FR2466173A1 - Tool for separating conductors on substrate - has capacitor which is discharged via two electrodes to melt conductor - Google Patents

Abstract

The tool has two electrodes brought into contact with the conductor being separated. The electrodes are positioned one on each side of the point of separation. A voltage is applied to the electrodes and a current passes locally through the conductor thereby evaporating the metal and producing the required break. The current is obtained by discharging a capacitor. The electrodes are held by a support that can move down towards the conductor or rotate so that the electrodes come into contact with it. The substrate is mounted on an X-Y table and can be positioned in a horizontal plane beneath the descending electrodes.

Description

 The invention generally relates to the modification of printed wiring on the surface of an insulating substrate and more particularly has for object a method for cutting certain conductors on the surface of said substrate, eliminating all risks of deterioration of neighboring conductors.

 For many years now, there has been a constant trend towards increasingly advanced miniaturization of electronic circuits and in particular the digital logic circuits used in computers. In this latter area, one actueDema * technology used is that of multilayer cabling. Integrated circuits containing the active components and in particular the circuits carrying out the desired logic functions are mounted on the surface of a ceramic plate (the generic term of substrate will be used later) carrying the conductors carrying out the various interconnections between the terminals of access to different integrated circuits. These conductors are most often deposited by screen printing on the substrate. However, this substrate must sometimes undergo wiring modifications requiring the cutting of one or more conductors.

However, the fineness and the brittleness of the printed wiring pose problems for carrying out such operations on the surface of the substrate, with suitable reliability; due to the risk of damage to the nose-up and / or active components (integrated circuits). As a result, this problem has not been resolved entirely satisfactorily so far.

 The invention proposes a new procedure for intervention on the substrate, as well as an apparatus capable of causing no deterioration of the substrates. The basic idea of the invention is relatively simple since it consists in passing a relatively large electric current between two points of the conductor which it is desired to cut, so as to destroy the part of the conductor, by heating and combustion or sublimation, lying between the two points of application of the electric current.

 More specifically, the invention therefore relates to a method of cutting conductors on the surface of a substrate, in particular screen-printed connections on said substrate, characterized in that it consists in positioning said substrate opposite two electrodes, to apply each electrode in electrical contact with a conductor which it is desired to cut and on either side of the location where it is desired to cause said cut to appear, and to apply an electric voltage between said electrodes, until at least part of it is destroyed of said conductor lying between the contact points of the two electrodes.

Preferably, the application of said electric voltage is carried out by connecting a charged capacitor between the two electrodes.

The invention also relates to an apparatus for cutting
selectively conductors supported adherently to the surface of a substrate, by implementing the method defined above, characterized in that it comprises an electrode support carrying at least two electrodes having their free ends close together on the other, a support of said substrate located opposite said electrodes, in that one of said supports or a part thereof is coupled to a mechanism for translation and / or rotation in a plane, preferably horizontal, in that at least part of one of said supports, possibly the same, is coupled to a translation mechanism in a direction substantially perpendicular to said plane, preferably vertical, and in that it further comprises a source of energy electric whose terminals are connected to said electrodes via a switching means.

 Furthermore, it is advantageous to define predetermined locations, on the surface of the substrate, for making the cuts. In particular, to be certain of being able to modify the wiring between the integrated circuits carried by the substrate at will, it suffices to reserve the possibility of isolating any terminal from any integrated circuit. This is why, we can arrange the wiring so that each integrated circuit lug is connected to a pad of the printed circuit (Roxt, parexemsse of a desired deposit with Indium-Lead) itself only connected to another pad analogous (located close to it and spaced a predetermined distance) by a fine conductive part susceptible other destroyed by the application of an electrical voltage between the two pads. In such a printed circuit arrangement, the pairs of pads are all arranged in two main perpendicular directions, since the integrated circuits have a rectangular base and are arranged and oriented on the substrate according to a modular grid.

When these rules for setting up and wiring the integrated circuits on the substrate are respected, the arrangement of the device defined above can be considerably simplified. It then suffices to make the substrate integral with an XY table and to have four parallel electrodes, movable substantially vertically in independent guide means and capable of coming to drop substantially freely by the action of their own weight up to come into contact with the substrate. In this type of device where it is not necessary to rotate the electrode support on itself, a first pair of electrodes has its electrodes located in a plane substantially parallel to the '' one of the directions of movement of the table
XY while the second pair of electrodes has its electrodes located in a plane substantially parallel to the other direction of movement of this same table XY; each pair of electrodes being associated with an independent lifting device, acting simultaneously on the two corresponding electrodes, to hold them above said substrate.

