JP2015090900A - Method for bonding electronic component with heat-bonding material, and connection structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a connection structure which enables the materialization of highly reliable bonding when bonding an electronic component to a substrate with a heat-bonding material.SOLUTION: A connection structure comprises: electrode layers formed on an electronic component; and a bonding layer disposed between the electrode layers and a substrate, and formed by a copper-containing sintered compact. Of the electrode layers, a layer in contact with the bonding layer is a copper alloy layer containing gold, platinum, nickel or palladium. The copper alloy layer has a thickness of 200-850 nm. The porosity of the bonding layer at or near an interface between the copper alloy layer and the bonding layer is 20% or less.

Description

  The present invention relates to a bonding method for bonding adherends of electronic components such as semiconductor packages and semiconductor chips by heating or heating under pressure using a heat bonding material containing metal fine particles and an organic dispersion medium, and The present invention relates to a connection structure formed by the method.

  Recently, semiconductor components have been rapidly increased in power, modularization, high integration, high reliability, and the like. The semiconductor operating temperature tends to be high due to heat generation of the semiconductor product accompanying an increase in current density for realizing high power, high integration, and the like of such mounting equipment.

  Conventionally, high-temperature lead solder that can withstand use at high temperatures has been used as a die-bonding material, but the use of high-temperature lead solder tends to be suppressed due to environmental problems, so it can withstand use at high temperatures. As a die-bonding material, attention has been focused on bonding with a conductive paste in which metal fine particles are blended, which enables bonding under conditions lower than that of a bulk metal without using lead.

  There is known a method of joining an electronic component (for example, a semiconductor chip) to a substrate or the like by heating and sintering under pressure using a metal powder-containing paste or a plate-like molded body for heat bonding mixed with metal powder. Yes. For example, there is a method of joining an electronic component to a substrate with copper metal powder and an adhesive (Patent Document 1).

  Moreover, paying attention to the thickness of the gold layer used when joining a gold electrode and a copper wire, it is known that the thickness of the gold layer is 0.5 to 5 μm in order to prevent Kirkendall voids ( Patent Document 2).

JP 2009-94341 A JP 2012-69691 A

  In general, a heat bonding material containing fine metal particles is placed between adherends and heated and pressed to form a bonded portion. As such a bonding method, using a flip chip bonder or a press, A method of mounting an electronic component (for example, a semiconductor chip) by applying pressure and heating is common.

  However, it has become clear that sufficient reliability cannot be obtained simply by bonding using these methods. In particular, because power devices are used in harsh environments, rigorous reliability tests (thermal shock tests and power cycle tests) are required. Even if they are joined by the conventional methods described above, reliability tests are possible depending on the joining conditions. It has been found that there is a big difference in the results.

  For example, simply joining as in Patent Document 1 described above does not allow the sintered body to have a constant state and cannot be joined with good reproducibility. In particular, there is no disclosure of pores that have an important influence on reliability, and there is a problem that highly reliable joining cannot be performed.

  Further, Patent Document 2 discloses a Kirkendall void at the joint interface due to the Kirkendall effect, and the gold layer should be as thin as possible. However, as a result of experiments conducted by the inventor, it has been found that Kirkendall voids are also generated in a 0.2 μm gold layer thinner than 0.5 μm, which is the thinnest in Patent Document 2. This phenomenon is considered to be caused by the difference between wire bonding and heating / pressure mounting, or the difference between copper wire and copper fine particles. For this reason, even if it uses the method currently disclosed by patent document 2, a highly reliable joining cannot be performed with a copper fine particle sintered compact.

  The objective of this invention is providing the joining method and connection structure which can implement | achieve reliable joining, when joining an electronic component to a board | substrate using a heat joining material.

  As a result of diligent research to solve the above-mentioned problems, the present invention shows that the higher the porosity of the copper fine particle sintered body and the chip electrode interface, the lower the reliability, and the electrode containing gold, platinum, nickel or palladium. Changed to an alloy electrode with copper, and it was found that the greater the thickness of the electrode after the change, the lower the reliability.

