JPS63502041A - Formation of conductors using improved mass displacement method - 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] Background of the development of a method for forming conductors using an improved bulk replacement method The present invention provides metallic powders in polymers with more aggressive or electropositive metals. Regarding the method of forming a conductor by substitution of Some of the metallic powder is then added so that the total volume of deposited metal on the surface is equal to the original gold at the surface. The total volume of metal powder is replaced by a more aggressive metal, and then this Thinly coated circuits are immersed in an electroless plating bath to increase the thickness of the more sensitive metal. The present invention relates to a method of forming printed circuits by adding

Many types of electronic devices are known in which various electrical components are interconnected by conductors. There is. Interconnect conductors include, for example, thick film fired conductor systems, polymer conductors and printed conductors. It can be formed by a variety of methods such as circuit boards.

For thick film fired conductors, conductive metal powder, ceramic or glass binders, and a suitable vehicle are screen printed onto the substrate. The conductor on this substrate The body pattern is then exposed to relatively high temperatures, typically between 650°C and 900°C. Fired. By the time the temperature rises to this firing temperature, the vehicle has volatilized and bonded to the metal. A mixture remains behind. At the firing temperature, more or less sintering of the metal occurs and , the bonding agent provides adhesion between the formed metal film and the substrate.

Precious metals such as gold, silver, platinum and palladium have traditionally been used for thick film fired conductors. It is used. Due to the high cost of these precious metals, copper, nickel and aluminum New conductive systems using aluminum are available on the market. This newer system Many of the problems with thick film firing are due to the special chemistry required to prevent oxidation during the firing process. It cannot be said that it is much cheaper than the grown line. Moreover, these systems are traditionally Tin makes soldering with some solders very difficult, and is required during formation. High firing temperatures preclude the use of low cost substrate materials.

In polymer conductive systems, the polymer is heavily mixed with a conductive metal and placed on the substrate. covered in The advantage of such a system is that the polymer can be catalyzed from room temperature to about 12 It can also be cured by heating at temperatures up to 5°C. This so-called cold As a result of "processing", a film of registered trademark Mylar (polyethylene terephthalate) This makes it possible to use fairly inexpensive substrates such as: The mechanism by which conductivity is acquired is All are imparted by contact between individual metallic particles. Only precious metals such as gold and silver , a metal that can be mixed into a polymer to give it satisfactory electrical conductivity. It was discovered that All other standard conductive metals oxidize over time, Electrical conductivity between particles decreases. Silver is the primary choice in polymer conductive systems However, silver-based products are caused by silver being partially leached by tin solder. and generally cannot be soldered. If the price of silver is about $10 per ounce However, these conductive systems, if used on very low cost substrates, It can compete with the system. However, if the price of silver were higher, these systems would It is not very competitive with standard circuit boards.

The techniques used to manufacture printed circuit boards are additive and subtraditional. It can be divided into active technology. For both additive and subtractive techniques The starting point is a glass-filled phenolic resin with copper foil bonded on the surface. It is a widely diversified base material ranging from filled epoxy resin. traditional additive In its preparation, the copper foil is very thin, typically on the order of 200 microinches. Re the resist is patterned so that the copper is exposed only in the desired areas of the conductor; The substrate is then plated to form a copper conductor approximately 1 mil thick. Plating cash register The copper is etched. In areas where conductors are not desired, Because the copper is only about 200 microinches thick, etching removes the copper. It is quickly removed leaving behind a 1 mil thick conductor. subtractive In this process, the initial thickness of the copper foil is typically between 1 and 2 mils. Etsutin Gresist is deposited everywhere desired on the conductor, the substrate is etched, and then The resist is removed. The resist prevents etching of the conductor at desired locations. Both additive and subtractive printed circuit board procedures Deposition of copper foil on the body, deposition and removal of resist, etching of printed circuit boards, Requires additional steps of drilling for component insertion and, in some cases, electroplating. do. The advantage of this technique is that the resulting circuit board is relatively easy to solder. It is in.

