JP4819516B2 - Conductive paste and ceramic multilayer circuit board using the conductive paste - Google Patents

Description

  The present invention relates to a conductive paste used as a conductor material of a ceramic multilayer circuit board used for manufacturing a high-density wiring circuit board, and a ceramic multilayer circuit board formed with a conductive portion using the conductive paste.

  Ceramic multilayer circuit boards are widely used as high-density wiring circuit boards. The ceramic multilayer circuit board is generally manufactured by the ceramic green sheet lamination method, for example, in the following procedure.

  First, via holes are punched in multiple ceramic green sheets for interlayer connection, formed by laser processing, etc., and via conductors are filled into the via holes of each ceramic green sheet by hole-filling printing to form via conductors. Thereafter, a wiring pattern is formed on each ceramic green sheet by a screen printing method using a conductive paste, and the ceramic green sheets are laminated and pressure-bonded, and the laminate is fired to form a ceramic multilayer circuit. The substrate is manufactured.

  Currently used ceramic multilayer circuit boards are roughly classified into high-temperature fired ceramic multilayer circuit boards such as alumina fired at 1300 ° C. or higher and low-temperature fired ceramic multilayer circuit boards fired at approximately 1000 ° C. or lower.

  Mo, W, etc. are used as conductor materials for high-temperature fired ceramic multilayer circuit boards, but when these metals are used, they must be fired in a reducing or inert atmosphere, and the electrical resistance of these metals Is relatively expensive.

  On the other hand, Ag, Ag-Pt, Ag-Pd, etc., which have low electrical resistance values, are used as conductor materials for low-temperature fired ceramic multilayer circuit boards. These metals have excellent electrical properties and are fired in air. There is an advantage that you can.

  However, even in a low-temperature fired ceramic multilayer circuit board that can be fired in air, if the binder component of the conductive paste contained in a large amount in the green sheet cannot be removed before firing the board, the organic compound that forms the binder is fired on the board. Occasionally, the gas evaporates and a gap or a crack may be generated between the wiring pattern made of the conductive paste and the ceramic substrate. Therefore, in order to prevent such a problem from occurring, in the manufacturing process of the conventional low-temperature fired ceramic multilayer circuit board, the binder removal process for sufficiently removing the binder component before firing the board is performed for several hours to several tens of hours. Then, the substrate was baked.

  However, since long-time debinding treatment significantly reduces productivity and causes a significant increase in cost, Patent Documents 1 and 2 improve debinding properties by employing a binder component that is easily thermally decomposed. Conductive pastes have been proposed.

  That is, Patent Document 1 discloses a conductive paste containing acrylic resin and alkyd resin as binder components in a ratio of 2 to 4 parts by weight of acrylic resin and 1 part by weight of alkyd resin.

Further, in Patent Document 2, when the viscosity at a shear rate of 0.2 sec ⁻¹ is η and the weight average molecular weight of the organic compound forming the binder is Ma, Ma> Mc in the range of 0 <Ma <10 ^10. if proportional to eta is Ma ⁿ (provided that n> 1), conductive paste, if Ma ≦ Mc eta contains a binder component present value Mc as proportional to Ma is disclosed.
JP-A-5-234424 JP 2000-76931 A

  However, since the acrylic resin used as the binder component of the conductive paste of Patent Document 1 has strong spinnability and adhesiveness, when forming a wiring pattern using the conductive paste containing this binder component In addition, the shape of the screen mesh is easily transferred to the wiring pattern, and as a result, irregularities may occur on the surface of the wiring pattern. In particular, when a fine wiring pattern having a line width of about 20 to 100 μm is formed, irregularities on the pattern surface cause the pattern to be disconnected when the substrate is baked, which is a fatal defect.

  Moreover, in the case of the electrically conductive paste described in Patent Document 2, it is necessary to use a binder component determined by a special relationship between the viscosity and the molecular weight, which requires extremely complicated preparation.

  The present invention has been made in view of such problems of the prior art, and its purpose is to provide a gap between the wiring pattern and the ceramic substrate even if the conductor paste and the ceramic green sheet are fired simultaneously. An object is to provide a conductive paste capable of easily obtaining a highly reliable ceramic multilayer circuit board without generating cracks and a ceramic multilayer circuit board formed with a conductor portion using the conductive paste. .

