ADHESIVE TRANSFER FILM AND METHOD FOR MANUFACTURING POWER MODULE SUBSTRATE BY USING SAME

The present disclosure relates to an adhesive transfer film for bonding a semiconductor chip and a spacer to a substrate and a method for manufacturing a power module substrate by using same, the adhesive transfer film being obtained by manufacturing an Ag sintering paste in the form of a film. The present disclosure can reduce the process time by minimizing a sintering process, and can reduce equipment investment cost.

TECHNICAL FIELD

The present disclosure relates to an adhesive transfer film and a method for manufacturing a power module substrate by using the same, and more specifically, to an adhesive transfer film prepared for bonding a semiconductor chip and a spacer to a substrate and a method for manufacturing a power module substrate by using the same.

BACKGROUND ART

A power module changes the voltage used in an electric vehicle from DC to AC and supplies it to a motor. Due to the high performance of electric vehicles, a semiconductor chip mounted on the power module has been changed from conventional silicon (Si) to silicon carbide (SiC) with excellent performance. Thus, heat dissipation is important because a power module using a SiC semiconductor generates high heat due to high voltage.

The power module is manufactured by utilizing a bonding scheme using Ag sintering paste in order to allow a semiconductor chip to be mounted between two substrates and improve heat dissipation of the semiconductor chip. However, in the case of bonding using Ag sintering paste, it is difficult to uniformly apply Ag sintering paste to a semiconductor chip or a spacer. In addition, when the spacer is placed on the semiconductor chip, additional adhesive application and secondary sintering are required, so the process time is long and expensive equipment is required.

In addition, the power module may be manufactured by using a soldering bonding scheme to prevent the semiconductor chip from being damaged in bonding each component, but the soldering bonding scheme may be separated due to low bonding strength.

SUMMARY OF INVENTION

Technical Problem

One object of the present disclosure is to provide an adhesive transfer film which has a uniform thickness and can be bonded without a void by manufacturing Ag sintering paste in the form of a film, can reduce the process time by minimizing the sintering process, and can reduce the equipment investment cost in a bonding process for bonding a semiconductor chip and a spacer to a substrate, and a method for manufacturing a power module substrate by using the same.

Another object of the present disclosure is to provide an adhesive transfer film that is capable of reducing the frequency of occurrence of burrs in the bonding process and lowering the unit cost by fabricating an adhesive layer made of Ag sintering paste in the form of a pattern on a film, and a method for manufacturing a power module substrate by using the same.

Still another object of the present disclosure is to provide an adhesive transfer film that has high thermal conductivity and high fracture strength after sintering and can minimize defects due to cracks, and a method for manufacturing a power module substrate by using the same.

Solution to Problem

In order to achieve the objects, an adhesive transfer film according to an embodiment of the present disclosure includes a base film; a sticky layer formed on the base film; and an adhesive layer formed on the sticky layer.

The adhesive layer includes an Ag adhesive layer, and the Ag adhesive layer includes 97 to 99 wt % of Ag powder and 1 to 3 wt % of a binder.

The base film includes a PET film, and the sticky layer includes OCA.

The adhesive layer is formed in a pattern shape on the sticky layer.

In addition, the adhesive layer is formed in a multilayer structure on the sticky layer.

The adhesive layer includes a first adhesive layer laminated on an upper surface of the sticky layer; a second adhesive layer laminated on an upper surface of the first adhesive layer; and a third adhesive layer laminated on an upper surface of the second adhesive layer, wherein the first and third adhesive layers include Ag powder made of nanoparticles, the first to third adhesive layers include Ag powders made of flake form nanoparticles, and an average particle diameter of the Ag powder included in the second adhesive layer is relatively smaller than average particle diameters of the Ag powders included in the first adhesive layer and the third adhesive layer.

A method for manufacturing a power module substrate includes a preparing step of preparing an adhesive transfer film; a temporary bonding step of transferring an adhesive layer on the adhesive transfer film to an object, and temporarily bonding the object to which the adhesive layer is transferred to a lower substrate by medium of the adhesive layer; and a main bonding step of bonding an upper substrate to an upper portion of the object temporarily bonded on the lower substrate and performing sintering to main bond the object between the lower substrate and the upper substrate.

The preparing step includes preparing a base film; forming a sticky layer on the base film; and forming an adhesive layer on the sticky layer.

The preparing step includes attaching an OCA film on a PET film; and forming an Ag adhesive layer by applying or printing Ag sintering paste on the OCA film and drying the Ag sintering paste applied or printed on the OCA film.

The preparing step includes preparing the adhesive transfer film to form an adhesive layer having a pattern shape corresponding to a position of the object.

In addition, the preparing step includes attaching an OCA film on a PET film; and mesh screen printing or stencil printing Ag sintering paste on the OCA film, and drying to form an Ag adhesive layer having a pattern shape.

In addition, the preparing step includes preparing a base film; forming a sticky layer on the base film; and forming the adhesive layer having a multilayer structure by coating Ag sintering paste on the sticky layer and drying the Ag sintering paste coated on the sticky layer three times or more.

The temporary bonding step includes fixing the adhesive transfer film to a die and fixing the object to an upper chuck for adsorbing and fixing the object using a vacuum; transferring the adhesive layer on the adhesive transfer film to the object by pressing the object fixed to the upper chuck toward the adhesive transfer film while heating the upper chuck and the die, respectively; raising the object to which the adhesive layer is attached by raising the upper chuck while maintaining a vacuum; transferring the upper chuck to an upper portion of the lower substrate; temporarily bonding the object to the lower substrate by pressing the object fixed to the upper chuck toward the lower substrate; and releasing the vacuum and raising the upper chuck.

In the temporary bonding step, the die is heated to a temperature of 80 to 100° C., and the upper chuck is heated to a temperature of 100 to 170° C.

In the main bonding step, the sintering is performed for 2 to 5 minutes while heating and pressing at 240 to 300° C.

In the temporary bonding step, the object includes a semiconductor chip, a first conductive spacer and a second conductive spacer, and the temporary bonding step includes a first temporary bonding step of transferring the adhesive layer on the adhesive transfer film to a lower surface of the semiconductor chip, and temporarily bonding the semiconductor chip to which the adhesive layer is transferred to an upper surface of the lower substrate by medium of the adhesive layer; a second temporary bonding step of transferring the adhesive layer on the adhesive transfer film to a lower surface of the first conductive spacer, and temporarily bonding the first conductive spacer to which the adhesive layer is transferred to an upper surface of the semiconductor chip by medium of the adhesive layer; and a third temporary bonding step of transferring the adhesive layer on the adhesive transfer film to a lower surface of the second conductive spacer, and temporarily bonding the second conductive spacer to which the adhesive layer is transferred to an upper surface of the lower substrate by medium of the adhesive layer.

A height of the second conductive spacer is equal to a sum of heights of the semiconductor chip, the adhesive layer, and the first conductive spacer.