Another advantage of this type of printed circuit board technology is that through-hole plating can be formed. The point is that This method involves adding several steps to the additive formation method. Ru. Drill a hole in the substrate and then place a layer on all areas except where the conductor is desired. Gist is applied. The substrate is then coated onto the exposed portion of the substrate, i.e. inside the hole. It is immersed in a tin chloride sensitizer to form a film. The substrate is then coated with palladium chloride It is sequentially immersed in a bath, an acid to dissolve the tin chloride, and an electroless copper bath. Final process , i.e. a very thin layer of copper is placed inside the hole which is activated by immersion in an electroless copper solution. A film is deposited. This "electroless copper" uses copper as a catalyst to cause a continuous plating reaction. It is precipitated by various catalytic reactions. Typically on the order of 24 to 50 microinches. Thickness can be obtained in half an hour. At this point, a thin copper film is deposited on the inner edge of the hole. the Subsequent electroplating gradually increases the thickness of the copper inside the hole as well as along all conductor tracks. That will happen. At this point, the various methods used become different. the simplest The method consists of simply stripping the resist and then etching, if no conductor traces are desired. By removing much thinner copper. In more complex methods, Electroplating of some tin solder along the conductor tracks and subsequent stripping of the plating resist , and so that the solder acts as an etching resist. Perform etching with high chromic acid.

The most significant drawback of printed circuit board technology is that it requires a significant number of manufacturing steps. , and this requires a large amount of related equipment. Moreover, the selection of the substrate is Limited to one of the available road board materials. manufacturing process and equipment This results in relatively high manufacturing costs and limited substrate materials, which can be used in equipment as substrate materials. result in the elimination of opportunities for the use of decorative or structural elements already required by .

Assigned to the same treaty as the present invention and incorporated herein in its entirety. In addition, U.S. Pat. No. 4,404.237 to Eichelberger et al. A method for forming electrical conductors by conversion reaction techniques is described. Simply put, Eichel Berger et al. reported that the desired conductor design was achieved using finely ground conductor powder, a curable resin, and a solvent. Discloses a method of coating a substrate with an ink composition comprising: hardenable The polymer is at least partially cured and then the resulting ink composition is contacted with a metal salt solution. The metal cation in this metal salt solution is the finely pulverized powder. is more noble (electropositive) than the metal in the salt and the anion in the powder and solution. Forms salts that are soluble in This method works on soda lime glass, plastic and Additionally, it can be applied to a variety of low cost substrate materials such as paper.

The bulk replacement method of Eichelberger et al. provides a low cost alternative.

However, it is possible to provide a conductor track thicker than that which could be obtained by bulk displacement reactions alone. is often desirable.

Outline of the invention It is an object of the invention to base conductor tracks of greater thickness than would be obtained by bulk replacement methods alone. The object of the present invention is to provide a means that can be applied on the body surface.

Another object of the invention is to provide a conductor system in which the conductor tracks have an increased thickness. be.

In accordance with one aspect of the invention, (a) at least 18 finely divided metals on a substrate; a powder composition, at least 1 t'Ji of curable polymer, and, although not required, , applying a desired pattern (design) with an ink composition containing a solvent; (b) ) at least partially curing the curable polymer; and (C ) The patterned substrate thus obtained is treated with the anion as part of the metal powder composition. the surface of the at least partially cured polymer wherein the cationic metal forms a salt; a metal salt in which the metal cation is more noble than the metal of said finely ground powder, such that it is deposited on contacting the coated substrate according to step (C) with a solution in an electroless plating bath. on the surface of the at least partially cured polymer by immersing it in The improvement is to further increase the thickness of the metal plated on the metal. , to provide printed circuits and other conductive patterns or designs. An improved method is provided.

Explanation of invention In its broadest aspects, the present invention provides metal-containing materials that are subjected to a bulking substitution reaction. Desired conductive pattern on a substrate with at least partially cured polymer and then increase the thickness of the conductive pattern using an electroless plating bath. Connotes increasing to. A preferred method for bulk displacement reaction is the same as in the present invention. No. 4, assigned to Assignee and incorporated herein by reference. No. 404.237.

The substrate on which the conductive pattern is formed is not limited, and the metal ink can adhere to it. Any insulator may be used. Therefore, ordinary printed circuit boards are Can be used in addition to lath-filled polyester, phenolic resin board, polystyrene, etc. be. Particularly important as a substrate for use in the present invention is silicone-impregnated glass. be. The use of such substrates may require technical practitioners to use high temperatures, e.g. It is possible to form a flexible circuit board that can withstand temperatures of about 300°C.

