The panel can be of any shape or configuration, for example a stripe shape or the like. However, in such cases, careful selection of adhesive sheets will be further required because large circuit board panels naturally expand the warping problem.

According to a preferred embodiment of the present invention, a cavity down circuit board (so-called substrate) is an electronic device such as a resistor device, a filter or an oscillator, a laser diode, a vertical cavity surface emitting laser, or the like, which can be applied by those skilled in the art. Any other chip type of optical or optoelectronic device may also be accommodated.

Although a new form of the invention has been described with reference to one or more specific embodiments, those skilled in the art should understand that various applications and modifications of the invention are possible. Therefore, the scope of the present invention should be limited only by the following claims.

As described above, according to the present invention, by first bonding two or a plurality of thermally conductive sheets and then bonding a hard heat diffusion element with the circuit board, it has excellent heat dissipation ability and a small weight, and is warped and twisted. Can produce a low cost plastic cavity down chip carrier.

Claims (6)

A method of attaching a rigid heat spreader element to a circuit board for manufacturing a cavity down plastic chip carrier, Providing a plastic circuit board having a first surface and a second surface opposed to the first surface and an opening used to receive the chip, the opening penetrating the plastic circuit board; Providing a first thermally conductive sheet having a first surface and a second surface opposed to the first surface; Providing a second thermally conductive sheet having a first surface and a second surface against the first surface and an opening for receiving the chip, the opening penetrating the second thermally conductive sheet; Bonding the first surface of the first thermally conductive sheet to the second surface of the second thermally conductive sheet using a first adhesive sheet that is at least one prepreg layer formed of a fiber reinforced resin; , Bonding the first surface of the second thermally conductive sheet to the second surface of the circuit board using a second adhesive sheet formed without prepreg And attaching the rigid heat spreader element to the circuit board. The method of claim 1, wherein the first adhesive sheet is formed of at least one prepreg. The method of claim 1, wherein the second adhesive sheet is formed of at least one adhesive layer. A method of attaching a rigid heat spreader element to a circuit board for manufacturing a cavity down plastic chip carrier, Providing a plastic circuit board having a first surface and a second surface opposed to the first surface and an opening used to receive the chip, the opening penetrating the plastic circuit board; Providing a first thermally conductive sheet having a first surface and a second surface opposed to the first surface; Providing a plurality of second thermally conductive sheets, each of the plurality of second thermally conductive sheets including a first surface and a second surface abutting the first surface and an opening for receiving the chip; Bonding the first surface of the first thermally conductive sheet to the second surface of one of the plurality of second thermally conductive sheets using a first adhesive sheet that is at least one prepreg layer; The second thermally conductive sheets are bonded to each other with an additional first adhesive sheet, wherein after the adhering step the second surface of the first thermally conductive sheet and the first surface of one of the plurality of second thermally conductive sheets are air Exposed during Bonding the first surface of one of the plurality of second thermally conductive sheets to the second surface of the circuit board using a second adhesive sheet formed without prepreg And attaching the rigid heat spreader element to the circuit board. 5. The method of claim 4, wherein the first adhesive sheet is formed of at least one prepreg. The method of claim 4, wherein the second adhesive sheet is formed of at least one adhesive layer.

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