JP3638486B2 - Semiconductor element mounting method and metal paste - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method of electrically connecting an electrode of a semiconductor element (chip, pellet, die, etc.) and a terminal electrode on a circuit board, and in particular, a semiconductor element by a face-down bonding method using a bonding metal paste. And a metal paste used for the method.
[0002]
[Prior art]
Conventionally, soldering has been generally used for electrical connection between connection terminals of electronic components and circuit pattern terminals on a circuit board. However, in recent years, for example, downsizing of IC flat packages and the like, increase in connection terminals, etc. Thus, the so-called pitch interval between the connection terminals is gradually narrowed, and it is becoming increasingly difficult to cope with the conventional soldering technique.
[0003]
Therefore, recently, for example, semiconductor elements such as chips, pellets, dies, etc., which are active and passive elements that are not packaged, which are called bare elements, are electrically mounted on a circuit board. In the case of mounting while being connected to the semiconductor device, solder bumps are formed in advance on the electrode pads of the semiconductor element, the solder bumps are disposed facing downward against the terminal electrodes of the circuit board, and are heated and fused to a high temperature. The so-called face-down bonding method is widely used. These solder bumps are generally formed on a three-layered metal thin film (Under Bump Metals) made of, for example, Cr (chrome), Cu (copper), and Au (gold) by using a resist, solder, plating, or vapor deposition. The
[0004]
This mounting method has been considered to be an effective method for mounting a semiconductor element because it has a high mechanical strength after connection and can collectively connect the electrodes of the semiconductor element and the terminal electrodes of the circuit board.
[0005]
[Problems to be solved by the invention]
However, in the semiconductor element mounting method using the conventional solder bumps described above, there is a risk that the solder spreads when heated and melted, and the solder bumps (electrodes) adjacent to each other may be short-circuited. There was a problem that sometimes it could not be done.
[0006]
A method has also been proposed in which a ball is formed of a metal paste having ultrafine metal particles, and the ball is used in place of the solder bump (see Japanese Patent Application Laid-Open No. 9-326416). However, the ultra-fine metal particles used here are, for example, ultra-fine metal particles by condensing ultra-fine particles consisting only of metal from the gas phase by evaporating the metal in a vacuum in the presence of some gas. It is considered to be ultrafine particles of a single metal produced by a method for obtaining fine particles, and it is considered that there are problems in terms of stability, physical properties, and cost.
[0007]
The present invention has been made in view of the above circumstances, and there is no risk of short-circuiting with an adjacent electrode even when connected to a fine pitch electrode, and the electrical connection has high stability, low cost, and high reliability. An object of the present invention is to provide a method for mounting a semiconductor device capable of realizing the above and a metal paste used in the method.
[0008]
[Means for Solving the Problems]
According to the first aspect of the present invention, the composite metal ultrafine particles obtained by coating the periphery of the core portion substantially composed of a metal component having an average particle diameter of 1 to 10 nm with a coating layer composed of an organic substance having 5 or more carbon atoms in advance. A step of preparing and preparing a metal paste by dispersing the composite metal ultrafine particles in a solvent, and attaching the metal paste onto a terminal electrode of a circuit board to form a metal paste ball mainly composed of the composite metal ultrafine particles. A semiconductor device comprising: a step of connecting a semiconductor element electrode on the metal paste ball using a face-down method; and a step of electrically connecting the semiconductor element and the circuit board by low-temperature firing. This is an element mounting method.
[0009]
According to this method, since the composite metal ultrafine particles can be produced in a chemical process in a liquid phase, a simple apparatus is used in a normal atmospheric atmosphere without using a large vacuum apparatus. Mass production is possible and the cost is low. Moreover, since the surroundings are coated with an organic compound, not only the cohesiveness in the solvent is small, but also stable and easy to handle, and therefore, a metal paste in which composite metal ultrafine particles are uniformly dispersed can be adjusted. In addition, process management is easy. Furthermore, since the particle size is uniform, all the composite metal superparticles are fused at a constant temperature during low-temperature firing.
[0011]
The melting point of the metal particles is known to decrease as the particle size decreases, but the effect starts to appear at 20 nm or less, and the effect becomes significant when the particle size is 10 nm or less. Therefore, the core portion substantially composed of a metal component having an average particle diameter of 1 to 10 nm is melt-bonded to each other at a temperature considerably lower than the melting point of the metal, thereby enabling low-temperature firing. In addition, the core metal and the coating layer that serves as a protective film for protecting the core metal can be strongly ionically bonded to improve dispersion stability in the solvent and to improve the property stability as particles. it can.
