DEVICE AND METHOD FOR MANUFACTURING PRINTED CIRCUIT BOARDS FOR ELECTRICAL AND/OR ELECTRONIC CIRCUITS

Abstract

A method for manufacturing printed circuit boards for electrical and electronic circuits, comprising an electrically nonconductive substrate (4) and electrically conductive tracks of homogenous thickness applied thereon, wherein the electrically conductive tracks are made of a material with a melting temperature higher than the melting temperature of soldering tin so that they will withstand the soldering of electronic components thereon by soldering tin without melting, characterized in that a print medium (3) comprising the material of the electrically conductive tracks is provided as a two-dimensional layer above the electrically nonconductive substrate (4) and is imprinted on the electrically nonconductive substrate (4) according to the desired conductor track layout, under the influence of heat selectively applied by a print head (2) onto the printing medium (3), whereby the printing medium (3) is transferred onto the substrate (4) by selectively melting or sintering the material for the electrically conductive tracks, wherein the print head (2) does not come into direct contact with the printing medium (3), since at least a foil-shaped carrier material carrying the two-dimensional layer of the printing medium (3) is situated between the print head (2) and the two-dimensional layer of the printing medium (3).

Claims

1. A method for manufacturing printed circuit boards for electrical and electronic circuits, comprising an electrically nonconductive substrate (4) and electrically conductive tracks of homogenous thickness applied thereon, wherein the electrically conductive tracks are made of a material with a melting temperature higher than the melting temperature of soldering tin so that they will withstand the soldering of electronic components thereon by soldering tin without melting, characterized in that a print medium (3) comprising the material of the electrically conductive tracks is provided as a two-dimensional layer above the electrically nonconductive substrate (4) and is imprinted on the electrically nonconductive substrate (4) according to the desired conductor track layout, under the influence of heat selectively applied by a print head (2) onto the printing medium (3), whereby the printing medium (3) is transferred onto the substrate (4) by selectively melting or sintering the material for the electrically conductive tracks, wherein the print head (2) does not come into direct contact with the printing medium (3), since at least a foil-shaped carrier material carrying the two-dimensional layer of the printing medium (3) is situated between the print head (2) and the two-dimensional layer of the printing medium (3).

2. The method according to claim 1, characterized in that the electrically conductive printing medium (3) is heated by means of a thermal print head (2).

3. The method according to claim 1, characterized in that at least one electrically nonconductive layer in the form of an electrically nonconductive printing medium (3) is imprinted on the substrate (4), preferably under the influence of heat on the printing medium (3).

4. The method according to claim 1, characterized in that electrical or electronic components such as resistors, voltage dividers, etc., are likewise imprinted on the substrate (4) by means of a resistive printing medium (3), and capacitors are imprinted by providing, one on top of the other, a bottom layer made of an electrically conductive printing medium (3), a middle layer made of a nonconductive printing medium (3), and a top layer made of an electrically conductive printing medium (3), etc.

5. A device (1) for manufacturing printed circuit boards for electrical and electronic circuits, comprising an electrically nonconductive substrate (4) and electrically conductive tracks of homogenous thickness applied thereon, wherein the electrically conductive tracks are made of a material with a melting temperature higher than the melting temperature of soldering tin so that they will withstand the soldering of electronic components thereon by soldering tin without melting, characterized by a device for providing a print medium (3) comprising the material of the electrically conductive tracks as a two-dimensional layer above the electrically nonconductive substrate (4), and a print head (2) for selectively heating the printing medium (3) according to a desired conductor track layout, in order to transfer this printing medium (3) onto the substrate (4) by a selective melting or sintering of the material for the electrically conductive tracks, wherein the print head (2) does not come into direct contact with the electrically conductive printing medium (3) to be printed, since at least a foil-shaped carrier material carrying the two-dimensional layer of the printing medium (3) is situated between the print head (2) and the two-dimensional layer of the printing medium (3).

