JP2012112008A - Ball for connection terminal, method for manufacturing the same, and method for forming connection structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ball for a connection terminal which is inexpensive and adapted to high-temperature solder, and to provide a method for forming a connection structure using the same.SOLUTION: The ball 20A for the connection terminal includes a ball-like core 1 and a silver oxide layer 4 containing AgO and provided to surround the core 1. When the silver oxide layer is heated to 100°C or higher in the presence of a reducing agent, a sintered silver layer is formed. Since the silver layer does not melt until reaching the melting point of silver, the connection structure of high reliability at high temperature is obtained.

Description

  The present invention relates to a connection terminal ball represented by a conventional solder-coated ball, a method of manufacturing the same, and a method of forming a connection structure using the same.

  Solder-coated balls, which are typical connection terminal balls, are mainly used to connect parts of electrical and electronic equipment. Specifically, the solder-coated balls are, for example, QFP (Quad Flat Package) having lead terminals around the component, BGA (Ball Grid Array) and CSP (Chip Size Package) which are relatively small and can be multi-pinned. It is used for input / output terminals of semiconductor packages such as

  The solder-coated ball has a configuration in which a solder layer containing lead (Pb) is provided on the surface of a microsphere made of a metal having a diameter of about 0.1 to 1.0 mm, for example. In recent years, lead-containing solder is being replaced with lead-free solder (Pb-free solder) in response to environmental problems. In view of such circumstances, Patent Document 1 and Patent Document 2 describe solder whose surface is covered with a tin-silver (Sn-Ag) solder layer that does not contain lead, and generation of voids during heating and melting is suppressed. A coated ball is disclosed.

  Solder is roughly classified into medium-low temperature solder (melting temperature: about 150 ° C. to about 250 ° C.) and high-temperature solder (melting temperature: about 250 ° C. to about 300 ° C.) depending on the soldering temperature. The medium / low temperature solder is mainly used when connecting an electronic component to a printed circuit board or the like, and the high temperature solder is mainly used when connecting an internal wiring or the like of the electronic component.

  The melting point of the Sn—Ag solder layer is about 216 ° C., and the solder-coated ball provided with this solder layer is suitably used for soldering in the middle / low temperature range. However, the Sn—Ag-based solder layer cannot be used for soldering in a high temperature range because it remelts in a high temperature range of about 250 ° C. to about 300 ° C. and deforms the ball.

  Therefore, Patent Document 3 focuses on the fact that silver nanoparticles (ultrafine particles having a particle size of several nanometers to several hundred nanometers) melt at a temperature much lower than silver in a bulk state. Silver-coated balls with layers have been proposed. The silver-coated ball described in Patent Document 3 is covered with a coating layer containing silver ultrafine particles having an average particle diameter of about 1 nm to 50 nm so as to cover the ball-shaped core. The silver ultrafine particles have a melting point of about 250 ° C. to about 300 ° C. Further, once solidified after solidification, the silver does not remelt until the melting point of silver (about 960 ° C.). Therefore, the silver-coated ball described in Patent Document 3 can be suitably used as a connection terminal ball for high-temperature solder.

JP 2004-114123 A JP 2004-128262 A International Publication No. 2006/126527

Hiroaki Tsuji, 6 others, “Development of joining process by in-situ generation of nanoparticles using silver oxide microparticles”, Abstracts of National Meeting of the Japan Welding Society, 83rd (2008-9), p. 406-407

  However, in order to produce the silver-coated balls described in Patent Document 3, a dispersion of ultrafine silver particles is required, and this dispersion has a problem that it is expensive.

  An object of the present invention is to provide a connection terminal ball for high-temperature solder, which is less expensive than the silver-coated ball described in Patent Document 3, and a method for forming a connection structure using the connection terminal ball.

The connection terminal ball of the present invention has a ball-shaped core and a silver oxide layer containing Ag ₂ O provided so as to surround the core.

In one embodiment, the silver oxide layer containing Ag ₂ O includes an anodized layer.

  In one embodiment, the connection terminal ball further includes a barrier layer formed on the surface of the core. The barrier layer is, for example, a Ni layer. In one embodiment, the Ni layer is a Ni plating layer. The thickness of the Ni plating layer is preferably more than 2 μm.

