JPS62179797A - Manufacture of multilayer system - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to multilayer systems and methods of manufacturing the underlying layered electrical conductors and electrical insulators in such multilayer systems.

A multilayer system is a configuration in which a number of conductor layers are supported on a substrate, separated from each other by insulating layers, but selectively interconnected by transparent coupling in the insulating layers.

In one example of a previously proposed system, each conductor layer is formed on a substrate and covered with a dielectric layer, which serves as a substrate for the next conductor layer. Holes are formed in the dielectric layer to enable interconnection between adjacent conductive layers. Such holes can be formed during screen printing (if the conductor is also screen printed).

Alternatively, it can also be formed later, for example by laser drilling.

The electrically conductive layer is formed by printing a thick film of particulate electrically conductive material onto the substrate using a screen printing method known in the art. The conductive film is then heated to promote sintering and adhesion of the layer to the substrate. The entire structure is then coated with a glass-forming dielectric and fired in a furnace at a temperature in the range of 600-900 DEG C. to melt the dielectric and promote adhesion of the dielectric to the substrate.

The conductive material may be copper or a copper-based material. However, screen printing methods generally have limited resolution. Because copper and copper-based materials are deposited as small particles rather than as a continuous solid layer, these particles are susceptible to oxidation throughout the deposited layer and are therefore treated with an inert environment, e.g. nitrogen, to prevent oxidation. Internal processing is required. In this case, the dielectric glass-forming materials must also be processed in a nitrogen environment, and these are generally difficult to process.

Furnaces with nitrogen environments are complex and expensive to operate. Not all dielectrics are suitable for firing in a nitrogen environment, and such tend to be somewhat porous. Even when constructed by stacking layers of insulation, the desired density is not achieved and the insulation remains porous.

One object of the present invention is to provide a multilayer system and an improved method of manufacturing a multilayer system.

According to the present invention, (a) a pattern of conductive oxidizable material is bonded to an electrically insulating surface of a substrate; (b) a portion of the pattern is oxidized; (d) firing the dielectric to a temperature sufficient to cause fusion of the dielectric, thereby oxidizing the fused dielectric; forming a bond between the pattern parts; the pattern is a continuous solid and the process (
A method for producing a multilayer system is provided, characterized in that in a) it is bonded to a substrate, and that only the outer layer of the pattern that is not bonded to the substrate is oxidized.

Steps (b) and (e) may be performed in any order.

In a preferred embodiment, steps (b) and (c) are performed in the reverse order. The dielectric is then an air-fireable dielectric, and in steps (b) and (d), oxygen diffuses through the coated dielectric to oxidize the outer layer of the pattern, and then The dielectric is fired at a temperature sufficient to cause fusion and adhesion (described above) to occur. Fusing also prevents oxygen from diffusing towards the pattern.

"Continuous solid" as used herein with respect to a pattern means that the oxidizable material in each part of the pattern is continuous, as opposed to, for example, a patterned layer of granules or a sintered patterned layer of the prior art. , gas impermeable and cohesive.

In addition, the term "bond" includes cases in which a continuous solid pattern is bonded directly or indirectly to a substrate,
Indirect, for example, is bonded to, or is integral with, a seed layer, which may be bonded directly or indirectly to the substrate.

The use of continuous solid patterns minimizes harmful internal oxidation of the pattern and also eliminates the need for sintering to promote its cohesion and adhesion (which requires stringent processing conditions to minimize oxidation). This means that it is possible to avoid Furthermore, surface oxidation and dielectric fusion can be effectively performed in air in a single step. This is because no precautions are required to limit oxidation. The range of ready-to-use dielectrics is greatly expanded over that which could be used in a nitrogen environment. Dielectrics fired in air are generally denser, primarily due to the greater amount of free oxygen available during the firing process.

