JP4692479B2 - Bonding materials and modular structures - Google Patents

Description

  The present invention relates to a bonding material and a module structure that do not contain lead.

  A bonding material in a module component in which a plurality of electronic components and semiconductor elements are mounted in one package (hereinafter, the bonding material in the module component is referred to as a “first bonding material”) is used when the module component and the motherboard are bonded. It is important for reliability that the first bonding material does not melt at the reflow mounting (secondary mounting) temperature (generally 240 to 260 ° C.). At present, the first bonding material generally used in the interior of the module component is a bonding material used for bonding the module component to the motherboard (hereinafter referred to as “second bonding material for bonding the module component to the motherboard”. A material having a melting point different from that of the bonding material.

First, the fabrication of module parts and the mounting process on the motherboard will be described with reference to FIG. FIG. 6 is a diagram showing module component production and a secondary mounting process on the mother board. As shown in FIG. 6A, the module component is manufactured by a first bonding material 102 (for example, containing lead as a main component and about 15% by mass of tin having a melting temperature of 288 ° C. on the module substrate 101. After printing (lead-tin alloy is used), a plurality of semiconductor elements 103 and electronic components 104 are mounted on the module substrate 101.

  Next, as shown in FIG. 6B, heating at 290 to 330 ° C. is performed by reflow mounting (primary mounting) to melt and bond the first bonding material 102, as shown in FIG. 6C. The module component 106 is manufactured using the sealing resin 105 or the like.

Next, as shown in FIG. 6 (d), the module component 106 includes a second bonding material 108 (for example, 3% by mass silver-0.5% by mass copper with the balance being tin and a melting point of about 217 ° C.), the electronic components including the module component 106 and the like are mounted on the motherboard 107, heated by 240 to 260 ° C. by reflow mounting (secondary mounting), and the second bonding material 108 is melted and bonded. (FIG. 6E). As described above, the first bonding material 102 used for the internal bonding of the module component 106 and the like is not remelted due to the reflow temperature at the time of mounting the motherboard (secondary mounting), and thus has a higher melting point than the second bonding material 108. (A solder material is generally used for the first bonding material 102 and the second bonding material 108).

  However, when a lead-tin alloy is used for the first bonding material 102, there is a concern that lead may be eluted into the soil from the solder material in the product that has become waste after the product is used. In recent years, therefore, interest in global environmental protection has been increasing, and lead-free solder (lead-free solder) has been developed. However, as a first bonding material 102 used in the module component 106, a bonding material that does not contain lead and has a melting temperature of 270 ° C. or more is not yet in practical use.

In response to the above problems, as a conventional technique, a bonding material composed of copper balls and tin balls is used, and an intermetallic compound layer of copper and tin (copper-tin intermetallic compound layer) is formed by reflow (primary and secondary mounting). By forming a melting point of about 400 ° C., tin is consumed by the intermetallic compound, and the amount of tin (melting point: 232 ° C.) decreases. As a result, it has been proposed that the bonding material does not remelt at the reflow temperature (240 to 260 ° C.) at the time of secondary mounting. (For example, refer to Patent Document 1). FIG. 7 is a diagram schematically showing this conventional bonding material. As shown in FIG. 7A, the bonding material composed of the copper ball 109 and the tin ball 120 is subjected to reflow (primary and secondary mounting) at 250 ° C. or higher, so that the tin ball 120 as shown in FIG. It melts to become molten tin 121, and the amount of tin decreases due to the formation of an intermetallic compound of copper and tin.
JP 2002-261105 A

  However, the above-mentioned joining material composed of copper balls and tin balls proposed as an alternative to the first joining material of the prior art is characterized by not being remelted at the secondary mounting temperature. Can be considered. Electronic parts used in module parts are subjected to various plating treatments as electrode plating materials, but can be broadly divided into tin and tin-based plating, and plating that does not use tin (gold plating, palladium plating, etc.) Divided into processing.

  When the former electrode plating is subjected to tin and tin-based plating, the first bonding material contains tin from the electrode plating during reflow (primary mounting), so the copper balls necessary for compound formation It is necessary to increase the amount.

  In the case where the latter electrode plating is a plating that does not use tin (for example, gold plating or palladium plating), if the first bonding material in which copper and tin balls are mixed with the above-mentioned tin plating is used, In comparison, the content of copper balls is large. As a result, the copper ball having a high melting point does not melt in the primary mounting, but only tin melts. At this time, melting of tin is consumed for forming an intermetallic compound layer with copper, and wetting of the first bonding material to the electronic component may be insufficient. Therefore, the connection strength between the first bonding material and the electronic component is reduced.