[0012]
According to a second aspect of the present invention, in the semiconductor device according to the first aspect, the core portion is positively charged Ag, Au or Pb ultrafine metal particles, and the coating layer is an organic anion. This is an element mounting method.
The invention according to claim 3 is characterized in that a metal having a high conductivity of about 0.1 to 1 μm and a resin component are added to the metal paste. This is the implementation method. Examples of the metal having a high conductivity include Ag, Au, Pd, and Al. Thereby, high electrical conductivity can be ensured via a metal, and the reliability of semiconductor element mounting can be improved.
[0013]
According to a fourth aspect of the present invention, there is provided the semiconductor element mounting method according to any one of the first to third aspects, wherein the low-temperature firing is performed in a temperature range of 200 to 250 ° C.
In the invention according to claim 5, the composite metal ultrafine particles in which the periphery of the core portion substantially composed of a metal component having an average particle diameter of 1 to 10 nm is coated with a coating layer composed of an organic substance having 5 or more carbon atoms in advance. A metal paste prepared and prepared by dispersing the composite metal ultrafine particles in a solvent.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
First, as shown in FIG. 1, composite metal ultrafine particles 14 including a core portion 10 substantially made of a metal component and a coating layer 12 made of an organic compound are produced. Such composite metal ultrafine particles 14 are stable because they are covered with the coating layer 12 made of an organic compound, and have a low tendency to aggregate in a solvent.
[0015]
The composite metal ultrafine particles 14 are composed of an organic compound and a metal salt that is a starting material, such as carbonate, formate, and acetate. Surrounding organic compounds. At this time, the organic compound and the metal component are present in an integrated state in a state where part or all of them are chemically bonded, and the conventional ultrafine particles stabilized by being coated with the surfactant. In contrast, it is highly stable and stable at higher metal concentrations.
[0016]
The average particle diameter of the core part 10 of the composite metal ultrafine particles 14 is 1 to 10 nm. By comprising in this way, the core part 10 can be fuse | melted at temperature considerably lower than melting | fusing point which the metal which comprises the core part 10 has, and, thereby, low temperature baking is attained.
[0017]
The composite metal ultrafine particles 14 are, for example, in a non-aqueous solvent and in the presence of an ionic organic substance, a metal salt such as carbonate / formate salt / acetic acid salt at a decomposition reduction temperature or higher and a decomposition temperature of the ionic organic substance or lower. It can be manufactured by heating. As the metal component, Ag, Au, or Pb is used, and as the ionic organic substance, a fatty acid having 5 or more carbon atoms, alkylbenzene sulfonic acid, or alkyl sulfonic acid is used.
[0018]
The heating temperature is not less than the decomposition reduction temperature of metal salts such as carbonates, formates and acetates and not more than the decomposition temperature of ionic organic substances. For example, in the case of silver acetate, the decomposition start temperature is 200 ° C. What is necessary is just to hold | maintain at the temperature which the above and ionic organic substance do not decompose | disassemble. In this case, the heating atmosphere is preferably an inert gas atmosphere so that the ionic organic matter is not easily decomposed, but it can be heated even in the air by selecting a non-aqueous solvent.
[0019]
Moreover, when heating, various alcohols can also be added and it becomes possible to accelerate reaction. The alcohol is not particularly limited as long as the above effects are obtained, and examples thereof include lauryl alcohol, glycerin, and ethylene glycol. Although the addition amount of alcohols can be suitably determined according to the kind of alcohol to be used, etc., it is usually about 5 to 20, preferably 5 to 10 parts by weight with respect to the metal salt 100.
[0020]
After the heating is completed, purification is performed by a known purification method. The purification method may be performed, for example, by centrifugation, membrane purification, solvent extraction or the like.
[0021]
For example, oleic acid is used as the organic anionic substance and silver acetate is used as the metal source. These are placed in a naphthenic high boiling point solvent having a boiling point of 250 ° C., heated at 240 ° C. for 3 hours, and further added with acetone. By carrying out precipitation purification, a composite metal ultrafine particle in which the periphery of a cluster-like positively charged Ag metal ultrafine particle (core metal) having an average particle diameter of about 10 nm is coated with an organic anion (coating layer) is produced. can do.
