JP2009185112A - Conductive adhesive and semiconductor device having the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a conductive adhesive which has improved heat conductivity and is excellent in heat radiability. <P>SOLUTION: Provided is the conductive adhesive 30 containing a main agent comprising an epoxy resin, a curing agent comprising an amine-based resin, a diluent for mixing the main agent and the curing agent, and further 8-quinolinol, as a resin 33, containing a block or flake-like first filler 31 comprising Ag, and a block or flaky second filler 32 comprising Ag and having a less thickness and a larger specific surface area than those of the first filler 31, as a conductive filler, wherein the total content of the conductive fillers 31, 32 is 84 to 90 wt.%. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a conductive adhesive containing a conductive filler made of Ag in a resin component, and a semiconductor device formed by bonding a semiconductor chip onto a lead frame via such a conductive adhesive.

  Conventionally, this type of semiconductor device generally has a semiconductor chip mounted on a lead frame via a conductive adhesive, and the semiconductor chip and the lead frame are joined by the conductive adhesive. And as such a conductive adhesive, the thing of following patent document 1-patent document 4 is proposed.

  This is a conductive adhesive used to mount electronic components on a circuit board, and realizes good joint strength, connection resistance characteristics, and excellent printability that can replace solder. .

Specifically, a main agent made of a resin containing a biphenyl type epoxy resin and a trifunctional phenol type epoxy resin with respect to a bisphenol type epoxy resin, a curing agent made of an amine-based resin, a diluent, and a scaly shape It consists of a conductive filler made of Ag particles.
JP 2000-319622 A JP 2003-206469 A JP 2003-221573 A JP 2003-335924 A

  However, when a semiconductor chip is bonded onto the lead frame using such a conductive adhesive, when a power element or the like is used as the semiconductor chip, it is necessary to dissipate the heat of the semiconductor chip from the lead frame. In this case, the conductive adhesive is required to satisfy further high heat dissipation (for example, 5 W / mk or more), but the conventional one is insufficient.

  The present invention has been made in view of the above problems, and has improved the thermal conductivity of a conductive adhesive, and has a conductive adhesive excellent in heat dissipation, and such a conductive adhesive. An object is to provide a semiconductor device.

  In order to achieve the above object, the present inventor has conducted intensive studies based on the conductive adhesives described in Patent Documents 1 to 4 described above.

  First, the resin component of the conductive adhesive includes a main agent made of a bisphenol-type epoxy resin, a curing agent made of an amine or phenolic resin, and a diluent for mixing the main agent and the curing agent. .

  Here, the conductive filler was in the form of a block or flake instead of the conventional scale-like one. Furthermore, the conductive filler was formed by mixing the first filler and the second filler having a smaller specific surface area than the first filler. This is intended to ensure thermal conductivity with the first filler having a relatively large thickness and to increase the contact area between the fillers with the second filler having a large specific surface area.

  And in order to improve thermal conductivity, the quantity of the conductive filler which consists of Ag with respect to this resin component was increased with 84-90 wt%. As a result, the thermal conductivity of the conductive adhesive was increased and the heat dissipation was improved, but there were too many conductive fillers, and the printability at the paste stage and the mechanical adhesion after curing were reduced.

  Therefore, when a diluent was added to such a level as to ensure the printability and adhesiveness, it was experimentally found that this time, there is too much diluent to obtain heat dissipation commensurate with the increase in conductive filler. (See FIG. 4 described later).

  As a result of diligent investigations on this, it has been shown that if 8-quinolinol is added, even if the amount of diluent is reduced, heat dissipation can be obtained in accordance with the increase in conductive filler while ensuring the above printability and adhesiveness. (See FIG. 4 described later). This is presumably because 8-quinolinol itself supplements the diluent function and the heat dissipation function. The present invention has been experimentally obtained as a result of such studies.

  That is, in the present invention, the resin (33) further contains 8-quinolinol, and the conductive filler has a block-like or flake-like first filler (31) made of Ag and a block-like or flake-like shape made of Ag. The second filler (32) is thinner than the first filler (31) and has a large specific surface area, and the content of the conductive filler (31, 32) is 84 wt% or more and 90 wt% or less. It is characterized by that.