  In addition, since the first bonding material is bonded by an intermetallic compound, it is important to control the heating temperature during reflow (primary and secondary mounting). Therefore, it is necessary to determine the mixing ratio of copper and tin balls for each product according to the heat capacity of the electronic component electrodes mounted in the module components and the electrode plating treatment of various electronic components. Inferior.

  The present invention relates to a bonding material used in a module component that is compatible and is not remelted even in secondary mounting, regardless of the electrode plating treatment of the electronic component mounted in the module component, and the bonding material. An object is to provide a used module structure.

In order to achieve the above object, the bonding material of the present invention comprises 15 to 30% by mass of copper particles, 0.2 to 0.8% by mass of copper , 0.02 to 0.2% by mass of germanium, and 69 to The solder ball is composed of only 84.78% by mass of bismuth , and the copper, germanium, and bismuth alone .

With this configuration, even when the electrode of the electronic component is other than tin and tin-based plating (for example, gold plating, palladium plating, etc.), 70 to 85% by mass of bismuth-copper-germanium (melting point: 274 ° C.) of the bonding material. Since it is melted by reflow heat at the time of primary mounting, the wettability to the electronic component is improved, and since there is no tin in the bonding material, there is no occurrence of remelting due to reflow at the time of secondary mounting.

  Even when the electrode of the electronic component is tin and tin-based plating, since copper particles are added to the bonding material, the intermixing of copper and tin forms a mixture of tin during reflow (primary mounting). Thus, it is possible to prevent remelting of tin at the time of secondary mounting. That is, the bonding material of the present invention forms an intermetallic compound with tin of electrode plating of electronic parts and copper particles in the bonding material by mixing copper particles with a material consisting of solder balls of bismuth, copper and germanium. In addition, the periphery of the intermetallic compound layer formed on the surface of the copper particles is covered with molten bismuth, copper, and germanium.

  Further, in the case of an electronic component plated other than tin, there is no metal having a melting point lower than the secondary mounting temperature (260 ° C.) (for example, a tin ball), and therefore it does not remelt. Therefore, even if the bonding material of the present invention is used for an electronic component that has been subjected to any treatment in electrode plating, it does not remelt after mounting, has high wettability to the electronic component, and becomes a highly common bonding material. .

  In the module structure of the present invention, a plurality of electronic components or semiconductor elements and the bonding material described above are used to form a bonding portion between the electrode of the electronic component or the electrode of the semiconductor element and the module substrate. It is characterized by that.

  With this configuration, even if the module structure of the present invention is mounted on a mother board and heated by reflow mounting (secondary mounting), the bonding material in the module structure does not remelt, so that the module structure is of high quality. It will be.

  As described above, according to the bonding material of the present invention, there is no metal (for example, tin: melting point 232 ° C.) that melts at the heating temperature (240 to 260 ° C.) of the secondary mounting in the bonding material. The bonding material does not melt. In addition, for the formation of intermetallic compound layers, it is not necessary to change the blending of copper and tin depending on the product such as reflow temperature conditions for primary mounting and secondary mounting, heat capacity of electronic components and electrode plating treatment. High bonding material. As a result, a lead-free bonding material can be provided in place of the first tin-lead bonding material.

According to the module structure of the present invention, Ri by the the use of a bonding material of the present invention, it is possible to provide a highly reliable module structure.

  Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1)
FIG. 1 is a diagram schematically showing a bonding material according to Embodiment 1 of the present invention. This bonding material (hereinafter referred to as the first bonding material 1) is used for internal bonding of module components, and FIG. 1 shows a state before reflow mounting (primary mounting). Bonding material 1 of the first, the solder ball 2 consisting of 0.2 to 0.8 wt% of copper and 0.02 to 0.2% by weight of germanium and 69 to 84.78% by weight of bismuth, 15 It consists of ˜30% by mass of copper particles 3 and is configured with a flux 4. The reason for using the solder balls 2 made of bismuth, copper, and germanium is that a melting temperature of 270 ° C. or higher can be obtained with bismuth, copper, and germanium. That is, the conditions to be satisfied by the first bonding material 1 are that a plurality of semiconductor elements and electronic components are mounted on a module substrate, melted by heating at 290 to 330 ° C. by reflow mounting (primary mounting), and internally sealed. The module part can be manufactured by a stop resin or the like, and the first part used for the internal joining of the module part by reflow heating (240 to 260 ° C.) at the time of secondary mounting in which the module part is mounted on the motherboard. The bonding material 1 is not remelted.