[0022]
Then, the composite metal ultrafine particles 14 are dispersed in a predetermined solvent such as toluene, and a metal having a high conductivity such as Ag, Au, Pd or Al, for example, about 0.1 to 1 μm and a resin component, if necessary. 2A, the metal paste is dropped onto a predetermined position of the terminal electrode 22 of the circuit board 20 to form a height mainly composed of the composite metal ultrafine particles 14 as shown in FIG. A metal paste ball 24 of about 2 μm is formed.
[0023]
Such metal paste has very fine composite metal ultrafine particles 14 which are dispersed particles, and is therefore almost transparent when the composite metal ultrafine particles 14 are mixed and stirred. By appropriately selecting the temperature and the like, physical property values such as surface tension and viscosity can be adjusted.
[0024]
Next, as shown in FIG. 2B, a so-called flip is performed in which the electrode pad portion provided on the semiconductor element 30 and the metal paste ball 24 are aligned using a face-down method with the semiconductor element 30 facing downward. The electrode pad portion of the semiconductor element 30 is connected to the metal paste ball 24 by a chip method, and leveling based on the weight of the semiconductor element 30 is performed as necessary.
[0025]
In this state, the semiconductor element 30 and the circuit board 20 are electrically connected by performing low temperature baking in a hot air oven at 200 to 250 ° C. for 30 minutes, for example. That is, a solvent such as toluene contained in the metal paste ball 24 is evaporated, and the composite metal ultrafine particles 14 which are the main components of the metal paste ball 24 are further converted into the core portion 10 of the coating layer (organic compound) 12 (see FIG. 1). The coating layer 12 is detached from the core portion 10 or decomposed and disappeared by heating at a temperature equal to or higher than the decomposition temperature of the coating layer 12 itself.
[0026]
In this manner, for example, by electrically connecting the semiconductor element and the circuit board by firing at a low temperature in a temperature range of 200 to 250 ° C., heat distortion hardly occurs, and solder is not used. A short-circuit can be avoided and connection at a finer pitch becomes possible.
[0027]
At this time, as described above, by using a metal paste to which a metal having a high conductivity is added, a high conductivity can be ensured through the metal and the reliability of semiconductor element mounting can be improved.
[0028]
【The invention's effect】
As described above, according to the present invention, there is no risk of short-circuiting with an adjacent electrode even when connecting to an electrode with a fine pitch, and high stability, low cost, and reliable electrical connection are realized. Thus, the semiconductor element can be mounted on the circuit board.
[Brief description of the drawings]
FIG. 1 is a diagram schematically showing the structure of composite metal ultrafine particles.
FIG. 2 is a diagram showing a semiconductor element mounting method according to an embodiment of the present invention in the order of steps.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Core part 12 Covering layer 14 Composite metal ultrafine particle 20 Circuit board 22 Terminal electrode 24 Metal paste ball 30 Semiconductor element

Claims (5)

Preparation of composite metal ultrafine particles in which the periphery of the core portion substantially consisting of a metal component having an average particle diameter of 1 to 10 nm is coated in advance with a coating layer made of an organic substance having 5 or more carbon atoms , A step of preparing a metal paste by dispersing in a solvent;
Attaching the metal paste onto a terminal electrode of a circuit board to form a metal paste ball mainly composed of composite metal ultrafine particles;
Connecting a semiconductor element electrode on the metal paste ball using a face-down method;
And a step of electrically connecting the semiconductor element and the circuit board by low-temperature firing. The core portion, Ag charged positively, with Au or Pb metal ultrafine particles, the coating layer, mounting method of a semiconductor device according to claim 1, characterized in that the organic anion.   3. The method of mounting a semiconductor element according to claim 1, wherein a metal having a high conductivity of about 0.1 to 1 [mu] m and a resin component are added to the metal paste.   The method for mounting a semiconductor element according to claim 1, wherein the low-temperature firing is performed in a temperature range of 200 to 250 ° C. 5. Preparation of composite metal ultrafine particles in which the periphery of the core portion substantially consisting of a metal component having an average particle diameter of 1 to 10 nm is coated in advance with a coating layer made of an organic substance having 5 or more carbon atoms; A metal paste characterized by being dispersed in a solvent.

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