The temperature sufficient to fuse the dielectric and to oxidize the outer layer of the pattern coated with dielectric may suitably be in the range of 600-900<0>C. It is generally desirable that any other components of the multilayer system (especially the substrate) do not melt at or below the firing temperature, and therefore all component materials and firing temperatures should be selected accordingly. It should be obvious.

In accordance with the present invention, the pattern comprises: (a) oxidizing portions of the pattern of conductive oxidizable material; (b) embedding the pattern in a sinterable dielectric; and (c) sintering the dielectric to oxidize the pattern. A method of manufacturing a multilayer system is also provided, characterized in that the pattern is a continuous solid, and that only the surface of the pattern is oxidized, comprising intimately bonding a fired dielectric layer to the oxidized portions.

The above steps (a) and (b) may be performed in any order.

In a preferred embodiment, steps (a) and (b) are performed in reverse order. In that case, the dielectric is a dielectric that can be fired in air, and in steps (a) and (e) is fired in air to oxidize the pattern surface and tightly bond the fired dielectric to the pattern. A vitreous layer is formed which provides a means for oxidation and prevents further diffusion of oxygen from the dielectric deeper into the pattern.

Suitable process parameters are as described above.

Further in accordance with the present invention, (a) a seed layer of a substance that is conductive and oxidizable but becomes non-conductive and glassy when oxidized is coated on an electrically insulating substrate; (b) the seed layer depositing a pattern of continuous solid electrical conductor thereon; (c) oxidizing the portions of the seed layer not in contact with the pattern through their entire thickness; (d) coating the entire body with a sinterable dielectric; and ( e
) A method for manufacturing a multilayer system is also provided, characterized in that the system is fired to fuse the dielectric Z.

Steps (c) and (d) may be performed in any order.

In a preferred embodiment steps (c) and (d) are performed in the reverse order. In that case, the dielectric is a dielectric that can be fired in air and is fired in air in steps (c) and (d) to oxidize the seed layer to the extent mentioned in (e) above. . The firing temperature is determined in steps (c) and (e).
) Of course, it must be sufficient to carry out Y.

Suitable process parameters are as described above. Further according to the invention, a substrate having at least one surface composed of an electrically insulating material; a continuous solid pattern of an oxidizable electrically conductive material bonded to said surface; And,
a continuous solid pattern having an oxidized outer layer not bonded to the surface; a coating of fired dielectric on both the pattern and the portion of the surface not bonded to the pattern;
Also provided is a multilayer structure comprising:

Preferred dielectric insulators in the system of the invention include any glass insulator that melts within the temperature range mentioned above, such as ESL4 from Electroscience Laboratories, Inc.
There are 770.

The conductive materials in the system of the invention are selected for their ability to meet the parameters of the method of the invention and their compatibility with the dielectric insulator, substrate and/or seed layer within the system of the invention. Thus, for example, the material must be able to be formed into a continuous solid pattern as defined above and/or be applied as is to a substrate or seed layer.

In a preferred embodiment (see below) this is done by a plating method, so the material must then be a plateable metal. If a seed layer is present, it is often convenient for the conductive material to be the same metal as the seed layer. Again, in order to be of practical use, for example in small circuits or microcircuits, the material must allow the formation of conductive patterns with very high resolution.

The conductive material must be oxidizable within the controllable limits of the method of the invention. In a preferred embodiment, this should be done with only oxygen diffusing through the dielectric coating during or after fusing.

The conductive material and/or its oxidized surface must be compatible with the dielectric insulator, substrate and/or seed layer. In a preferred embodiment, the dielectric insulator is an air-sinterable dielectric, in particular a glass-forming insulator, with which the conductive material and/or its oxidized surface must be compatible.

Suitable conductive substances for the above reasons include chromium,
There are copper, silver and palladium, and their alloys.