The ink used in the present invention is produced by mixing finely ground metal powder and a solvent. blends with polymers that can control viscosity and flow properties. Metal is ink medium and stable in the cured polymer, obtained in finely divided form, and Which metal is higher in the activity series of the metal group than the metal used in the quantity displacement reaction? This may be the case. The most preferred metal is iron due to its availability and low cost. , nickel, zinc, or a mixture thereof. Metal powder is usually about 50 microns. 25 microns or less, preferably about 25 microns or less, most preferably about 10 microns or less It has a particle size of If the ink is deposited by screen printing method, the metal particles are It must be large enough to pass through the screen. Screen printing method is preferred However, in a non-limiting sense, pad flexo printing, stencils, rotogravure, It is noted that other types of application techniques may also be used, including offset printing and offset printing methods. The polymer used in the Any material can be used as long as it has a certain degree of adhesion to crushed metal powder. It may also be a mixture of materials. Representative polymers are those described in the aforementioned U.S. Pat. 04.237.

The polymers and inks used in this invention include fillers, dyes, pigments, waxes, Various other materials such as stabilizers, lubricants, curing catalysts, polymerization inhibitors, wetting agents, adhesion promoters, etc. It can be made to contain.

The amounts of finely ground metal powder and polymer are adjusted to facilitate the subsequent bulking displacement reaction. an amount of metal particles present on the surface of the at least partially cured ink; It is said that the amount will be such that Generally, to obtain the best effect, metals should be hardened. It should constitute about 60% to about 80% of the volume of the mixture after curing.

To adjust the viscosity and flow characteristics to match the desired printing style during ink formation , a solvent is used. Generally speaking, the solvent will maintain the viscosity of the ink at about 15°C at 25°C. ．． Adjust from 000 centipoise to approximately 200,000 centipoise used in sufficient quantities. For screen printing purposes, preferably the viscosity is about s o, ooo centipoise to about 150,000 centipoise.

Eligible solvents or diluents are aliphatic or aromatic and contain up to about 30 carbon atoms. A typical solvent is U.S. Patent No. 4,404.23. It is described in the specification of No. 7. The viscosity and flow of the ink during application to the substrate is appropriate. It is relatively non-volatile at room temperature, and the curing temperature of polymers is also low. It is preferable to use solvents that are highly volatile at temperatures other than the application temperature. stomach.

The ink is applied to the substrate to obtain the desired conductor pattern on the substrate. example For example, standard printed circuit coating techniques are utilized. cause premature curing of the ink at a temperature where the viscosity and flow properties of the ink are appropriate for the application technique. For example, any temperature may be used. Although not necessary, to the ink substrate Preferably, at least a portion of the solvent is evaporated after application of, but before curing.

Evaporation exposes additional metal powder and transfers the substrate to the conductive film formed on top. Enough metal to give and less to act as a binder to bind the metal particles together. Increasing the ratio of metal powder to polymer to achieve a balance with too little polymer It will help you. The drying process is carried out at a temperature of about 70°C to about 150°C, preferably about 110°C to about 150°C. at a temperature of from about 130°C for about 0°1 to 1 hour, more preferably from about 0.25 to 0. ．． It is preferable to carry out the treatment for 5 hours.

Following application, the ink polymer is cured by the most convenient method. If autocatalyst is added If added, the polymer will cure on its own without the addition of an initiator.

When using an ultraviolet initiator, the substrate with the conductive pattern placed on it is exposed to the curing reaction of the initiator. It can be passed under a source of high intensity ultraviolet light to initiate the reaction. Currently preferred is 10 at a temperature of 0°C or higher, preferably about 140°C to about 200°C, for about 0.1 to about 1 hour. Heat curing accelerated by exposure for a period of time, preferably from about 0.15 to about 0.5 hours. It is to adopt a method. As a result of this process, the cured polymer cures the substrate. The result is a closely packed metal bonded to the High percentage of metal, as well as selected Due to the shrinkage of the polymer, the conductive pattern thus obtained is May have some electrical conductivity due to physical contact.

In some cases it is desirable to only partially cure the polymer. . For example, components can be mounted by inserting lead wires into polymer ink. There are cases where this is desirable. In such cases, provide adhesive for the lead wires. The polymer can be partially cured or gelatinable polymers can be used to are using. In some situations, it is desirable to simply gel the polymer.