  In one embodiment, the thickness of the silver oxide layer is 0.1 μm or more and 50 μm or less. The thickness of the silver oxide layer is preferably more than 2 μm.

  In one embodiment, the average particle size of the core is 0.05 mm or more and 1.5 mm or less.

  In one embodiment, the core is made of metal or resin. The core is made of copper (Cu), gold (Au), platinum (Pt), nickel (Ni), cobalt (Co), iron (Fe), manganese (Mn), titanium (Ti), molybdenum (Mo). And a single metal or an alloy containing at least one metal element selected from the group consisting of aluminum (Al). The core may be formed of silicon (Si).

The method of manufacturing a connection terminal ball according to the present invention includes a step of forming a silver plating layer so as to surround a ball-shaped core, and a silver oxidation containing Ag ₂ O by anodizing the surface of the silver plating layer. Forming a physical layer.

  The method for forming the connection structure of the present invention includes a step of preparing any one of the above connection terminal balls and a substrate having terminals, and a reducing agent in a state where the connection terminal balls are in contact with the terminals. And heating the connection terminal ball to a temperature of 100 ° C. or higher in the presence of the connection terminal, wherein the core of the connection terminal ball and the terminal are connected by a sintered silver layer. Form. The reducing agent may include alcohols, carboxylic acids, or amines. The atmosphere for performing the reduction is not particularly limited, and may be a non-oxidizing atmosphere or air (air).

  According to the present invention, there are provided a connection terminal ball for high-temperature solder, which is cheaper than the silver-coated ball described in Patent Document 3, and a method for forming a connection structure using the same. In addition, according to the present invention, there is provided a connection terminal ball capable of forming a connection structure even when processed at a temperature lower than that of the silver-coated ball described in Patent Document 3.

(A) And (b) is sectional drawing which shows typically the structure of silver covering ball | bowl 10A, 10B used for manufacture of the ball | bowl for connection terminals of embodiment by this invention. (A) And (b) is sectional drawing which shows typically the structure of ball | bowl 20A, 20B for connecting terminals of embodiment by this invention. (A)-(c) is a schematic diagram for demonstrating the method of forming a connection structure using the connection terminal ball | bowl 20A of embodiment by this invention. It is a figure which shows the DSC curve when the ball | bowl for connection terminals of the Example by this invention is heated in presence of a reducing agent (1-undecanol).

  Hereinafter, with reference to the drawings, a connection terminal ball according to an embodiment of the present invention, a manufacturing method thereof, and a connection structure forming method will be described. Note that the present invention is not limited to the illustrated embodiment.

  As will be described later with reference to FIG. 2, the connection terminal ball according to the embodiment of the present invention has a ball-shaped core and a silver oxide layer provided so as to surround the core. When the silver oxide layer is thermally decomposed at a temperature of about 100 ° C. or higher in the presence of a reducing agent, silver nanoparticles are generated, and the silver nanoparticles are rapidly sintered to form a silver layer. Silver nanoparticles become coarse during the sintering process. Since the silver layer formed by sintering the silver nanoparticles does not melt up to the melting point of silver (about 960 ° C.), when the connection terminal ball of the embodiment is used, a reliable connection structure at a high temperature is obtained. can get. The heating temperature is preferably about 150 ° C. or higher. This is because the time required for the production of silver nanoparticles becomes longer.

The connection terminal ball according to the embodiment of the present invention utilizes a phenomenon that silver nanoparticles are generated by reducing silver (I) (Ag ₂ O) and / or silver (II) (AgO). ing. This phenomenon itself is disclosed in Non-Patent Document 1. As described in Non-Patent Document 1, when a mixture obtained by adding a reducing agent (triethylene glycol: TEG) to a silver oxide paste containing silver oxide microparticles (particle size of about 1 to 2 μm) is heated, silver oxide is obtained. The paste is reduced to silver with a sharp exothermic peak at 150 ° C. In the process of reductive decomposition of silver oxide, silver nanoparticles (particle size of about 10 to 40 nm) are generated, and the silver nanoparticles are sintered immediately after generation. Generation and sintering of silver nanoparticles occurs at about 100 ° C., and a silver layer having a nano-order thickness is formed on the surfaces of the substrates to be joined, which contributes to bonding. The above Non-Patent Document 1, as silver oxide, but silver oxide (I) (Ag ₂ O) is described, occurs similar phenomenon silver oxide (II) (AgO). Since silver oxide microparticles are used in this method, it is difficult to uniformly coat the connection terminal balls (average particle diameter of the core: 0.05 mm or more and 1.5 mm or less). In addition, silver oxide microparticles are also expensive.