  Moreover, it turned out that the said porosity and the thickness of a copper alloy electrode are determined by the pressure at the time of sintering.

  That is, this invention makes the summary the invention described below.

  Heating comprising metal fine particles (P) having an average primary particle diameter of 2 to 500 nm and an organic dispersion medium (S) containing one or more polyhydric alcohols having two or more hydroxyl groups in the molecule. A bonding method and connection structure for an electronic component in which a bonding material (M) is arranged between adherends of the electronic component and bonded by heating or heating under pressure, and the pressure during sintering is controlled. A bonding method and a connection structure for electronic parts, wherein the porosity of the interface between the sintered body and the chip electrode and the thickness of the alloyed chip electrode are optimized.

  According to the present invention, when the heat bonding material (M) is disposed between the adherends of the electronic component and bonded between the adherends by heating or heating under pressure, the outermost surface of the copper and the chip electrode is bonded. A copper alloy is formed between gold, platinum, nickel or palladium. At that time, by setting the porosity immediately below the chip electrode to 20% or less of the bulk porosity, it is possible to prevent breakage due to the increased porosity due to alloying, and to realize strong bonding it can.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows schematically the joining method of the electronic component which concerns on embodiment of this invention, (a)-(c) is a figure explaining the process. It is sectional drawing which shows roughly an example of the connection structure which concerns on this embodiment. (A) is a graph which shows the relationship between the porosity immediately under a chip electrode layer, and the lifetime of a thermal shock test, (b) is the Au-Cu alloy layer thickness in a chip electrode layer, and the lifetime of a thermal shock test. It is a graph which shows the relationship. It is a graph which shows the relationship between a sintering pressure and the porosity directly under a chip electrode layer.

  An electronic component bonding method according to the present invention includes an organic dispersion medium containing metal fine particles (P) having an average primary particle diameter of 2 nm to 500 nm and one or more polyhydric alcohols having two or more hydroxyl groups in the molecule. A bonding method in which a heat bonding material (M) containing (S) is disposed between adherends of electronic components and bonded by heating or heating under pressure, and the bonding pressure is controlled. Therefore, highly reliable bonding can be performed by optimizing the porosity of the interface between the sintered body and the chip electrode layer and the state of the copper alloy electrode.

Hereinafter, the present invention will be described in detail.
[1] Heat bonding material (M)
The heat bonding material (M) is an organic dispersion medium (S) containing metal fine particles (P) having an average primary particle diameter of 2 nm to 500 nm and one or more polyhydric alcohols having two or more hydroxyl groups in the molecule. ).

  The heat-bonding material (M) is, for example, a sheet-shaped heat-bonded molded body (T1) or a heat-bonded paste-like substance (T2) at room temperature, and the metal fine particles (P) are dispersed in the organic dispersion medium (S). doing. The heat-bonding material (M) includes a patterned product made of the heat-bonding material (M) on the surface to be bonded (for example, the surface of the ceramic plate (C)), and a conductive metal plate (K) on the patterned material. Is placed and heated in a temperature range in which the metal fine particles (P) are sintered, the polyhydric alcohol (A1) reduces and activates the surface of the metal fine particles (P), and the metal fine particles (P) are sintered together. Promote. As a result, the electrode and the substrate can be electrically and mechanically joined as in the case of using the paste containing nano-sized metal fine particles. When the heat bonding material (M) is heated and sintered, the organic dispersion medium (S) is removed by decomposition, evaporation, or the like.

  The ratio (mass ratio) of the organic dispersion medium (S) / metal fine particles (P) in the heat bonding material (M) is 10/90 to 70 in order to obtain a stable bonding force in consideration of patterning and sinterability. / 30 is desirable, but the ratio is determined depending on whether the sheet-shaped heat-bonded molded body (T1) or the heat-bonded paste-like substance (T2) is selected.