The ink-designed substrate then has some of the metal powder further down the activity column. , that is, subjected to a bulking substitution reaction in which the metal is replaced by a more aggressive metal. This process is , the known chemical behavior of metals, i.e. any metal is It takes advantage of the fact that one salt is displaced by a metal from an aqueous solution. . In U.S. Pat. No. 4,404°237, Eichelberger et al. At the same time, the metal enters the solution from the surface of the polymer and somewhat below the surface. It has been found that on said surfaces considerably more severe metal deposition occurs. Like this, Responsible for amounts added to those that would result in a one-to-one exchange with powdered metal at the surface. metal is deposited on the surface. Additional metal from the solution is transferred to the substrate by the polymer Plating both the original 6 adhering gold particles and the substituted metal particles. , which connects all the metal particles on the surface, resulting in a conductive pattern on the printed conductor pattern. Forms a contact film with a neutral metal. Eichelberger et al. It has been found that inches of conductive material can be accumulated from solution. Preferably, the above The more responsible metal is copper.

A skilled person will know that the thickness of conductive material that can be accumulated is approximately equal to the original metal grains in the polymer. It depends on the exchange rate and exchange ability of replacing the particles with the more harmful metal particles contained in the bulk replacement solution. You will understand that there are restrictions. Thus, approximately 300 microinches Even if it is possible to obtain thicker conductor paths by such a bulk replacement method, A conductor path with a thickness ranging from about 3 times to about 10 times the thickness obtained by the quantity replacement method. It is often desirable to use

Therefore, we have now developed a method for bulk replacement by immersing the substrate in a conventional electroless plating bath. It has been found that additional more aggressive metals can be deposited on conductor tracks provided by It was. The more aggressive metals deposited by electroless plating baths can be removed by bulk displacement methods. It may be the same as or different from the heavier metal being coated.

Electroless plating is well known in the industry and is described in the Encyclopedia of Chemical Technology'', 3rd edition, Volume 8, pp. 73g-750, John ・Wiley & Sons, Inc. (1979) [“Encyclopedia” or CheIlical Technology”, Th1rd Edi tlon, Vol. 8. pages 738-750, John Vlley and 5ons, 1979]. In terms of steps, there is no The electrolytic plating solution contains a metal salt of the metal to be plated, a reducing agent, a pH adjuster or a buffer. liquid, complexing agent, and one or more for adjusting stability, film properties, deposition rate, etc. Contains the above additives. Of course, metal salts and reducing agents are consumed during the plating process. Because of this, it needs to be replenished at periodic intervals. A suitable plating bath is using copper salts, and all of which are incorporated herein by reference. U.S. Patent No. 2.874.072, U.S. Patent No. 2.938.805, U.S. Patent No. 2,996.4 No. 08, No. 3,075.855, No. 3,075,856 and No. 3', 649 It is described in each specification of No. 350. Particularly preferred are the same assignees as the present invention. Stabilized Copper Plating Bath of Agins U.S. Pat. No. 3,649,350 It is. Ancillary patents describing bath stabilizers and property modifiers and deposition aids are , “Breaking of Plastics with Metals”, John Ma Kuzimot, pp. 62-93, Noyes Data Corporation (1974) ) [“Plating of Plastlcs vtth Metals ”, John McoerIIlott, pages 82-93.Noye s Data Corporation, 1974]. No electricity Patents relating to the production of printed circuits by deplating are for the purpose of and for the purpose of limitation. Instead, the following examples are given. All parts and percentages are If there is no weight, it is based on weight.

Example R.T. Buoy 615 knee 12g and R.T. Buoy 615 Bee 1.2 grams (available from General Electric Company), 90 grams of finely ground copper and nickel blend and Tsurpetz 10010. A printing ink was prepared by mixing 5 grams.

The ink thus obtained was applied to a silicone-impregnated glass cloth (Lauer Cambani). (available from ) and cured by heating at 150°C for 15 minutes. Ta. Then in accordance with Eichelberger U.S. Pat. No. 4,404,237 , the printed substrate was immersed in a water bath containing a copper salt to carry out a bulk displacement reaction. mosquito The resulting printed circuit with copper conductor tracks approximately 200 microinches thick was , then 1710 ml of deionized water, 20 ml of MacBrex 7921 copper complexing agent solution 0m1. Macbrex 7920 copper/formaldehyde solution 60ml 1. Macbre x7922 caustic solution 28ml 1. Macbrex 7924 cyanide solution 2m l, an electroless copper coat consisting of 9 grams of MacBrex 7923 formaldehyde solution. immersed in a bath.

The copper in the electroless plating bath is deposited on top of the copper by bulking displacement reaction, forming a 1.5 mil thick layer. Provided with copper conductor tracks.

