NL8001942A - METHOD FOR MANUFACTURING A PRINTED CIRCUIT OR CONDUCTIVE CHAIN THEREFOR, MATERIALS FOR USE IN THE METHOD AND APPARATUS FOR MANUFACTURING PRINTED CIRCUITS OR CHAINS THEREFOR - Google Patents

Description

<è%

A method of manufacturing a printed circuit or conductive circuit therefor, materials for use in the method and apparatus for manufacturing printed circuits or circuits therefor.

The invention relates generally to printed circuits and in particular to a new, improved method of manufacturing, modifying and / or repairing printed circuits, as well as materials for use therein and an apparatus for use in the manufacture of printed circuits circuits or chains and on the printed circuits or chains by the method.

Conventional printed circuits are generally manufactured by what can best be described as a "subtractive" method, in which printed circuit carrier plates laminated with one or more conductive layers are etched to remove certain portions of a conductive layer, while other parts remain behind according to a specific pattern that applies to the circuit in question. The related art requires the application of relatively complex photographic operations that require high capital investment for etching and electroplating equipment and associated auxiliary equipment such as cameras and the like. In general, the time required to design and manufacture a printed circuit with conventional techniques is quite long and requires a large number of skilled technicians. As a result, there are relatively few companies capable of manufacturing printed circuits with conventional techniques. Due to the time and cost involved in the manufacture of a printed circuit, the standard methods are also not very suitable for the production of small series of printed circuits, even if 800 1 9 42 * 2 * the printed circuit otherwise a very desirable product.

The object of the invention is now to provide an improved method for the production of printed circuits or electrical circuits that formed part thereof, and in particular a method with which both small and large series of printed circuits or chains can be manufactured quickly and inexpensively.

Another object of the invention is to provide new materials and associated equipment for manufacturing printed circuits by an additive method. Another object of the invention is to provide improved printed circuits or circuits.

According to the invention, there is provided a method for the production of a printed circuit on a carrier plate, wherein a carrier plate is printed in a particular circuit pattern with a conductive metal-containing ink, the printed pattern is covered with a conductive metal powder, the presses powder into the ink, hardens the ink and removes the excess powder. Then, a conductive solder paste is applied to the wafer over the printed circuit or circuit or a portion thereof and alloyed with the powder and the ink.

The invention also relates to the materials for the additive manufacturing of printed circuits or circuits, comprising a conductive ink consisting of an epoxy resin containing conductive metal powders, preferably copper powder, and a catalyst as filler, and comprising a solder paste consisting of a lead-tin alloy with powdered antimony suspended in a binder and a powerful flux.

The invention also relates to a press for pressing the metal powder into the ink, comprising a number of rollers or rolls of gradually increasing hardness to exert a gradually higher pressure on the wafer.

The invention will be further described and elucidated hereinafter with reference to the figures, of which figure 1 shows a block diagram of the various steps in the manufacture of printed circuits or 800 1 9 42 * 4 3 circuits according to the invention.

Fig. 2 shows a perspective view of a carrier plate for manufacturing a printed circuit or circuit according to the invention.

FIG. 3 is a perspective view of a screen mask for use in printing the carrier plate with a printed circuit or circuit.

Fig. 4 is a longitudinal section of a screen mask carbon black, such as is used, for example, for applying the conductive ink to the carrier plate.

Fig. 5 shows a perspective view of a support plate printed with the conductive ink.

Fig. 6 shows a perspective view of sprinkling the carrier plate with conductive powder.

FIG. 7 is a longitudinal sectional view of a device for applying pressure to a printed metal powder-coated support plate as used in the present invention.

Fig. 8 is a perspective view of a screen mask as used in printing a solder resist onto the support plate with layers applied thereon.

Fig. 9 is a detail cross-section or enlarged scale of a portion of a printed circuit manufactured in accordance with the invention and

Fig. 10 is a similar sectional view to FIG. 9 of a modified embodiment of a printed circuit manufactured in accordance with the invention.

According to the invention, an electrically conductive circuit or circuit is applied to a support surface, for example on a support plate 10, by printing materials for the circuit or circuit on the plate. The wafer 10 may be suitably made of some material suitable for use as a printed circuit support carrier. Plates of this type must be electrically insulating 800 1 9 42 t * 4 and are usually quite thin and rigid, although flexible support surfaces may be used for some applications.