  The heat bonding material (M) can be obtained by dispersing the metal fine particles (P) in the organic dispersion medium (S) using a known mixer, kneader or the like. As the heat-bonding material (M), it is possible to use high-purity metal fine particles (P) that do not contain impurities such as those contained in the solder paste, so that the bonding strength and conductivity can be improved. Become.

(1) Metal fine particles (P)
The metal fine particles (P) may be only metal fine particles (P1) having a sinterability and having an average primary particle diameter of 2 nm to 500 nm, and further to the metal fine particles (P1), an average primary particle diameter of 0.5 μm to 50 μm fine metal particles (P2) can be used in combination. As the metal fine particles (P1), fine particles of copper or copper alloy can be used.

  Unlike the case of the solder paste, the metal fine particles (P) used for the heat-bonding material (M) can use at least one kind of high-purity copper fine particles as they are, so that the bonded body is excellent in bonding strength and conductivity. Can be obtained. In general, in the case of solder paste, flux (organic component) is contained in order to remove the oxidation of the copper pad portion of the substrate to be mounted, and further, Al, Zn, Cd are contained as a small amount of impurities contained in the metal material. In many cases, metals such as As are contained.

(A) Metal fine particles (P1)
The metal fine particles (P1) are not particularly limited as long as they are metal fine particles having an average primary particle diameter of 2 nm to 500 nm. When the average particle diameter of the primary particles of the metal fine particles (P1) is less than 2 nm is accompanied by manufacturing difficulties, if the average particle diameter of the primary particles is larger than 500 nm, a precise conductive pattern cannot be formed, The firing process becomes complicated. The metal fine particles (P1) in the metal fine particles (P) are preferably 10% by weight or more and 100% by weight or less. Sinterability can be improved by setting the metal fine particles (P1) in the metal fine particles to 10% by weight or more.

(B) Metal fine particles (P2)
In addition to metal fine particles (P1) with an average primary particle diameter of 2 nm to 500 nm, metal fine particles (P2) with an average primary particle diameter of 0.5 μm to 50 μm are dispersed and used in the heat bonding material (M). You can also The metal fine particles (P2) are not particularly limited, but are selected from gold, silver, copper, platinum, palladium, tungsten, nickel, iron, cobalt, tantalum, bismuth, lead, indium, tin, zinc, titanium, and aluminum. One kind or two or more kinds of fine particles can be used, and copper is particularly preferable.

  In particular, when metal fine particles (P2) having an average primary particle diameter of 0.5 μm to 50 μm are further used as metal fine particles (P2) and metal fine particles (P2) having an average primary particle diameter of 2 nm to 500 nm. The metal fine particles (P1) are dispersed in between, and the free movement of the metal fine particles (P1) can be effectively suppressed during the heat treatment, and the dispersibility and stability of the metal fine particles (P1) are improved. As a result, a porous body having a more uniform particle size and pores can be formed by heating and firing.

  The average primary particle diameter of the metal fine particles (P2) is preferably 0.5 μm to 50 μm. If the average primary particle diameter of the metal fine particles (P2) is less than 0.5 μm, the effect of adding the metal fine particles (P2) does not appear, and if it exceeds 50 μm, firing may be difficult.

  Here, the average particle diameter of primary particles means the diameter of primary particles of individual copper fine particles constituting the secondary particles. The primary particle diameter can be measured using an electron microscope. The average particle size means the number average particle size of primary particles.

(2) Organic dispersion medium (S)
The organic dispersion medium (S) contains one or two or more polyhydric alcohols (A1) having two or more hydroxyl groups in the molecule, but the compound (A2) having an amide group as another organic solvent. , An amine compound (A3), a low-boiling organic solvent (A4) and the like can be contained.