  Since the connection terminal ball according to the embodiment of the present invention is manufactured as follows, the connection terminal ball is inexpensive and has high uniformity in the thickness of the silver oxide layer.

  1A and 1B are schematic cross-sectional views of silver-coated balls 10A and 10B used for manufacturing a connection terminal ball according to an embodiment of the present invention.

  A silver-coated ball 10A shown in FIG. 1A includes a ball-shaped core 1 and a silver layer 2 provided so as to surround the core. The core 1 is made of metal or resin, and is typically made of copper (Cu). The core 1 is made of gold (Au), platinum (Pt), nickel (Ni), cobalt (Co), iron (Fe), manganese (Mn), titanium (Ti), molybdenum (Mo), and aluminum (Al). You may form with the metal simple substance or alloy containing the at least 1 sort (s) of metal element selected from the group. The core may be formed of silicon (Si).

  The average particle diameter of the core 1 is, for example, not less than 0.05 mm and not more than 1.5 mm, and is appropriately selected depending on the application. The silver layer 2 is a silver plating layer formed by, for example, an electrolytic plating method or an electroless plating method. Silver plating is performed by a known barrel plating method. The thickness of the silver layer 2 is appropriately set so that the final thickness of the silver oxide layer is 1 μm or more and 50 μm or less. Since the silver layer 2 does not melt up to the melting point of silver (about 960 ° C.), the silver-coated ball 10A cannot be used to form a connection structure.

  A silver-coated ball 10B shown in FIG. 1B is different from the silver-coated ball 10A shown in FIG. 1A in that it further includes a barrier layer 3 formed on the surface of the core 1. The barrier layer 3 prevents the elements constituting the core 1 from diffusing into the silver layer 2. For example, if the core 1 is made of copper, copper may diffuse into the silver layer 2 and impair the uniformity of the silver layer 2. In order to prevent this, it is preferable to form the barrier layer 3 with nickel (Ni). The Ni layer 3 may be, for example, a Ni plating layer formed by a known plating method. The thickness of the barrier layer 3 is, for example, 1 μm or more and 5 μm or less. In order to ensure the barrier effect, the thickness of the barrier layer 3 is preferably more than 2 μm.

  2A and 2B are schematic cross-sectional views of connection terminal balls 20A and 20B according to an embodiment of the present invention. The connection terminal balls 20A and 20B are obtained by oxidizing the silver layer 2 of the silver-coated balls 10A and 10B shown in FIGS. 1 (a) and 1 (b), respectively.

  A connection terminal ball 20 </ b> A shown in FIG. 2A has a ball-shaped core 1 and a silver oxide layer 4 provided so as to surround the core 1. The junction strength of the finally obtained junction structure becomes higher as the silver oxide layer 4 is thicker, and the thickness of the silver oxide layer 4 is preferably more than 2 μm and 10 μm or less. However, the bonding strength also depends on the pressing conditions during bonding. In the joining using the connection terminal ball 20A, the force concentrates at one point where the connection terminal ball 20A and the terminal are in contact with each other. Therefore, when a sufficiently large force is applied, the thickness of the silver oxide layer 4 becomes 0.1 μm. But sometimes it can be joined. Between the silver oxide layer 4 and the core 1, an unoxidized silver layer 2b remains.

  The connection terminal ball 20B shown in FIG. 2B is provided so as to surround the ball-shaped core 1, the barrier layer 3 formed on the surface of the core 1, and the core 1 and the barrier layer 3. And a silver oxide layer 4. Between the silver oxide layer 4 and the core 1, an unoxidized silver layer 2b remains.

