GB2186434A

GB2186434A - Making printed circuits

Info

Publication number: GB2186434A
Application number: GB08700717A
Authority: GB
Inventors: Yamahiro Iwasa
Original assignee: Asahi Chemical Research Laboratory Co Ltd
Current assignee: Asahi Chemical Research Laboratory Co Ltd
Priority date: 1986-01-14
Filing date: 1987-01-13
Publication date: 1987-08-12
Anticipated expiration: 2007-01-13
Also published as: JPS62163395A; JPH0213957B2; GB2186434B; GB8700717D0

Abstract

A method of forming electric circuits on a base board comprises the steps of laminating the board (1) on both sides with copper (8), providing a through-hole (4) in the board, etching both sides of the board to provide the required circuits (C1) thereon, applying a plating resist (6) to both sides of the board leaving parts of the circuits uncovered, applying electrically conductive copper paste (9) to both sides of the board to connect with the circuits, heating the board to harden the paste, plating copper (10) on the paste to provide a second circuit layer (C2) on each side of the board, and electrolessly plating copper (10) on the inner periphery of the through-hole to interconnect the circuits on opposite sides of the board. <IMAGE>

Description

SPECIFICATION A method for forming electric circuits on a base board The invention relates to a methodforforming elec- trically conductive circuits on a base boad, and more particularly relates to a methodforforming at least four laminations of circuits on the base board.

It has been general practice to form a resistorcircuit or an electricity storing circuit on a copper laminated base board by soldering a lead or a chipshaped resistor or a condenser onto the copper laminated base board. The finished product is therefore bulky in addition to requiring so many processing steps and the resultant high cost including the cost of the resistor or a condenser. In the conventional method, the loading density of the printcircuit base board is lower, and the reduction of product weight and of production process is difficult.

Moreover since soldering is required, there is often a misarrangement of leads and a misinsertion of the resistor or the condenser.

Further when form ing complex circuits on the copper laminated base board, it becomes necessary to electrically connect the circuits to each other. Conventionally, a through-hole is provided to electrically connect the circuits on both sides of the base board because it has been impossible to form the circuits of morethantwo laminations on one side of the base board. Even ifthethroughhold is provided, it has been impossibletoform morethantwo laminations of circuits, that is, one located on one side of the base board and the other located on the other thereof.

It has been proposed to form more than two lami nations of circuits on one side of a ceramics base board. For example, in case of the hybrid IC, it is usual to employ a paste of precious metal such as platinum-palladium orsilver-palladiumto form the circuits and the terminals thereof, and to employ a paste of ruthenium oxide to form a resistor and then to burn the base board at a high temperature (700 1000 C). Further it has been proposed to form more than two laminations of circuits on one side of a base board by printing a tungsten (W paste) and an isolating paste alternately on an alumina green sheet and then by burning the alumina green sheetatatemperature of about 1600 C. However, since such methods require a high temperature burning treatment,the ingredients of circuit structure to be used are limited and the equipment required is costly. The methods are therefore not suitable for producing print-circuit boards for general use in combination with electronic apparatus.

It is therefore desired to establish an industrial methodforforming more than two laminations which may be treated at a lowertemperature. In this case, it becomes necessary to develop on electrically conductive copper paste which has a property of electrically high conductivity and is specifically adapted to a metal plating, especially to a copper plating and which may be obtained at a lower cost. It has however been difficult in practice, to use the electrically conductive paste, because the copper particles in the paste are readily oxidised when the paste is heated to be hardened at a temperature of approximately 1500, and the paste has a high electric resistance and reduce the soldering property.Generally the conventional electrically conductive copper paste is easily oxidised with a heat for hardening the paste, in contrast to the precious metal such as silver. The oxidisation of copper powder in the paste will increase the electrical resistance and decrease the solding property. These defects have made the conventional electrically conductive paste practically useless. Further it has been required to activate the surface of the hardened electrically conductive copper paste by means of a catalyst so as to expose the copper powder from the resin paste so thatthe exposed copper powder may act as the binder, that is, so many neuclei for the subsequent metal plating.

Thus the conventional electrically conductive paste requires many processing steps.

Japanese Utility Model application Serial No.5542460 discloses a specific method in which a high dielectric resist of polybutadiene is used as a dielect ric coat, an adhesive paste, for example, of 20% of phenol resin, 63% of copper powder, and 17% of sol- vent is used to form designed circuits, the adhesive paste is thickened to 20 ij by means of a nonelectrolytic plating, and then the plated adhesive paste is coated with copper so as to form the electrically conductive circuits of more than two layers on one side of a base board. This method has never been industrially reduced to practice.