Chromium, copper and their alloys are also suitable for the seed layer, which may not be present. Other suitable materials include gold, rhodium, and mixtures and alloys thereof. In the method in which the unpatterned seed layer is oxidized, any electrically conductive material may be used, which has the property of becoming non-conductive when oxidized, and which has a ceramic or glass form. properties that provide strong bonding between ceramic, glass, or glass-ceramic substrates and dielectric coating layers;
It has both characteristics.

It is often expedient to deposit the seed layer on another metal adhesive by a plating method, in particular an electroless plating method.

The multilayer system and method of manufacturing the system are illustrated with reference to the accompanying drawings.

The multilayer systems and improved methods of making them described below are particularly relevant to the production of lower (ie, closer to the substrate) conductive layers and dielectric insulators in multilayer (at least two layer) systems.

The following description also relates specifically to embodiments of systems whose parts include an oxidized seed layer throughout their entire thickness. The following description also relates specifically to method embodiments in which coating with a dielectric insulator is followed by an air calcination oxidation of the continuous solid. However, without further mention, it is clear that aspects of the invention lacking any of these items can be easily obtained by omitting the corresponding items in the method of explanation below. - As shown in FIG. 1, a seed layer 4 is introduced onto the long side of the substrate 2 and bonded thereto.

The substrate 2 is a ceramic which softens at a temperature substantially higher than the melting point of the air-fired dielectric insulator to which it is then applied.
Glass or glass-ceramic materials are suitable.

If the substrate 2 is a ceramic, it is preferably selected from the group consisting of glass, alumina, aluminum nitride and silicon carbide. Suitable glasses and glass-ceramics each have a high melting point. There are borosilicate glasses and barium glasses, which are borosilicate glasses, and high-melting glasses containing dissolved metal oxides.

The substrate 2 is a metal plate with the above-mentioned substance on it, for example, 0.
A coating having a thickness of 25 to 0.75 μm may also be suitable. Suitable sheet metals include iron, cobalt,
There may be nickel and copper and alloys thereof, such as stainless steel or low carbon steel. The seed layer 4 may conveniently be copper.

If the seed layer 4 is copper, it can be applied by known electroless plating methods (e.g. hydrogen/copper on a micro-etched substrate surface).
By adsorbing a reducing system such as palladium ions/palladium metal and reducing copper ions from solution onto its surface, electroless plating deposition of a copper seed layer'&0.2-4 μm, e.g. about 2 μm, especially 05-1 μm It may be convenient to introduce and bond onto the substrate (by performing up to a thickness of .

Although it has been explained that the seed layer 4 is formed by electroless deposition,
It will be understood that the scales may be formed by thin films, as is known, or equivalently by metallurgical methods.

Referring again to FIG. 1, a continuous solid knot 8 (as described above) of a suitable oxidizable metal (as described above), preferably copper, is then formed on the seed plate 4.

The continuous solid pattern 8 may be suitably formed in situ, for example by selective masking and plating of the seed layer 4.

Alternatively, the seed layer 4 can be omitted and the pattern 8 can be formed directly on the substrate 2 by other methods. Such other methods may also be used for the formation of the knots 8 on the seed layer 4.

In one such method, the conductive turns 8 are
It is formed by sputtering or vapor depositing the conductor through a mask. In this embodiment, it is preferred to first deposit the material, such as chromium, titanium or tantalum, in an overlapping adhesive pattern. or,
The substrate is uniformly coated over the entire surface by plating, sputtering or vapor deposition, and the conductive material is selectively removed by wet etching or sputtering or plasma etching to leave the desired pattern.

In another method, a conductive pattern is formed on a substrate by resist-defined electroless plating using a catalyst such as palladium. Alternatively, automatic contactless electroplating methods can also be used.

Yet another method involves chemically bonding conductive materials directly to the substrate at high temperatures. The conductive turn is
The conductive material is then selectively removed using a resist.

It is within the scope of the invention to form the continuous solid pattern 8 elsewhere (not on the substrate 2) and apply it to the substrate 2 (or seed layer 4).