The main bonding step includes forming the adhesive layer on the lower surface of the upper substrate to be placed to correspond to the first conductive spacer and the second conductive spacer that are temporarily bonded on the lower substrate; and fixing the upper substrate to an upper chuck, and main bonding a temporary bonding body of the semiconductor chip and the first conductive spacer, and the second conductive spacer between the upper substrate and the lower substrate by heating and pressing the upper substrate fixed to the upper chuck toward the lower substrate.

An AMB substrate or a DBC substrate is used for the upper substrate and the lower substrate.

Advantageous Effects of Invention

According to the present disclosure, the silver sintering paste is manufactured in the form of a film and used for bonding the semiconductor chip and the spacer to the lower substrate. In addition, according to the present disclosure, the adhesive layer is formed on the final upper substrate in a printing scheme, and is sintered by heating and pressing while being bonded to the spacer of the lower substrate.

Therefore, according to the present disclosure, because it is possible to main bond the spacer on the lower substrate and the upper substrate without the need to turn over the lower substrate, the sintering may be simplified once, thereby reducing the process time and equipment investment cost.

In addition, according to the present disclosure, the base film may control the flatness of the lower surface of the adhesive layer for bonding the semiconductor chip and the spacer between the lower substrate and the upper substrate, and the flatness of the upper surface of the adhesive layer may be controlled by the pressing force of the upper chuck, so that the thickness of the adhesive layer is formed thinly and uniformly. Therefore, according to the present disclosure, it is possible to uniformly bond the upper substrate and the lower substrate, thereby contributing to improving the reliability of a power module product.

In addition, according to the present disclosure, mass production is possible by patterning the adhesive layer, and a plurality of objects such as semiconductor chips may be temporarily bonded to a substrate with one transfer, so that it is possible to reduce the amount of the adhesive transfer film used and greatly reduce the temporary bonding process time.

In addition, according to the present disclosure, because the patterned adhesive layer is transferred in one-to-one correspondence with the object, the burrs generated during transfer may be greatly reduced, and the area of the adhesive layer using Ag in the adhesive transfer film may be greatly reduced, thereby greatly reducing the product cost.

In addition, according to the present disclosure, the adhesive transfer film, in which an Ag adhesive layer having a multilayer structure is formed on the base film, may be prepared by coating the Ag sintering paste on the base film three times or more and drying it, and the adhesive transfer film may be used to bond a semiconductor chip and a spacer to a substrate.

The Ag adhesive layer having a multi-layer structure has a small shrinkage rate in sintering because the Ag powder particles have a flake form. In addition, because the Ag adhesive layer has a multi-layer structure and different powder particles, there is an advantage in removing residual stress, which is the initiation point of cracks, so that defects due to cracks after sintering may be minimized, and high breaking strength (tensile strength) of 50 MPa or more may be secured.

In addition, by minimizing pores when semiconductor chips and spacers are bonded to a substrate by applying a pressure sintering scheme, the above-described multi-layered Ag adhesive layer may secure high thermal conductivity and the sintering time may be reduced, thereby improving process efficiency.

DESCRIPTION OF EMBODIMENTS

An adhesive transfer film10according to the first embodiment of the present disclosure may be used for bonding an object such as a power semiconductor chip, a conductive spacer (CQC), an insulating spacer to a substrate.

As shown inFIG.1, the adhesive transfer film10according to the first embodiment of the present disclosure includes a base film11, a sticky layer12formed on the base film11, and an adhesive layer13formed on the sticky layer12. The adhesive transfer film10is fabricated of an Ag sintering paste in the form of a film. A PET film is applied for the base film11, an OCA film is applied for the sticky layer12, and an Ag adhesive layer is applied for the adhesive layer13. The Ag adhesive layer13is used for good heat dissipation properties.

The Ag adhesive layer includes 98 to 99 wt % of Ag powder and 1 to 2 wt % of a binder. The content of Ag powder in the Ag adhesive layer is increased to increase thermal conductivity.

Ag has good heat dissipation properties with high thermal conductivity, and allows the adhesive layer to have conductivity. The binder allows Ag to have high adhesion and to be uniformly applied. The Ag adhesive layer enables low-temperature sintering by maximizing the content of Ag powder and minimizing the content of the binder in the uniformly applicable range. The low-temperature sintering temperature may be in the range of 240 to 300° C.

When the content of the binder is lowered to 1 to 2 wt %, the organic content is lowered, so that the thermal decomposition and sintering temperature of the Ag adhesive layer may be lowered by about 60 to 100° C. The low sintering temperature enables fast sintering of the Ag adhesive layer. The rapid sintering of the Ag adhesive layer reduces the shrinkage rate during sintering and prevents cracking of the sintered layer, thereby lowering the defect rate.

The Ag adhesive layer contains Ag powder in the form of nanoparticles. Since Ag powder has a liquid phase temperature of 900° C. or higher, sintering is possible in a range of 240 to 300° C., and Ag solder cannot be sintered in a range of 240 to 300° C. because the liquid phase temperature is 200° C. or higher. Therefore, the Ag adhesive layer needs to contain Ag powder, not Ag solder, in the form of nanoparticles.

The Ag adhesive layer has a high thermal conductivity of 200 to 300 W/mK, a shear strength of 50 MPa or more, and a viscosity of 40 to 100 kcps, which has high adhesion on various surfaces. It is possible to use Au instead of Ag, but it is preferable to use Ag in terms of cost.

The adhesive transfer film10may be formed by attaching an OCA film on the base film11, applying or printing Ag sintering paste on the OCA film, and drying it. Alternatively, the adhesive transfer film10may be formed by applying or printing Ag sintering paste on the base film11and drying it. The printing may be screen printing or stencil printing.

The sticky layer12improves the releasability of the adhesive layer13to the base film11. The Ag sintering paste contains 97 to 99 wt % of Ag powder and 1 to 3 wt % of the binder in the same manner as the Ag adhesive layer.

The adhesive transfer film10prepared in the form of a film may make the height of the adhesive layer13very uniform. When bonding an object between two substrates, the height of the adhesive layer13must be uniform such that a tolerance does not occur between the two substrates and any problems do not occur in the final product.

In addition, when the adhesive transfer film10is used in bonding an object between two substrates, it is possible to reduce a void and stand-off defects compared to a conventional paste process of applying a paste to an object and bonding it to a substrate. The void means that pores are generated in the adhesive layer13after sintering, and the stand-off defect means that an object is inclined to one side without being flatly bonded to the substrate.

The adhesive transfer film10may have a thickness of 75-100 μm of the base film11. The thickness of the adhesive layer13may be 40 to 60 μm, preferably 50 μm. The adhesive transfer film10may control the thickness and voids of the adhesive layer13.

The adhesive transfer film10may be applied to a method for manufacturing a power module substrate.

As shown inFIG.2, a method for manufacturing a power module substrate by using the adhesive transfer film10according to the first embodiment of the present disclosure may include transferring an adhesive layer to an object40by using the adhesive transfer film10, and temporarily bonding the object40to which the adhesive layer13has been transferred to an upper surface of a lower substrate20.