6. The device (1) according to claim 5, characterized in that the print head (2) has at least one heating device or a heating conductor (18) having a number of individual sections that can be selectively supplied with current or voltage in order to induce heat at a spot and thus print a pixel at that location.

7. The device (1) according to claim 5, characterized in that the print head (2) has at least one heating device, preferably a laser, having a number of individual optical fiber sections which in each case end at different spots and may be selectively controlled with the beam of the laser in order to induce heat at a spot and thus print a pixel at that location.

8. The device (1) according to claim 5, characterized by a transport device for moving the substrate (4) relative to the print head (2).

9. The device (1) according to one of claim 8, characterized in that the printing medium (3) is applied to a film-like carrier (6) that is unwound from a supply spool (7), along the substrate (4) to be imprinted, onto a laydown spool (8).

10. The device (1) according to claim 9, characterized in that the transport speed of the film-like carrier (6) in the area between the supply spool (7) and the laydown spool (8) is equal to the transport speed (5) of the substrate (4) to be imprinted.

11. The device (1) according to claim 5, characterized by multiple printing devices, each having one thermal print head (2) and one supply spool and laydown spool (7, 8) for each strip- or film-like carrier material (6) provided with the printing medium (3), the printing devices being situated in succession in the transport direction (5) of the substrate (4) to be imprinted.

12. The device (1) according to claim 5 characterized by a thermal print head (2) for selectively heating an electrically conductive printing medium (3) according to a desired conductor track layout, in order to transfer this printing medium (3) onto the substrate (4), wherein the thermal print head (2) does not come into direct contact with the electrically conductive printing medium (3) to be printed, since a carrier material carrying the electrically conductive printing medium (3) is still situated in between.

13. The device (1) according to claim 5 characterized by a print head (2) for selectively heating an electrically conductive printing medium (3) comprising particles of a metal or metal alloy with a melting point of 1.500° C. or less to a temperature of at least 80% of the melting point of the regarding metal or metal alloy, according to a desired conductor track layout, in order to transfer this printing medium (3) onto the substrate (4), wherein the particles of a metal or metal alloy are sintered or melted together, and wherein the print head (2) does not come into direct contact with the electrically conductive printing medium (3) to be printed, since a carrier material carrying the electrically conductive printing medium (3) is still situated in between.

14. The device (1) according to claim 5, characterized in that the device for providing the printing medium (3) is designed such that the thickness (ti) of the two-dimensional layer of the printing medium (3) varies only between a minimum thickness (t.sub.l,min) and a maximum thickness (t.sub.l,max), where it applies:
(t.sub.l,max−t.sub.l,min)/t.sub.l≤ε, with ε=0.2, or ε=0.1, or ε=0.05, or ε=0.02, or ε=0.01.

15. The device (1) according to claim 5, characterized in that the homogenity of the thickness (t.sub.t) of the electrically conductive tracks applied onto the electrically nonconductive substrate (4) is such that the thickness (t.sub.t) varies only between a minimum thickness (t.sub.t,min) and a maximum thickness (t.sub.t,max), where it applies:
(t.sub.t,max−t.sub.t,min)/t.sub.t≤ε, with ε=0.2, or ε=0.1, or ε=0.05, or ε=0.02, or ε=0.01.

16. The device (1) according to claim 5, characterized by a device for removal of the foil-shaped carrier material together with unused portions of the two-dimensional layer from the electrically nonconductive substrate (4), after the electrically conductive tracks have been applied on the electrically nonconductive substrate (4).

17. The device (1) according to claim 16, characterized in that the device for removal of the foil-shaped carrier material together with unused portions of the two-dimensional layer from the electrically nonconductive substrate (4) is in the shape of a laydown spool (8) situated downstream of the print head (2), for winding the foil-shaped carrier material together with unused portions of the two-dimensional layer.