  According to this, the heat conductivity of a conductive adhesive (30) can be improved, and the conductive adhesive (30) excellent in heat dissipation can be provided.

  Here, it is preferable that the content rate of an electroconductive filler (31, 32) is 84 to 88 wt%.

  The main agent is preferably a bisphenol F type epoxy resin or a bisphenol A type epoxy resin. Moreover, it is preferable that a hardening | curing agent is a novolak-type phenol resin more than imidazole or a binuclear body.

  The diluent is preferably phenyl glycidyl ether having a para-tert-butyl group.

  Since this material reacts with a reaction system material such as an epoxy resin which is the main agent at the time of curing and is easily taken into this reaction system material, it is difficult to volatilize at 250 to 255 ° C. which is a solder reflow temperature of ordinary Pb-free solder. The weight loss rate at the temperature is small. Therefore, when the semiconductor device using the conductive adhesive is solder reflowed and connected to another member, the conductive adhesive can be prevented from rupture due to the volatilization of the diluent.

  Further, when the weight of the first filler (31) in the conductive adhesive is x and the weight of the second filler (32) is y, the first filler (31) and the second filler (32) The mixing ratio x: y is preferably 80:20 to 95: 5.

The first filler (31) has an average particle diameter of 1 to 20 μm, a specific surface area of 0.10 to 0.50 m ² / g, and a tap density of 5.0 to 7.5 g / ml. Is preferred.

The second filler (32) preferably has a specific surface area of 0.50 to 1.20 m ² / g and a tap density of 4.0 to 6.5 g / ml.

  In the present invention, the semiconductor chip (20) is mounted on the lead frame (10) via the conductive adhesive (30) having the above characteristics, and the semiconductor chip (20) is formed by the conductive adhesive (30). Provided is a semiconductor device (100) in which a lead frame (10) is joined. According to this, heat dissipation of the conductive adhesive (30) can be improved, and heat dissipation from the semiconductor chip (20) to the lead frame (10) can be promoted.

  In addition, the code | symbol in the bracket | parenthesis of each means described in the claim and this column is an example which shows a corresponding relationship with the specific means as described in embodiment mentioned later.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a schematic cross-sectional configuration of a semiconductor device 100 according to an embodiment of the present invention, and FIG. 2 is a diagram showing an enlarged configuration of a conductive adhesive 30 in FIG.

  The semiconductor device 100 is configured as a small mold package such as a QFN (Quad Flat Nonloaded) package having no outer lead, and a semiconductor chip is formed on the island 11 of the lead frame 10 via a conductive adhesive 30. 20 is mounted.

  The lead frame 10 includes an island 11 on which the semiconductor chip 20 is mounted and a lead 12 for electrical connection with the outside of the semiconductor device 100. The lead frame 10 is made of a normal lead frame material such as Cu or 42 alloy, and is formed by patterning a plate material by etching or pressing. Further, here, the surface of the lead frame 10 is subjected to Ni roughening Pd—PPF plating, and the specific surface area is 1.3 to 1.5.

  The semiconductor chip 20 is formed by a general semiconductor process, and is, for example, an IC chip formed by forming a transistor element or the like on a chip made of a silicon semiconductor.

  Here, the back surface of the semiconductor chip 20 and the island 11 are connected via the conductive adhesive 30, but no electrode may be formed on the back surface of the semiconductor chip 20, or an electrode such as Au. May be formed.

  As shown in FIG. 1, an electrode such as Al (not shown) is provided on the surface of the semiconductor chip 20, and this electrode and the lead 12 of the lead frame 10 are made of a wire 40 made of Au, Al, or the like. Are connected and electrically connected. The wire 40 is formed by ordinary wire bonding or the like.

  The lead frame 10, the semiconductor chip 20, and the wire 40 are sealed with a mold resin 50. The mold resin 50 is made of a normal mold material such as an epoxy resin.