Here, as is well known, silver oxide includes Ag ₂ O and AgO. Ag ₂ O is sometimes called silver oxide, and AgO is sometimes called silver peroxide. Both Ag ₂ O and AgO produce silver nanoparticles by reduction, and the silver nanoparticles are easily sintered. However, since the oxygen content is small, silver (I) oxide (Ag ₂ O) is preferable from the viewpoint of ease of reduction. Accordingly, the silver oxide layer 4 preferably contains Ag ₂ O. When the silver layer 2 is oxidized, it is preferable to use a method for efficiently producing Ag ₂ O. For example, a silver oxide layer containing Ag ₂ O can be formed by anodizing the surface of the silver layer 2. By anodizing the silver layer, the silver oxide layer (anodized layer) can be substantially composed only of Ag ₂ O.

  For example, using the connection terminal balls 20A, a connection structure can be formed, for example, by a process as shown in FIGS.

  First, as shown in FIG. 3A, a connection terminal ball 20A and a substrate 30 having terminals 18 are prepared. The substrate 30 is, for example, a BGA or CSP interposer. The terminal 18 is composed of, for example, a stacked body of a copper (Cu) layer 12, a nickel (Ni) layer 14, and a gold (Au) layer 16. Each metal layer constituting the terminal 18 is formed by, for example, a plating method.

Next, as shown in FIG. 3B, in a state where the connection terminal ball 20A is in contact with the terminal 18, the connection terminal ball 20A is moved to about 100 ° C. or more, preferably about 250 in the presence of a reducing agent. Heat to a temperature above ℃. As the reducing agent, alcohols, carboxylic acids, or amines can be used alone or in admixture of plural kinds. The atmosphere for performing the reduction need not be a reducing atmosphere (for example, a hydrogen atmosphere), and may be a non-oxidizing atmosphere (for example, an inert gas atmosphere or a nitrogen atmosphere) or air (air). When there is no fear of oxidation of the bonded portion or the bonded body, for example, when the bonded portion is formed of a noble metal, the bonding may be performed in the atmosphere. When the silver oxide layer 4 is heated to a temperature of about 100 ° C. or more in the presence of a reducing agent, it is reductively decomposed to produce silver nanoparticles, and a layer 6 containing silver nanoparticles is formed. The silver oxide layer 4 preferably contains Ag ₂ O.

  When the connecting terminal ball 20A is further heated within the above temperature range, the generated silver nanoparticles are rapidly sintered, and the silver nanoparticles are sintered and formed as shown in FIG. 3 (c). A silver layer 8 is formed. At this time, the silver layer 2b remaining without being oxidized also forms the silver layer 8 together with the layer 6 containing silver nanoparticles. However, silver nanoparticles become coarse by sintering. In this way, a connection structure through the silver layer 8 is formed. Since the silver layer 8 is formed without melting, the joint portion is almost a point, but has a sufficient joint strength. Further, since the silver layer 8 does not melt up to the melting point of silver (about 960 ° C.), it has high bonding strength even at high temperatures.

  According to experiments, it is preferable to heat to a temperature of 250 ° C. or higher in order to obtain sufficient bonding strength. The bonding strength increases as the heating temperature increases. However, when the heating temperature exceeds about 400 ° C., the rate of increase in strength decreases. Although depending on the heat resistance temperature of the bonded structure, the heating temperature is preferably 400 ° C. or lower in consideration of the throughput and the like. Moreover, it is preferable to pressurize with heating, and the pressure is preferably in the range of 0.1 MPa to 20 MPa. If the pressure is less than 0.1 MPa, a sufficient bonding force may not be obtained, and if it exceeds 20 MPa, the bonded portion may be damaged. Although the time for heating and pressurizing depends on the temperature, it is generally from 1 minute to 60 minutes. The lower the temperature, the longer the time required to generate and sinter silver nanoparticles. For example, when the heating temperature (maximum temperature reached) is 100 ° C. and the pressure is 2.5 MPa, it is preferable to hold for 30 minutes to 60 minutes (including the temperature rising time) in order to obtain sufficient bonding strength. When a resin (for example, polyethylene terephthalate (PET)) is used for the core, the heating temperature and pressure may be set in consideration of the heat resistance and strength of the resin.

  Examples are shown below.

  After Cu plating (core diameter 0.5 mm) was Ni-plated, strike silver plating and silver plating (thickening) were performed. Each plating condition is shown below.