A method for manufacturing a power module substrate includes a preparing step of preparing the adhesive transfer film10, a temporary bonding step of transferring an adhesive layer on the adhesive transfer film to an object, and temporarily bonding the object to which the adhesive layer has been transferred to a lower substrate by a medium of the adhesive layer, and a main bonding step of bonding the upper substrate30to an upper portion of the object40temporarily bonded on the lower substrate20and performing sintering to bond the object40between the lower substrate and the upper substrate30.

The preparation step is a step of pre-coating an adhesive layer on the base film.

The preparing step includes preparing the base film11, forming the sticky layer12on the base film11and forming the adhesive layer13on the sticky layer12. As an example, the preparing step includes attaching an OCA film on a PET film, and applying or printing an Ag sintering paste on the OCA film, and drying it to form the Ag adhesive layer. As the base film11, a polycarbonate (PC) film may be used in addition to a polyester (PET) film. However, compared to the PC film, the PET film is advantageous in maintaining the flatness of the lower surface of the adhesive layer13. The flatness of the upper surface of the adhesive layer13may be controlled by the pressing force of the upper chuck3. When the flatness of the adhesive layer13is not good, the adhesive layer is bent during sintering.

As shown inFIG.2, the temporary bonding step includes step s1of fixing the adhesive transfer film10to a die1and fixing the object40to an upper chuck3for adsorbing and fixing the object40by using a vacuum, step s2of transferring the adhesive layer13on the adhesive transfer film10to the object40by pressing the object40fixed to the upper chuck3toward the adhesive transfer film10while heating the upper chuck3and the die1, respectively, step s3of raising the object40to which the adhesive layer13is attached by raising the upper chuck3while maintaining a vacuum, step s4of transferring the upper chuck3to an upper portion of the lower substrate20, step s5of temporarily bonding the object40to the lower substrate20by pressing the object40fixed to the upper chuck3toward the lower substrate20, and step s6of releasing the vacuum of the upper chuck3and raising the upper chuck3. The steps s1to s3are steps of transferring the adhesive layer13from the adhesive transfer film10to the object40, and the steps s5and s6are steps in which the object40to which the adhesive layer13is transferred temporarily bonded to the lower substrate20.

In the step s1, the upper chuck3picks up the object40in a vacuum.

In the step s2, the adhesive layer13is transferred to the lower surface of the object40. In the step s2, the die1is heated to a temperature of 80 to 100° C. and the upper chuck3is heated to a temperature of 100 to 170° C. Preferably, the die is heated to a temperature of 80 to 100° C., and the upper chuck3is heated to a temperature of 160° C. Pressurization may be performed at 1 to 4 MPa. When the heating temperature of the upper chuck3is higher than the heating temperature of the die1, the adhesive layer13may be strongly adhered to the object40having a higher temperature.

In the step s3, the adhesive layer13is picked up while being attached to the object. In the step s3, the adhesive layer13is attached to the lower surface of the object40by transfer and is separated from the base film11. In this case, since the sticky layer12is not separated from the base film11, the adhesive layer13may be separated cleanly.

In the step s4, the object40is transferred to the upper portion of the lower substrate20to temporarily bond the object40on the lower substrate20. The lower substrate20may be an AMB substrate or a DBC substrate.

In the step s5, the object40is temporarily bonded on the lower substrate20by pressing the object40fixed to the upper chuck3toward the lower substrate20. In the step s5, the die1is heated to a temperature of 80 to 100° C. and the upper chuck3is heated to a temperature of 100 to 170° C. Preferably, the die1is heated to a temperature of 80 to 100° C., and the upper chuck3is heated to a temperature of 160° C. Pressurization may be performed in the range of 1 to 4 MPa.

In the step s6, the temporary bonding is completed by releasing the vacuum and raising the upper chuck3. As described above, the adhesive transfer film10is heated using the die1heated to a temperature of 80 to 100° C., and the object40is heated using the upper chuck3heated to a temperature of 100 to 170° C. Then, when the upper chuck3is lowered to allow the object40to be pressed toward the adhesive transfer film10, the adhesive layer13on the adhesive transfer film10may be transferred to the lower surface of the object40having a higher temperature.

After the temporary bonding step, performed is a step of main bonding the object40between the lower substrate20and the upper substrate30by bonding and sintering the upper substrate (refer to reference numeral30inFIG.4) to the upper portion of the object40temporarily bonded on the lower substrate20. The sintering may be performed for 2 to 5 minutes while heating and pressing at 240 to 300° C. The pressing may be performed in the range of 8 to 15 MPa.

The pressing is to prevent void from being generated. The pressing increases the density to significantly reduce the sintering process time. Therefore, when the pressing and sintering are performed, the adhesive layer13is dense without holes, so that the heat conduction is increased and the heat dissipation property is excellent. In addition, the pressing enables fast sintering.

The sintering temperature and time during the main bonding may be adjusted within the above-described range to shorten the mass production time. For example, for sintering during main bonding, it is preferable to perform pressing at 250° C. for 5 minutes, but the pressing may be performed at 300° C. for 2 minutes to improve mass productivity. The sintering is intended to improve bonding strength. The flatness of the adhesive layer13is secured by performing the pressing with a uniform pressure.

The temporary bonding step and the main bonding step may be performed respectively or may be performed simultaneously. The simultaneous execution means that the temporary bonding step may be omitted and the main bonding step may be performed. For example, in the step s5, the object40fixed to the upper chuck3is heated and pressed toward the substrate20at a temperature of 240 to 300° C. and a pressure of 8 to 15 MPa for 2 to 5 minutes to main bond the object40to the substrate20without the temporary bonding.

FIG.3illustrates an example of a power module substrate according to the first embodiment of the present disclosure.

The power module has a multi-layer structure of the lower substrate20and the upper substrate30, and a semiconductor chip40ais interposed between the lower substrate20and the upper substrate30. The semiconductor chip includes a power semiconductor chip such as Si, SiC, or GaN.

The lower substrate20and the upper substrate30include ceramic substrates each including a ceramic substrate21and a metal substrate22brazed to at least one surface of the ceramic substrate21to increase the heat dissipation efficiency of the heat generated from the semiconductor chip40a. The ceramic substrate21may be, for example, one of Al2O3, AlN, SiN and Si3N4. The metal layer22includes an electrode pattern for mounting the semiconductor chip40aand an electrode pattern for mounting a driving element as a metal foil brazed on the ceramic substrate21, respectively. As an example, the metal foil may be an aluminum foil or a copper foil. As an example, the metal foil is fired at 780 to 1100° C. on a ceramic substrate to be brazed to the ceramic substrate. In the embodiment, an AMB substrate or a DBC substrate is described as an example, but a TPC substrate or a DBA substrate may be applied. However, in terms of durability and heat dissipation efficiency, AMB substrates are most suitable.

A semiconductor chip40a, a first conductive spacer40band a second conductive spacer40ctransfer the adhesive layer13on the adhesive transfer film10, and are bonded between the20and the upper substrate30by using the adhesive layer13. The adhesive layer13is an Ag adhesive layer having high heat dissipation.

An insulating spacer (refer to reference numeral40dinFIG.5) is used to maintain a gap between the lower substrate20and the upper substrate30when using a substrate having an upper and lower multilayer structure, and when electricity needs to pass between the lower substrate20and the upper substrate30, conductive spacers40band40care used. In this case, the Ag adhesive layer having high heat dissipation is used to prevent heat generated in the semiconductor chip40afrom being diffused to the upper substrate30through the lower substrate20.