After many years of research, the applicants are now able to produce electrically conductive copper pastes that avoid the defects associated with the prior art mentioned above. The newly developed electrically conductive copper pastes include the electrically conductive copper paste ACP-020, ACP-030 and ACP-007P P of Asahi Chemical Research Labora- tory Co. Ltd. The electrically conductive copper paste ACP-030 is substantially composed of 80% by weight of copper powder, and 20% by weight of synthetic resin and is extremely excellent in the electric conductivity, but more or less deteriorated in the soldering property.The electrically conductive pasteACP020 is substantially composed of 85% by weight of copper powder and 15% by weight of synthetic resin, and is slightly lower than the ACP-020 as to the electric conductivity, but excellent in the soldering property. In the last plate, the electrically conductive copper paste ACP-007P is an improvement of the ACP-030 and may be subjected to a metal plating such as a copper chemical plating without using a catalyst. In otherwords,the copper paste has excellent metal plating properties.

One object of the invention isto eliminate the defects and disadvantages of the prior art. This is achieved by the effective use of the newly developed electrically conductive copper paste having the specially excellent metal plating property to form the electrically conductive circuits of more than two laminations on one side of a copper laminated base board, that is, to firstly form a first lamination circuit on the copper lamination of the base board, subse quentlyto coat the mentioned electrically conductive copper paste of excellent metal plating property on the parts ofthefirst lamination circuitswhich are to b connected to a second layercircuitsto beformed on thefirst lamination circuits, subsequently to heat the electrically conductive paste to harden the same, subsequently to apply a metal plating on the coated electrically conductive copper paste to increase the electric conductivity of the copper paste to that ofthe copper lamination, therebyforming the second lamination circuits on the first layer circuits.

In this way, at leasttwo laminations of circuits may be formed on one side of the copper laminated base plate, and accordingly at least four laminations of circuits may beformed on the base board, which are electrically connected to each other via a throughhole. Thus the finished product may be provided at almost half the cost required to produce the conventional product. It is another object of the invention to provide the circuits of at least four laminations on both sides of the copper laminated base board including a resistor circuit on each side thereof, wherein a resistor paste of a predetermined value of electric resistance is coated on a plating -resistant resist on both sides of the base board, and is then heated to be hardened.An electrically conductive paste is then coated on both sides of the base board so asto electrically con nect to the resistor paste at leasttwo circuits of first lamination located on both sides of the resistor paste orthe circuit of second lamination on one side ofthe resistor paste.

The electrically conductive paste is then heated to be hardened to thereby form a resistor circuit on each side of the base board. An activation treatment is performed to the inner periphery ofthe throughhole, and then a non-electrolytic copper plating is performed on the inner periphery of the through holeto providethereat a copper plating layerto electrically connect the circuits offirst lamination on both sides ofthe base board. Thus the circuits of at least four laminations are formed on both sides of the base board including the resistor circuit. Hence no separate operation is needed to insert or to attach and solderthe resistor elementtothe base board.

Thus an extremely thin resistor circuit is obtained.

It is still another object ofthe invention to form the circuits of at leastfour laminations on both sides of the copper laminated base board including an electricity storing circuit, wherein a dielectric paste having a property of storing electricity is coated on a part of a circuit offirstorsecond lamination on each side ofthe base board, and then is heated to be hardened.

An electrically conductive paste is then coated on both sides ofthe base board in a manner as to elec- trically connect to the dielectric paste another circuit offirst or second lamination on each side of the base board. The electrically conductive paste is then heated to be hardened to form thereat an electricity storing circuit on each side ofthe base board. An activation treatment is then performed to the inner periphery ofthe through-hole and then a nonelectrolytic copper plating is performed on the inner periphery ofthe through-hole to provide thereat a copper plating layer to electrically connected the circuits of first lamination on both sides of the base board. Thus the circuits of at leastfour laminations are formed on the base board including the electricity storing circuit on each side ofthe base board.

Here again, no separate operation is needed to insert orto attach and solder the condenser to the base board. Thus an extremely thin electricity storing circuit may be obtained.

It is still another object of the invention to provide a reliable print circuit having the circuits of at leastfour laminations formed on both sides thereof including a resistor circuit or an electricity storing circuit on each side thereof, the print-circuit board having a high loading density with reduction of weight and being produced in an extremely reduced processes without possible misarrangement of leads or mis- insertion of a resistor element or a condenser.

