JPH051562B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Field of Application) The present invention relates to a conductive paste for a ceramic substrate, and more particularly to a dotting conductive paste for mounting a silicon chip. (Conventional technology and problems) In recent years, electronic devices have become significantly thinner and more compact, and as the degree of integration increases, reliability has further improved.
Its uses are also continuing to expand. monolithic
ICs are rapidly increasing in density and becoming smaller, and on the other hand, in the field of hybrid ICs, large-scale hybrid ICs with excellent heat resistance and shock resistance are becoming more popular, especially in industrial equipment such as automotive control circuits and power supply devices. There is a strong tendency to Recent hybrid IC
In addition to active components such as diodes, transistors, and semiconductor ICs, coils and
It is equipped with most electrical components such as transformers and capacitors. Hybrid integrated circuits have been developed that have further increased the degree of integration and have dramatically improved reliability. These hybrid ICs have individual components or IC elements mounted on a ceramic substrate, or
It is constructed using thick film technology. Normally, a silicon IC chip is bonded to an alumina substrate containing about 96% Al ₂ O ₃ using a bonding paste, but a more durable bonding force is required. Usually, Au-based paste, solder, glass, etc. are used in bonding methods for ceramic dips. Au-based paste has excellent conductivity,
It is extremely stable chemically, has the best bondability with Au wire, is easily alloyed with Si, and has extremely good adhesion to substrates, but it has the disadvantage of being expensive. In order to solve this problem, we replaced Au with Ag and added Pd to prevent migration, which is a disadvantage of Ag.
Pastes have been developed. These conventional pastes are made by mixing metal powder with vitreous metal oxide and kneading the mixture using a vehicle, and their adhesion to the alumina substrate relies solely on sintered bonding of glass frit. However, glass frit has the disadvantage that it is susceptible to thermal shock and its adhesive strength deteriorates due to heat during the process of baking the substrate to form a package or due to changes in environmental temperature during use. In order to improve the adhesion with the alumina substrate, attempts have been made to chemically bond it with the alumina substrate by adding a small amount of Cu, etc., but as long as glass frit is used, it is difficult to dramatically improve the thermal deterioration characteristics. It was hot. In other words, if Cu fine powder is simply added, it will separate from other metal fine powders due to the difference in specific gravity in the vehicle, resulting in poor dispersion during dotting, not only will it not form a uniform paste film, but will also result in alumina Since it is not sufficiently diffused into the substrate, the adhesive strength of the film becomes insufficient. In addition, areas where Cu is segregated during the firing process are locally oxidized and colored, making it impossible to obtain a film with a uniform and smooth surface. In order to solve these problems, the present applicant previously proposed a conductive paste containing as essential components a fine silver powder and a composite fine powder of silver and copper (Japanese Patent Application No. 1983-
18914 etc.). According to this, the above-mentioned problems can be effectively solved, but recently, a ceramic substrate with a new structure has come into use, and there is a demand for the development of a conductive paste that can also deal with this. That is, the conventional ceramic substrate has a cavity 2 formed on a substrate 1, as shown in FIG.
has a simple shape with a generally concave cross section, and after bonding a metallized surface 3 with paste into this cavity, a Si chip 5 is fixed via a preform 4 such as Al/2Si, and then Al, Cu, A jumper wire 6 made of Au or the like was connected between the Si chip 5, the metallized surface 3, and the lead frame 7. However, in such a cavity cross-sectional structure, when connecting the jumper wire 6, it is necessary to jump the wire to a considerable depth within the minute gap, which makes the wire bonding process cumbersome and reduces production. It was interfering with sexuality. Therefore, recently, a substrate 1 having a cavity with a cross-sectional structure having a stepped portion 10 and a projection 11 as shown in FIGS. 1A and 2A has been devised.