Ni plating (thickening) conditions:
Composition of plating solution: nickel sulfate 240 g / L, nickel chloride 45 g / L, boric acid 30 g / L, plating temperature: 50 ° C., current density: 0.1 A / dm ² , plating time: 120 minutes The thickness was 3 μm.

Strike silver plating conditions:
Composition of plating solution: silver cyanide 2 g / L, potassium cyanide 75 g / L, plating temperature: 20 to 30 ° C., current density: 0.3 A / dm ² , plating time: 60 seconds (thickness measured at 0.1 μm or less) Impossible)

Silver plating (thickening) conditions:
Composition of plating solution: silver cyanide 45 g / L, potassium cyanide 110 g / L, potassium carbonate 10 g / L, plating temperature: 20 to 30 ° C., current density: 0.1 A / dm ² , plating time: 120 minutes The thickness of the plating film was 10 μm.

  The silver plating film was anodized under the following conditions.

Anodizing conditions:
Electrolytic solution: potassium hydroxide (or sodium hydroxide): 3 mol / L, anodizing temperature: 20-30 ° C., current density: 0.1 A / dm ² , anodizing time: 120 minutes

By the anodic oxidation, a portion of about 4 μm from the surface of the 10 μm thick silver plating film was anodized to form a silver oxide layer containing Ag ₂ O.

  The connection terminal balls obtained as described above were immersed in 1-undecanol (manufactured by Wako Pure Chemical Industries, Ltd.) as a reducing agent, and then subjected to a joining experiment. A single connection terminal ball is arranged between two substrates obtained by applying Ag plating (thickness: about 4 μm) to a Cu plate, and the pressure is increased from room temperature to 250 MPa in a state of being pressurized at 2.5 MPa in the atmosphere. Heated to ° C. The heating time including the temperature raising time (temperature raising rate: 10 ° C./min) was 150 seconds. As a result of evaluating the bonding strength after cooling to room temperature, it was confirmed that the bonding strength was sufficient.

  Moreover, the result of having performed differential scanning calorimetry (DSC) about the ball | bowl for connection terminals to which the said 1-undecanol adhered was shown in FIG. The heating rate was 10 ° C./min. As can be seen from FIG. 4, an exothermic peak due to the reduction reaction is observed at around 190 ° C.

  Thus, when the connection terminal ball of the example is heated in the presence of a reducing agent, the silver oxide layer is reduced, silver nanoparticles are generated, and a silver layer in which the silver nanoparticles are sintered is formed, A junction structure through the silver layer is formed.

  The present invention is used for forming a connection structure in a semiconductor device or a circuit board, in particular, a connection structure requiring high temperature reliability.

1 Core 2, 2b Ag layer (Ag plating layer)
3 Barrier layer (Ni layer)
4 Silver oxide layer 6 Layer containing silver nanoparticles 8 Silver layer formed by sintering silver nanoparticles 10A, 10B Silver-coated balls 12 Cu layer 14 Ni layer 16 Au layer 18 Terminal (pad)
20A, 20B Connection terminal ball 30 Substrate

Claims (8)

A ball-shaped core,
A connection terminal ball comprising: a silver oxide layer containing Ag ₂ O provided so as to surround the core.   The connection terminal ball according to claim 1, wherein the silver oxide layer includes an anodized layer.   The connection terminal ball according to claim 1, further comprising a barrier layer formed on a surface of the core.   The connection terminal ball according to claim 1, wherein the silver oxide layer has a thickness of 0.1 μm or more and 50 μm or less.   The connection terminal ball according to claim 1, wherein the core has an average particle diameter of 0.05 mm or more and 1.5 mm or less.   The connection terminal ball according to claim 1, wherein the core is made of metal or resin. Forming a silver plating layer so as to surround the ball-shaped core;
Forming a silver oxide layer containing Ag ₂ O by anodizing the surface of the silver plating layer. Preparing a connection terminal ball according to any one of claims 1 to 6 and a substrate having a terminal;
Heating the connection terminal ball to a temperature of 100 ° C. or higher in the presence of a reducing agent in a state where the terminal ball is in contact with the terminal.
A method of forming a connection structure in which the core of the connection terminal ball and the terminal are connected by a sintered silver layer.

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