In accordance with the present invention we propose a method forforming electrically conductive circuits on a base board comprising the steps of: a) attaching copper laminations on both sides of the base board to provide a copper laminated base board; b) processing the copper laminated base board to provide a through-hole extending all through the thickness ofthe copper laminated base board; c) performing a catalyst treatment of the copper laminated base board; d) wasing the copper laminated base board; e) etching both sides ofthe copper laminated base board to form thereon a plurality of circuits offirst lamination including a circuit formed around said through-hole on each side of said copper laminated base board; f) coating a plating-resistant resist on both sides of the copper laminated base board except the circuits offirst lamination; g) heating the copper laminated base board to harden said plating-resistant resist; h) coating an electrically conductive copper paste on both sides of the copper laminated base board in a manner as to electrically connect at least two circuits of first lamination on each sides of the copper laminated base board; i) heating the copper laminated base board to harden the electrically conductive copper paste; j) making a pre-plating treatment to the copper laminated base board; k) performing a chemical copper plating on the surface of the electrically conductive paste of the copper laminated base board to provide thereat a circuit of second lamination on each side of the copper laminated base board; I) coating the plating-resistant resist on both sides of the copper laminated base board except a part of the circuits offirst lamination formed around the through-hole; m) heating the copper laminated base board to harden the plating-resistant resist; n) performing an activation treatment to the inner periphery of the through-hole; and o) performing a non-electrolytic copper plating on the inner periphery of the through-hole to provide thereat a copper plating layer to electrically connect the circuits of first lamination on both sides of the copper laminates base board.

In one embodiment,for producing circuitlaminations including a resistive circuit, the method comprises between the steps k) and I) above the steps of: p) coating the resistor paste on the platingresistant resist of a predetermined electric resistance value on both sides ofthe copper laminated base board; q) heating the copper laminated base board to harden said resistor paste; r) coating an electrically conductive paste on gboth sides of the copper laminated base board in a mannerastoelectricallyconnecttothe resistor paste at least two of the circuits of first lamination located on both sides of the resistor paste or the circu it of second lamination located on one side ofthe resistor paste on each side of the copper laminated base board; and s) heating the copper laminated base board to harden the electrically conductive paste to form thereat a resistorcircuiton each side ofthe copperlaminated base board.

In another embodiment, for producing circuit laminations including an electricity storing circuit, the methods comprises between the steps k) and I) above the steps of: t) coating a dielectric paste having a property of storing electricity on part of one of the circuits offirst lamination or of second lamination on each side of the copper laminated base board; u) heating the copper laminated base board to harden the electric paste; v) coating an electrically conductive paste on both sides ofthe copper laminated base board in a manner asto electrically connect to the dielectric paste one of the circuits offirst lamination located adjacent thereto orthe circuit of second lamination on each side of the copper laminated base board; and w) heating the copper laminated base board to harden the electrically conductive paste to form thereat an electricity storing circuit on each side ofthe copper laminated base board.

Otherfeatures and advantages will be apparent from the following description by way of example, of embodiments of the invention with reference to the attached drawings in which: Figures 1 to 11 show a first embodiment of the in vention, ofwhich: Figure 1 is a copper laminated base board shown in vertical section; Figure2 is a copper laminated base board shown in vertical section and having a through-hole therein; Figure 3 is the copper laminated base board shown in vertical section and having a catalyst treat ment applied thereto; Figure 4is a copper laminated base board shown in vertical section and washed and dried; Figure 5 is the copper laminated base board shown in vertical section and having an etching resistant resist coated thereon;; Figure 6 is the copper laminated base board shown in vertical section and having an etching treatment applied thereto to form thereat the circuits offirst lamination; Figure 7 is the copper laminated base board shown in vertical section and having a platingresistant resist coated thereon; Figure 8 is the copper laminated base board shown in vertical section and having an electrically conductive copper paste coated thereon; Figure 9 is the copper laminated base board shown in vertical section and having a chemical copper plating applied thereto; Figure 10 is the copper laminated base board shown in vertical section and having a platingresistant resist coated thereon;; Figure 17 is the copper laminated base board shown in vertical section and having a nonelectrolytic copper plating applied to the inner peripheryofthethrough-hole; Figures 12 through 15 show a second embodiment of the invention, of which: Figure 12 is the copper laminated base board as shown in Figure 9, but having a resistor paste coated thereon; Figure 13 is the copper laminated base board shown in vertical section and having an electrically conductive paste coated thereon; Figure 14 is the copper laminated base board shown in vertical section and having a platingresistant resist coated thereon; Figure 15isthe copper laminated base board shown in vertical section and having a nonelectrolytic copper plating applied to the inner peripheryofthethrough-hole;; Figures 16to 79 show a third embodiment of the invention of which: Figure 16 is the copper laminated base board as shown in Figure 9, but having a dielectric paste coated thereon; Figure 17 is the copper laminated base board shown in vertical section and having an electrically conductive paste coated thereon; Figure 18 is the copper laminated base board shown in vertical section and having a platingresistant resist coated thereon; Figure 19 is the copper laminated base board shown in vertical section and having a nonelectrolytic copper plating applied to the inner periphery of the through-hole.