(I) Polyhydric alcohol (A1)
Examples of the polyhydric alcohol (A1) include ethylene glycol, diethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2- having two or more hydroxyl groups in the molecule. Butanediol, 1,3-butanediol, 1,4-butanediol, 2-butene-1,4-diol, 2,3-butanediol, pentanediol, hexanediol, octanediol, Glycerol, 1,1,1-trishydroxymethylethane, 2-ethyl-2-hydroxymethyl-1,3-propanediol, 1,2,6-hexanetriol, 1,2,3-hexanetriol, 1,2 , 4-butanetriol, threitol, erythritol, pentaerythritol, pentitol, 1-propanol, 2-propanol, 2-butanol, -Methyl 2-propanol, xylitol, ribitol, arabitol, hexitol, mannitol, sorbitol, dulcitol, glyceraldehyde, dioxyacetone, threose, erythrulose, erythrose, arabinose, ribose, ribulose, xylose, xylulose, lyxose, glucose , Fructose, mannose, idose, sorbose, growth, talose, tagatose, galactose, allose, altrose, lactose, isomaltose, glucoheptose, heptose, maltotriose, lactulose, and trehalose 1 type or 2 types or more selected from can be raised.

  Since these polyhydric alcohols have reducing properties, the surface of the metal fine particles (P) is reduced, and further heat treatment causes the polyhydric alcohol (A1) to continuously evaporate, and the atmosphere in which the liquid and vapor exist. When reduced and fired at, sintering of the metal fine particles (P) is promoted.

  In consideration of the sinterability of the heat bonding material (M), it is preferable that the organic dispersion medium (S) contains 40% by mass or more of the polyhydric alcohol (A1).

(B) Compound having an amide group (A2)
As the compound having an amide group (A2), N-methylacetamide, N-methylformamide, N-methylpropanamide, formamide, N, N-dimethylacetamide, 1,3-dimethyl-2-imidazolidinone, N, Examples thereof include one or more selected from N-dimethylformamide, 1-methyl-2-pyrrolidone, hexamethylphosphoric triamide, 2-pyrrolidinone, ε-caprolactam, and acetamide.

  The compound (A2) having an amide group can be blended in the organic dispersion medium (S) so as to be 10 to 80% by mass.

(C) Amine compound (A3)
The amine compound (A3) is selected from aliphatic primary amines, aliphatic secondary amines, aliphatic tertiary amines, aliphatic unsaturated amines, alicyclic amines, aromatic amines, and alkanolamines. Examples of the amine compound include one or more kinds, and specific examples thereof include methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, n-propylamine, di-n-propylamine, and tri-n-propylamine. , N-butylamine, di-n-butylamine, tri-n-butylamine, t-propylamine, t-butylamine, ethylenediamine, propylenediamine, tetramethylenediamine, tetramethylpropylenediamine, pentamethyldiethylenetriamine, mono-n-octylamine , Mono-2Echi Hexylamine, di-n-octylamine, di-2ethylhexylamine, tri-n-octylamine, tri-2ethylhexylamine, triisobutylamine, trihexylamine, triisooctylamine, triisononylamine, triphenylamine , Dimethyl coconut amine, dimethyl octyl amine, dimethyl decyl amine, dimethyl lauryl amine, dimethyl myristyl amine, dimethyl palmityl amine, dimethyl stearyl amine, dimethyl behenyl amine, dilauryl monomethyl amine, diisopropyl ethyl amine, methanol amine, dimethanol amine, Trimethanolamine, ethanolamine, diethanolamine, triethanolamine, propanolamine, isopropanolamine, diisopropano Ruamine, triisopropanolamine, butanolamine, N-methylethanolamine, N-methyldiethanolamine, N, N-dimethylethanolamine, N-ethylethanolamine, N-ethyldiethanolamine, N, N-diethylethanolamine, Nn -1 type, or 2 or more types selected from -butylethanolamine, Nn-butyldiethanolamine, and 2- (2-aminoethoxy) ethanol can be mentioned. An amine compound (A3) can be mix | blended so that it may become 0.3-30 mass% in an organic dispersion medium (S).