With this structure, the stepped portion 10 and the protrusion 11
By forming the metallized surface 3 with paste also on the wire 6, the wire 6 can be jumped by a minimum distance, and the wire bonding process can be simplified. However,
Although the idea of such a structure is good, in reality, a conductive paste that can form the metallized surface 3 on the stepped portion 10 and the protruding portion 11 with the same quality as that on the flat portion has not been developed, and it has not been put to practical use. At present, the development of a conductive paste that can be applied to a ceramic substrate with such a new structure has been desired. (Object of the Invention) The present invention has been made specifically to meet the above-mentioned needs, and its purpose is to provide a dotting conductive paste for a deep dip IC.
It has good adhesion to the side walls of stepped parts and protrusions provided in the substrate cavity, and also increases the adhesive strength between the alumina substrate and silicon chip, and has excellent heat resistance and
It is an object of the present invention to provide a fritless type dotting paste that has excellent impact resistance, is easy to use, and is inexpensive. (Structure of the Invention) In order to achieve the above object, the conductive paste according to the present invention contains at least a fine silver powder, a composite fine powder of silver and copper, and one or two of yttrium oxide and vanadium pentoxide as essential components. and the silver fine powder contains flaky silver particles in an amount of 30% or more of the total silver fine powder, and the flaky silver particles have an average size of 5 μm or less and are approximately circular with a major axis (a) and a minor axis (b). ,
The gist is that the thickness (c) is c<1 μm and c<1/5 (a, b). The present invention will be explained in detail below based on examples. In the present invention, the silver fine powder used has a particle size of 10 μm or less, preferably an average particle size (D ₅₀ ) of 0.5 to 5 μm. If it is larger than 10 μm, the dispersibility in the vehicle will be poor, and there is a risk that the needle will be clogged during dotting. The above-mentioned fine silver powder must contain 30% or more of flake-like silver particles. The flaky silver particles have a shape as shown in FIG. 4, have an average particle size of 5 μm or less, (i) ab, a, b≫c, (ii) a thickness of 1 μm or less,
c is less than 1/5 of a and b. Flake-like silver particles are produced by turning silver particles obtained by a reduction method or an electrolytic method into flakes by stamping or crushing with a ball mill, and at this time, it is preferable to soak them in a fatty acid to prevent the flakes from adhering to each other. It may also be obtained by cutting silver foil into pieces. Other fine silver powders do not need to be special, and silver powder obtained by ordinary reduction methods or electrolytic methods can be used. is preferred. The above flaky silver particles
If it is less than 30%, the adhesion to the side wall of the substrate cavity will not be good, so it is necessary to mix it in at least 30%. Although it is effective to make 100% of the fine silver powder into flake-like silver particles, the strength of the metallized layer deteriorates and there are slightly more pores on the surface. Next, the composite fine powder of silver and copper only needs to maintain the bond between the silver particles and the copper particles in the vehicle, and plating powder, co-precipitated powder, mechanical alloy powder, etc. can be used. In particular, mechanical alloy powder is obtained by mixing and pulverizing silver and copper powders by rotating them at high speed in a ball mill, and the silver particles and copper particles are mechanically interlocked and bonded, and no binder is used. It is possible to maintain a strong bond between silver particles and copper particles without causing any damage. When mechanical alloy powder is used, it has the advantage that composite powders having a wide range of Cu contents can be arbitrarily selected and used. The particle size of the composite powder of silver and copper is 10 μm or less, preferably the average particle size (D ₅₀ ) is 0.5 to 5 μm. The content of copper in the composite powder of silver and copper is 20-70%, preferably 40%
~60% is appropriate. If the copper content is less than 20%, the film strength will not be sufficient, and if it exceeds 70%, the effect of composite powdering will be lost. Further, it is desirable that the specific gravity value be as close as possible to an intermediate value between that of silver and copper in order to improve dispersibility in the vehicle. The copper content in the metal powder in the conductive paste is 0.1 to 10%, preferably 2 to 5%. If the copper content is less than 0.1%, diffusion into the alumina will be insufficient and adhesive strength will not increase. It also has a copper content of 10
%, the oxidation of copper becomes significant, resulting in even more adverse effects. The metal powder content in the conductive paste must be 60 to 90%; otherwise, a paste viscosity that is easy to handle cannot be obtained. When adding ytosodium oxide (Y ₂ O ₃ ), it is preferably produced by a chemical method and has a purity of 99.6% or more. The average particle size of the particles is preferably 5 μm or less, and the smaller the particle size, the better in order to improve strength or improve dispersibility. When the average particle size is 10 μm or more, uniform dispersibility is poor and surface smoothness is unfavorable. The amount of yttrium oxide added is 20 ppm to 2%, preferably 0.05 to 1% in the solid component of the paste.
