Patent Application
20080095926
Various lead free solder particles are prepared, and using the lead free solder particles, metal wirings were formed inside holes of a substrate to prepare the circuit boards.
As shown in
The electric oven 2 is supplied with the starting material from the starting-material supply cylinder 1 for melting the starting material. A first atmosphere gas, stored in a first gas tank 12, is fed to an upper portion of the electric oven 2. A second atmosphere gas and a third atmosphere gas stored in a second gas tank 13 and a third gas tank 14, respectively, are fed to the granulation chamber 5.
The pressure in the electric oven 2 is controlled by using a first valve 15 and a first evacuation unit 18. The pressure in the granulation chamber 5 is controlled using a second valve 16, a third valve 17, and a second evacuation unit 19. If the pressure in the electric oven 2 is maintained slightly higher than atmospheric pressure and the pressure in the granulation chamber 5 is maintained slightly lower than atmospheric pressure, the difference in pressure allows the starting material melted in the electric oven 2 to be fed to the dish-shaped rotary disk 7 through the nozzle 4. The molten starting material fed to the dish-shaped rotary disk 7 is atomized into fine droplets with the centrifugal force of the dish-shaped rotary disk 7 and the fine droplets are solidified into spherical particles by quenching. The spherical particles are fed to the screening filter 10 through the discharge pipe 9 and then screened therewith.
In the first step, the molten starting material is fed onto the dish-shaped rotary disk 7 in an inert atmosphere such as an argon atmosphere and then atomized into fine droplets with centrifugal force and the fine droplets are brought into contact with the inert atmosphere such that the fine droplets are solidified into the spherical particles by quenching.
When a high-speed rotary body has a disk or cone shape, the centrifugal force applied to the molten metal greatly varies depending on a portion of the rotary body to which the molten metal is fed; even-size spherical particles are hardly obtained. However, the molten starting material is fed to an end zone of the dish-shaped rotary disk 7 having a concaved portion and therefore the constant centrifugal force of the end zone thereof is applied to the molten starting material; hence, the formed fine droplets are even in size. The fine droplets are quenched in a mixture of the second and third gases and therefore solidified into the spherical particles, which are then collected. The second and third gases can be argon.
The granulation of the molten metal has been investigated using an apparatus similar to the centrifugal granulation apparatus. The investigation has shown that droplets of the melt are solidified into fine particles having a composite structure by quenching and the fine particles are self-assembled such that the fine components are isolated from each other with inclusions or cavities depending on the composition of a starting material and/or the type of an atmosphere gas used. The term “self-assembling” means that uniform molten metal automatically forms a composite structure during atomization and solidification of the present invention.
As increasing the rotational speed of the dish-shaped rotary disk 7, the size of the obtained spherical particles is reduced. When the dish-shaped rotary disk 7 has a diameter of 35 mm and a depth of 5 mm, the rotational speed thereof can be 30,000 rpm or more to obtain spherical particles having an average size of 1-300 nm.
The principal torch 30 includes a first plasma gas supply unit for supplying a plasma gas PL, a first-product supply unit 301 for supplying the micrometer-size particles, and an anode 302. The auxiliary torch 33 includes a second plasma gas supply unit for supplying the plasma gas PL and a cathode 331. When plasma is generated between the anode 302 and the cathode 331, flows of the plasma gas PL are discharged from the first and second plasma gas supply unit and intersect with each other. Since the plasma gas PL is electrically conductive, a conductive path extending from the tip of the auxiliary torch 33 to the tip of the principal torch 30 is formed.
The micrometer-size particles are fed to the first-product supply unit 301 and then discharged therefrom along a central axis 32. In this operation, an inert gas such as argon is discharged from the first gas supply unit 34 simultaneously with the feed of the micrometer-size particles. The inert gas flows along the central axis 32 and serves as a protective gas. Hence, the micrometer-size particles are prevented from being scattered and therefore can be treated at a rate close to 100%. As shown in
After the micrometer-size particles are subjected to a first plasma reaction as described above, a second plasma reaction is applied with the second reaction gas supply unit 35.
A gas used in this step can be argon. The feed rate of the reaction gas can be 1 to 30 L/min.
Thereby treated micrometer-size particles are fed to a granulation chamber 5 and then subjected to granulation as described above with reference to
Various solder alloys including indium (In), tin (Sn), gallium (Ga) and bismuth (Bi) were treated by the apparatus as shown in
The solder alloy was fed to an electric oven 2 included in the centrifugal granulation apparatus, thereby melting the solder alloy. The molten solder alloy passed through a nozzle 4 to reach a granulation chamber 5. In the granulation chamber 5, the molten solder alloy was fed onto a dish-shaped rotary disk 7 and then atomized into droplets with the centrifugal force created by the high-speed rotation of the dish-shaped rotary disk 7 and the droplets were quenched. The formed spherical particles having a composite structure were obtained. In this step, argon was used and the pressure in the granulation chamber 5 was about 0.3 MPa.
The micrometer-size particles as obtained had an averaged particle size of about 15 μm.
Thereby prepared lead free solders as Examples 1 to 9 are summarized in Table 1.
A starting material containing indium (In), tin (Sn), gallium (Ga), and bismuth (Bi) was subjected to the apparatus as shown in
Thereby obtained lead free solder as Example 13 has a composition of Bi: 25.33 wt %, In: 6.17 wt %, Ga: 0.78 wt % and Sn: 67.72 wt %. The lead free solder as Example 13 is of fine spherical particles having a particle size of 100 to 200 nm and a sphericity of about −1% to +1%.
Various micrometer-size particles of lead free solder alloy were prepared by melting starting metal materials under the atmospheric circumstance, using a stainless steel vessel. The starting material was heated at a temperature of 250 to 300° C. The compositions of Comparative Examples 1 to 9 are summarized in Table 1 below.
An insulating substrate is provided. On the insulating substrate, a non-through hole having a diameter of 23 μm and aspect ration (depth/diameter) of about 7 was formed. The substrate was put into a chamber, and the pressure of the inside chamber was reduced into 0.2 Pa. The particles as prepared in accordance with Examples 1-13 and Comparative Examples 1-12 were used. The particles were molten at a temperature 5% higher than the melting point. For example, the particles of Example 1 were heated at about 126° C. in a melting pot. The substrate was applied to supersonic wave of 55 to 65 kHz. The molten metal was poured into the hole. Then, the reduced pressure was recovered and the pressure inside the chamber was increased into atmospheric pressure. The supersonic wave was continued for 5 minutes. The molten metal was solidified by cooling.
Comparing
The conductivity was measured with respect to the metal wirings by using Examples and Comparative Examples. The results are summarized in Table 1. In one embodiment, the conductivity of the metal wiring of the present invention can be less than 100 μΩcm, and in another embodiment, the conductivity of the metal wiring of the present invention can be from 1 μΩcm to 30 μΩcm, and in yet another embodiment, the conductivity of the metal wiring of the present invention can be from 5 μΩcm to 20 μΩcm.
From the results of the X-ray images and the conductivity, the metal wiring of the present invention was found that it has superior conductivity compared with the ones by using conventional metal particles.