  Here, a method for obtaining a bonding material having a melting temperature of 270 ° C. or higher will be described. In order to obtain a bonding material having a melting temperature of 270 ° C. or higher, it is effective to select a binary alloy (alloy consisting of two elements) whose eutectic point temperature is 270 ° C. or higher as the base (base material). is there. In that case, when selecting a combination of elements having an eutectic point temperature of 270 ° C. or higher from many elements, the importance and price of element toxicity are important. Elements such as Pb, Hg, Sb and Se are excluded from the point of toxicity.

  Next, a method for selecting a binary alloy will be described. FIG. 2 is a graph showing the eutectic point temperature of the binary alloy. The numerical value shown at the intersection of the element on the vertical axis and the element on the horizontal axis indicates the eutectic point temperature of the alloy composed of these two elements. FIG. 2 shows that the eutectic point temperature of, for example, a Sn—Ag alloy is 221 ° C., and the eutectic point does not exist in the Ni—Cu alloy. Moreover, it turns out that the combination of Bi and Cu or the combination of Bi and Ge gives the alloy whose eutectic point temperature is 270-300 degreeC.

Here, it is known that the eutectic alloy of Bi and Cu contains 99.5 mass % Bi and 0.5 mass % Cu (Bi-0.5% Cu). Further, it is known that a eutectic alloy of Bi and Ge contains 99% by mass of Bi and 1% by mass of Ge (Bi-1% Ge). However, the price of the aforementioned Ge is about 420 times as high as that of Cu. From the viewpoint of providing an inexpensive material, the combination of Bi and Cu is considered advantageous. A Bi—Cu alloy containing 0.2 to 0.8% by mass of Cu is an excellent bonding material in that it does not melt at a temperature below 270 ° C. However, in the test by the meniscus method, the knowledge that the wettability is low is obtained. Since the Bi—Cu alloy contains a large amount of Bi of 99.5% by mass, the amount of oxide generated in the alloy is increased, which is considered to affect the wettability. It is considered that the oxidation of Bi can be suppressed by adding a trace amount of an element that oxidizes preferentially over Bi to the Bi—Cu alloy. Examples of elements that oxidize preferentially over Bi include Ge, Al, Li, and P. In particular, in order to suppress oxidation of the Bi—Cu alloy, it is suitable that the Ge content is 0.02 to 0.2 mass %. As a result, a solder material containing 0.2 to 0.8% by mass of copper and 0.02 to 0.2% by mass of germanium and 69 to 84.78% by mass of bismuth was selected.

  The purpose of the copper particles added to the solder material is to melt the first bonding material 1 inside the module component by heating during reflow mounting (secondary mounting) when the electrode plating of the electronic component inside the module component is tin. This is because an intermetallic compound of copper and tin is formed. In addition to copper, zinc, silver, etc. that can easily form an intermetallic compound with tin are also possible. Moreover, the addition amount with respect to the solder ball 2 which consists of bismuth, copper, and germanium of the copper particle 3 should be small. This is because reducing the addition amount of the copper particles 3 has a melting point of about 1084 ° C., and it is not necessary to consider melting at the reflow temperature at the time of primary mounting, so the addition amount of the copper particles is large. This is to prevent a decrease in the wet spreading property of the first bonding material 1 to the component electrodes. Therefore, it is desirable to reduce the diameter of the added copper particles and increase the surface area.

The content of the copper particles 3 is preferably 15 to 30% by mass of the bonding material. However, the content of the above-mentioned copper particles 3 is calculated from the volume and density of the electrode plating (5 μm to 10 μm) of the electronic parts that are generally used at present, but the electrode plating of the electronic parts is set to 2 μm or less. Thus, the content of the copper particles 3 is considered to be 5% by mass or less. Electrode plating In general, the land of module boards for electronic components is almost unified in the industry from the viewpoint of bonding reliability, mounting conditions, and mounting area. In addition, the size of the electrode is also standardized in the industry according to the size of the electronic component. In the 0603 size of the chip capacitor used this time, the maximum amount of electrode plating tin mixed into the first bonding material 1 on the land of the module substrate is expected to be about 30% by mass . Therefore, the maximum content of the copper particles 3 is set to 30% by mass in relation to the land of the module substrate with respect to almost electronic components. The fact that the copper particles 3 are not added to the first bonding material 1 by 30% by mass or more is because the copper particles 3 do not melt in the reflow mounting at the time of module component manufacture, so by increasing the content, There is a possibility that the wettability of the first bonding material 1 to the electrode is lowered. On the other hand, the minimum required mass of the copper particles 3 was 15% by mass based on the evaluation described later.