In the illustrated embodiment, the copper seed layer 4 is coated with a photocurable resist to a thickness in the range of 12-50 microns, preferably 25 microns. The resist 6 is exposed to a light pattern corresponding to the desired conductor pattern. The uncured portions of the resist 6 are then selectively dissolved in a conventional liquid (see FIG. 2) to selectively expose the underlying copper layer 4.

The exposed copper layer 4 is then electroplated with solid copper to a thickness and width that exceeds the thickness of the seed layer in all places, e.g. It is removed by an appropriate method. The result, shown in Figure 3, is that a thick continuous solid pattern 8 is built on a thin conductive layer.

In FIG. 3, a thick film 10 (e.g. 35-55 .mu.m, especially about 45 .mu.m) of air-fired dielectric is then deposited, covering the copper layers 4 and 8. is preferred. Preferably, the dielectric is in the form of glass particles with a melting temperature in the range of 600-900C, suspended in ethylcellulose dissolved in butyl calpitol. After screen printing, the dielectric 10 is dried to evaporate the butyl calpitol. The ethylcellulose then acts as a binder for the glass particles.

The entire assembly is then fired in air at a temperature in the range of 600-900'C to burn out the ethylcellulose binder and melt or fuse the glass to form a dense, substantially non-porous glass matrix. Form an electrical insulator layer.

This firing process ensures that the copper seed layer 4 in the form of identical overlapping copper and the continuous solid pattern 8 have a thickness of the seed layer, i.e. 0
．． This results in oxidation to a depth of 2-4 μm (see Figure 4). The depth to which copper undergoes oxidation depends on factors such as the firing temperature, the degree of vitreousness of the insulator, and the melting point of the glass. Care should be taken to ensure that oxidation occurs to a depth of . The result is that the entire seed layer 4 that is not covered by the conductive layer 8 is oxidized to form a non-conductive copper oxide, while the continuous solid pattern layer 8 is for example 7 μm thick with a 2 μm thick seed layer. It is clear that the continuous solid conductor of is not oxidized to a depth of only 2 μm and this does not affect the electrical conductivity of the conductor.

The net result is that the conductor 8 becomes embedded in the air fired dielectric 10. It will be appreciated that oxidation of the outer skin of the continuous solid conductor pattern 8 causes the insulator to become intimately bonded with the conductor. Furthermore, the presence of a glass layer on the oxidized outer surface of the conductor prevents further oxygen diffusion from the insulator to the conductor. Finally, a pattern of through holes is provided in the dielectric layer 10 ( 6th
(see hole 12 in the figure), providing access to the electrical conductor 8.

The through holes 12 can be made by laser drilling, etching or polishing.

The through holes 12 can be made by screen printing (for example) before firing the assembly.

Instead, laser drilling and etching methods,
Polishing methods can also be used.

It will be appreciated that the multilayer system described above offers many advantages.

By changing the copper seed layer 4 to copper oxide, the substrate 2
and a glassy forming material exhibiting high adhesion to the dielectric 10. The adhesion of the copper conductor 8 to the substrate can also be improved by sintering if the copper oxide bond is formed by diffusion of oxygen from the oxygen-containing substrate, for example alumina.

In short, the function of the oxidized copper seed layer 4 is that during the firing process it becomes non-conductive and is present in the dielectric insulator 5.
When combined with oxides such as PbO, BaO, and SiO2, it leads to the formation of a glassy substance. Thus, the glassy insulator, when melted, dissolves the copper oxide seed layer. Also, since the steel seed layer is composited with a ceramic, glass, or glass-ceramic substrate, a very strong bond is formed between the substrate and the insulator.

Prior to firing, when a copper seed layer is not present between the substrate and the insulator, a conventional agent may be included in the vitreous insulator to promote direct adhesion between the substrate and the insulator. . However, this is usually unnecessary.

removing the portion of the seed layer 40 that is not located under the copper conductor pattern by converting the seed layer 4 into an electrical insulator;
No more requirements.