In reference to Figures 1 to 11, a plymer base board 1 has copper laminated 8 attached to base sides thereof, and thus formed u p as a copper laminated base board 3 as shown in Figure 1. The copper laminated base board 3 is then processed so as to have a through-hole 4 extending therethrough in thevertical direction as shown in Figure 2. The copper laminated base board 3 is then treated with a catalyst so asto be provided with metal particles 5 as indicated by dots on both sides thereof and on the inner per iphery4aofthrough-hole4asshown in Figure 3.

The catalyst treatment of the copper laminated base board 3 is made with a catalyst of palladium chloride (Pdc12) and tin chloride (Sncl2) or an alkali catalystsolution of palladium only, and then the metal particles 5 of palladium are attached on the faces of the copper laminated base board 3 as mentioned above. The metal particles 5 are used as the nucleusesto expose the coppertherearound in the subsequent non-electrolytic copper plating.Since both palladium and copper are a metal and little energy is required to provide a surface between the two substances and have the atomic arrangements of a substantially same period (both are of the facecentered cubic lattice and the lattice constants are approximating such as 3.8898A and 3.61 soy respectively), the copper is progressively exposed on the colloid palladium in the non-electrolytic copper plating and thus the copper plating may be applied on the metal particles 5.

Now in the description, it is to be noted thatthe method for performing a chemical copper plating afterthe catalysttreatment has been made is called a "non-electrolytic copper plating" herein, and the method for performing a chemical copper plating on an electrically conductive copper paste without making a catalysttreatmentthereon is called a "chemical copper plating" herein.

Afterthecatalysttreatment has been finished, the copper laminated base board 3 is washed and is then dried as shown in Figure 4. Thus the metal particles 5 are eliminated from the copper laminated base board 3 except the metal particles attached to the inner periphery4a ofthe through-hole 4. An etching resistantresist7 is coated on both sides ofthe copper laminated base board 3 except the predetermined portions 3a thereof which remain to have no electrically conductive circuits C1 of first lamina- tion formed thereon as shown in Figure 5. Then the copper laminated base board 3 is processed with etching to form on both sides thereof a plurality of electrically conductive circuits C1 offirst lamination by means ofthe copper laminations 8 as shown in Figure 6.In this case, one of the circuits C1 offirst lamination is designed to beformedaroundthe through-hole 4 on each side ofthe copper laminated base board 3.

Then a plating-resistant resist 6 is coated on the portions 3a ofthe copper laminated base board 3 where no circuits C1 of first lamination are formed as shown in Figure 7, the resist 6 being, for example, the plating-resistant resist CR-2001 developed by Asahi Chemical Research Laboratory Co., Ltd.. The copper laminated baseboard 3 is then heated atthetemperature 1 50 C byway of example for about 30 min utes so as to be hardened.Then, as shown in Figure 8, an electrically conductive copper paste 9, for example, the electrically conductive copper paste ACP007P developed by Asahi Chemical Research Laboratory Co., Ltd. is coated on both sides of the copper laminated base board 3 by way of a screen printing in a manner that at leasttwo of the electricallyconduct- ivecircuits C1 may be electrically connected to each other on both sides of the base board 3, and then the copper laminated base board 3 is heated atthetemperature 1 50"C for 30-60 minutes so as to be hardened.

The copper laminated base board 3 is then processed with a pre-plating treatment. Namely the base board 3 is washed for several minutes with a water solution of 4-5% byweightofcausticsoda (NaOH) by way of example, and then is applied with a surfacetreatmentfor several minutes by means of a water solution of 5-10% by weight of hydrochloric acid (HCI). With this surface treatment, many copper particles are exposed on the surface of the electrically conductive copper paste 9 from among the binderthereof, which may be used as the nucieuses in the next process of copper plating. In this case, it is noted thatthe catalyst treatment is not needed which may otherwise be needed in the normal nonelectrolytic copper plating.

In the next place, the copper laminated base board 3 is immersed in a chemical copper plating bath to perform a chemical copper plating on the surface of the electrically conductive copper paste 9 as shown in Figure 9. As the result, copper plating layers 10 are provided in formation of the electrically conductive circuits C2 of second lamination provided on both sides of the copper laminated base board 3, each of which is electrically connected to at least two electrically conductive circuits C1 offirst lamination adjacent thereto. This chemical copper plating bath is pH 11-13 and is of the temperature 65 -75 C, and the thickness of the copper plating layer 10 is morethan 5#m with a plating speed being 1.5Fm-3 > m per hour.