For the present purpose, platelets from phenolic resins, glass fiber laminates, impregnated board or the like can be used. Ideally, the plate should be resistant to the heat generated by soldering, exhibit electrical insulating properties, and be resistant to physical shock and vibration. In any case, the wafer 10 is first brought into the desired shape, in the embodiment shown in Fig. 2, the wafer has a substantially rectangular shape with a pair of tongues 12 and 14 integral with the wafer on one side so that the plate can be inserted in a chassis in the usual way. This shape of the plate is shown by way of example only, because many forms of printed circuit board carrier plates are in use, both with and without protruding tongues. If a large number of carrier plates are to be manufactured, some of the circuits or circuits can be printed on a large plate and the plate can then be cut into separate small plates. The carrier plate is provided with a number of small holes 16 through which the connecting wires of switching elements are inserted when the circuit circuit is pressed, to which circuit components must be soldered. The flat plate 10 is first cleaned with a suitable solvent, for example isopropanol or ethyl ethyl ketone.

After the wafer 10 has been cleaned and is ready for use, a screen printing mask 18 is placed on the wafer as shown in Figs. 3 and 4. The screen printing mask 18 is provided with the desired circuit or circuit pattern. In practice, a screen printing machine made of a stainless steel screen cloth with a mesh size of 0.083-0.094 mm has been found to give very satisfactory results. The pattern on the screen printing mask 18 has open portions 20 at the location of the chain strips to be printed on the support plate and is closed in the places where no image is to be printed on the support plate. With the screen printing mask 18 correctly positioned on the backing plate 800 1 942 * t 5, a conductive ink 22 is applied through the screen printing mask 18 to the surface of the backing plate 10, as the ink passes through the openings 20 in the screen printing mask whereby the pattern of the circuit or circuit is applied to the carrier plate, as shown in Fig. 5.

The ink 22 according to the invention is an ink consisting of a resin system with a metal as a filler; the ink suitably consists of a phenolic resin with a conductive metal powder, preferably copper powder with a particle size of 0.044 mm as filler therein. The ink also contains an acid which acts as a catalyst in the curing of the ink and which also serves to remove any oxides that may be present on the copper.

The ink can be applied to the carrier plate by hand, although for normal production purposes the use of a screen printing technique gives the most satisfactory results, because it can obtain a clean and sharp image and such a screen printing technique is relatively inexpensive. As shown in Fig. 4, a doctor blade 24 can be used to spread the ink 22 over the screen printing mask so that the ink penetrates the screen printing area at the image and is deposited on the support plate. As shown in Fig. 5, the printed plate 10 shows an image of the circuit or circuit composed of chain segments 26, corresponding to the circuit or chain model on the screen printing mask 18, in that each segment of the circuit or circuit is in the form of ink 22 is printed on the support plate.

While the ink in the circuit or circuit segments 26 printed on the support plate is still wet, the segments of the circuit or circuit are covered with a conductive metal powder 28, for example by dusting or dusting with metal powder; Copper powder with a particle size of up to 0.044 mm has been found to give satisfactory results. The powder 28 must be scattered or sprayed over the circuit or circuit pattern within a few minutes of printing the carrier plate. Preferably, the dusting or dusting with the metal powder should take place within 5 minutes. There should be an excess of 8 00 1 9 42 *. ♦ Sprinkle or stew 6 powder on the backing plate to ensure that the ink is completely covered by the powder, even if excess powder may be present on the surface of the backing plate. After the carrier plate has been completely sprinkled or dusted with the copper powder, the carrier plate is gelated by a press device 30 equipped with rollers or rollers (see Fig. 7) in which press device the copper powder 28 in the ink of the circuit or circuit segments 26 is pressed so that it is held there intimately.

