JPH0867901A - Alloy powder for conductive paste and its production - Google Patents

Abstract

PURPOSE: To obtain allay powder for a paste which has excellent oxidation resistance and migration resistance and is suitable for production of fine electronic circuits by specifying the compsn. ratio, of an Au-Ag alloy. CONSTITUTION: The alloy compsn. is composed, by weight, of 5 to 90% Au, 10 to 95% Ag and the balance inevitable impurities. Production of the alloy powder for the paste is executed by the following stages : (l) The Au and Ag powders having a prescribed average grain size, preferably <=10μM are mixed at the prescribed compsn. ratio. (2) The mixture is frictionally crushed by mechanical pulverizing means, such as ball mills. At this time, the Au and Ag powders are made into finer flaky state and are made into the state of shortening the distance between the atoms by laminating and tightly adhering the Au and the Ag to as to easily alloy both in the next heating stage. (3) While the heating time for alloying by heating the flaky powders to 200 to 800 deg.C varies with the grain sizes of the flaky powders, the heating time may be about 10 to 180 minutes. (4) The powders subjected to the heating treatment are frictionally ground again by the mechanical pulverizing means.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to chip-on-board (COB) mounting of bare chip ICs, flip chip ICs, etc.
The present invention relates to an alloy powder for a conductive paste used for manufacturing other fine electronic circuits and a method for manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, Ag-Pd alloy powder or Ag-Cu alloy powder has been used as a conductive paste alloy powder used for COB mounting or the like due to the problem of Ag migration. Here, the migration of Ag is a phenomenon in which Ag ionizes and moves, loses electric charge at the destination and precipitates there. When such migration occurs, the circuit eventually short-circuits,
It will no longer function as an electronic component.

These fine powders for conductive paste are mixed with a resin such as epoxy or polyester and a solvent such as butyl carbitol acetate to form a paste, and a pattern is formed on a substrate by a method such as screen printing. Alternatively, after being applied to the joint portion by a method such as transfer, the solvent is removed and it is solidified. The substrate thus formed may be mounted on a larger substrate to form a multi-chip module. At this time, since the soldering is used for the connection between the substrates, the substrate is kept at 200 ° C.
It will be exposed to the above temperature.

When Ag-Pd alloy powder is used as the powder for conductive paste, at the above soldering temperature,
Since Pd acts as a catalyst and decomposes the resin added as a solidifying agent, there is a disadvantage that it does not solidify sufficiently. In addition, as a powder for conductive paste, Ag-C
When u alloy powder is used, Ag is used in Ag-rich alloys.
There is a problem of migration, and since the Cu-rich alloy does not have sufficient oxidation resistance at the soldering temperature,
There is the inconvenience of impairing the stability of the life of electronic components.

[0005]

In view of the above situation,
The problem to be solved by the present invention is that the electric resistance is sufficiently small for a conductive paste, the oxidation resistance is excellent in heating at a temperature of about soldering, and there is no catalytic action, and the migration resistance of Ag is high. (EN) An excellent and stable alloy powder for conductive paste and a method for producing the same. Therefore, as a result of investigating various alloy systems with Ag, it was confirmed that the Au-Ag alloy powder can solve the above problems as the alloy powder for the conductive paste.

[0006]

The alloy powder for a conductive paste according to the present invention for achieving the above object comprises: Alloy composition is wt%, Au: 5 to 90%, Ag: 1
It is characterized by 0 to 95% and other irreversible impurities. 2. As a method for producing the alloy powder for the conductive paste,
A step of mixing the Au powder and the Ag powder, a step of grinding the mixed powder with a mechanical grinding means, a step of heating the ground powder at a temperature of 200 to 800 ° C., and the heated powder Is ground by a mechanical grinding means.

In the alloy powder for conductive paste of the present invention, A
By using a u-Ag-based alloy, the problem of Ag migration is avoided, the electrical resistance is low enough for conductive paste, and the oxidation resistance at soldering temperature (200-220 ° C) is also sufficient. The possessed alloy powder for conductive paste can be provided.

The reason for limiting the Au content in the present invention is as follows. If it is less than 5%, migration of Ag cannot be avoided, and addition of 5% or more is inevitable. The migration resistance is improved as the added amount of Au is increased, but if 90% or more, the effect is saturated and 90
% Or less.

In the method for producing an alloy powder for a conductive paste according to the present invention, first, an Au powder having a predetermined average particle size and an Ag powder having a predetermined average particle size are mixed at a ratio to achieve a desired composition. Then, it is ground by mechanical grinding means, for example a ball mill. At this time, Au powder and Ag
The powder is more finely pulverized by a ball mill into a preferable flake shape, and at the same time, in the obtained flake powder, Au fine powder and Ag fine powder are laminated inside the flake powder so that they are physically adhered to each other. As they come into contact with each other, the interatomic distance between them becomes extremely short.

In the case of a ball mill, for example, the conditions of grinding by mechanical crushing means are appropriately selected depending on factors such as the type of ball mill, the diameter of the ball, the inner diameter and rotation speed of the ball mill, and the mixing ratio and particle size of the powder. Because it is done, it cannot be decided unequivocally. Since shortening the interatomic distance in the above flake powder promotes alloying of the flake powder during the heat treatment described below, the Au powder and Ag used
The average particle size of the powder is preferably 10 μm or less.