Subsequently the plating-resistant resist 6 is coated on both sides ofthe base board 3 except the through-hole 4 and the circuits C1 of first lamination formed around thethrough-hole 4, and then the base board is heated to harden the resist 6. Then an activator treatment is made to the inner periphery 4a of the through-hole 4as shown in Figure 10, and then a non-electroanalytic copper plating is performed to the inner perphery 4a to form thereat a copper plating layer 10 to electrically connectthe circuits C1 of first lamination each located aroundthethrough hole 4 on both sidesofthecopperlaminated base board 3. In this way, at least four-lamination circuits C1, C2 are formed on both sides ofthe copper laminated base board 3 as shown in Figure 11.In this case, the circuits C1 formed around the through-hole 4 on both sides of the copper laminated base board 3 are electrically connected to each other bythe copper plating layer 10 formed on the inner periphery 4a of the through-hole 4.

Thus the electrically conductive circuits C2 Of second lamination are formed with the copper plating layer 10 and the electrically conductive copper paste 9 on both sides ofthe copper laminated base board 3, and the circuits C1, C2 of at leastfour laminations are formed on both sides of the copper laminated base board 3, and thus a print-circuit base board l2isfinished upasshown in Figure 11.

In this invention, it is understood that a subtractive method and an additive method are properly combined to easily form the circuits C1, C2 Of at leastfour laminations on both sides of the copper laminated base board 3.

Now in reference to Figures 1 through 9 and Figures 12 through 15, a second embodiment of the invention will be explained with the same reference numerals with the aforementioned first embodiment with respect the parts common to both embodiments. In the second embodiment the processes are same with the first embodiment until the circuits C1, C2offirstandsecond laminations areformed on both sides of the copper laminated base board 3 in Figure 9. Therefore the explanation of the processes is omitted therein, and the explanation of the processesfrom Figures 12through 15toform a resistor circu it will be made hereunder.

As shown in Figure 12, a resistor paste 14 of a predetermined value of electric resistance is coated on the optional plating-resistant resist 6 on both sides of the copper laminated base board 3, and then the base board 3 is heated to harden the resistor paste 14. Then as shown in Figure 13, an electrically conductive paste 15 such as a silver paste is coated on both sides ofthe copper laminated base board 3 in a manner asto electrically connect the circuits C1 of first lamination located on both sides laterally of each resistor paste 14, and is heated to be hardened so as to form resistor circuits 13 on both sides of the copper laminated base board 3. Thus the copper laminated base board 3 hasthecircuitsC1,C2ofat least four laminations including the resistor circuit 13 formed on both sides thereof.

Subsequently as shown in Figure 14, the plating- resistant resist 6 is coated on both sides of the copper laminated base board exceptthethroughhole 4 and the circuits C1 of first lamination formed aroundthethrough-hole 4 in the same manner as in Figure 10 ofthefirstembodiment,loofthefirst embodiment, and then is heated to be hardened. In the next place an activation treatment is performed to the inner periphery 4a ofthe through-hole 4, and then a non-electroanalytic copper plating is performed to provide thereat the copper plating layer 10 to electrically connectthe cir cu its C1 offirst lamination each located around the through-hole 4 on both sides of the copper laminated base board 3 as shown in Figure 15.In this way, the circuits C1, C2 of at leastfour laminations including the resistor circuit 13 are formed on both sides ofthe copper laminated base board 3, and a print-circuit base board 22 isfinished up. Thusaccording tothe second embodiment, the circuits C1,C2 of at least four laminations including the resistor circuit 13 are formed on both sides ofthe copper laminated base board 3 by means ofthe proper combination ofthe subtractive method and the additive method.

Now in reference to Figures 1 through 9 and Figures 16through 19, athird embodimentoftheinvention will be explained with the same reference numerals with the aforementioned first and second embodiments with respect to the parts common to the three embodiments. In the third embodiment, the processes are same with the first and second em bodiments until the circuits C1, C2 offirst and second laminated base board 3 in Figure 9. Therefore the explanation of the processes is omitted herein, and the explanation of the processes from Figures 16 through 19 to form an electricity storing circuitwill be made hereunder.