It has been found that when added in an amount of %, it has a remarkable effect on improving adhesive strength. No effect is observed if the amount added is less than 20ppm, and if it exceeds 2%, Y ₂ O ₃
precipitates, adversely affecting surface smoothness and inhibiting die attachability. In order to maintain surface smoothness and improve adhesion strength, it is preferable to add 0.05 to 1% to the solid components of the paste. When adding vanadium pentoxide (V ₂ O ₅ ),
It is preferably chemically produced and has a purity of 99.9% or higher. The average particle size is 5μm or less,
Preferably, the finer the particle size is 2 μm or less, the better the dispersibility and the better the effect on strength. On the other hand, the average particle size
If it is 5 μm or more, it is unfavorable in terms of strength, surface smoothness, and uniform dispersibility. The addition rate _{of V2O5} is 20~
500ppm is optimal. No significant effect on strength is observed below 20 ppm. Adding more than 500 ppm will not only change the color tone, but also increase the number of pores and roughen the surface, resulting in particularly poor die attachability (difficult to attach Si). Y ₂ O ₃
is effective at firing temperatures of 900°C or higher;
The effect is not significant below ℃. To maintain strength more stably over a wider temperature range
Preferably, it is added together with Y ₂ O ₃ . The vehicle disperses the metal powder uniformly, has appropriate viscosity and surface tension when used, and has the function of smoothly spreading the powder onto the surface to which it is applied. As the vehicle used in the present invention, commonly used organic solvents such as terpineol, butyl carbitol, ethyl cellulose, butyl carbitol acetate, and texanol can be used. In the paste state, the viscosity is adjusted to be high in order to avoid separation and segregation of fine metal powder particles, but when used, it is diluted with a solvent and adjusted to a viscosity of 40 to 450 cps. By configuring the paste as above,
It has strong bonding strength that can withstand thermal shock and has significantly improved thermal deterioration resistance. Furthermore, the paste according to the invention has good dispersibility during dotting, resulting in an excellent surface film with smooth and uniform baking characteristics. Furthermore, even when applied to a substrate having a structure having stepped portions or protrusions 11 as shown in FIGS. 1 and 2, the adhesion to the side walls is good. In the conductive paste of the present invention having the above structure, platinum or palladium can be added to the metal powder, if necessary. Furthermore, a copper organic substance can also be added to the paste as required. Of course, it goes without saying that components other than these can be added. The optionally added components exemplified above will be explained below. When platinum is added, it is added only as a composite fine powder of silver and platinum or as a fine platinum powder. The paste containing platinum added to the above-mentioned essential components has strong bonding strength that is particularly resistant to thermal shock and has significantly improved resistance to thermal deterioration.It also prevents silver migration and improves wire bonding and fine line properties. , has the effect of improving solder properties and conductivity. Also, when connecting wires to the cavity, Al wire has the great advantage of being usable. Since platinum is chemically stable, it is effective to improve the above characteristics even when mixed alone, but using a composite powder with silver is even more effective because it is uniformly dispersed in the vehicle. As the composite powder of silver and platinum, plating powder, co-precipitated powder, mechanical alloy powder, etc. can be used. A suitable content of platinum in the composite powder is 5 to 60%. Mechanical alloy powders with high platinum content can be easily obtained. The powder particle size of the composite powder is 10μm or less,
The average particle diameter (D ₅₀ ) is preferably about 5 μm.
The platinum content is based on the metal particles in the paste.