InFIG.3, one second conductive spacer40cis located in the center of the lower substrate20, and four first conductive spacers40bare spaced apart from each other around the second conductive spacer40c. The first conductive spacer40bis bonded to the upper surface of the semiconductor chip40aand is bonded to the upper substrate30. In the method for manufacturing a power module substrate according to the first embodiment of the present disclosure, the semiconductor chip40aand the first conductive spacer40bare laminated bonded between the lower substrate20and the upper substrate30. In addition. the second conductive spacer40cmay be bonded between the lower substrate20and the upper substrate30to have the same height as the sum of the heights of the semiconductor chip40aand the first conductive spacer40b, thereby obtaining heat dissipation characteristics and electrical conductivity.

FIG.4illustrates an example of the method for manufacturing a power module substrate according to the first embodiment of the present disclosure, which includes temporarily bonding a semiconductor chip, a first conductive spacer, and a second conductive spacer to the lower substrate ofFIG.3, and bonding and sintering the upper substrate thereon.

As illustrated inFIGS.4A to4C, a method for manufacturing a power module substrate includes a first temporary bonding step s10of transferring the adhesive layer13on the adhesive transfer film10to a lower surface of the semiconductor chip40a, and temporarily bonding the semiconductor chip40ato which the adhesive layer13is transferred to an upper surface of the lower substrate20by medium of the adhesive layer13, a second temporary bonding step s20of transferring the adhesive layer13on the adhesive transfer film10to a lower surface of the first conductive spacer40b, and temporarily bonding the first conductive spacer40bto which the adhesive layer13is transferred to an upper surface of the semiconductor chip40aby medium of the adhesive layer13, and a third temporary bonding step s30of transferring the adhesive layer13on the adhesive transfer film10to a lower surface of the second conductive spacer40c, and temporarily bonding the second conductive spacer40cto which the adhesive layer13is transferred to an upper surface of the lower substrate20by medium of the adhesive layer13.

In the first temporary bonding step s10, the semiconductor chip40ais a power semiconductor chip such as Si, SiC, or GaN.

In the second bonding step s20, the first conductive spacer40bis an interconnection spacer (CQC). In addition, in the third temporary bonding step S30, the second conductive spacer40cis an interconnection spacer (CQC). The interconnection spacer CQC is used when electricity needs to pass between the lower substrate20and the upper substrate30. The interconnection spacer (CQC) may be formed in the form of a conductive metal block or in the form of a block in which a conductive metal is coated on the outer surface of an injection-molded product. The height of the second conductive spacer40cis the same as the sum of the heights of the semiconductor chip40a, the adhesive layer13, and the first conductive spacer40b.

The lower substrate20may be an AMB substrate or a DBC substrate. In the first to third temporary bonding steps, the upper chuck3fixes the semiconductor chip40a, the first conductive spacer40b, and the second conductive spacer40cto the upper chuck3by vacuum suction.

In the first to third temporary bonding steps s10to s30, the heating and pressing by the upper chuck3are performed for about 20 seconds at a temperature of 100 to 170° C. and a pressure of 1 to 4 MPa. In this case, the die1is heated and maintained at a temperature of 80 to 100° C.

After the third temporary bonding step s30, performed is the main bonding step of bonding and sintering the upper substrate30to the upper portions of the first conductive spacer40band the second conductive spacer40ctemporarily bonded to the lower substrate20, thereby main bonding the semiconductor chip40a, the first conductive spacer40b, and the second conductive spacer40cbetween the lower substrate20and the upper substrate30.

As shown inFIG.4D, the main bonding step includes step s40of forming the adhesive layer13on the lower surface of the upper substrate30to be placed to correspond to the first conductive spacer40band the second conductive spacer40cthat are temporarily bonded on the lower substrate20, and step s50of fixing the upper substrate30to an upper chuck3, and main bonding a temporary bonding body40′ of the semiconductor chip40aand the first conductive spacer40b, and the second conductive spacer40cbetween the upper substrate30and the lower substrate20by heating and pressing the upper substrate30fixed to the upper chuck3toward the lower substrate20. In the main bonding step, the heating and pressing are performed for 2 to 5 minutes at a temperature of 240 to 300° C. and a pressure of 8 to 15 MPa.

The adhesive layer13of the temporary bonding step becomes a sintered adhesive layer13′ after performing the main bonding step. Because the sintered adhesive layer13′ is dense without voids by pressing and sintering, the bonding strength is improved and the sintered adhesive layer13′ functions as an excellent heat dissipation electrode.

FIG.5illustrates another example of the power module substrate according to the first embodiment of the present disclosure.

The power module substrate shown inFIG.5includes the lower substrate20, two second conductive spacers40clocated in the center of the lower substrate20, and four first conductive spacers40bdisposed on both sides of the second conductive spacer40c, respectively and bonded to a semiconductor chip40a. In addition, four insulating spacers40dare located at the corners of the lower substrate20.

The first conductive spacer40band the second conductive spacer40care interconnection spacers (CQC), and the insulating spacer40dforms a heat dissipation space between the lower substrate20and the upper substrate30. The insulating spacer40dmay be formed of a ceramic material. The first conductive spacer40band the second conductive spacer40cperform three functions of heat dissipation and electrical conduction. The insulating spacer40dforms a space between the two substrates to perform a heat dissipation function.

In the case of the power module substrate shown inFIG.5, the semiconductor chip40a, the first conductive spacer40b, and the second conductive spacer40cand the insulating spacer40dmay be bonded to the lower substrate20at a uniform height through the processes shown inFIG.4.

A method for manufacturing a power module substrate illustrated inFIG.6includes a temporary bonding step s100of temporarily bonding the semiconductor chip40a, the first conductive spacer40b, the second conductive spacer40cand the insulating spacer40d, to which the adhesive layer13on the adhesive transfer film is transferred, to the lower substrate20by medium of the adhesive layer13, and a main bonding step s200of main bonding the semiconductor chip40a, the first conductive spacer40b, the second conductive spacer40c, and the insulating spacer40donto the lower substrate20by sintering the semiconductor chip40a, the first conductive spacer40b, the second conductive spacer40c, and the insulating spacer40d,20which are in a temporarily bonding state, on the lower substrate.

In the temporary bonding step s100, the die1on which the lower substrate20is placed may be heated to 80 to 100° C., and the upper chuck for temporarily bonding each object40to the lower substrate20may be heated to a temperature of 100 to 170° C.

In the main bonding step s200, the die1′ on which the lower substrate20is placed may be heated to 240 to 300° C., and a heating and pressurizing press5for main bonding each object40to the lower substrate20may perform pressing at a pressure of 8 to 15 MPa while heating to a temperature of 240 to 300° C.

Meanwhile, although the example shown inFIG.6has been described as temporarily bonding and sintering the object40only to the lower substrate20, the main bonding step in which the upper substrate30is bonded and sintered to the object40in the state of temporarily bonding the object40to the lower substrate20may be performed.