18. The method according to claim 1, characterized in that the printing medium (3) is provided in a two-dimensional layer of a thickness (t.sub.l) which varies only between a minimum thickness (t.sub.l,min) and a maximum thickness (t.sub.l.max) where it applies:
(t.sub.l,max−t.sub.l,min)/t.sub.l≤ε, with ε=0.2, or ε=0.1, or ε=0.05, or ε=0.02, or ε=0.01.

19. The method according to claim 1, characterized in that the homogenity of the thickness (t.sub.t) of the electrically conductive tracks applied onto the electrically nonconductive substrate (4) is such that the thickness (t.sub.t) varies only between a minimum thickness (t.sub.t,min) and a maximum thickness (t.sub.t,max), where it applies:
(t.sub.t,max−t.sub.t,min)/t.sub.t≤ε, with ε=0.2, or ε=0.1, or ε=0.05, or ε=0.02, or ε=0.01.

20. The method according to claim 1, characterized in that the foil-shaped carrier material is removed together with unused portions of the two-dimensional layer from the electrically nonconductive substrate (4), after the electrically conductive tracks have been applied on the electrically nonconductive substrate (4).

21. The method according to claim 20, characterized in that the foil-shaped carrier material is removed together with unused portions of the two-dimensional layer from the electrically nonconductive substrate (4) by winding it on a laydown spool (8).

Description

[0052] Further features, particulars, advantages, and effects based on the invention result from the following description of one preferred embodiment of the invention, and with reference to the drawings, which show the following:

[0053] FIG. 1 shows a side view of a device according to the invention for manufacturing printed circuit boards for electrical and electronic circuits, including a thermal print head;

[0054] FIG. 2 shows a view of the bottom side of the thermal print head from FIG. 1, in the direction of the arrows II-II;

[0055] FIG. 3 shows another embodiment of a thermal print head in a view according to FIG. 1; and

[0056] FIG. 4 shows a printing system comprising multiple printing devices.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0057] Within the scope of the invention, for manufacturing printed circuit boards for electrical and electronic circuits, a device 1 is used which has a print head 2 for selective, localized heating of individual print spots or pixels of an electrically conductive printing medium 3 that is present in planar form, so that the printing medium is sintered, fused on, or melted at the selected print spots or pixels, and after being transferred to a substrate 4 situated underneath or adjacently, the printing medium resolidifies there in the form of a combined matrix, resulting in the desired conductor tracks, in the ideal case without transfer resistances.

[0058] A transport device for setting the printed circuit board substrate 4 to be imprinted in motion 5 with respect to the print head 2 is not illustrated in FIG. 1. This may be a roller track or a conveyor belt, or also an oscillating plate.

[0059] In addition, a heating device may be situated in front of the print head, viewed in the transport direction 5, in order to preheat the printed circuit board substrate 4, thus reducing the heat that is to be generated by the thermal print head 2. This could be a thermal radiator along which the flat, in particular plate-shaped, substrate 4 is moved. On the other hand, it is also sufficient to preheat the printed circuit board material 4 in an oven, for example, from which it may then be removed, in a batchwise manner, for example, at the correct temperature.

[0060] The printing medium 3 is situated on the side or surface of a film-like carrier material 6 which faces the substrate 4, and which extends between the print head 2 and the substrate 4, at which location it may be transported synchronously with the transport movement 5.

[0061] The carrier material 6 preferably has the shape of a long strip that may be unwound from a supply spool 7 and a laydown spool 8.

[0062] With regard to the unwinding speed, it should also be ensured that it is preferably completely synchronous with the transport movement 5 of the substrate 4, so that preferably no relative movement occurs between the flat elements, namely, the substrate 4 on the one hand and the carrier material 6 on the other hand. This requires that, among other things, the supply spool 7 is situated upstream from the print head 2 with respect to the transport direction 5 of the substrate 4, while the laydown spool 8 is situated downstream from the print head 2.

[0063] The axles or shafts 9 of the supply spool 7 on the one hand and of the laydown spool 8 on the other hand may be adjustable in a direction perpendicular to the level of the substrate 4 to be imprinted, so that in the area of the print head 2 the section of the carrier film 6 bearing the printing medium 3 is always oriented parallel to the substrate 4, and preferably rests flatly against same.