In order to achieve the above object, the conductive paste of the present invention forms at least one of via conductors and wiring patterns of the ceramic green sheet in a ceramic multilayer circuit board obtained by laminating and firing ceramic green sheets. used, the conductive powder, a binder component consisting of an organic compound, and an organic solvent seen including, prior to firing of the ceramic green sheet, the binder component by debinding at 400 to 450 ° C. is performed The conductive paste contains silver powder and silver oxide powder as the conductive powder, and the silver oxide powder is selected from Ag ₂ O powder and AgO powder, and the silver powder from 55 to 89.9 wt%, in the configuration that the silver oxide powder containing 0.1 to 15.0 wt%

  The average particle size of the silver powder is preferably in the range of 0.3 to 10.0 μm.

  It is preferable to form a conductor portion of the ceramic multilayer circuit board using the conductive paste.

  The conductive paste of the present invention contains silver powder and silver oxide powder as conductive powder, and silver oxide causes the following reaction at about 400 ° C.

2Ag ₂ O → 4Ag + O ₂
2AgO → 2Ag + O ₂
That is, since silver oxide undergoes a reduction reaction at about 400 ° C., by performing a heat treatment (debinding treatment) at a temperature at which the silver oxide undergoes a reduction reaction before firing the substrate, oxygen produced as a result of the reduction reaction ( O ₂ ) decomposes the organic compound as the binder component, and the debinding is promoted. As a result, it is possible to obtain a highly reliable ceramic multilayer circuit board in which gaps and cracks are unlikely to occur between the wiring pattern and the board during subsequent firing of the board.

  In this case, if the average particle diameter of the silver powder is less than 0.3 μm, it is possible to print a wiring pattern with a fine line width, but there is a disadvantage that it is burnt and burnt during firing. On the other hand, when the average particle diameter of the silver powder exceeds 10.0 μm, there is a disadvantage that it becomes difficult to print a wiring pattern having a fine line width having a line width of 100 μm or less and a line interval. Therefore, by setting the average particle size of the silver powder in the range of 0.3 to 10.0 μm, it is possible to form a wiring pattern with a fine line width without disconnection during firing. In addition, the average particle diameter in this application means the particle diameter in 50 volume% in an accumulation graph when the arithmetic mean value of the major axis and minor axis of a powder is measured with the laser diffraction type particle size distribution measuring apparatus by Microtrac.

If the silver oxide powder is less than 0.1% by weight, the effect as an oxygen supply source for thermal decomposition of the binder component may not be sufficiently expected. On the other hand, when the silver oxide powder exceeds 15.0% by weight, there is a disadvantage in that the shrinkage rate during sintering of the ceramic substrate and the conductor is inconsistent and the substrate is warped. Therefore, by containing 0.1 to 15.0% by weight of silver oxide powder, there is no such inconvenience, and the effect of promoting binder removal can be sufficiently expected. As silver oxide powder, both Ag ₂ O powder and AgO powder can be expected to promote binder removal, so either one can be used alone, but both Ag ₂ O powder and AgO powder should be used in combination. You can also.

  Then, if the conductive portion of the ceramic multilayer circuit board is formed using the conductive paste, a highly reliable ceramic multilayer circuit board can be obtained without generating a gap or a crack between the wiring pattern and the ceramic board. Can do.

Next, an example of a method for forming a conductor portion of a low-temperature fired ceramic multilayer circuit board using the conductive paste of the present invention will be described in the order of steps.
(1) Molding of low-temperature fired ceramic green sheet A green sheet of low-temperature fired ceramic is tape-molded by a doctor blade method or the like. At this time, as the low-temperature fired ceramic, for example, a mixture of CaO—SiO ₂ —Al ₂ O ₃ —B ₂ O ₃ glass 50 to 65 wt% and alumina 35 to 50 wt% can be used. In addition, for example, low-temperature fired ceramic materials such as a mixture of PbO—SiO ₂ —B ₂ O ₃ glass and alumina, MgO—Al ₂ O ₃ —SiO ₂ —B ₂ O ₃ glass, cordierite crystallized glass, etc. Can also be used.
(2) Cutting of green sheet and formation of via hole Next, the tape-formed low-temperature fired ceramic green sheet is cut into a predetermined dimension, and then a via hole is punched at a predetermined position.
(3) Filling the via hole with the conductive paste and printing the wiring pattern Next, filling the via hole with the conductive paste filling method and printing the wiring pattern with the conductive paste on the ceramic green sheet.

  The mixing ratio of the conductive powder composed of silver powder and silver oxide powder in the silver-based conductive paste used at this time and the organic vehicle formed by dissolving the binder component in an organic solvent adopts a general mixing ratio. be able to. For example, the weight ratio can satisfy (70/30) ≦ (conductive powder / organic vehicle) ≦ (90/10). If the conductive powder is less than 70 parts by weight (the organic vehicle is more than 30 parts by weight), sufficient conductivity cannot be secured, while the conductive powder is more than 90 parts by weight (the organic vehicle is less than 10 parts by weight). This is not preferable because a high paste viscosity cannot be obtained, and work efficiency in filling via holes and wiring pattern printing is reduced.