In reference to Figure 16, a dielectric paste 18 is coated on a part of a circuit C1 of first lamination orof a a circuit C2 of second lamination on each side ofthe copper laminated base board 3, and then is heated to be hardened. Then as shown in Figure 17, an electrically conductive paste 19 such as silver paste is coated on both sides of the copper laminated base board 3 in a manner so asto electrically connect the dielectric paste 18to another circuit C1 spaced from the circuit C1 on which the dielectric paste 18 is coated with the plating-resistant resist 6 being located therebetween, and then the electrically conductive paste 19 is heated to be hardened. Thus an electricitystoring circuit 1 6 is formed on each side of the copper laminated base board 3.Then as shown in Figure 18, the plating-resistant resist 6 is coated on both sides ofthe copper laminated base board 3 except the through-hole 4and the circuits of first lamination located around the through-hole 4, and is then heated to be hardened. An activation treatment is then performedtotheinnerperiphery4aofthethrough-hole 4, and then a non-electrolytic plating is performed on theinnerperiphery4atoformthereatthecopper plating layer 10 to electricallyconnectthe circuits C1 each located around the through-hole4 on both sides of the copper laminated base board 3 as shown in Figure 19. Thus the circuits C1, C2 of at leastfour laminations including the electricity storing circuits 1 6 are formed on both sides of the copper laminated base board 3.

In Figure 17 the electrically conductive paste 19 is connected only to the circuit C1 on the rightsideof the plating-resistant resist 6 on each side ofthe base board 3. The electrically conductive paste 19 may however be connected to the circuit C2 of second lamination.

In this way, the subtractive method and the additive method are properly combined to form the electrically conductive circuits C1, C2 of at least four laminations including the electricity storing circuit 16 on both sides of the copper laminated base board 3, and thus a print-circuit base board 32 is finished up as shown in Figure 19.

In the embodiment the circuits C1, C2 of first and laminations are formed one on the otheron each side of the copper laminated base board 3. The circuits are however not limited to the two lamination on each side of the base board 3. The same processes may be repeatedly performed on the platingresistant resist 6 on each sdie of the base board 3 to form more than three laminations of circuits,that is, of circuits, that is, more than six laminations of circuits in all on both sides ofthe copper laminated base board 3.

Further it would be necessary to briefly explain the electrically conductive copper paste, the electrically resistant paste, the plating resistant paste and the dielectric paste which are used in this invention.

As to the paste ACP-007P developed byAsahi Chemical Research Laboratory Co. Ltd. byway of ex ampleforan electrically conductive copper paste which is specifically adapted to a copper plating, itis generally known that copper is easily oxidised, and more especially copper in the condition of powder particles may be more easily oxidised because the exposed outer surface is enlarged. In contrast to the non-oxidisable paste of precious metals, it becomes necessary to provide a paste of such ingredients as to remove the oxidised film of the copper powder particles and also to prevent the reoxidisation of the copper particles. In order to provide an electrically conductive copper paste which may be easily used and easily secured to a base material, it is important to properly select and easily secured to a base material, it is important to properly select and properly mix the ingredients such as copper powder, binder, special additive (for example, anthracene, anthracene carboxylic acid, anthradine, anthranilic acid), dispersant and solvent.

The copper particles are different in the configuration thereof depending upon the production method thereof. In the electrolytic method, the copper particles are deposited in high purity and also in branched shapes. In the reduction method wherein the oxides are reduced by a reducing gas, the copper particles are provided in spongy and porous shapes.

The electrically conductive copper paste to be used in connection with this invention is required to havethefollowing properties: 1. To be easily coated by way of screen printing in formation of fine patterns.

2. Fixedly secured to the base board.

3. To be resistant against a high temperature alkali bath of copper chemical plating.

4. Fixedly secured to the copper plating.

5. Having an invariable viscosity in the elapse of time to maintain a stabilized printability.

In orderto satisfy the above mentioned requirementsthe electrically conductive copper paste is required to contain the copper particles of high purity in the branch shapes as deposited by the electrolysis and/orthe copper particles of porous spongy shapes as reduced from the metal oxides. The copper particles may be processed into flakes.

Further in order to highten the content rate ofthe copper particles inthe paste, it is requiredtofillthe copper particles of different sizes and shapes to a maximum density.

As to the binder ofthe electrically conductive copper paste, the binder is required to act as a vehicleforso much copper particles and as an effective adhesive to the base board. Furtherthe binder must resist againstthe alkali bath of a copper chemical plating.

Itwasfound thatthe electrically conductive copper paste was bestwhenthe copper paste contained the epoxy resin which has a largercontent rate of copper particles and hightensthe deposition rate ofthe plating, and further increases the adhesive property of the plating film.

With respect to the property ofthe copper plating deposited on the electrically conductive copper paste ACP#07P, P, the copper plating is reddish brown and paste like and has a viscosity of 300-500ps at the temperature of 25"C. The adhesive property to a copper laminated base board and to a resin base board has been confirmed by a taping test. Further the adhesive property to the electrically conductive paste has been confirmed bythe taping test. The soldering property is more than 96% asto the extension rate and is more than 3.0 kg as to the tensile force (3 x3mm2).