 Each lifting device comprises for example at least one electromagnet magnetically coupled with the electrodes.

The invention will be better understood and other objects, details and advantages thereof will appear better in the light of the following explanatory description of an apparatus in accordance with the principle of the invention, given solely by way of example and made with reference to the accompanying non-limiting drawings in which
- Figure 1 is a general elevation view of the conductor cutting device according to the invention, with partial section at the electrode support
- Figure 2 is a view along arrow z in Figure 1 with partial section of the electrode support
- Figure 3 is a view on a very large scale of a part of an equipped substrate on which it is desired to cut the conductors
- Figure 4 shows the same part of the substrate in position on the device of Figures 1 and 2
- Figure 5 is a detail view on a larger scale of one of the electrodes of the apparatuswet showing a device for raising and lowering the electrodes according to a first embodiment
- Figure 6 shows a horizontal section on a larger scale of the electrode support at the line
VI-VI of figure 5
- Figures 7 and 7a show views respectively in plan and in section of the substrate support of the apparatus according to the invention;
- Figure 8 is an electrical diagram illustrating the interconnection between the electrodes and an energy source # I # ctr ## e; and
- Figure 9 shows the simplified diagram of a device for raising and lowering the electrodes according to a second embodiment.

Figures 1 and 2 show the general arrangement of a device according to the invention. This comprises a base 11 and an electrode support 12 having substantially the shape of a bracket mounted on this base. The foot 13 of this bracket has a telescopic structure with controlled elongation (for example by means of a cam controlled by an electric motor or of a heli cordas screw-nut device) to allow the release of the electrodes and facilitate the positioning of the substrate 14 under these electrodes. The substrate is mounted and positioned on a substrate support 15 itself mounted on a translation and / or rotation mechanism in a horizontal plane. In the example described, this mechanism is only a translation mechanism in two perpendicular directions, namely an XY table 16. The electrode support 12 comprises a housing 17 situated vertically from the XY table 16 and containing, according to the 'example described in which the electrodes are movable vertically, guide means and actuation means of said electrodes. The housing 17 could be pivoted about a vertical axis, with respect to the rest # of the support of electrodes in the form of a bracket, this to orient the two electrodes relative to the substrate. However, due to the nature of the substrates on which it is desired to intervene, it has been considered preferable to provide two pairs of electrodes in perpendicular planes. For example, the apparatus represented in FIGS. 1 and 2 comprises a first pair of electrodes 18 having its electrodes 18a, 18b admitting a plane of symmetry substantially parallel to the direction X of movement of the table
XY 16 and a second pair of electrodes 19 having its electrodes 19a, 19b admitting a plane of symmetry substantially parallel to the direction Y of this same table XY 16.

 Indeed, if we refer to Figure 3 which illustrates a substrate 14 on which one wishes to intervene, it is understood that this substrate carries several integrated circuits such as 20, with a substantially square or rectangular base surface and of which the access lugs 21 extend in two perpendicular directions.

Of course, when the substrate 14 is placed on the support 15, the two perpendicular directions of alignment of the access lugs 21 are coincident with the directions X, Y of the table 16.

The lugs 21 are welded to studs 22 located at the periphery of the integrated circuit 20 and opposite the lugs 21. Each stud 22 is connected to an identical stud 23, immediately adjacent, by a thin conductor 24 of the printed circuit carried by the face upper of the substrate 14. In this way, if it is desired to isolate certain lugs 21 of the integrated circuit 20 from the rest of the printed circuit, in order to carry out a modification of wiring, it suffices to make a break between the corresponding pads 22 and 23, that is to say according to the invention, to destroy the conductor 24. Now, taking into account the orientation of the integrated circuits 20 on the substrate 14, it clearly appears that all the conductors 24 are arranged in two preferential orientations than the we will make coincide with the directions X and Y above. According to an advantageous technological choice, one or the other of the pairs of electrodes described above is therefore used depending on the orientation of the conductor 24 which one wishes to destroy . For this, the substrate is moved using the XY table 16 to bring the aforementioned conductor below a pair of electrodes 18 or 19 and the pair is lowered so that the ends of the electrodes come into electrical contact with the two pads 22, 23 corresponding; the other pair of electrodes remaining in the high position.