(D) Organic solvent (A4)
The organic solvent (A4) is an organic solvent having a boiling point at normal pressure of 60 to 120 ° C. (boiling point refers to a boiling point at normal pressure; the same applies hereinafter) and a relatively low boiling point.

  As an organic solvent (A4), 1 type, or 2 or more types selected from the alcohol, ether, and ketone which have one hydroxyl group in a molecule | numerator are preferable.

  Examples of the alcohol having one hydroxyl group in the molecule include methanol (64.7 ° C), ethanol (78.0 ° C), 1-propanol (97.15 ° C), 2-propanol (82.4 ° C), One or more selected from 2-butanol (100 ° C.) and 2-methyl 2-propanol (83 ° C.) can be exemplified. Examples of the ether include diethyl ether (35 ° C.), methyl propyl ether (31 ° C.), dipropyl ether (89 ° C.), diisopropyl ether (68 ° C.), methyl t-butyl ether (55.3 ° C.), t-amyl. Examples thereof include one or more selected from methyl ether (85 ° C.), divinyl ether (28.5 ° C.), ethyl vinyl ether (36 ° C.), and allyl ether (94 ° C.). Examples of the ketone include one or more selected from acetone (56.5 ° C.), methyl ethyl ketone (79.5 ° C.), and diethyl ketone (100 ° C.).

  By including the organic solvent (A4), which is a low-boiling organic solvent, in the organic dispersion medium (S), the viscosity of the organic dispersion medium (S) can be adjusted to improve the accuracy of pattern formation.

  About 1-30 mass% of organic solvents (A4) can be mix | blended in an organic dispersion medium (S).

[2] Chip Electrode Layer The chip electrode layer is composed of one or more metal layers formed on the back surface of a chip (microchip, Si chip, IC chip, etc.). The thickness of the outermost layer (first layer) in the chip electrode layer before bonding is 20 nm to 250 nm, preferably 20 nm to 200 nm. In the examples described later, the experiment was conducted with the thickness of the outermost layer before sintering fixed at 200 nm, but it goes without saying that the thickness of the outermost layer before sintering is not limited to 200 nm.

  The thickness of the outermost layer before joining is considered to be better when it is relatively thin. However, if the outermost layer before sintering is too thin, pinholes are generated in the outermost layer and the layer in contact with the outermost layer (second layer) is oxidized, which causes problems in mounting and wafer level tests. For this reason, it is considered that the thickness of the outermost layer is preferably 20 to 200 nm.

  The outermost layer is made of gold, platinum, nickel or palladium, and is preferably made of gold. The layer in contact with the outermost layer is preferably formed of Ni, Ti, W, Ni, Ta alone or a nitride thereof, or TiW. When the outermost layer is a gold layer, the layer in contact with the outermost layer is preferably a layer that has a low diffusion rate with copper and functions as a barrier metal. When the layer in contact with the outermost layer is not a barrier metal but is formed of copper or a material having a high diffusion rate of copper, it is not preferable because it is substantially the same as the thickness of the gold layer. The gold layer or barrier metal is preferably formed by sputtering or vacuum deposition.

[3] Joining Method An example of a joining method of the chip electrode layer and the substrate will be described with reference to FIG. Hereinafter, a case where the outermost layer (first layer) of the chip electrode layer is Au and the layer (second layer) in contact with the outermost layer is Ti is taken as an example.

  As shown in FIG. 1 (a), bonding is performed between a substrate 2 and a semiconductor chip 3 (chip 6 and electrodes (Ti layer 5 / Au layer 4)), which are adherends, by using a sheet-shaped heat bonding material 1. The laminated body is arranged in a stack, and the laminated body is introduced into an apparatus capable of being pressed in a vacuum. In addition, when the heat bonding material 1 is paste-like, application | coating or a printing method can be used.