  Here, the surface of the island 11 opposite to the semiconductor chip 20 side and the surface of the lead 12 opposite to the wire 40 connection side are exposed from the mold resin 50. Thereby, the heat of the semiconductor chip 20 is radiated on the opposite surface of the island 11 through the conductive adhesive 30, and the semiconductor device 100 and the outside are connected on the opposite surface of the lead 12. Can be connected.

  As shown in FIG. 2, the conductive adhesive 30 includes an epoxy resin main agent, an amine or phenol resin curing agent, a diluent for mixing the main agent and the curing agent, and other components. It consists of a resin 33 containing a curing catalyst and a coupling agent, and conductive fillers 31 and 32 mixed with the resin 33.

  The materials used for the conductive adhesive 30 such as the resin 33 and the conductive fillers 31 and 32 have a function of improving the wettability between the conductive fillers 31 and 32 and the resin 33, and are a cured product having high purity and low water absorption. It exhibits characteristics such as becoming a cured product having heat resistance, and is intended to obtain high connection reliability. Further, it is selected in consideration of workability and paste suitability.

  In such a semiconductor device 100, the semiconductor chip 20 is mounted on the island 11 of the lead frame 10 via the paste-like conductive adhesive 30, and the conductive adhesive 30 is heated and cured to perform bonding. Thereafter, wire bonding is performed between the semiconductor chip 20 and the lead 12 to perform connection by the wire 40, and thereafter, this is put into a mold (not shown) and sealed by the mold resin 50, thereby producing the product. Is done.

  Next, the conductive adhesive 30 in the semiconductor device 100 will be further described. The conductive adhesive 30 of the present embodiment includes an epoxy resin as a main agent, an amine resin as a curing agent, a curing catalyst, a diluent, and conductive fillers 31 and 32.

  The conductive fillers 31 and 32 are made of Ag, and the blending ratio with the resin 33 is 90/10 to 96/4. Particularly preferred is 92/8 to 94/6. This is because it is optimal for setting the Ag filler content in the cured product to a target value.

  Here, the epoxy resin used as the main agent includes a liquid bisphenol type epoxy resin in consideration of workability, a solid biphenyl type epoxy resin and a trifunctional phenol type epoxy resin in the bisphenol resin in order to have heat resistance. A liquid epoxy resin containing, a liquid epoxy resin having a naphthalene skeleton, a hydrogenated epoxy resin, an aliphatic epoxy resin, an alicyclic epoxy resin, or the like can be used.

  In this example, bisphenol F type epoxy resin or bisphenol A type epoxy resin is adopted as the main agent. Either of these may be used. Moreover, as a hardening | curing agent, imidazole or a phenol resin is used, and both of these may be used. In addition, as a phenol resin used as a hardening | curing agent, a bisphenol F type phenol resin, an allyl phenol resin, a novolak type phenol resin, etc. are employable.

  Moreover, as a diluent, the thing whose weight decreasing rate in 250-255 degreeC is 80% or less is preferable, for example. In this example, the diluent employs phenyl glycidyl ether having a tert-butyl group at the para position. FIG. 3 is a diagram showing the chemical structural formula of this phenylglycidyl ether.

  As shown in FIG. 3, the phenyl glycidyl ether with tert-butyl at the para position is highly reactive because there is no steric hindrance in the reactive group as shown in FIG. It reacts with the reaction system material and is easily taken into the main agent, and there are few unreacted residual diluents. Therefore, at a temperature of 250 to 255 ° C., which is a solder reflow temperature of ordinary Pb-free solder, it is difficult to volatilize and the weight reduction rate at the temperature is small.

  For this reason, in this embodiment, when the semiconductor device 100 is solder reflowed by the lead 12 and connected to another member, bursting of the conductive adhesive 30 due to the evaporation of the diluent, so-called popcorn phenomenon is minimized. Can be prevented.