Further, when milling with a ball mill or the like, if 0.1 to 5% by weight of stearic acid or an appropriate amount of acetone is added to the mixed powder, the crushing-flaking process can proceed smoothly. It is possible because it is possible. The flake powder obtained by the above grinding treatment is then heated. By this heating, A stacked inside the flake powder
u and Ag interdiffuse at the contact interface of each other and Au-Ag
It is converted to an alloy and becomes Au-Ag alloy flake powder.

Since the Au-Ag interatomic distance in the Au powder and the Ag powder is shortened by the above-mentioned milling treatment, mutual alloying is possible by heating at a relatively low temperature of 200 ° C. When heated at a high temperature exceeding 800 ° C., the flake powder sinters and it becomes difficult to disintegrate, so the upper limit of the heat treatment temperature is set to 800 ° C.

Although the heating time varies depending on the heating temperature and the particle size of the flake powder, about 10 to 180 minutes is sufficient. The heat-treated powder is ground again by a mechanical grinding means such as a ball mill to obtain fine flake powder.

[0014]

EXAMPLE An Au powder having an average particle size of 1 μm, an Ag powder having an average particle size of 1 μm, Cu and Pd powder were blended so as to have the composition shown in the composition column of Table 1. And 100 g of acetone are added,
A ball mill made of tool steel having an inner diameter of 95 mm and a length of 130 mm was put together with 100 g of SUJ2 balls having a diameter of 5 mm, and the ball mill was operated at 60 rpm for 50 hours.
Thereafter, the ball and the powder were separated, the powder was heat-treated in an argon atmosphere under the conditions shown in the column of heat treatment in Table 1, and further ground for 10 hours in a ball mill to obtain an alloy powder. In Comparative Example 2, when the raw material powders were mixed and ground and then heat-treated at 850 ° C., the powder was sintered and could not be disintegrated, so the subsequent test was not performed.

The oxidation resistance of these powders at the soldering temperature was evaluated. The oxidation resistance was evaluated by measuring the weight change with a thermobalance while raising the temperature in the atmosphere and measuring the temperature at which the weight change occurred. As shown in Table 1, except for Comparative Examples 5 and 6, the results showed a temperature of 250 ° C. or higher, and it was confirmed that good oxidation resistance was exhibited at the soldering temperature (200 to 220 ° C.). Each of the above powder 70
30 parts by weight of an epoxy resin as a solidifying agent and 10 parts by weight of butyl carbitol acetate as a solvent were added to and mixed with parts by weight to form a paste. When the particle size of the powder in this paste was measured using a particle gauge, the maximum diameter and the average diameter were 3 μm and 2 μm, respectively.

The paste was evaluated for heat resistance, electric resistance and migration resistance. In addition, a current-potential curve was obtained for each sample and the elution potential was evaluated. The evaluation of heat resistance is as follows. Au with an end surface area of 4 mm ²
The paste is applied to the end faces of the terminals, and the solvent is evaporated and solidified while being pressed against the end faces of the opposing terminals.
A test piece was obtained by heating at 0 ° C. for 3 minutes. A tensile force was applied in a direction perpendicular to the terminal surface, and the tensile force at break was measured. The results are shown in Table 1, Examples 1-7.
Indicates a breaking load of 300 g or more, and it was confirmed to have good heat resistance.

The electrical resistance was measured by a 4-probe method after forming a film with a film thickness of 20 μm on a glass epoxy substrate by metal mask printing. The results are shown in Table 2,
It was confirmed that both the examples and the comparative examples show a low electric resistance of 5 × 10 ⁻⁴ Ωcm or less. Next, the following tests were performed to evaluate the migration resistance. The paste was printed on a glass epoxy substrate using a metal mask, and the solvent was evaporated to solidify to form a migration measurement electrode. After dropping 20 μl of deionized water between the electrodes,
A direct current voltage of 5 V was applied, and the time until the current started to flow between the electrodes was measured, and this was taken as the migration time.
As can be seen from Table 2, in Examples 1 to 7, no current started to flow even after 1000 seconds or longer, and showed good migration resistance as compared with Comparative Examples 1, 3 and 4. It was confirmed.

Next, the current-potential curve of each sample was measured for elution and the potential was measured. As a result, it was confirmed that the better the migration resistance, the higher the elution and the higher potential.

As is clear from Tables 1 and 2, the alloy powder according to the present invention has a sufficiently small electric resistance value as a conductive paste and is excellent in heat resistance, oxidation resistance and migration resistance. I understand.

[0020]

As described above, the alloy powder of the present invention has a sufficiently low electric resistance as a conductive paste, and when heated at a soldering temperature as compared with a conventional alloy powder of this kind. This alloy powder for conductive paste has excellent oxidation resistance, has no catalytic action, and has excellent migration resistance, and has a high practical value.

[0021]

[Table 1]

[0022]

[Table 2]

Claims (2)

[Claims] 1. The alloy composition is wt%, Au: 5 to 90%,
Ag: 10 to 95%, other irreversible impurities alloy powder for conductive paste. 2. A step of mixing Au powder and Ag powder, a step of grinding the mixed powder by a mechanical grinding means, and a step of heating the ground powder at a temperature of 200 to 800 ° C. The method for producing an alloy powder for a conductive paste according to claim 1, comprising a step of grinding the heated powder with a mechanical grinding means.