0.2-10%, preferably 0.5-3.0%. When the platinum content is less than 0.2%, no additive effect is observed,
If it exceeds 10%, the effect of cost reduction will not be apparent. When palladium is added, it is preferably added as a composite fine powder of silver and palladium, but fine palladium powder can also be added alone. By adding palladium,
In addition to having strong bonding strength that can withstand thermal shock and significantly improved thermal deterioration resistance, it is particularly effective in preventing silver migration, improves wire bonding properties and soldering properties, and has a smooth and homogeneous surface. It has the effect of forming a film. It is a widely known fact that pastes containing palladium have the effect of preventing silver migration, but pastes containing palladium alone have the disadvantage that the palladium is oxidized during the firing process, resulting in a rough surface. However, when using a powder made of palladium and silver,
An extremely flat film can be obtained while preventing the oxidation of palladium. Co-precipitation powder, mechanical alloy powder, and plating powder can be used as the composite powder of silver and palladium. The content of palladium in the composite powder is
10-40%, preferably 20-30% is easy to use. The particle size of the composite powder is preferably 10 μm or less, and the average particle size (D ₅₀ ) is preferably about 5 μm. The content of palladium is 0.2-30%, preferably 0.5-10%, based on the metal particles in the paste. This is because if the palladium content is less than 0.2%, the effect of addition is not recognized, and even if it is added more than 30%, no significant improvement in properties can be expected. When adding a copper organic substance, it is added in such a range that the total amount of pure copper in the paste is 0.1 to 10%. The copper organic substance used here is

【formula】 Or

[Formula] (R is a saturated hydrocarbon) The cyclic terpene derivative may be represented by the general formula R-S-Cu-S-R. The copper content is generally between 3 and 10% by weight. Specifically, there are resinate copper, copper aryl mercaptide, copper terpene methide, and the like. These organic coppers exist in a state dissolved in a solvent in the paste. Organic copper is produced using the IR method (Infra
−Red Absorption Spectrum, NMS method (Nuclear Magnetic
Its presence can be determined by distinguishing it from metallic copper using methods such as Resonance (nuclear magnetic resonance method). The effects of using copper organic matter are (i) Since it is a liquid, it mixes well with the vehicle;
A paste with excellent dispersibility is possible. (ii) There is almost no segregation even when dotted onto a substrate. (iii) In the firing process, the Ag/Cu composite powder and Y ₂ O ₃ powder mainly contribute to the adhesive strength with the substrate, and the copper organic matter is uniformly dispersed, promoting sintering between the metallized layers. effective. Therefore, variations in adhesive strength are reduced, and a product with stable strength can be obtained. (Example) Metal powder shown in Table 1 and Y ₂ O ₃ and/or V ₂ O ₅
Further, organic copper was used as appropriate, and terpineol, butyl carbitol, and ethyl cellulose were used as vehicles, and the mixture was kneaded in a three-roll mill to prepare a paste. Silver powder contains 0-100% flaky silver particles,
Flake-like silver particles are obtained by crushing reduced silver powder with a stamp mill using stearic acid to obtain an average particle size of 5 μm.
In the following, those having a substantially circular shape with a major axis (a) and a minor axis (b), a thickness (c) of c<1 μm, and c<1/5 (a, b) were classified and used. The other silver powder used was a commercially available reduced powder, with a purity of 99.9% and a particle size of 1 to 4 μm.
As the composite powder of silver and copper, electroless plating powder containing 20% copper and mechanical alloy powder obtained by mixing and pulverizing 50% silver powder and 50% copper powder at high speed in a ball mill were used. The particle size of the composite powder was classified to 10 μm or less. As platinum, a commercially available fine powder of 0.5 to 0.8 μm and a coprecipitated powder with a ratio of silver and platinum of 85:15 were classified to 5 μm or less and used. In addition, palladium has a commercially available particle size
A fine powder of 0.8 to 1.8 μm and a coprecipitated powder having a weight ratio of silver and palladium of 7:3 were used, which were classified to 5 μm or less. A commercially available Y ₂ O ₃ with an average particle size of 1.2 μm and a purity of 99.8% was used. V ₂ O ₅ has an average particle size of 3 μm or less and has a purity of 99.9%.