In a variation of the method described above, the copper pattern layer 8
After the electromethodization step and before the residual resist removal step, the copper pattern 8 is coated with a metal film 14 that prevents oxygen diffusion into the copper conductive pattern 8. Particularly suitable metals for this purpose are nickel, palladium, gold, silver, chromium, rhodium, and alloys of any of these metals.

This coating process advantageously reduces the amount Z of patterned copper that converts to copper oxide during the air firing process. Diffusion barrier coating 14 is particularly useful for covering copper areas where through holes are to be formed. This is because otherwise those copper areas would be constantly exposed to air and therefore subject to oxidation.

In yet another modified embodiment, the membrane 1 for preventing oxidation
4 is coated with a thin film of copper between the film and the dielectric, which acts as an adhesive layer after firing the system.

In yet another variation, two resist steps and two copper plating steps are performed.

Excess resist is removed and conductive pattern 8 is covered with dielectric 10 (7). The first resist is a thin layer formed by spinning a wet film resist into very high definition tracks (eg 10 μm wide and 4 μm thick). The second resist is a thick layer deposited using a layered dry film resist process, forming track-like shapes 25 μm thick and 35 μm wide, or locations corresponding to where through-holes are formed in the insulator. It is something.

It will be appreciated that the multilayer system may be double-sided functional.

In such systems, the substrate is provided with a plurality of through holes and conductive layers are formed on both sides of the substrate simultaneously. At the same time, a conductive material is deposited into the pores to connect the two conductive layers.

Although in the embodiment described above the seed layer is left intact on the substrate throughout the process, it is of course possible to remove the seed layer from areas other than directly beneath the conductive pattern prior to the dielectric deposition step. It is understood that. In this case, the seed layer 4
The material does not need to be oxidizable and may be, for example, gold.

FIG. 7 shows an example in which the substrate 2 is used when the metal sheet 2A is coated with an electrically insulating layer 2B.

[Brief explanation of drawings]

1-6 are cross-sectional views of a multilayer system at various stages of an example of the manufacturing method of the present invention. FIG. 7 is a cross-sectional view of an example of a modified multilayer system. 2: Substrate 4: Seed layer 6: Resist 8: Pattern (conductive) 10: Dielectric (insulating) 12: Through hole Patent applicant Imperial Chemical Innodustries PLC Engraving of drawings (no change in content) ) Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Procedural amendment (method) % formula % 1. Indication of the case Relationship with the case of the applicant Applicant's address In 〇 Soat ・ + 7 2 Kashi ・ Inter `` ° S L source ゛ ε - Elle 4, Agent 5, Date of amendment order 1985 ρ Month 2Σ (Delivery date) Power of attorney, typed translation, and drawings

Claims (3)

[Claims] (1) (a) bonding a pattern of conductive oxidizable material to an electrically insulating surface of a substrate; (b) oxidizing portions of the pattern; and (c) bonding the pattern and a portion of the substrate surface to the pattern. (d) baking the dielectric to a temperature sufficient to cause fusion of the dielectric; the pattern 8 is a continuous solid, and optionally the substrate 2
is bonded to the substrate 2 in step (a) by coating the surface of the pattern 8 with a seed layer 4, and only the outer layer of the pattern 8 that is not bonded to the substrate 2 is oxidized. manufacturing method. (2) step (c) is carried out before step (b); the dielectric 10 is a dielectric that can be fired in air; and the seed layer 4 is a conductive combustible material but becomes non-active when oxidized. A method according to claim 1, characterized in that it is electrically conductive and glass-forming. (3) a substrate having at least one surface composed of an electrically insulating material; a continuous solid pattern of oxidizable electrically conductive material bonded to the surface; an oxidized outer surface not adhered to the surface; A multilayer structure comprising: a continuous solid pattern having layers; an air-sinterable dielectric coating on both the pattern and the portion of the surface not bonded to the pattern.