The components of the electrically conductive copper paste and the conductivity thereof are mentioned in detail inthesameapplicant'sJapanese Patent applications 55-6609 (laid open: 56-103260) (corresponding U.S. patent No.4353816) and 60216041 (corresponding U.S. patent application of serial No.06/895716), and therefore the description thereof is omitted herein.

With respect to the electrically resistant paste, the paste contains a refined powder of carbon or graphiteorthelikeofhigh purity as an electrically conductive element and a heat hardened resin such as epoxy resin, phenol resin, melamine resin, acrylic resin or the like as a binder, and further contains, as a viscosity modifier, a solvent which is evaporated slowlyata high temperature.

The components of the electrically resistant paste are each required to have a specific property. For example, as the functional powder, the particles must be fine and uniform and further of high purity as well as high quality. Further the particles must be of little difference in the electric resistance value and must be familiarwith the resin to be mixed therewith.

As to the property of polymer, it is preferable that the paste is easily dissolved with the particles and will not be filmy if placed for a long time in a normal temperature. The paste further is required to be not hardened at a normal temperature and to be quickly hardened when heated. The hardened paste must not be vary in volume and must be slightlyflexible and further easily adhesive to the base board.

Furtherthe paste must be resistant against heat and humidity, and also must be easily adhesive to the un dercoat as will as to the overcoat.

As to the property of solvent, the paste is required to be stabilized in the successive printing operations, that is, notto fill the prints and not be deteriorate the emulsion film. The paste is further required to be slow in the evaporation speed at a normal temperature and reluctant to absorb water, not to abruptly change the viscosity thereof at the tem- perature i 1 00C and to have no poison and/or irritating smell ata normal temperature and in the vapor at thetime of heating.

The electrically resistant paste such as the paste TU-1 K has been developed by Asahi Chemical Research Laboratory Co., Ltd. so as to fully satisfythe requirements as mentioned above. The electrically resistant paste maintains very stabilized resistance, that is, the resistance variation rate is only about 0.5% at the soldering temperatures at 240 C. Further the paste will notabruptlyabsorbtheheatandwill not respond to the heat until the soldering temperature is reached as actually indicated by a heat difference analysis curve, and therefore the volume variation of the resistor is extremely small.

With respect to the plating resistant resist such as the resist CR-2001 developed by Asahi Chemical Research Laboratory Co., Ltd. so as to be used in the present invention, this resist is coated on a firstcircuit which is not electrically connected to a second circuit which isto be formed on the first circuit.

Therefore the resist is required to have an isolating property and at the same time an alkali resistant pro perty. Actuallythe resist has been developed to maintain the acidity more than 4 hours in the alkali bath of 70 C and of pH1 2 just like the copper chemical plating bath.

Similar to the electrically conductive copper paste ACP-007P,the resist contains as a main component an epoxy resin and is printed through a 180-mesh polyester screen and then is heated for 30 minutes at the temperature 1 500C so as to be hardened. The printing film is preferably 15-30 m so asto resist chemicals and voltages. The main features are asfol- lows: The resist is easily adhered to the base on which the resist is coated, and to a copper lamination and further is not deteriorated is immersed in the alkali bath of pHl2fora long time. The resist is quite safe in the practical use because the hardener to be used is alkali having little poison.The resist is coated by way of screen printing and has a hardener lOg mixed with the principal component 1 00g thereof, and is hardened in a set time 15-30 minutes atthe temperature 1 50-200"C.

The plating resistant resist is green in the condition of ink and has an adhesion (cross-cut) 100/100 on a copper lamination, a surface hardness of more than 8H when measured by a pencil, a solvent resistant property (in trichloroethylene) by more than 15 sec., a soldering heat (260'C) resistant property of more than 5 cycles, a surface isolation resistance value of more than 5 x 1013Q avolume resistance value of 1 x 1014#-cm, a voltage (15XXm) resistant property of more than 3.5kV and a dielectric tangent (1 MH#)oflessthan0.03.

The dielectric paste to be used in the invention has been developed as corresponding to the types 1 and 2 ofthe chip condenser standards, and the electro static capacity is 1 00pF-1 000pF. The dielectric paste is produced from the barium titanate (BaTiO3) which is burned into flakes or into a plate and is ground into particles of 211m-10lim which are then mixed with a binder with more than 50% by weight of the particles, which are further mixed with an organic solvent and is kneaded into a paste. For a binder, a resin such as phenol resin, epoxy resin, melamine resin, et., may be used. For a solvent, butyl carbithol may be used as a main element together with carbithol or butyl cellsole.