As one manufacturing method of the 1st joining material 1, the metal which consists of bismuth, copper, and germanium is mix | blended, mixed and fuse | melted. Thereafter, as a general ball production, the solder balls 2 having a spherical shape are obtained by utilizing the surface tension of the above-mentioned blended materials by heating and melting in a medium in a non-oxidizing atmosphere. Similarly, the copper particles 3 can be manufactured. However, since the oxidation proceeds when the particle size is about 5 μm or less, it is necessary to mix the uniform copper particles 3 with the flux 4 and the like in a non-oxidizing atmosphere. Then, 15-30 mass % copper particles 3 (the particle diameter of the copper particles 3 adopts about 1 μm) which is a prescribed composition of the spherical solder balls 2 and the copper particles 3 to which the flux 4 is adhered, and 0.2-0. .8 were combined mass% of copper and 0.02 to 0.2 wt% of germanium and from 69 to 84.78 mass% bismuth formulations. The required minimum content of the copper particles 3 was determined by remelting evaluation of the first bonding material 1 manufactured as described above.

As a remelting evaluation method, after printing the first bonding material 1 on the module substrate, an electronic component (chip capacitor 0603: tin-plated product with electrode plating of 5 μm) is mounted, and reflow mounting temperature (primary mounting) 280- The first bonding material 1 was melted at 290 ° C. to bond the electronic component (chip capacitor 0603) and the module substrate. This module board is subjected to a shear strength test of electronic components (chip capacitor 0603) in an environment of 260 ° C. which is the maximum temperature of the secondary mounting reflow temperature. The presence or absence was confirmed. When remelted, there was no bonding strength and the cross-sectional surface was a smooth surface (not plastically broken). As a result (Table 1), the minimum required mass of the copper particles was set to 15% by mass .

(Embodiment 2)
Next, the joining material in Embodiment 2 of this invention is demonstrated.

  The copper particle diameter used for a copper particle was 0.5-30 micrometers. When the particle diameter is larger than the diameter of the solder ball of the current bonding material (generally about 20 to 30 μm), problems such as clogging in the printing mask occur in the printing process for supplying the first bonding material to the module substrate. Therefore, the maximum diameter is set to 30 μm. Since the surface area of the copper particles increases as the diameter decreases, it is easy to form an intermetallic compound against the contamination of tin used for electrode plating of electronic components. Therefore, it is desirable to reduce the diameter. However, when the thickness is 0.5 μm or less, the oxidation of the particles is promoted as the particle size of the copper particles is reduced. Further, since the surface energy increases as the particle diameter is reduced, the particles are sintered (the particles are attracted). Accordingly, a copper particle diameter of 1 μm to 10 μm is suitable at the present stage.

(Embodiment 3)
Next, the joining material in Embodiment 2 of this invention is demonstrated.

  FIG. 3 is a view showing a state in which the surface of the copper particles 3 in the first bonding material 1 is plated with germanium, gold, or palladium. The plating thickness applied to the copper particles 3 was 1 μm or less, and the surface of the copper particles was plated by an electroplating method. By densely plating the surface of the copper particles, there is an effect of suppressing the formation of an oxide film and preventing the copper particles 3 from being sintered (particles are attracted). When the copper particles 3 are oxidized, problems occur in the printability as the first bonding material 1 and the wetting and spreading of the first bonding material 1 to the electronic component. In addition, since the surface of the copper particles 3 is protected from oxidation, there is no need to use a flux with a strong activity for preventing the copper particles 3 from being oxidized, and the selection range of the flux is widened. Can be improved. Therefore, it is highly effective to subject the copper particles 3 to a plating process having a high diffusion rate.

(Embodiment 4)
Next, the module structure in Embodiment 4 of this invention is demonstrated.

First, a case where the first bonding material is used for a module structure (for example, a power amplifier (PA) module) will be described. The PA module is composed of a plurality of electronic components and semiconductor elements. And solder balls on the module substrate made of 0.2 to 0.8 wt% of copper and 0.02 to 0.2% by weight of germanium and 69 to 84.7% by weight of bismuth, 15-30% by weight of copper The first bonding material made of particles is printed, a plurality of electronic components are mounted on the module substrate, and the first bonding material is melted by reflow (primary mounting) heating at about 290 ° C. Connect. Thereafter, the flux adhering to the module substrate surface from the first bonding material is washed, and the semiconductor element and the module substrate are heated and bonded using a conductive paste (silver paste or the like). (At this time, for example, when an electronic component plated with tin and tin is bonded by reflow (primary mounting) with the first bonding material, even if the formation of the intermetallic compound of copper and tin is delayed, (It is possible to compensate for the formation of intermetallic compounds with the heating temperature when curing the conductive paste) Then, the electrode of the semiconductor element and the electrode of the module substrate are connected using a gold wire and mounted on the module substrate A module part is manufactured by using a sealing resin or the like for the electronic part or the semiconductor element.