  Thereafter, the laminate is pressed with a pressure plate of 3 MPa to 13 MPa, preferably 4.5 MPa to 12 MPa with a press plate incorporating a heater, and evacuated to sufficiently reduce the pressure (FIG. 1B). At this time, since the atmospheric pressure is also applied to the laminate, the hydraulic pressure and air pressure of the press plate are adjusted in consideration of the atmospheric pressure.

  Thereafter, the heater plate is heated at a predetermined temperature and time to heat the laminated body (FIG. 1B). When the heating and sintering temperature reaches about 190 to 300 ° C., it is preferably held for about 10 to 40 minutes. Then, the press is finished and the laminate is taken out.

  Thus, by performing heating and sintering in a state where the substrate 2, the heat bonding material 1 and the chip 3 are in contact with each other, the copper fine particles (P) in the heat bonding material 1 are sintered and become porous. The bonding layer 1 ′ is formed, and the adherends are bonded to each other (FIG. 1C). At this time, the Au layer 4 is changed to the Au—Cu alloy layer 4 ′ by being heated and sintered in contact with the heat bonding material 1. In addition, in this embodiment, although the laminated body is heated under predetermined pressure, you may join by heating a laminated body under no pressure.

[4] Connection structure after bonding The thickness of the bonding layer 1 ′ formed by the bonding method is 50 μm to 500 μm. When the thickness of the bonding layer 1 ′ is less than 50 μm, when a component (power device) that generates a large amount of heat is mounted on the conductive metal plate (K), heat generated when the heat generated from the component is transferred to the lower metal plate. The resistance is reduced, but the reliability of the junction is reduced. On the other hand, if it exceeds 500 μm, there arises a disadvantage that the thermal resistance is increased.

  Further, as described above, the Au layer 4 of the chip electrode layer is changed to the Au—Cu alloy layer 4 ′ containing copper after the heat bonding. The thickness of the Au—Cu alloy layer 4 ′ is 200 nm or more and 850 nm or less, preferably 200 nm or more and 750 nm or less, more preferably 200 nm or more and 700 nm or less. In addition, at the interface between the Au—Cu alloy layer 4 ′ and the bonding layer 1 ′, the porosity of the bonding layer is 20% or less, preferably 17.5% or less, more preferably 15% or less. When the porosity of the bonding layer 1 ′ at the interface exceeds 20%, the mechanical strength decreases and the bonding reliability decreases. Note that the measurement position of the porosity is not limited to the interface, and may be in the vicinity of the interface, specifically within the range of 300 nm from the interface to the bonding layer 1 'side.

  Moreover, it is preferable that copper in the Au—Cu alloy layer 4 ′ after heat bonding is contained in an amount of 5% or more, preferably 10% or more from the viewpoint of bondability.

  Next, the present invention will be described more specifically with reference to examples. The present invention is not limited to these examples. The materials and evaluation methods used in the examples and comparative examples are described below.

(Examples 1-4 and Comparative Example 1)
(1) Used material (a) Preparation of heat-bonding material Heat-bonding material was obtained by blending 80 g of copper fine particles having an average primary particle diameter of 50 nm with a dispersion medium composed of 20 g of glycerin and sufficiently mixing with a mortar. The obtained heat-bonding material was pressed into a heat-bonded sheet having a thickness of 0.5 mm, and the heat-bonded sheet was cut to produce a heat-bonded molded body.
(B) Substrate and electronic component (i) Substrate In the example, an oxygen-free copper plate having a semi-hardened tempered substrate was used. The substrate thickness is 1.2 mm.
(Ii) Electronic components A silicon chip having a length, width and thickness of 7 mm × 7 mm × 0.23 mm is prepared, and a chip electrode layer of Ti / Au = 100 nm / 200 nm is formed on the etched surface of the silicon chip by sputtering. Formed.

(2) Joining method A heat-bonded molded body was placed between the substrate and the electronic component to produce a laminate, and the laminate was placed in the chamber. Thereafter, in a state where the laminated body was pressed at a predetermined pressure, vacuuming was performed to sufficiently reduce the pressure in the chamber, and then the heat-bonded molded body was heated and sintered to bond the substrate and the electronic component. Also, a plurality of similar laminates were produced, and joining was performed in the same manner while changing the pressure during sintering.