  Further, as shown in FIG. 2, the conductive fillers 31 and 32 are each composed of a block-shaped Ag or a flake-shaped first filler 31 and a second filler 32 each having a thickness of 1 μm or more. The filler 32 is thinner than the first filler 31 and has a large specific surface area. The first filler 31 having a relatively large thickness ensures thermal conductivity, and the second filler 32 having a large specific surface area increases the contact area between the fillers.

  In addition, in the conductive adhesive 30 before curing, that is, the conductive adhesive 30 as a paste, the content of the conductive fillers 31 and 32 in the entire conductive adhesive 30 is 84 wt% or more and 90 wt% or less. 84 wt% or more and 88 wt% or less is desirable. In particular, in order to ensure a thermal conductivity of 5 W / m · K and to connect with high reliability, 86 wt% or more and 88 wt% or less are preferable.

  Further, when the weight of the first filler 31 in the conductive adhesive 30 is x and the weight of the second filler 32 is y, the mixing weight ratio x: y of the first filler 31 and the second filler 32 is: 80: 20-95: 5. In particular, x: y = 85: 15 to 90:10 is preferable. With this ratio, the number of contact points between the fillers is large and high thermal conductivity can be realized while maintaining the coating properties and the dispensing properties.

In the present embodiment, the first filler 31 has an average particle diameter of 1 to 20 μm, a specific surface area of 0.10 to 0.50 m ² / g, and a tap density of 5.0 to 7.5 g / ml. It is. Preferably, the specific surface area is 0.20 to 0.40 m ² / g, and the tap density is 5.5 to 6.9 g / ml. This is to ensure thermal conductivity.

The second filler 32 of the present embodiment has a specific surface area of 0.50 to 1.20 m ² / g and a tap density of 4.0 to 6.5 g / ml. The specific surface area is preferably 0.60 to 0.80 m ² / g and the tap density is 4.2 to 5.8 g / ml. This is to increase the number of contact points.

  And the conductive adhesive 30 of this embodiment contains 8-quinolinol as the resin 33 further. For example, 8-quinolinol is added by about 1 wt% in the entire conductive adhesive 30 before curing. The 8-quinolinol improves the wettability between the conductive fillers 31 and 32 and the resin 33, thereby preventing fluidity failure due to the repelling of the fillers 31 and 32 and the resin 33 during die mounting.

  In addition, since the familiarity between the fillers 31 and 32 and the resin 33 is improved, it is possible to reduce the amount of diluent which is not good for paste characteristics by about 0.5 wt% to 1 wt%, and the thermal conductivity margin. Goes up.

  That is, in the conductive adhesive 30 in which the conductive fillers 31 and 32 are increased compared with the conventional one in order to improve the thermal conductivity, the paste printability and the mechanical adhesiveness are lowered due to too much conductive filler, but 8-quinolinol. Suppresses the deterioration of these characteristics.

  FIG. 4 is a diagram showing the results of an experimental investigation on the effect of adding 8-quinolinol in the conductive adhesive 30 of the present embodiment. The content of the conductive fillers 31 and 32 (unit: wt%) is shown on the horizontal axis, and the thermal conductivity (unit: W / m · K) of the conductive adhesive 30 after curing is shown on the vertical axis.

  Here, the composition of the main agent, the curing agent, the diluent, and the conductive fillers 31 and 32 in this investigation is within the above-mentioned range, and the conductive fillers 31 and 32 are those for which 8-quinolinol is added and those for which 8-quinolinol is not added. The thermal conductivity was examined by changing the content of. The amount of 8-quinolinol added was 1 wt%. Further, the sample shown in FIG. 4 is obtained by adding a diluent in an amount sufficient to ensure adequate printability and adhesiveness.

  As shown in FIG. 4, in the case where 8-quinolinol is not added (8-quinolinol is not added), the heat dissipation commensurate with the increase in the conductive fillers 31 and 32 when the filler content is between 84 wt% and 88 wt%. It is difficult to obtain sex. This is probably because the amount of diluent is too large.