  The preferable composition of the conductive paste for exhibiting the effects of the present invention and obtaining good electrical characteristics is that when the total is 100 parts by weight, the silver powder is 55 to 89.9 parts by weight, and the silver oxide powder is 0.00. 1 to 15.0 parts by weight, organic vehicle is 10 to 30 parts by weight, and the blending ratio of silver oxide powder may be less than silver powder, so the effect of the particle size of silver oxide powder on electrical characteristics is silver It seems to be relatively small compared to the powder, but in order to form a fine line width wiring pattern without disconnection during firing, the average particle diameter of the silver oxide powder is 0. It is preferable to make it the range of 3-10.0 micrometers.

  Although it does not limit as a binder component which comprises an organic vehicle, Ethyl cellulose can be used and an ethyl carbitol acetate, a butyl carbitol acetate, a terpineol etc. can be used as an organic solvent.

  For example, by adding 20 parts by weight of an organic vehicle in which ethyl cellulose is dissolved in terpineol to 80 parts by weight of the conductive powder, the conductive paste is sufficiently kneaded and dispersed using a three-roll apparatus. Obtainable.

The silver powder contained in the conductive paste for wiring pattern printing and the silver powder contained in the conductive paste for filling via holes are not necessarily the same, and the former silver powder has a relatively small particle size (0.3 to 3.0 μm), and the latter silver powder can also have a relatively large particle size (3.0-10.0 μm). In this way, the paste using the silver powder having a small particle diameter can form fine wiring, and the paste using the silver powder having a large particle diameter can reduce the cost.

  Furthermore, in order to improve the adhesiveness between the conductive paste and the ceramic substrate, a glass component can be contained in the conductive paste in an amount of 0.1% by weight or more. Since solder wettability may deteriorate, it is preferable to add a predetermined amount of a glass component as necessary.

In order to improve solder corrosion resistance, the conductive paste can contain 0.1 wt% or more of Pt powder or Pd powder, but more than 0.5 parts by weight of Pt powder or Pd powder is added. Even if the effect is saturated, the manufacturing cost is increased. Therefore, it is preferable to add a predetermined amount of Pt powder or Pd powder as necessary.
(4) Lamination and pressure bonding After filling the via holes with the conductive paste and printing the wiring pattern, the green sheets of each layer are laminated and pressure-bonded to be integrated.
(5) Debinder treatment Before firing the laminate, the laminate is heated to about 400 to 450 ° C. and held for 1 to 2 hours to produce a binder component composed of an organic compound as a result of the silver oxide reduction reaction. It is removed by thermal decomposition with oxygen. The ratio of the case of including both of Ag ₂ O powder and AgO powder as silver oxide powder for binder removal promotion, Ag ₂ O powder is Ag ₂ O powder from the ratio AgO powder 20 parts by weight is 80 parts by weight 80 It is preferable that AgO powder is contained in the range of the ratio which is 20 weight part by weight.
(6) Firing The laminate after the binder removal treatment is fired at a firing peak temperature of 800 to 950 ° C. (preferably around 900 ° C.) and held at the peak temperature for 20 to 60 minutes to obtain a low-temperature fired ceramic multilayer circuit board. Obtainable.

  FIG. 1 is a cross-sectional view of an example of a low-temperature fired ceramic multilayer circuit board manufactured through the process as described above, where 1 is a wiring pattern, 2 is a via hole filled with a conductive paste, and 3 is a ceramic green sheet.

  In addition, alumina green sheets are laminated and pressure-bonded on both sides of the green sheet laminate in the firing step, fired at 800 to 950 ° C. while applying pressure, and after firing, the alumina green sheets on both sides are removed to form a low-temperature fired ceramic multilayer circuit board. It can also be manufactured. By doing in this way, the curvature of a board | substrate based on the difference of the thermal contraction behavior of a conductor and a ceramic and peeling of a conductor can be suppressed.

  Examples of the present invention will be described below. However, the present invention is not limited to the following examples, and can be appropriately changed and modified without departing from the technical scope of the present invention.