In the method for manufacturing a power module substrate according to the first embodiment of the present disclosure described above, the base film11may control the flatness of the lower surface of the adhesive layer13, and the flatness of the upper surface of the adhesive layer13may be controlled by the pressing force of the upper chuck3, so that it is possible to form the adhesive layer13to have a thin and uniform thickness.

In addition, in the method for manufacturing a power module substrate according to the first embodiment of the present disclosure described above, since the bonding process is completed by bonding the semiconductor chip40aand the first conductive spacers40bonto the lower substrate20in a stacked manner by using the adhesive transfer film10and then performing a final one-time sintering process, the process can be minimized, the process time can be reduced, and the equipment investment cost is also reduced.

When the operation of temporarily bonding the semiconductor chip40ato the lower substrate20and temporarily bonding the first conductive spacer40bto the semiconductor chip40ais performed using Ag sintering paste, it is inconvenient to temporarily bond the semiconductor chip40aand the first conductive spacer40bto the lower substrate20and then perform first sintering, and additionally apply an Ag sintering paste on the first conductive spacer40bto bond the upper substrate30to the first conductive spacer40band perform secondary sintering, but it is difficult to apply the Ag sintering paste uniformly. In addition, because the pressing is performed for each sintering process, the process time is lengthened, and expensive equipment is required for the application of the Ag sintering paste, thereby increasing the equipment investment cost. Therefore, it is effective to manufacture Ag sintering paste in the form of a film and apply it to a method for manufacturing a power module substrate in terms of reducing process time and equipment investment cost.

Hereinafter, an adhesive transfer film according to a second embodiment of the present disclosure and a method for manufacturing a power module substrate by using the same will be described with reference toFIGS.7to12. For convenience of description, descriptions of the same components as those of the first embodiment shown inFIGS.1to6will be omitted, and differences will be mainly described below.

As shown inFIG.7, the adhesive transfer film10according to the second embodiment of the present disclosure is manufactured by forming Ag sintering paste on a film in the form of a pattern.

The adhesive transfer film10may be formed by attaching an OCA film on the base film11and printing Ag sintering paste in a pattern form on the OCA film and drying it. Alternatively, the adhesive transfer film10may be formed by printing Ag sintering paste in a pattern form on the base film11and drying it. In the scheme of printing the adhesive layer13in a pattern form, mesh screen printing or stencil printing may be applied to uniformly control the height of the adhesive layer13. In the stencil printing, a stencil metal mask having a pattern-shaped hole is disposed on the upper surface of the base film11and screen-printed to form an adhesive layer pattern of a certain thickness. The mesh screen printing is a printing scheme of transferring an adhesive layer pattern onto a base film by using a screen mesh. As the mesh screen, a screen mesh is used, which is manufactured by chemically treating (coating) a certain area of a finely woven fabric type to form a film on the mesh to prevent the paste from passing therethrough and to transmit the paste through the development operation of only a part of the desired image area.

FIG.8illustrates a method for manufacturing a power module substrate by using an adhesive transfer film according to a second embodiment of the present disclosure.

As shown inFIG.8, in the method for manufacturing a power module substrate according to the second embodiment of the present disclosure, the adhesive layer13may be transferred to the object40using the adhesive transfer film10, and the object40to which the adhesive layer13is transferred may be temporarily bonded to the upper surface of the lower substrate20. The adhesive layer13is formed on the base film11in a pattern shape corresponding to a position corresponding to the object40. As described above, when the adhesive layer13is formed on the base film11in a pattern shape corresponding to the position corresponding to the object40, it is possible to reduce the amount of the adhesive transfer film10used and defects caused by burrs.

A method for manufacturing a power module substrate includes a preparing step of preparing the adhesive transfer film10, a temporary bonding step of transferring an adhesive layer on the adhesive transfer film to an object, and temporarily bonding the object to which the adhesive layer is transferred to a lower substrate by a medium of the adhesive layer, and a main bonding step of bonding the upper substrate30to an upper portion of the object40temporarily bonded on the lower substrate20and performing sintering to main bond the object40between the lower substrate and the upper substrate30.

In the preparing step, the adhesive layer13is pre-coated on the base film11in a pattern shape corresponding to the position corresponding to the object.

The preparing step includes preparing the base film11, forming the sticky layer12on the base film11, and forming the adhesive layer13having a pattern shape on the adhesive layer12by a stencil printing or mesh screen printing scheme. As an example, the preparing step includes attaching an OCA film on a PET film, and applying or printing an Ag sintering paste on the OCA film, and drying it to form the Ag adhesive layer. As the base film11, a polycarbonate (PC) film may be used in addition to a polyester (PET) film. However, compared to the PC film, the PET film is advantageous in maintaining the flatness of the lower surface of the adhesive layer13. The flatness of the upper surface of the adhesive layer13may be controlled by the pressing force of the upper chuck3. When the flatness of the adhesive layer13is not good, the adhesive layer is bent during sintering.

As shown inFIG.8, the temporary bonding step includes step s1of fixing the adhesive transfer film10to a die1and fixing the object40to an upper chuck3for adsorbing and fixing the object40by using a vacuum, step s2of transferring the adhesive layer13on the adhesive transfer film10to the object40by pressing the object40fixed to the upper chuck3toward the adhesive transfer film10while heating the upper chuck3and the die1, respectively, step s3of raising the object40to which the adhesive layer13is attached by raising the upper chuck3while maintaining a vacuum, step s4of transferring the upper chuck3to an upper portion of the lower substrate20, step s5of temporarily bonding the object40to the lower substrate20by pressing the object40fixed to the upper chuck3toward the lower substrate20, and step s6of releasing the vacuum of the upper chuck3and raising the upper chuck3. The steps s1to s3are steps of transferring the adhesive layer13from the adhesive transfer film10to the object40, and the steps s5and s6are steps of temporarily bonding the object40to which the adhesive layer13is transferred object40to the lower substrate20.

After the temporary bonding step, performed is a step of main bonding the object40between the lower substrate20and the upper substrate30by bonding and sintering the upper substrate (refer to reference numeral30inFIG.4) to the upper portion of the object40temporarily bonded on the lower substrate20. The sintering may be performed for 2 to 5 minutes while heating and pressing at 240 to 300° C. The pressing may be performed in the range of 8 to 15 MPa.

FIG.9illustrates a method for manufacturing a power module substrate according to an embodiment of the present disclosure, which includes temporarily bonding a semiconductor chip, a first conductive spacer, and a second conductive spacer to the lower substrate, and bonding and sintering the upper substrate thereon.

As illustrated inFIGS.9A and9B, a method for manufacturing a power module substrate includes a first temporary bonding step s10of transferring the adhesive layer13on the adhesive transfer film10to a lower surface of the semiconductor chip40a, and temporarily bonding the semiconductor chip40ato which the adhesive layer13is transferred to an upper surface of the lower substrate20by medium of the adhesive layer13, and a second temporary bonding step s20of transferring the adhesive layer13on the adhesive transfer film10to the lower surface of the first conductive spacer40band the lower surface of the second conductive spacer40c, and temporarily bonding the first conductive spacer40band the second conductive spacer40cto which the adhesive layer13is transferred to the upper surface of the semiconductor chip40aand the upper surface of the lower substrate20by medium of the adhesive layer13, respectively.