  On the other hand, in the case where 8-quinolinol is added (with 8-quinolinol added), the thermal conductivity linearly increases with the increase in the conductive fillers 31 and 32 when the filler content is between 84 wt% and 88 wt%. The rate is increasing. That is, the heat dissipation corresponding to the increase in filler is obtained. This is considered to be because the amount of the diluent could be reduced from, for example, 6.8 wt% to 6.3 wt% by adding 8-quinolinol.

  The same tendency as that shown in FIG. 4 is obtained in the range of the constitution of the main agent, curing agent, diluent, and conductive fillers 31 and 32 described above. That is, according to the present embodiment, it is possible to improve the thermal conductivity of the conductive adhesive 30 and provide the conductive adhesive 30 having excellent heat dissipation.

  Further, the physical properties of the conductive adhesive 30 of this embodiment before or after curing will be further described. For example, the glass transition temperature of the conductive adhesive 30 after curing is 70 to 130 ° C. In particular, 100-120 degreeC is preferable.

  The viscosity of the conductive adhesive 30 before curing is 15 to 30 Pa · s. In particular, 20 to 25 Pa · s is preferable from the viewpoint of workability. Moreover, the thixo index of the conductive adhesive 30 before curing is 4 to 6.5. Particularly, 5 to 6 is preferable from the viewpoint of workability. Moreover, it is preferable that the volatile component of the conductive adhesive 30 before curing is 7.5% or less from the suppression of the popcorn phenomenon after reflow.

Moreover, the elastic modulus of the conductive adhesive 30 after curing is 8 to 15 GPa at 25 ° C. and 0.4 to 1.0 GPa at 200 ° C. If it does so, it can connect with sufficient adhesive strength. Furthermore, 9 to 13 GPa at 25 ° C. and 0.6 to 0.8 GPa at 200 ° C. are preferable. Moreover, the specific resistance of the conductive adhesive 30 after curing is 1 × 10 ⁻⁴ Ω · cm or less. Then, the electrical connection becomes good.

  Further, the amount of bleed of the conductive adhesive 30 before curing is preferably 200 μm or less for reasons such as contamination of nearby bonding pads. Then, even in the case of a fine pitch package or component connection, it is possible to connect without contaminating adjacent bonding connections.

  Moreover, the impurity content of the conductive adhesive 30 before curing is 20 ppm or less for Cl ions and 10 ppm or less for Na ions. By doing so, the resin after curing can be highly purified, and a highly reliable connection becomes possible.

Moreover, the bending strength of the conductive adhesive 30 after curing is 35 N / mm ² or more. If it does so, the film | membrane intensity | strength of a conductive adhesive can be made high and a highly reliable connection will be attained. Moreover, the normal temperature shear strength of the conductive adhesive 30 after curing is 10 N / mm ² or more, and the high temperature shear strength is 1 N / mm ² or more. Then, high connection strength can be obtained even at room temperature or high temperature.

  Moreover, the linear expansion coefficient of the conductive adhesive 30 after curing is 30 to 50 ppm below the glass transition point and 45 to 125 ppm above the glass transition point. Then, high connection reliability can be obtained. Particularly preferred is 35 to 45 ppm below the glass transition point and 65 to 90 ppm above the glass transition point.

  Moreover, the curing conditions for the conductive adhesive 30 are 135 to 155 ° C. and 60 to 70 minutes. In particular, the recommended condition is preferably 145 ° C. for 60 minutes. Further, the thickness of the cured conductive adhesive 30 shown in FIG. 1 is, for example, 25 μm or more.

  In addition, as shown in FIG. 4 above, the thermal conductivity of the conductive adhesive 30 is 2 W / m · K or more, particularly 5 W / m · K or more when the filler content is 86 wt% or more. When the thermal resistance is confirmed by the product structure, there is a reduction effect of 1 ° C./W than the conventional conductive adhesive.

  In addition, an additive that improves the wettability between the conductive fillers 31 and 32 and the resin 33 may be added to the conductive adhesive 30. For example, by adding a silicone-based or fluorine-based leveling agent, the low viscosity region at the time of curing becomes longer, and the fluidity of the conductive adhesive 30 is improved, so that a highly reliable connection is possible.