The press 30 comprises a number of pairs of rolls or rollers 32 arranged in pairs, each pair of rollers having an increasing durometer hardness from one end to the other end, for example the first pair of rolls or rollers may have a durometer hardness 45, while the the next pair may have a hardness of 50, followed by a pair with a hardness of 55 and a final pair with a hardness of 60. The rollers or rollers are mounted in a rigid frame 34 and the lower rollers of the series are driven by a common drive system so as to pass the carrier plate from left to right through the pressing device 20, as schematically shown in Fig. 7. The top rollers or rollers can be individually adjusted by screws 36 provided with springs 38 which provide pressure is applied to the top set of rollers or rollers. Thus, as the carrier sheet 10 is introduced into the slit of the first pair of rollers or rollers 25, the copper powder will be pressed down into the ink and the pressure exerted will gradually increase as the carrier sheet moves through the pressing device. This pressing treatment leads to intimate contact between the metal powder and the ink. Once the carrier plate has passed through the press, the excess copper powder is removed from the carrier plate, after which the carrier plate with the image can be fed through the press again. By initially sprinkling or sprinkling an excess of copper powder on the carrier plate, the entire printed circuit or circuit is covered with the powder and this ensures that no ink is taken up during pressing 800 1 9 42 * 7 by the rollers or rollers and further transferred to the rollers or rollers. The end result is that the pressed image of the circuit or chain remains sharp and clean. There is a certain relationship between the surface tension of the resin 5 used and the pressure exerted by the rollers or rollers. As more pressure is gradually applied to the picture, an even surface is obtained without distortion of the image.

After the pressing operation is completed, the ink is then cured. In practice, the printed circuit 10 or chain can be pre-cured at 70-90 ° C for 10-15 min. Followed by post-cure or final cure for 1-2 h at 125 ° C. The cure can be accomplished at different ways, for example by placing the plate in a circulating air oven or, for example, by using infrared lamps. After the ink has completely cured, the circuit or circuit segments 26 adhere tightly to the support plate 10 and the copper powder 28 forms an integral part of the chain or circuit segments 26. Any loose copper powder or excess copper powder 28 is removed, for example, by means of a vacuum (by suction) or other suitable manner.

The next step in the manufacture of the printed circuit or circuit consists in applying a solder paste to the same chain or circuit segments 26 that have been sprinkled or dusted with copper powder and are now cured. For this purpose, a similar screen printing mask can be used as the screen printing mask 18 which was initially used to print an ink image on the support plate; however, a screen printing mask is now used on a slightly coarser screen printing mesh, for example a screen printing mesh having a mesh size of 0.165-0.150 mm with a slightly wider image thereon, to ensure that the printed circuit or circuit is completely covered by the image. The solder paste used herein preferably consists of a mixture of a lead-tin alloy with powdered antimony in a flux and with a binder whereby the metal powders remain suspended in the paste. Two 35 solder pastes which have proved to be very suitable are a 60/40 solder 800 1 9 42 ar-m 8 with 1% ethylene glycol, sold by Bow Solder Products Co., Ine., And the second a 60/40 paste in marketed by Electronic Fusion Devices, Ine. denoted by type number 2037. The paste has a creamy consistency and is printed onto the circuit or chain in the same manner as indicated in Figs. 3 and 4 using the screen printing mask and squeegee. The flux in the solder should preferably be a very active flux and should preferably consist of a strong mineral acid. A preferred solder paste composition is a solder paste composition containing 3-6 wt.% Zinc chloride, 80 wt.% Of a pre-alloyed mixture of lead-tin alloy and antimony and the balance a binder. After the solder paste is applied, it forms a solder layer 40 on top of the circuit or circuit segments 26. After the printing 15 is completed with a solder, the solder is alloyed with the underlying ink layer and the copper powder by heating the plate with the circuit or circuit at the melting point of the solder, generally at a temperature between 325 and 550 ° C, depending on the composition of the solder. The heating can take place in 20 different ways, for instance by means of infrared lamps which are used together with a moving belt on which the carrier plate with the circuit lies and which moves at a speed of for instance 3 m / min. In any case, the solder is heated to the melting point so that the solder forms an alloy with the ink and the copper powder to form a conductive printed circuit on the support plate. Applying the solder to the underlying ink and the copper powder greatly enhances the conductivity of the circuit or circuit and serves to firmly adhere the solder to the support plate.

After the alloying has taken place in the base solder, a solder resist pattern 42 can be selectively applied over the printed circuit or circuit and the carrier plate. The solder resist is a dielectric material that serves to insulate those portions of the carrier plate that will not be connected to any contact, connecting wire 800 1 9 42

* V

9 or the like which will be attached to the picture later. The solder resist may suitably be an epoxy material and serves to prevent solder from a "wave soldering machine" from adhering to other parts of the circuit when parts are soldered to the carrier plate. The solder resist can be applied by screen printing in the manner described above, using a screen printing mask 44 showing the pattern one wishes to apply to the printed circuit board plate already applied. Normally, the solder resist pattern will differ from the circuit pattern on the carrier plate in that certain parts of the circuit or circuit need to be covered and others not.