In the first temporary bonding step s10, because the adhesive layer13is formed on the base film11in a shape corresponding to a position corresponding to the semiconductor chip40a, clean transfer is possible without burrs.

In the second temporary bonding step s20, the first conductive spacer40band the second conductive spacer40care interconnection spacers (CQC). The height of the second conductive spacer40cis the same as the sum of the heights of the semiconductor chip40a, the adhesive layer13, and the first conductive spacer40b

The lower substrate20may be an AMB substrate or a DBC substrate. In the first and second temporary bonding steps s10and s20, the upper chuck3fixes the semiconductor chip40a, the first conductive spacer40b, and the second conductive spacer40cto the upper chuck3by vacuum suction.

After the second temporary bonding step s20, performed is the main bonding step of bonding and sintering the upper substrate30to the upper portions of the first conductive spacer40band the second conductive spacer40ctemporarily bonded to the lower substrate20, thereby main bonding the semiconductor chip40a, the first conductive spacer40b, and the second conductive spacer40cbetween the lower substrate20and the upper substrate30.

As shown inFIG.9C, the main bonding step includes step s30of forming the adhesive layer13on the lower surface of the upper substrate30to be placed to correspond to the first conductive spacer40band the second conductive spacer40cthat are temporarily bonded on the lower substrate20, and step s40of fixing the upper substrate30to an upper chuck3, and main bonding a temporary bonding body40′ of the semiconductor chip40aand the first conductive spacer40b, and the second conductive spacer40cbetween the upper substrate30and the lower substrate20by heating and pressing the upper substrate30fixed to the upper chuck3toward the lower substrate20. In the main bonding step, the heating and pressing are performed for 2 to 5 minutes at a temperature of 240 to 300° C. and a pressure of 8 to 15 MPa.

The adhesive layer13of the temporary bonding step becomes a sintered adhesive layer13′ after performing the main bonding step. Because the sintered adhesive layer13′ is dense without voids by pressing and sintering, the bonding strength is improved and the sintered adhesive layer13′ functions as an excellent heat dissipation electrode.

FIG.10illustrates another example of the method for manufacturing a power module substrate according to the second embodiment of the present disclosure.

The method for manufacturing a power module substrate enables mass production by using a patterned adhesive layer.

As shown inFIG.10A, the plurality of semiconductor chips40amay be fixed to the upper chuck3manufactured in the form of a jig to fix the plurality of semiconductor chips40a. As shown inFIG.10B, the adhesive transfer film10may be manufactured such that the adhesive layer13is formed in a pattern shape corresponding to positions corresponding to the semiconductor chips40a. In this case, because the semiconductor chips40amay be fixed at each position and the adhesive layer13may be transferred to the semiconductor chips40aat a time through a one-time heating and pressing process, the temporary bonding process time may be significantly reduced.

As shown inFIG.11, the upper chuck3is provided with a vacuum suction line S, so that the semiconductor chip40amay be fixed at a set position by vacuum suction. The adhesive transfer film10is formed with the adhesive layer13in a pattern shape corresponding to a position corresponding to the semiconductor chip40a. The adhesive layer13is pre-printed on the base film11and dried.

As shown inFIG.12, according to the method for manufacturing a power module substrate capable of mass production, the adhesive transfer film10having a patterned adhesive layer13is fixed to the die1, and the semiconductor chips40aare fixed to the upper chuck3by using a vacuum suction line S. Next, the upper chuck3is heated with the heating and pressing press5, and the semiconductor chips40afixed to the upper chuck3are pressed toward the adhesive transfer film10while heating the die1with a heater, thereby transferring the adhesive layers13on the adhesive transfer film10to the semiconductor chips40a. Next, while maintaining the vacuum, the upper chuck3is raised to raise the semiconductor chips40ato which the adhesive layer13is attached.

The die1is heated to a temperature of 80 to 100° C. by using an internal heater, and the upper chuck3is heated to a temperature of 100 to 170° C. by using the heating and pressing press5. Preferably, the die is heated to a temperature of 80 to 100° C., and the heating and pressing press5is heated to a temperature of 160° C. The pressing may be performed at 1 to 4 MPa. When the heating temperature of the heating and pressing press5is higher than the heating temperature of the die1, the adhesive layers13may be strongly adhered to the semiconductor chips40ahaving a higher temperature.

As shown inFIG.12, the adhesive layer13attached to the semiconductor chip40ahas an end contracted due to the temperature of the transfer process. Because the patterned adhesive layer13is transferred to the semiconductor chip40a, it is possible to significantly reduce the burr factor that may occur when transferring.

When the adhesive layer13is formed on the entire surface of the base film11and the adhesive layer13is transferred to the semiconductor chip, the end of the adhesive layer13, which is transferred to the semiconductor chip40awhile the upper chuck3is raised, may be torn off to generate burrs.

As described above, the method for manufacturing a power module substrate according to the second embodiment of the present disclosure is capable of mass production by patterning the adhesive layer13. That is, the semiconductor chips40amay be arranged in advance to correspond to the positions at which they are to be mounted on a power module by using the upper chuck3manufactured in the form of a jig. Then, the adhesive transfer film10having the adhesive layer13patterned to transfer the adhesive layer to the position of the semiconductor chip40aon the upper chuck3may be prepared, and the adhesive layer13may be transferred to the lower surface of the semiconductor chip40athrough heating and pressing. Thus, the semiconductor chip may be temporarily bonded to the DBC substrate or AMB substrate with one transfer, so that it is possible to reduce the amount of adhesive transfer film used and greatly reduce the temporary bonding process time. In addition, because the patterned adhesive layer is attached to the semiconductor chip in a one-to-one correspondence, it may be effective in that it is possible to greatly reduce the generation of residues during transfer, and the area of the adhesive layer using Ag is greatly reduced, thereby significantly reducing the product cost.

Hereinafter, an adhesive transfer film according to a third embodiment of the present disclosure and a method for manufacturing a power module substrate by using the same will be described with reference toFIGS.13to15. For convenience of description, descriptions of the same components as those of the first embodiment shown inFIGS.1to6will be omitted, and differences will be mainly described below.

As shown inFIG.13, the adhesive transfer film10according to the third embodiment of the present disclosure is an Ag coated dry film which is prepared by coating Ag sintering paste on a PET film and drying it, where the adhesive layer13has a multilayer structure. The adhesive layer13may be three layers or more. The adhesive layer13includes a first adhesive layer13alaminated on a top surface of the sticky layer12, a second adhesive layer13blaminated on a top surface of the first adhesive layer13a, and a third adhesive layer13claminated on a top surface of the second adhesive layer13b.

The average particle diameter of the Ag powder particles included in the first adhesive layer13aand the third adhesive layer13cis different from the average particle diameter of the Ag powder particles included in the second adhesive layer13b. Preferably, the average particle diameter of the Ag powder particles included in the second adhesive layer13bis relatively smaller than that of the Ag powder particles included in the first adhesive layer13aand the third adhesive layer13c. When the adhesive layer13is formed in a multilayer structure and the average particle diameter of Ag powder particles included in each layer is different, the shrinkage rate during sintering differs.