[0064] When the supply spool and laydown spool 7, 8 are pressed against the substrate 4 in a frictionally locked manner, this frictional locking ensures that the peripheral speed 10, 11 of the supply spool and laydown spool 7, 8 is always equal to the transport speed 5 of the substrate 4, regardless of the instantaneous diameters of these two spools 7, 8, which in fact continuously change in the course of unwinding from the supply spool 7 to the laydown spool 8. Of course, such synchronicity between the spool peripheral speeds 10, 11 on the one hand and the transport speed 5 on the other hand could also be achieved by suitable control or regulation, which, however, means increased design complexity. In contrast to the first embodiment, where the supply spool and laydown spool 7, 8 are passively driven, i.e., their drive is received by the substrate 4 to be imprinted, in the latter case it would also be necessary to provide (separate) drives for the two spools 7, 8.

[0065] The print head 2 is controlled by a control device 12, preferably according to a conductor track layout stored therein. The control device 12 may be connected to the print head 2 via one or more preferably electrical control lines 13 that maintain contact with the print head 2 via a plug-in device 14, for example.

[0066] FIG. 2 illustrates one possible embodiment of the print head 2 in a more detailed view. A socket 17, provided with plug-in contacts 16, for inserting the plug 14 of the control device 12 is apparent on one side, for example on an upstream end-face side 15 of the print head 2.

[0067] The actual thermal heating device 18 of the print head 2 extends perpendicularly with respect to the transport direction 5 of the substrate 4, preferably along a straight line 19. This may be a linearly extending heating conductor 18 made of a very resistive material, for example tungsten, which is also the material of the heating wires in light bulbs.

[0068] A large number of feed lines 20, 21 branch off from this heating conductor 18, preferably in alternation in the transport direction 5 and opposite the transport direction.

[0069] Every other one of these feed lines 20, preferably the ones that branch off in the direction 5 opposite from the plug socket 17, are connected to one another and thus short-circuited, and are connected to a shared contact 16, preferably a ground contact at that location.

[0070] The remaining feed lines 21, which preferably branch off from the heating conductor 18 in the direction toward the plug socket 17, i.e., preferably opposite the transport direction 5, are each connected to a voltage supply, in particular to a contact pin 16 having a supply voltage, via a semiconductor switch 22.

[0071] The individual semiconductor switches 22 may be addressed via a line bus as a component of the feed line 13 and the corresponding plug-in contacts in order to selectively switch them on when the section of the heating conductor 18 associated with a semiconductor switch 22 is to be heated in order to print a pixel at the location in question.

[0072] The chassis 23 of the print head 2 is preferably made of ceramic or some other material that is suitable for high temperatures. The melting or softening temperature of this material should in particular be higher than the maximum operating temperature of the heating conductor 18.

[0073] In particular when the substrate 4 is preheated to a temperature just below the operating temperature of the heating conductor 18 by means of a heating device, not illustrated, or in an oven, only a small amount of energy needs to be supplied within the print head, so that, due to the additional quantity of heat, the temperature of the section of the heating wire 8 in question increases to the desired operating temperature.

[0074] Of course, it would also be possible in principle to use some other energy converter instead of a heating wire 18 to focus the necessary quantity of heat onto a spot of the substrate 4 to be imprinted. A comparatively large quantity of energy could be generated by means of a laser, for example, provided that the laser beam of the laser is guided to the spots in question, depending on the desired conductor track layout, and at that location is directed onto the carrier material 6 or preferably through same, directly into the printing medium 3.

[0075] This could take place, for example, by means of a plurality of optical fibers that are coupled on one end to the laser, and that on their other free end are each associated with a pixel or spot. Individual pixels or spots may be selectively heated by controlling, by means of light switches, the luminous flux between the laser and the optical fiber according to the desired conductor track layout.