  In the semiconductor device 100 of this embodiment, the semiconductor chip 20 is mounted on the lead frame 10 via the conductive adhesive 30, and the semiconductor chip 20 and the lead frame 10 are joined by the conductive adhesive 30. The conductive adhesive 30 includes, as a resin 33, a main agent made of an epoxy resin, a curing agent made of an amine resin, and a diluent for mixing the main agent and the curing agent. It is configured to include particles made of Ag.

  In this embodiment, in such a semiconductor device 100, the resin 33 of the conductive adhesive 30 before curing used further contains 8-quinolinol, and the conductive filler is a flaky first filler 31 made of Ag. And a second filler 32 having a flake shape made of Ag and thinner than the first filler 31 and having a large specific surface area, and the conductive filler content is 84 to 90 wt%.

  And since the heat dissipation of the conductive adhesive 30 is improved, heat dissipation from the semiconductor chip 20 to the lead frame 10 is promoted. In the conductive adhesive 30 after curing in the semiconductor device 100 in which the conductive adhesive 30 is cured, the content of the conductive filler is 90 wt% or more and 96 wt% or less.

(Other embodiments)
Moreover, although the said embodiment described the example which applied the conductive adhesive 30 about small IC packages like QFN, in addition to that, two members are adhere | attached via the conductive adhesive 30. For example, the present invention can be applied to other hybrid ICs, mold ICs, and the like.

1 is a schematic cross-sectional view of a semiconductor device according to an embodiment of the present invention. It is an enlarged view of the conductive adhesive in FIG. It is a figure which shows the chemical structural formula of pt-butyl phenyl glycidyl ether. It is a figure which shows the investigation result of the addition effect of 8-quinolinol in the said embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Lead frame, 20 ... Semiconductor chip, 30 ... Conductive adhesive agent,
31 ... 1st filler of conductive adhesive, 32 ... 2nd filler of conductive adhesive,
33 ... Resin of conductive adhesive, 100 ... Semiconductor device.

Claims (9)

The resin (33) includes a main agent made of an epoxy resin, a curing agent made of an amine or phenol resin, and a diluent for mixing the main agent and the curing agent, and particles (31, 31) made of Ag as a conductive filler. 32) In a conductive adhesive comprising
The resin (33) further contains 8-quinolinol,
The conductive filler is a block-like or flake-like first filler (31) made of Ag and a block-like or flake-like shape made of Ag, which is thinner than the first filler (31) and has a large specific surface area. 2 fillers (32),
A conductive adhesive, wherein a content of the conductive filler (31, 32) is 84 wt% or more and 90 wt% or less. The conductive adhesive according to claim 1, wherein the content of the conductive filler (31, 32) is 84 wt% or more and 88 wt% or less. The conductive adhesive according to claim 1 or 2, wherein the main agent is a bisphenol F type epoxy resin or a bisphenol A type epoxy resin. The conductive adhesive according to any one of claims 1 to 3, wherein the curing agent is imidazole or a novolak-type phenolic resin having a binuclear form or more. The conductive adhesive according to claim 1, wherein the diluent is phenyl glycidyl ether having a tert-butyl group at the para position. When the weight of the first filler (31) in the conductive adhesive is x and the weight of the second filler (32) is y, the first filler (31) and the second filler (32). The conductive adhesive according to any one of claims 1 to 5, wherein the mixing ratio x: y is 80:20 to 95: 5. The first filler (31) has an average particle diameter of 1 to 20 μm, a specific surface area of 0.10 to 0.50 m ² / g, and a tap density of 5.0 to 7.5 g / ml. The conductive adhesive according to any one of claims 1 to 6, characterized in that: The second filler (32) has a specific surface area of 0.50 to 1.20 m ² / g and a tap density of 4.0 to 6.5 g / ml. The electrically conductive adhesive as described in any one. A semiconductor chip (20) is mounted on the lead frame (10) via the conductive adhesive (30) according to any one of claims 1 to 8, and the conductive adhesive (30) A semiconductor device comprising a semiconductor chip (20) and the lead frame (10) joined together.

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