(3) Evaluation method About the produced silicon chip mounting sample, the thermal shock test which makes 30 cycles at -55 degreeC and 30 minutes at 200 degreeC 1 cycle was done. A sample is taken out every 100 times, visually inspected for cracks and peeling, then observed with an ultrasonic microscope, and when 2000 times, the peeled area is 10% or less. The case where the area exceeded 10% was determined to be unacceptable. The peeled area was calculated as a ratio of the total peeled area to the area of the connection back surface of the chip.

  Also, in order to observe the inside of the sample and confirm the state of pores in the bonding layer, the sample is embedded in resin to produce a resin molded body, and the resin molded body is cut and polished in a direction perpendicular to the chip. A cross section of the sample was obtained. Then, the cross section of the sample was grind | polished with the cross section polisher made from JEOL.

  Next, an observation image was obtained by observing the cross section with a magnification of 5000 times by SEM. Based on this observation image, parallel to the interface at a position 100 nm away from the interface between the bonding layer and the Au—Cu alloy layer in the chip electrode layer (position A in FIG. 2, hereinafter also referred to as immediately below the chip electrode layer). A line segment having a length of 20 μm was drawn, the sum of the lengths of the portions corresponding to the holes on the line segment was measured, and divided by the total length, thereby obtaining the porosity in the vicinity of the interface.

  Further, the porosity of the bulk (bonding layer) is determined by placing a line segment having a length of 20 μm parallel to the interface at a position 10 μm away from the interface between the bonding layer and the Au—Cu alloy layer (position B in FIG. 2). Then, SEM observation was performed at the same magnification, and the porosity was calculated.

表１および図３の結果から、チップ電極層直下の空孔率が高いほど冷熱衝撃試験の寿命回数が少なく、チップ電極層直下の空孔率が２０％を超えると、信頼性に乏しく実用に耐えないことが分かる。また、焼結後のチップ電極層におけるＡｕ−Ｃｕ合金層厚さが厚いほど信頼性が乏しく、厚さ８５０ｎｍ以上では実用に耐えない。 Table 1 shows the results evaluated by the above evaluation method. Further, based on the results in Table 1, the relationship between the porosity immediately below the chip electrode layer and the number of lifetimes of the thermal shock test, and the relationship between the thickness of the Au-Cu alloy layer in the chip electrode layer and the number of lifetimes of the thermal shock test are shown. The graphs obtained are shown in FIGS. 3 (a) and 3 (b), respectively.

From the results of Table 1 and FIG. 3, the higher the porosity directly under the chip electrode layer, the fewer the number of lifetimes of the thermal shock test, and when the porosity directly under the chip electrode layer exceeds 20%, the reliability is poor and practical. I can't stand it. In addition, the thicker the Au—Cu alloy layer in the chip electrode layer after sintering, the lower the reliability, and the thickness of 850 nm or more is not practical.

  The chip electrode layer and the heat-bonded molded body are bonded together by the reaction between the gold of the electrode layer and the copper fine particles of the heat-bonded molded body, which are alloyed and integrated. Therefore, the outermost layer of the chip electrode layer needs to be made of a metal that is alloyed with copper at a relatively low temperature to form an alloy at a wide ratio. As such a metal, gold, platinum, nickel or palladium is present, but gold having a solid solution as in this embodiment is preferable.

  On the other hand, when copper and gold are alloyed by firing, peripheral copper moves to the gold layer due to the Kirkendall effect, and vacancies develop in the copper layer formed immediately below the chip electrode layer. Excessive voids weaken the mechanical strength of the part, so excessive alloying deteriorates reliability.

  The thicker the chip electrode layer after sintering, the more peripheral copper is collected in the Au-Cu alloy layer. Therefore, the thickness of the chip electrode layer after sintering is the same as that in the chip electrode layer before sintering. The gold layer thickness (200 nm) or more and 850 nm or less is preferable.