As in the embodiment, when the Ag powder particles, which are included in the second adhesive layer13bwhich is the intermediate layer and have an average particle diameter which is relatively smaller than the average particle diameter of the Ag powder particles included in the third adhesive layer13cand the first adhesive layer13awhich are upper and lower layers of the second adhesive layer13bare applied, during sintering, the shrinkage rate of the second adhesive layer13bhaving a relatively small average particle diameter is greater than that of the first adhesive layer13aand the third adhesive layer13c, so that the shape of both ends of the adhesive layer13may be controlled to be concave. When the shape of both ends of the adhesive layer13is controlled to be concave, stress in the central portion of the adhesive layer13may be relieved to increase the breaking strength (tensile strength).

Furthermore, the adhesive layer13may enable dense sintering even when the adhesive layer13having a thick overall thickness is applied by applying Ag powder particles having a small average particle diameter to the center.

In the fracture phenomenon due to flexure due to thermal stress, in most cases, fracture proceeds as cracks occur along the bonding surface of heterogeneous interfaces. However, when the adhesive layer13has a multi-layer structure, the bonding strength is enhanced during sintering of a single material, so that the center of the sintered adhesive layer13is more likely to be the starting point of cracks than the bonding surface of the heterogeneous interface.

That is, by forming the adhesive layer13having a multi-layer structure using an Ag sintering paste in which Ag particle sizes are clearly distinguished, it is possible to prevent the occurrence of cracks at the heterogeneous interface. In addition, the shape of both ends of the adhesive layer13may be controlled by configuring layers differently from each other so that the shrinkage rate is different depending on the Ag particle size to prevent cracks from occurring in the center of the adhesive layer13. Thus, the stress in the center of the adhesive layer13is relieved to increase the breaking strength.

As shown inFIG.13, the adhesive layer13having a multilayer structure on the adhesive transfer film10is transferred to the object40, and then the upper chuck3fixing the object40heats and presses the object40toward the substrate20, thereby sintering and bonding the object40and the substrate20. The shape of both ends of the sintered adhesive layer13″ is a concave shape by the second adhesive layer13b, in which relative shrinkage occurs more than that of the first adhesive layer13aand the third adhesive layer13c, and stress relief in the center is possible. In addition, the sintered adhesive layer13″ has a high thermal conductivity because it has a higher sintered density than the others at the center. The thermal conductivity is high at the minimum pore condition.

As shown inFIG.14, Ag powder particles included in the adhesive layer13are made of flake form nanoparticles. Specifically, the first adhesive layer13ato the third adhesive layer13cinclude Ag powder particles made of flake form nanoparticles, and the average particle diameter of the Ag powder particles included in the second adhesive layer13bis relatively smaller than that of the Ag powder particles included in the first adhesive layer13aand the third adhesive layer (13c).

The Ag powder particles formed in a flake form improve sinterability while minimizing the amount of organic binder. Moreover, the Ag powder particles in the flake form have less shrinkage during sintering, better bonding strength, and higher shear strength compared to the Ag powder particles of a nano-size sphere form. When the amount of the organic binder in the adhesive layer13is large, gas may be generated when the temperature rises to 350 to 400° C. due to overvoltage, and cracks may occur in the adhesive layer. Accordingly, the embodiment includes Ag powder particles made of flake form nanoparticles such that the content of the organic binder is minimized and the content of Ag powder particles is maximized. In an embodiment, the flake form has a flat elliptical shape with a thickness of several nanometers.

As described above, the adhesive transfer film10is an Ag coated dry film in which an Ag sintering paste is coated three times or more on a PET film and dried to form an Ag adhesive layer having a multilayer structure on a base film.

The method for manufacturing a power module substrate using the adhesive transfer film10according to the third embodiment of the present disclosure includes a preparing step of preparing the adhesive transfer film10, a temporary bonding step of transferring an adhesive layer on the adhesive transfer film to an object, and temporarily bonding the object to which the adhesive layer is transferred to a lower substrate by a medium of the adhesive layer, and a main bonding step of bonding the upper substrate30to an upper portion of the object40temporarily bonded on the lower substrate20and sintering to main bond the object40between the lower substrate and the upper substrate30.

In this case, the preparation step is a step of pre-coating an adhesive layer13on the base film11.

The preparing step includes preparing the base film11, forming the sticky layer12on the base film11, and forming the adhesive layer13having a multi-layer structure by coating and drying the Ag sintering paste on the sticky layer12three times or more.

For example, the preparing step includes attaching an OCA film on a PET film, and forming an Ag adhesive layer composed of three layers by applying or printing an Ag sintering paste on the OCA film and performing drying three times.

The Ag adhesive layer employs an Ag powder particles of the second adhesive layer13constituting an intermediate layer, which have the average particle diameter relatively smaller than the average particle diameter of the Ag powder particles of the third adhesive layer13and the second adhesive layer13formed on the upper and lower portions of the intermediate layer, so that the shape of both ends of the Ag adhesive layer is controlled to relieve the stress of the intermediate layer during sintering. In addition, the Ag adhesive layer uses Ag powder particles having a flake form.

As shown inFIG.15, although the adhesive layer13″ having the multilayer structure sintered through the temporary bonding step and the main bonding step shrinks, the shrinkage rate is as small as about 6%. Moreover, the adhesive layer13does not shrink well up and down, and small shrinkage occurs on both sides because Ag constituting the adhesive layer13has a flake form. The flake form increases the bonding strength of the adhesive layer13″ to improve the breaking strength.

Table 1 below shows the characteristics of the Ag adhesive layer (embodiment) and the Sn—Ag solder layer (comparative example) obtained by sintering the adhesive layer according to the third embodiment of the present disclosure compared to pure Ag. The Ag adhesive layer according to the third embodiment includes 98 to 99 wt % of Ag powder and 1 to 2 wt % of a binder.

As shown in Table 1, the Ag adhesive layer according to the third embodiment of the present disclosure has a high thermal conductivity of 200 W/mK, and a tensile strength of 50 MPa or more which is higher than that of a Sn—Ag solder layer. Thus, it may be understood that the thermal conductivity and tensile strength of the Ag adhesive layer according to the third embodiment of the present disclosure are superior to those of the Sn—Ag solder layer.

FIG.16is a view illustrating a flexure that occurs while repeating cooling and heating in a semiconductor chip of a power module.FIG.17is an SEM photograph comparing crack characteristics by applying an Ag adhesive layer (third embodiment) according to an embodiment of the present disclosure and Sn solder (comparative example) to a power module.

As shown inFIG.16, the operating temperature of the semiconductor chip of the power module is 150 to 250° C., and the flexure occurs while cooling and heating is repeated.

As shown inFIGS.17A and17B, when a semiconductor chip is bonded to a substrate with a Sn solder (SAC305, SN100C), as the result of 800 tests at an operating temperature of −40 to 125° C., cracks occurred on the Sn solder bonding surface as shown in the SEM photograph.