Using a three-roll apparatus, a silver powder having an average particle size shown in Table 1 below, a silver oxide powder, and an organic vehicle in which ethyl cellulose is dissolved in terpineol are blended as shown in Table 1 and kneaded and dispersed. As a ceramic green sheet, a square shape (1 inch × 1 inch) obtained by mixing 60 wt% CaO—Al ₂ O ₃ —SiO ₂ —B ₂ O ₃ glass and 40 wt% alumina is obtained. × 300 μm thickness).

  A wiring pattern as shown in FIG. 2 is formed on the ceramic green sheet by screen printing using the conductive paste, and then the ceramic green sheet is kept at 400 ° C. for 1 hour in a belt-type firing furnace. After heat treatment under atmospheric conditions, the mixture was cooled to room temperature, and then baked in the same belt-type baking furnace under atmospheric conditions at a peak temperature of 890 ° C. and a peak temperature holding time of 20 minutes. And the clearance gap between the wiring pattern and a board | substrate in the ceramic circuit board obtained as a result, and the curvature of the board | substrate were evaluated. In FIG. 2, L indicates the line width, and S indicates the line interval. Note that the evaluation of the gap between the wiring pattern and the substrate and the warpage of the substrate described in Table 1 described later is based on an evaluation method as described below.

  As a method of evaluating the gap between the wiring pattern and the substrate, the ceramic substrate after firing was placed on a surface plate and visually observed, and as a result, no gap was found between the wiring pattern and the substrate. There is no gap (symbol ○), and there is a slight gap (symbol △) when there is a gap with the board in a part of the wiring pattern, and there is a gap between the board and the board in almost the entire area of the wiring pattern. What was recognized was defined as a gap (symbol x).

  As shown in FIG. 3, the substrate warpage is evaluated by placing the fired ceramic substrate 4 on the surface plate 5 and maximizing the distance between the lower surface 4 a of the substrate 4 and the upper surface 5 a of the surface plate 5. When the value h is measured with a gap gauge, when the maximum value h of the interval is 20 μm or less, the value is good (symbol ○), and when the maximum value h of the interval is 25 to 35 μm, the value is slightly bad (symbol Δ). Those having a maximum interval h of 50 μm or more were defined as defective (symbol x). When the maximum value h of the interval is 20 μm or less, it is a good level suitable for practical use.

  As shown in Table 1, according to Examples 1 to 11 of the present invention, there is no gap between the wiring pattern and the substrate, the warpage of the substrate is a good level suitable for practical use, and a highly reliable ceramic. It is a circuit board.

However, in Comparative Examples 1 to 5, since Ag ₂ O is not blended in the conductive paste, the binder component cannot be thermally decomposed before the substrate is baked, and the binder component is a gas when the substrate is baked. It evaporated and a gap was formed between the wiring pattern and the substrate, and the substrate was also warped.

In Comparative Example 6, since Ag ₂ O is excessively blended in the conductive paste, the binder component can be thermally decomposed and removed before firing the substrate, and no gap is generated between the wiring pattern and the substrate. However, there was a mismatch in the sintering timing and shrinkage rate between the conductor paste and the ceramic substrate, and the substrate warped.

In Comparative Example 7, Ag ₂ O is blended in the conductive paste, but since the blending amount is small, the amount of binder removed by thermal decomposition before firing the substrate is small, and the remaining binder component is present during firing of the substrate. The gas evaporated and a gap was generated between the wiring pattern and the substrate.

In Comparative Examples 6 and 7, the same results as above were obtained when AgO was used instead of Ag ₂ O.

It is sectional drawing of an example of a low-temperature baking ceramic multilayer circuit board. It is a figure which shows an example of the wiring pattern by screen printing. It is a figure explaining the evaluation method of the curvature of a substrate.

Explanation of symbols

1 Wiring pattern 2 Via hole 3 Ceramic green sheet 4 Ceramic substrate 5 Surface plate

Claims (3)

In a ceramic multilayer circuit board obtained by laminating ceramic green sheets and firing, the binder component is used for forming at least one of via conductors and wiring patterns of the ceramic green sheets, and made of conductive powder and an organic compound. When, viewed contains an organic solvent, prior to firing of the ceramic green sheet, wherein the binder component is removed by debinding at 400 to 450 ° C. is performed, in the conductive paste,
Contains silver powder and silver oxide powder as conductive powder ,
The silver oxide powder is selected from Ag ₂ O powder and AgO powder;
A conductive paste comprising 55 to 89.9% by weight of the silver powder and 0.1 to 15.0% by weight of the silver oxide powder .   The conductive paste according to claim 1, wherein the average particle size of the silver powder is in the range of 0.3 to 10.0 µm. A ceramic multilayer circuit board obtained by forming a conductor portion using the conductive paste according to claim 1 .

Images