Example 1: The electrically conductive copper pasteACP-007P was directly printed on a paper phenol base board and heated at the temperature of 1 50'C for a predetermined time so as to be hardened. Then the alkali and acidtreatmentwas performed to the base board and subsequently the chemical copper plating was performed to provide a chemical copper plating layer of 611m thickness. A lead (tin coated lead 0.5mm#) was soldered (within 3 seconds) to the measuring terminal. In this case, it was found that the soldertensile strength (kg/3 x 3 mm2) was 5.1 kg when the paste was hardened in 30 minutes, and 5.9 kg when the paste was hardened in 60 minutes.

In case a glass epoxy resin base board was em plyed on the same condition, it was found thatthe tensile strength was 5.9 kg when the paste was hardened in 30 minutes, and 6.2 kg when the paste was hardened in 60 minutes.

Example2: The plating-resistant resist CR-2001 was printed on a phenol resin base board and was heated at the temperature of 150for30 minutes so asto be hardened. Subsequently the electrically conductive copper paste ACP-007P was printed and heated at the temperature of 1 500C for a predetermined time so asto be hardened. Then the alkali and acid treatment was performed, and then the chemical copper plating was performed to provide a copper plating layer of 6#m thickness. A lead (tin coated lead 0.5 mum+) was soldered (within 3 seconds) to the measuring terminal. In this case, itwasfoundthatthesolderten- sile strength (kg/3 x 3mm2) was 5.9 kg when the paste was hardened in 30 minutes, and 6.1 kg when the paste was hardened in 60 minutes.

In case a glass epoxy resin base board was employed on the same condition, it was found thatthe soldertensile strength was 6.1 kg when the paste was hardened in 30 minutes, and 6.9 kg when the paste was hardened in 60 minutes.

Claims

1. A method for forming electrically conductive circuits on a base board comprising the steps of: a) attaching copper laminations on both sides of the base board to provide a copper laminated base board; b) processing the copper laminated base board to provide a through-hole extending all through the thickness ofthe copper laminated base board; c) performing a catalyst treatment of the copper laminated base board; d) washing the copper laminated base board; e) etching both sides of the copper laminated base board to form thereon a plurality of circuits of first lamination including a circuit formed around the through-hole on each side of the copper laminated base board; f) coating a plating-resistant resist on both sides of the copper laminated base board except the circuits ofthefirst lamination;; g) heating the copper laminated base board to harden the plating-resistant resist; h) coating an electrically conductive copper paste on both sides of the copper laminated base board in a manner as to electrically connect at least two circuits of first lamination on each side ofthe copper laminated base board; i) heating the copper laminated base board to harden the electrically conductive copper paste; j) making a pre-plating treatment to the copper laminated base board; k) performing a chemical copper plating on the surface of the electrically conductive paste of the copper laminated base board to provide thereat a cir cuit of second lamination on each side of the copper laminated base board;; I) coating the plating-resistant resist on both sides ofthe copper laminated base board except a part of the circuits of first lamination formed around the through-hole; m) heating the copper laminated base board to harden the plating-resistant resit; n) performing an activation treatment to the inner periphery of the through-hole; and o) performing a non-electrolytic copper plating on the inner periphery of the through-hole to provide thereat a copper plating layerto electrically connect the circuits offirst lamination on both sides ofthe copper laminated base board.

2. AmethodaccordingtoClaim 1 andcomprising between steps k) and I), the steps of: p) coating a resistor paste on the platingresistant resist of a predetermined electric resistance value on both sides ofthe copper laminated base board; q) heating the copper laminated base board to harden said resistor paste; r) coating an electrically conductive paste on both sides ofthe copper laminated base board in a manner as to electrically connect to the resistor paste at least two of the circuits offirst lamination located on both sides of the resistor paste or the circuit second lamination located on one side of the resistor paste on each side of the copper laminated base board; and s) heating the copper laminated base board to harden the electrically conductive paste to form thereat a resistor circuit on each side of the copper laminated base board.

3. A method according to Claim 1 and comprising between the steps k) and I), the step of: t) coating a dielectric paste having a property of storing electricity on a part of one of the circuits of first lamination or of second lamination on each side of the copper laminated base board; u) heating the copper laminated base board to harden the dielectric paste; v) coating an electrically conductive paste on both sides of the copper laminated base board in a manner as to electrically connect to the dielectric paste one of the circuits of first lamination located adjacent thereto or the circuit of second lamination on each side of the copper laminated base board; and w) heating the copper laminated base board to harden the electrically conductive pastetoform thereat an electricity storing circuit on each side of the copper laminated base board.