The solder resist layer may also serve as an insulator between successive chain layers which are successively applied to one side of the carrier plate, as schematically shown in Fig. 10. Other chains or circuits may be applied over a layer of solder resist using the same techniques as were used for the first circuit or circuit mounted directly on the carrier plate. In practice, if a number of circuit or circuit patterns are to be formed in successive layers on one side of the wafer, the solder paste layer 40 on the chain or circuit closest to the support wafer should have a higher melting point than the solder paste layers in the further outward chains or circuits so that the bottom solder will not flow or melt again when the outer chains or circuits are alloyed.

Figure 10 shows a plate with two chain layers on top of each other. The first chain comprises a chain segment 26 which has been dusted with copper powder, has been hardened and is alloyed with a layer of solder paste 40, after which the chain is then covered with a layer of solder resist 42. On top of the layer of solder resist 42, a further switching segment or chain segment 26 'is conductive ink printed on which copper powder has been fired and over which a layer 40 'of solder paste is alloyed with the ink and copper powder 35. The different printed circuits or chains printed one on top of the other can cross each other, or can be built up in any number of layers as accidentally required for the circuit or circuit concerned. Using the techniques described above, the method of the invention can also be used to repair conventional printed circuits or to make changes on such conventional printed circuit board plates.

The conductive ink used in the method according to the invention consists of a thermosetting resin 10 containing electrically conductive metal powders as filler. A preferred formulation of such ink is a two-part system comprising a phenol (resorcinol) resin incorporating copper powder as a filler and adding a catalyst, for example, anhydrous isopropanol and phosphoric acid. The anhydrous isopropanol should be pure and preferably should have a purity of at least 99%. Likewise, the phosphoric acid should be reagent grade phosphoric acid. The anhydrous isopropanol not only functions as a catalyst, but also serves as a partial diluent to control the viscosity of the ink. Although the use of phosphoric acid is preferred, other inorganic acids can also be used to advantage. The acid not only serves as a catalyst, but also serves to remove any oxides that may be present in the copper powder. Since the oxides inhibit conductivity, it is desirable to remove any oxides that may be present.

The preferred composition conductive ink is prepared by first heating the phenol (resorcinol) heirs at 130 ° C until the degree of polymerization has advanced to a stage 30 where the resin has a viscous to toffee-like consistency. The viscosity of the resin can be adjusted using anhydrous isopropanol. The copper powder is then added; it is preferable to use untreated copper powder with a particle size of at most 0.044 mm, quality 200 RL. Sufficient copper powder is added to reach a filler content of 800-75 wt.%. That is to say, on a total of 100 g of ink, the ink contains 25 g of resin and 75 g of copper powder. If the material is not to be used immediately, it should be stored in a refrigerator at approximately 4 ° C to inhibit further polymerization. If the material 5 is to be used for printing a support plate, it is first brought to room temperature, after which the catalyst is added, preferably in an amount of about 6% by weight of the material. The catalyst mixture preferably consists of equal amounts by weight of phosphoric acid and isopropanol, ie 6% catalyst consists of 3% phosphoric acid and 3% isopropanol.

Other materials which can be used in the method according to the invention include anhydrous isopropanol which is used as a diluent, as already indicated above, and also as a cleaning agent for the screen printing masks if necessary. A detergent very suitable for this purpose consists of a mixture of equal amounts of isopropanol and methyl ethyl ketone.

The solder paste may consist of a mixture of 60 parts by weight. lead and 40 parts by weight. tin with 1% 20 ethylene glycol added thereto. The solder may also have a different composition depending on the desired melting point. The solder paste should be of such consistency that it can be applied to the desired locations through a stainless steel screen printing mesh of the type described above.

Although the invention has been described above in particular by way of examples of embodiments, all kinds of modifications and variations are possible within the scope of the invention. For example, although various ranges for temperatures, duration, and other parameters have been mentioned in connection with the preferred embodiments, various variations and modifications can be employed in this regard. For example, the flexibility of the printing ink can be controlled by adjusting the ratio between epoxy and phenol. Also, instead of copper powder, other conductive metals, for example, silver, aluminum, etc., can be used.