A commercially available product was used. Commercially available resinate copper was used as the organic copper. The blending ratio of resinate copper was 4 parts by weight based on the entire paste. The copper content in resinate copper is 6.4%, so it comes from resinate copper.
The proportion of pure Cu is 0.256 parts by weight. The vehicle component used was a 1:1 mixture of terpineol and butyl carbyl, with 12% ethyl cellulose added to the solvent. The viscosity at that time was measured using a Brookfield viscometer HBT using spindle No. 14, and it was 200 ± 50 Kcps.
It was hot. Next, the paste was adjusted to a final viscosity of about 100 cps using a 1:1 mixed solution of butyl carbitol and terpineol as a thinner, and used for dotting. The substrate is black alumina (96% Al ₂ O ₃ , dimensions
52.2 x 13.2 x 1.9 mm), the approximate dimensions of the cavity are 8.0 x 8.0 mm, the depth is 0.50 mm, the width of the stepped portion is 1.0 mm, and the cross section is 0.05 mm deep (Figure 5). reference). The alumina substrate was used after cleaning with trichlorolene. 2x2 on this cavity
A ×0.1 mm silicon chip was attached by dotting. The dotting device used was one manufactured by Iwashita Engineering. After dotting the conductive paste, it was dried at 120° C. for 20 minutes, and then fired in an atmospheric atmosphere using a 4MC type thick film firing furnace manufactured by Watkins Johnson. The firing conditions were a 60 minute profile and a peak temperature of 910°C for 10 minutes. The surface of the paste film thus obtained was observed, and the surface roughness was measured using a surface roughness meter manufactured by Tokyo Seimitsu. Fifty samples were used for each level. Further, using an Au preform of 2.5 x 2.5 mm x 25 μm, a silicon chip was bonded at 450°C using a die attach device manufactured by West Bond. Adhesive strength tests and heat resistance tests were conducted on the thus obtained Surdip IC. These results are shown in Table 2. Adhesive strength was determined by die attachability and die push test. Die attachability is determined by the scrubbing time during adhesion, and the ○ mark in the table indicates that adhesion was achieved in a short time. The dipstick test was performed on the test piece after the heat resistance test using a particle bond tester manufactured by Engineered Technical Products. ○ mark in the table is 20
If all individual test pieces show die failure,
The x mark indicates that all 20 test pieces had peeled off. The mark △ indicates that film peeling occurred in 1 or more and 5 or less of the 20 test pieces. For heat resistance tests, a thermal cycle test and a thermal shock test were conducted. The test conditions are thermal cycle test.
Based on MLLL-STD883B 1010・2
I went with CONDITION C. Thermal shock test is also MILL-STD 883B 1011・2, CONDTION
I went with C. Additionally, the state of adhesion of the metallized surface to the side wall of the substrate cavity was investigated for 50 substrates. The results are shown in Table 2. The judgment criteria are as shown in Figure 6a, if there is electrical continuity between the bottom 12 and the top 13 for all the boards, it will be passed (marked with ○).
As shown in Figure b, it does not attach to the side wall 14 (in the figure,
(on the left) or even if it was attached, it was thin at the step upper part 13 (in the figure, right side), and cases where there was no electrical conduction between the bottom part 12 and the step upper part 13 were determined to be rejected (marked with an x). Furthermore, a wire bonding test was conducted. The test equipment used a wire bonder made by West Bond (USA), and a 25 μmφ Al wire (1% Si) was used.
(added) were pressed together using ultrasonic waves as shown in FIG.
The test method was to pull the neck part vertically using a wire pull tester (Fig. 8a), and examine its strength and fracture mode at various temperatures. The results are shown in Table 2. In addition, in the same table, "unmeasurable" means that the wire peeled off when the adhesive strength was 25 kg or less.
Also, regarding wire bondability, ○ marks are
If the breaking load is 10 g or more and the breakage A as shown in Fig. 8b does not occur for all the pieces (10 pieces), △ mark indicates that peeling mode occurred for 5 or more pieces out of 10 pieces, and × mark indicates that This shows the case where the test was impossible due to peeling.