Meanwhile, as shown inFIG.17C, the Ag adhesive layer according to the third embodiment of the present disclosure was tested 800 times at an operating temperature of −40 to 125° C., and no cracks were observed.

FIG.18is an SEM photograph and graph illustrating a microstructure according to the binder content of the Ag adhesive layer (third embodiment) of the present disclosure.FIG.19is an SEM photograph and graph illustrating a microstructure according to the binder content of Sn solder (comparative example).

In detail,FIG.18Ais an SEM photograph of an Ag adhesive layer (third embodiment) of the present disclosure sintered at 250° C. for 10 minutes.FIG.18Bis a graph illustrating weight loss and calorimetric measurement results according to the binder content of the embodiment ofFIG.18A.

FIG.19Ais an SEM photograph of Sn solder sintered at 250° C. for 10 minutes.FIG.19Bis a graph of weight loss and calorie measured according to the binder content of the embodiment ofFIG.19A.

As shown inFIGS.18and19, it may be confirmed that as the content of the binder, which is an organic material, is minimized, the pores are minimized. Thus, it may be understood that by minimizing unnecessary organic materials, excellent sintering properties are secured and cracks of the sintered layer are prevented. However, for uniform diffusion of Ag powder particles, the content of the organic binder is preferably 1 to 2 wt %. The uniform adhesive layer13may be formed only when the Ag powder particles are uniformly diffused.

FIG.20shows the Ag adhesive layer (third embodiment) of the present disclosure which is sintered at 250° C. for 30 minutes without pressing.

FIG.20Bis an enlarged view ofFIG.20A, and as a result of sintering the Ag adhesive layer at 250° C. for 30 minutes without pressure, adhesive strength of 60 MPa or more was secured. In addition, it can be confirmed that, even when the Ag adhesive layer is sintered without pressure, the organic matter is minimized, so that the thermal conductivity of at least about 150 W/mK is secured.

FIG.21is a photograph of the structure of the sintered Ag adhesive layer (Ag sintered layer) after press-sintering the Si semiconductor chip to which the Ag adhesive layer is transferred on the substrate. In this case,FIG.21Ais a photograph of an Ag adhesive layer formed through 150 μm mask stencil printing on a base film, andFIG.21Bis a photograph of an Ag adhesive layer formed through 200 μm mask stencil printing on a base film.

The Ag adhesive layer shown inFIGS.21A and21Bwas press-sintered at 240° C. for 4 minutes at 15 MPa. After press-sintering, a dense bonding layer with a porosity of 7 to 8% was confirmed. InFIG.21, sufficient bonding was possible even when the sintering time was short, and adhesive strength of 50 MPa or more and thermal conductivity of about 300 W/mK were secured. It is confirmed that the porosity is secured at 7 to 8% by minimizing organic materials after sintering, and it is confirmed that the thermal conductivity is increased due to the minimum pore condition.

FIG.21shows that the pores are minimized by press-sintering the adhesive layer, and inFIG.20, many pores confirmed by sintering without pressure are observed. Thus, it may be understood that the press-sintering has the effect of increasing the thermal conductivity by minimizing the pores.

FIG.22illustrates a comparison of the adhesive strength of the Ag adhesive layer according to the third embodiment of the present disclosure with those of other companies (comparative example).

There is Semipowerrex® (Korea) as a third-party product. In both the embodiment and the comparative example, sintering was performed at 290° C. for 150 sec.

As confirmed inFIG.22, it may be confirmed that the embodiment obtains sufficient bonding strength within a short time of about 2 minutes at a temperature of 290° C., and the bonding strength is very high as 65 MPa or more.

FIG.23is a general photograph of the fracture surfaces of the embodiment and comparative example ofFIG.22.FIG.24is an SEM photograph of the fracture surfaces of the embodiment and comparative example ofFIG.22.

As shown inFIG.23, in the embodiment, a portion of the Ag adhesive layer was separated, whereas in the comparative example, the bonding surface between the adhesive layer and the substrate was broken.

As shown inFIG.24, in the shape of the fracture surface, the Ag adhesive layer was broken in the middle of the Ag adhesive layer, and in the comparative example (manufactured by other companies), the entire adhesive layer was separated from the substrate. This phenomenon is because, in the embodiment, the central portion of the Ag adhesive layer has a higher sintering density than other portions and the Ag powder particles have a flake form. In the comparative example, the Ag powder particles are almost spherical. Moreover, the embodiment bursts at about 65 MPa and the comparative example bursts at about 23 MPa.

FIG.25illustrates a comparison of the shrinkage rate, flexure occurrence, and microstructure of the Ag adhesive layer according to the third embodiment of the present disclosure and those of a comparative example (manufactured by another company).

The embodiment and comparative example were sintered for 60 minutes at a temperature of 270° C. in a non-pressurized state.

As shown inFIG.25, in the embodiment, about 6% shrinkage occurred, and in the comparative example, about 24% shrinkage occurred. In addition, in the embodiment, the flexure did not occur after sintering, whereas in the comparative example, the flexure occurred after sintering. In addition, in the embodiment, a flake form was confirmed in the microstructure measured by SEM, whereas in the comparative example, a spherical form was confirmed.

From the above results, it may be confirmed that the shrinkage rate of the Ag adhesive layer of the embodiment is 20% less than that of the comparative example, and it may be understood that it contributes to reducing defects due to jig tolerance after bonding of the semiconductor chip.

FIG.26is a graph comparing the weight loss of the Ag adhesive layer according to the third embodiment of the present disclosure and the comparative example (manufactured by other companies).FIG.27is a graph of measured calories of the Ag adhesive layer according to the third embodiment of the present disclosure and the comparative example (manufactured by another company).

It is confirmed that the Ag adhesive layer according to the embodiment has a lower thermal decomposition and sintering temperature is lowered by 60 to 100° C. at an organic content of 1 to 2 wt % compared to that of the comparative example (manufactured by another company). Thus, it may be expected that the low sintering temperature enables fast sintering.

The Ag adhesive layer according to the third embodiment of the present disclosure described above may secure a thermal conductivity of 150 W/mK in non-pressure sintering, a thermal conductivity of 280 W/mK or more in pressure sintering using test equipment, and a thermal conductivity of 300 W/mK or more in using official pressure equipment.

In addition, the Ag adhesive layer according to the third embodiment of the present disclosure has a small shrinkage rate because the Ag powder particles have a flake form. In addition, because the Ag adhesive layer includes a multilayer structure and different powder particles, which has an advantage in removing residual stress, defects due to cracking after sintering may be minimized, and high breaking strength (tensile strength) of 50 MPa or more may be secured.

Best embodiments of the present disclosure are disclosed in the drawings and specification. Although specific terms have been used above, they are only used for the purpose of describing the embodiments and are not used to limit the meaning or scope of the present disclosure described in the claims. Therefore, it will be understood by those skilled in the art that various modifications and equivalent other embodiments of the present disclosure are possible therefrom. Accordingly, the true technical scope of the present disclosure should be defined by the technical spirit of the appended claims.