800 1 9 42 12

Furthermore, instead of by hand-sprinkling or dusting, the copper powder or other metal powder is also applied in another manner, for example by means of a vibrating feeder via a conveyor belt, by electrostatic means or in another suitable manner. . Likewise, the solder layer may also be applied by "wave soldering techniques" or the like, rather than by printing via a screen printing mask, when such wave soldering technique is used, the solder will directly form an alloy with the copper powder or other metal powder which forms in and on the ink layer without the need for separate heating. Yet another modification that can be applied is to use an ordinary resinous ink which does not include metal powder, in which case the conductivity of the final layer is provided by applying it to the ink layer. ink scattered powder and the solder layer.

800 1 9 42

Claims (18)

Method for manufacturing an electrically conductive circuit or circuit on a dielectric surface, characterized in that (a) a layer of a resinous thermosetting ink is applied to that surface according to a determined circuit pattern, (b} a applies a layer of electrically conductive metal particles over the ink layer, (c) the ink layer hardens and (d) applies a layer of an electrically conductive solder to the layer of metal particles and alloys more. 2. Process according to claim 1, characterized in that a dielectric layer is selectively applied over the solder layer. 3. A method according to claim 1 or 2, characterized in that the metal particles are pressed into the ink layer before the ink layer is cured. Method according to claim 3, characterized in that the metal particles are pressed into the ink layer by applying a gradually higher pressure. 5. A method according to any one of the preceding claims, characterized in that the ink and the solder layer are both applied by means of a printing technique, 6. Method according to claim 2, characterized in that a second electrically conductive circuit or circuit is applied over the applied dielectric layer by applying a second electrically conductive resinous ink on the dielectric layer according to a determined pattern, a second layer of electrically conductive metal particles over this second ink layer, harden the second ink layer and apply the second layer of electrically conductive solder over the second layer of metal particles 30 and heat the second chain at a sufficiently high temperature such as the second solder layer melt. A method according to any one of the preceding claims, characterized in that the ink used is an electrically conductive ink. 8. A method according to any one of the preceding claims, characterized in that the solder layer is applied by "wave soldering". 9. A method according to claim 6, characterized in that the melting point of the first solder layer is higher than the melting point of the second solder layer. 10. Electrically conductive ink for use in printing an electrically conductive circuit or circuit on a dielectric surface, characterized in that it consists of (a) a thermosetting resin, (b) conductive metal particles dispersed in this resin and (c) a catalyst, wherein (d) the resin, the metal particles and the catalyst are present in the ink in weight percentages of about 23 wt%, 71 wt% and 6 wt%, respectively. Electrically conductive ink according to claim 15, characterized in that the thermosetting resin is a phenolic resin. Electrically conductive ink according to claim 11, characterized in that the resin consists of resorcinol. Electrically conductive ink according to claim 11, characterized in that the conductive metal particles are copper particles 20 with an average particle size of 0.044 mm. Electrically conductive ink according to Claims 10-13, characterized in that the catalyst consists of equal amounts by weight of anhydrous isopropanol and an inorganic acid. Electrically conductive ink according to claim 25, characterized in that the acid is phosphoric acid. 16. Device for use in the manufacture of printed circuit boards comprising a first layer of conductive ink and a layer of conductive particles over it, characterized in that this device consists of (a) a frame, (b) a number of pairs of rollers mounted in the frame and (e) means for driving at least one roller of each pair, (d) the rollers being mounted so as to establish a straight path between each pair of rollers where a carrier plate with thereon mounted layers can be fed and wherein (e) the rollers 35 along the web have progressively greater hardness. 80 0 1 9 42 17. Printed circuit consisting of (a) a support with a dielectric surface, (b) at least one switch or chain segment adhered to that surface, (c) said switch or chain segment a layer of a metal powder containing resinous ink, a layer of an electrically conductive metal powder adhered to the surface of the ink and a layer of an electrically conductive solder alloyed with the layer of metal powder. 18. Printed circuit according to claim 17, characterized in that a layer of an electrically insulating material is present over at least a part of the dielectric surface and of the switching or circuit segment. 800 1 9 42