【table】

【table】

【table】

[Table] As shown in Table 2, especially in fine silver powder, 30
Invention Nos. 1 to 13 containing % or more of flaky silver particles,
Nos. 30 to 32 and 34 to 36 all had good metallized surfaces, no color unevenness, and good adhesion to the side walls. Of course, it also has good die attachability, good heat resistance, and excellent wire bondability. In contrast, it does not contain any flaky silver particles (No.
14, 16) or in comparative examples containing only a small amount (No. 15), the adhesion to the side walls was insufficient.
Items that contain sufficient silver flake particles but do not contain composite fine powder of silver and copper (No. 17, 18, 21, 22,
25, 26) and those containing appropriate amounts of Y ₂ O ₃ or V ₂ O ₅ (No.
19, 20, 21, 22, 27, 28) have poor die attachability and heat resistance, weak wire adhesion strength, or poor wire bondability. (Effects of the Invention) As detailed above, according to the present invention, the adhesive strength is high and the heat resistance and impact resistance are excellent.
It is possible to provide a fritless type dotting paste that is easy to use and inexpensive, and it can be applied to a new structure of a ceramic substrate having stepped portions or protrusions, so its practical effects are extremely large.

[Brief explanation of drawings]

FIG. 1 and FIG. 2 are partial cross-sectional views showing an example of application of the paste and an example of the third dip structure according to the present invention;
Fig. 3 is a partial cross-sectional view showing a normal sardip structure, Fig. 4 is a diagram showing the shape of flaky silver particles used in the present invention, and Fig. 5 is a shape of a sardip structure used in an example of the present invention. , dimensions (mm), FIG. 6 is an explanatory diagram showing the adhesion state of the metallized surface, and FIGS. 7 and 8 are diagrams explaining the wire bonding test method. DESCRIPTION OF SYMBOLS 1... Substrate, 2... Cavity, 3... Metallized surface, 5... Si chip, 6... Jumper wire, 10... Stepped portion, 11... Projection,
12...bottom, 13...step top, 14...side wall.

Claims (1)

[Claims] 1. Consisting of a solid component and a vehicle, the solid component contains at least 60 to 90% in total of fine silver powder and fine composite powder of silver and copper, and has a copper content of 0.1
~10% and further contains one or two of 20ppm to 2% of yttrium oxide and 20 to 500ppm of vanadium pentoxide, in which the silver fine powder contains flaky silver particles as a whole of the silver fine powder. of
30% or more, and the flaky silver particles have an average particle size of
A conductive paste having a diameter of 5 μm or less, a substantially circular shape with a major axis (a) and a minor axis (b), and a thickness (c) of c<1 μm and c<1/5 (a, b). . 2 The solid component contains a composite fine powder of silver and platinum or a fine platinum powder, and has a platinum content of 0.2 to 10
% of the conductive paste according to claim 1. 3. Claim 1, wherein the solid component contains a composite fine powder of silver and palladium or a fine palladium powder, and has a palladium content of 0.2 to 30%.
Conductive paste as described in section. 4 Consists of a solid component, a copper organic substance, and a vehicle,
The solid component contains at least 60 to 90% in total of fine silver powder and composite fine powder of silver and copper, has a copper content of 0.1 to 10%, and further contains 20 ppm to 2% of sodium nitrite oxide. , a conductive paste further containing a copper organic substance in a range where the total amount of pure copper in the paste is 0.1 to 10%; Silver particles have an average particle size of 5 μm or less, and a long diameter
(a) Almost circular with short axis (b), thickness (c) of c < 1 μm,
A conductive paste characterized in that, and c<1/5 (a, b). 5 The solid component contains a composite fine powder of silver and platinum or a fine platinum powder, and has a platinum content of 0.2 to 10
% of the conductive paste according to claim 4. 6. Claim 4, wherein the solid component contains a composite fine powder of silver and palladium or a fine palladium powder, and the palladium content is 0.2 to 30%.
Conductive paste as described in section.