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Claims (29)

[Claims] 1. (a) Performing a bulk displacement reaction, After that, (b) increasing the thickness of the metal by electroless plating; and the metal applied by the electroless plating method is caused by the bulk substitution reaction. A method of applying metal to a substrate, which may be the same or different from the metal applied to the substrate. 2. Metal applied by bulk substitution reaction and gold applied by electroless plating The method according to claim 1, wherein the genus is the same. 3. 3. The method according to claim 2, wherein the metal is copper. 4. An article manufactured by the method of claim 1. 5. 5. The article of claim 4, wherein the article is a printed circuit. 6. (a) on a substrate at least one finely ground metal powder composition and at least one applying a desired design with an ink composition comprising a curable polymer; (b) at least partially curing said curable polymer; and ( c) The patterned substrate thus obtained is subjected to said at least partially cured Metal cations are added to the fine powder to deposit more noble metals on the surface of the polymer. contacting the crushed metal powder with a metal salt solution that is nobler than the metal; Thickness of nobler metal plated onto the surface of at least partially cured polymer By immersing the patterned substrate obtained in (c) in an electroless plating bath. A method for producing designs on a substrate, the improvement being to increase the number of designs. 7. The substrate is glass-filled polyester, phenolic resin plate, polystyrene, and silicone. 7. The method of claim 6, wherein the glass is selected from the group consisting of silicone impregnated glasses. 8. 7. The method of claim 6, wherein the ink composition further includes an effective amount of a solvent. 9. Finely ground gold layer from the group consisting of iron, nickel, zinc and mixtures thereof The method of claim 6 which is selected. 10. 7. The metal powder composition of claim 6, wherein the metal powder composition has a particle size of less than about 50 microns. Method. 11. 7. The metal powder composition of claim 6, wherein the metal powder composition has a particle size of less than about 25 microns. Method. 12. 7. The metal powder composition of claim 6, wherein the metal powder composition has a particle size of less than about 10 microns. Method. 13. Claim 6, wherein the ink composition is applied by a screen printing method. Method. 14. The finely ground metal powder composition contains about 60% to about 60% of the volume of the ink composition after curing. 7. The method of claim 6, comprising up to 80% coverage. 15. The viscosity of the ink composition is from about 15,000 centipoise at 25°C. 7. The method of claim 6, wherein the range is about 200,000 centipoise. 16. The viscosity of the ink composition is from about 15,000 centipoise at 25°C. 9. The method of claim 8, wherein the range is about 200,000 centipoise. 17. The viscosity of the ink composition is from about 50,000 centipoise at 25°C. 7. The method of claim 6, wherein the range is about 150,000 centipoise. 18. The viscosity of the ink composition is from about 50,000 centipoise at 25°C. 9. The method of claim 8, wherein the range is up to about 150,000 centipoise. 19. Claims where part of the solvent is evaporated after the ink is applied but before curing The method described in Box 8. 20. Evaporation of the solvent is performed at a temperature of about 70°C to about 150°C for about 0.1 to about 1 hour. 20. A method according to claim 19, which is carried out by heating. 21. The method according to claim 6, wherein the metal more noble than the metal in the finely pulverized metal powder is copper. . 22. The method according to claim 9, wherein the metal more noble than the metal in the finely pulverized metal powder is copper. . 23. (c) The metal applied in the process and the metal applied by electroless plating are the same. The method according to claim 6. 24. 24. The method of claim 23, wherein the metal is copper. 25. (a) on a substrate at least one finely ground metal powder composition and at least Applying a desired design with an ink composition containing one type of curable polymer. , (b) at least partially curing the curable polymer; (c) The patterned substrate thus obtained is treated with metal cations such as those of the finely ground metal. contacting with a metal salt solution that is nobler than the powdered metal; and (d) immersing the patterned substrate obtained in (c) in an electroless plating bath; , Articles of manufacture manufactured by a method comprising: 26. 26. The article according to claim 25, wherein the article is an electrical conductor. 27. The finely ground metal powder is made of a group consisting of iron, nickel, zinc and mixtures thereof. 27. The conductor according to claim 26, which is selected from the following. 28. Claim 27, wherein the metal more noble than the metal of the finely pulverized metal powder is copper. conductor. 29. Copper is a metal that is applied by dipping the substrate in an electroless plating bath. The conductor according to claim 28.