[0076] An optimal energy yield or effectiveness is obtained when a laser in the red and/or infrared spectrum is used, so that the radiant power is delivered predominantly or exclusively as heat radiation.

[0077] In addition, so-called fiber lasers, a specialized form of solid-state lasers, appear to be particularly suitable. A doped core of a glass fiber is used as active medium, so that a fiber laser is thus a glass laser having properties of an optical fiber. The laser radiation is conducted by the laser-active fiber, and is highly intensified due to the comparatively long length.

[0078] Fiber lasers are generally optically pumped by coupling radiation of at least one diode laser in parallel to the fiber core, into the cladding of the fiber core or into the fiber core itself. A structure having so-called double-clad fibers delivers a higher power output; the pump radiation from the thick cladding passes into the active fiber core in a distributed manner.

[0079] Erbium, ytterbium, and/or neodymium may be used as doping elements for the laser-active fiber core. Usually only the middle portion of the glass fiber is doped.

[0080] Fiber lasers have electro-optical efficiencies of greater than 30%, as well as excellent beam quality, a long service life, and a compact, maintenance-free, robust design. In pulsed operation, fiber lasers may be used to achieve high peak intensities, and thus a high power density, to generate temperatures above the melting point T.sub.S of metals such as silver (T.sub.S=961° C.) or copper (T.sub.S=1085° C.) at specific points. With this technique, it is thus possible to manufacture even continuous conductor tracks made of copper.

[0081] If necessary, multiple printing devices, each having one print head 2 and one supply spool and laydown spool 7, 8, may be situated in succession in the transport direction 5 of the strip- or film-like carrier material 6 in order to print multiple layers of electrically conductive and electrically nonconductive structures one on top of the other, or optionally also structures made of specialized materials such as dielectrics, for example for manufacturing a film capacitor. However, for layers that are to be printed one on top of the other, it should be ensured that structures that are already applied are not remelted, which could result in undesirable short circuits between various layers. Therefore, it is recommended to limit the number of layers that are to be printed one on top of the other, and preferably to laminate multiple substrate layers 4 onto one another which have already been appropriately imprinted in each case.

[0082] Furthermore, FIG. 1 shows a transport device 24 for moving the substrate 4 relative to the print head 2 in the direction of the movement 5. The transport device 24 may have the form of an endless conveyor belt which is spanned over two rollers 25, one of which is driven by a motor 26.

[0083] The velocity of the movement 5 which is imparted to the substrate 4 by the transport device 24 shall be the same as the velocity of the movement of the printing medium 3 on the foil-shaped carrier material 6.

[0084] FIG. 3 shows another embodiment of the invention where the print head 2 comprises at least one heating device in the form of a laser 27, and a number of individual optical fiber sections 29 which in each case end at different spots and may be selectively excited with the beam of the laser 27 under control of a selector 28 in order to induce heat at a spot and thus print a pixel at that location.

[0085] FIG. 4 shows a printing system with multiple printing devices 1a′, 1b′, 1c′, each having one thermal print head 2′ and one supply spool and laydown spool 7′, 8′ for each strip- or film-like carrier material 6′ provided with the printing medium 3′, the printing devices being situated in succession in the transport direction 5′ of the substrate 4′ to be imprinted.

[0086] It is to be noted that some or all of the multiple printing devices 1a′, 1b′, 1c′ may be embodied like the printing device 1 of FIG. 1, of course.

LIST OF REFERENCE NUMERALS

[0087]

TABLE-US-00001 1 device 2 print head 3 printing medium 4 substrate 5 transport movement 6 carrier material 7 supply spool 8 laydown spool 9 axle, shaft 10 peripheral speed 11 peripheral speed 12 control device 13 control line 14 plug-in-device 15 upstream end-face side 16 plug-in contacts 17 socket 18 heating conductor 19 straight line 20 feed line 21 feed line 22 semiconductor switch 23 chassis 24 transport device 25 roller 26 drive motor 27 laser 28 selector 29 optical fibers