  In addition, in joining using metal fine particles, pressure and heat are required at the time of sintering. However, excessive pressure promotes alloying of the interface between the chip electrode layer and the heat-bonded molded body more than necessary. It is thought that reliability will be poor. However, the sintering temperature cannot be changed because it governs the decomposition and reaction of the reducing agent of the heat bonding material.

  FIG. 4 is a graph showing the relationship between the sintering pressure and the porosity just below the chip electrode layer. In FIG. 4, it can be seen that the porosity decreases as the sintering pressure is lowered. Since it is assumed that the porosity becomes the same as the porosity of the bulk when the sintering pressure is lowered, it is understood that the sintering pressure is preferably 3 MPa or more and 13 MPa or less.

  Therefore, as shown in Examples 1 to 4, if the porosity immediately below the chip electrode layer is 20% or less of the bulk porosity and the thickness of the chip electrode layer is 850 nm or less, the number of lifetimes is It can be seen that more than 2000 times, a reliable and strong bond can be realized. On the other hand, as shown in the comparative example, when the sintering pressure exceeds 13.5 MPa, the porosity immediately below the chip electrode layer exceeds 20% of the bulk porosity, and the number of lifetimes is less than 2000 times. It turned out to be inferior in reliability.

Claims (10)

A connection structure for bonding a substrate and an electronic component by sintering a heat bonding material,
At least one electrode layer formed on the electronic component;
A bonding layer disposed between the at least one electrode layer and the substrate and formed of a sintered body containing copper;
Of the at least one electrode layer, the first layer in contact with the bonding layer is a copper alloy layer containing any material selected from the group consisting of gold, platinum, nickel and palladium,
The thickness of the copper alloy layer is 200 nm or more and 850 nm or less, and the porosity of the bonding layer at or near the interface between the copper alloy layer and the bonding layer is 20% or less Structure.   The thickness of the copper alloy layer is 200 nm or more and 750 nm or less, and the porosity of the bonding layer at or near the interface between the chip electrode and the bonding layer is 17.5% or less. Item 1. A connection structure according to Item 1.   The thickness of the copper alloy layer is 200 nm or more and 700 nm or less, and the porosity of the bonding layer at or near the interface between the chip electrode and the bonding layer is 15% or less. The connection structure described.   The connection structure according to any one of claims 1 to 3, wherein a porosity of the bonding layer within 300 nm from an interface between the copper alloy layer and the bonding layer is 20% or less. body. The at least one electrode layer comprises a plurality of electrode layers;
5. The connection structure according to claim 1, wherein the second layer in contact with the first layer is made of Ti, W, Ni, Ta alone or a nitride thereof. 6.   The connection structure according to claim 1, wherein a thickness of the bonding layer is 50 μm to 500 μm. A method for joining electronic components, in which a substrate and an electronic component are joined by sintering a heated joining material,
An electronic component comprising a heat bonding material comprising copper fine particles having an average primary particle diameter of 2 nm to 500 nm and an organic dispersion medium containing one or more polyhydric alcohols having two or more hydroxyl groups in the molecule. A method for joining electronic parts, wherein the electronic component is disposed between at least one electrode layer provided on the substrate and the substrate and joined by heating or heating under pressure.   The method for joining electronic components according to claim 7, wherein the substrate and the electronic components are joined under a pressure of 4.5 MPa to 12 MPa.   Of the at least one electrode layer, a first layer made of any material selected from the group consisting of gold, platinum, nickel, and palladium having a thickness of 20 to 200 nm is applied to the heat bonding material. The method for joining electronic parts according to claim 7 or 8, wherein the heating joining material is heated after contact.   The electronic component joining according to any one of claims 7 to 9, wherein the second layer in contact with the first layer is formed of a single substance of Ti, W, Ni, Ta or a nitride thereof. Method.

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