After that, a second bonding material (for example, 3% by weight silver-0.5% by weight copper with the balance being tin and having a melting point of about 217 ° C.) is printed on the motherboard, and after mounting the module parts, reflow (secondary mounting) Connect the motherboard with the module parts. As a result, by using the first bonding material of the present invention, it is confirmed using the same evaluation method as in Embodiment 1 that the first bonding material does not remelt at the reflow temperature at the time of secondary mounting. It was.

  In addition, when the cross-sectional analysis was performed using SEM or the like, the first bonding material was not a copper-tin compound, but copper particles having a particle diameter of 0.3 to 30 μm. It was detected that it was present. This range of particle diameter is presumed to be the following consideration.

  FIG. 4 is a cross-sectional view of the module substrate after the tin-plated electrode is reflow-mounted with the first bonding material. When the electrode plating of the electronic component is tin plating 6, the solder balls in the first bonding material 1 are melted at the time of primary mounting, and the molten solder balls 8 and the copper particles 3 are used for bonding. It is speculated that the outer surface 7 of the copper particles 3 was compounded, relatively small copper particles (0.5 μm diameter, etc.) became 0.3 μm, and other copper particles were also smaller than the original copper particle diameter. Is done. This is because the particle size after mounting is somewhat smaller because a compound of copper and tin is formed.

  Next, the case where the electrode plating is plating that does not use tin (gold, palladium, etc.) will be described. FIG. 5 is a cross-sectional view of the module substrate after reflow mounting a plated electrode that does not use tin with a first bonding material. When the electrode plating of the electronic component is plating 9 that does not use tin (such as gold or palladium), it is assumed that the copper particles 3 in the first bonding material 1 remain and exist in a diameter of 0.5 to 30 μm. The

  As described above, since the module structure of the present invention is manufactured using the bonding material of the present invention, the bonding material in the module structure is not remelted even after the secondary mounting. I can say that.

  According to the present invention, at a reflow temperature when a module component is mounted on a mother board, the joint portion in the module component can be joined without being remelted by heat during reflow. In addition, it is possible to supply a solder material that does not contain lead, which is an environmentally hazardous substance. In addition to bonding inside the module, it can also be applied to die bonding materials, flip and BGA connection applications.

The figure which showed typically the joining material in Embodiment 1 of this invention Diagram showing eutectic point temperature of binary alloy The figure which showed the state by which the surface was plated by the germanium, gold | metal | money, or palladium to the copper particle in the 1st joining material Sectional view after reflow mounting the electrode plated with tin on the module substrate with the first bonding material Sectional view after reflow mounting the plated electrode without using tin on the module substrate with the first bonding material Diagram showing module component fabrication and secondary mounting process on motherboard Schematic illustration of prior art bonding materials

DESCRIPTION OF SYMBOLS 1 1st joining material 2 Solder ball 3 Copper particle 4 Flux 5 Plating 6 Tin plating 7 Outer surface 8 Molten solder ball 9 Plating which does not use tin 101 Module substrate 102 First joining material 103 Semiconductor element 104 Electronic component 105 Sealing resin 106 Module component 107 Motherboard 108 Second bonding material 109 Copper ball 120 Tin ball 121 Molten tin

Claims (5)

15 to 30% by mass of copper particles, 0.2 to 0.8% by mass of copper , 0.02 to 0.2% by mass of germanium and 69 to 84.78% by mass of bismuth , A joining material that consists of germanium and bismuth to form solder balls . The bonding material according to claim 1, wherein the copper particles have a diameter of 0.5 μm to 30 μm. The bonding material according to claim 1 or 2, wherein a surface of the copper particles is plated with any of germanium, gold, silver, nickel, or palladium. A module in which a plurality of electronic components or semiconductor elements and a bonding material according to any one of claims 1 to 3 are used to form a junction between an electrode of the electronic component or the electrode of the semiconductor element and a module substrate. Structure. 5. The module structure according to claim 4, wherein the bonding portion includes copper particles having a particle diameter of 0.3 μm to 30 μm.

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