It is this situation which is illustrated in FIG. 4. It will be noted in this connection that the substrate 14 is not necessarily mounted alone on the XY table 16, - by means of the support 15. In fact, the modifications of rearing can be decided after the substrate 14 has been mounted on a printed circuit 25 with "windows" carrying a plurality of such substrates arranged opposite the windows and connected to the printed circuit 25 by peripheral lugs 26. In such a case, however, correct positioning is nevertheless ensured by means of the substrate 14 on which it is desired to intervene and which is placed in a precise position in the support 15; the printed circuit 25 simply resting on stops (not shown) integral with the table
XY 16. Figures 7 and 7a illustrate in more detail the structure of the substrate support 15.This consists mainly of a base 30 provided with four bases 31 on which the four corners of a substrate 14 shown in line must bear. ghost in FIG. 7. One of the bases (31a) is surmounted by a square 32, cut in the mass and serving as a reference for the positioning of the substrate 14. Another neighboring base (31b) comprises a stop 32a, the the innermost face is in the same plane as one of the arms of the bracket 32. Leaf springs 34 keep the edge of the substrate 14 in abutment against the bracket 32 and the stop 32a. In addition, the base 30 is mounted on the XY table 16 by means of a vertical axis 35 so that an additional angular adjustment is possible, thanks to a micrometric adjustment mechanism 36.

 FIGS. 5 and 6 show more precisely the arrangement of the electrodes inside the housing 17.

Each electrode (for example the electrode 18a shown in FIG. 5) comprises an electrode body 40, cylindrical, guided in two coaxial sleeves 41 and 42, of corresponding diameter. These sleeves are for example made of Teflon and spaced apart longitudinally by a certain distance to allow free travel to a lateral projection 43 extending longitudinally along the body of electrodes 40 and comprising two plane and parallel surfaces. Rollers 44 mounted in free rotation on an axis integral with the housing 17 are respectively in contact with the planar surfaces of the projection 43 to prevent any possibility of rotation of the electrode relative to the sleeves. Indeed, the electrode body 40 is extended by a contact tip 45 which is not located in the axial extension of said body but curved and directed in the direction of the contact tip of the other electrode of the same pair (obvious technological constraints preventing to bring-together and reduce the dimensions of the electrode bodies below certain limits). It was therefore necessary to carefully prevent any rotation of the electrode body 40 which could cause offset of the tips contact 45 of the electrodes of the same pair. In addition, each pair of electrodes is associated with an independent lifting device, acting simultaneously on the two corresponding electrodes to hold them above the substrate.

In the example shown a lifting device is constituted by two electromagnets 46 magnetically coupled with the electrodes of the corresponding pair. The coils 47 of the electromagnets are therefore connected to be connected to a source of electric current (47b) via a control switch (47a) corresponding respectively to each pair of electrodes. Of course, one could also provide a single electromagnet of type 46 for each pair of electrodes, magnetically coupled to these electrodes by a pole piece of suitable configuration. In this mode, the aim is simply to maintain the electrodes of each pair in the high position, by magnetic attraction, when the corresponding electromagnet (s) are supplied; the descent control of the electrodes is done simply by gravity, after cutting the current in the electromagnets.

 FIG. 8 is an electrical diagram illustrating the interconnection between the electrodes and the source of electrical energy which advantageously consists of a capacitor 50 capable of discharging via a thyristor 51. The electrodes of pairs 18 and 19 are connected two by two in parallel (since only two of the four electrodes will actually be in contact with the printed circuit of the substrate at the time of a cutting operation) and the two groups of electrodes thus produced are respectively connected to earth and to the thyristor cathode 51, via a polarity inverter circuit 52 and another inverter 53. The common contact of this inverter 53 is connected to the circuit 52 and to the electrodes, its working contact T is connected to the thyristor cathode 51 and its rest contact R is connected to a continuity checking circuit 54 associated with a display means 55. In practice, the circuit 54 can have the struct e of a simple ohmmeter since its simply to check that a closed electrical circuit has been established between the contact tips of the two electrodes lowered on the substrate (that is to say that the electrode tips are actually in contact with two pads 22, 23 interconnected by a conductor 24. When this verification has been carried out, the inverter 53 is tilted to its working position and therefore establishes a connection between the cathode of the thyristor 51 and the polarity inverter circuit. The r81e of this circuit 52 is to choose the polarity of the electric discharge relative to the terminal 21 of the integrated circuit 20 in the vicinity of which one operates, - depending on whether this terminal corresponds to an input or an output of a logic tool enclosed in this integrated circuit. The anode of the thyristor 51 is connected to one of the terminals of the capacitor 50, the other terminal of which is connected to ground. The switch means constituted by the thyristor 51, the polarity reversing circuit 52, the inverter 53 and the pairs of electrodes 18 or 19 form a discharge circuit 56 of the capacitor 50. A charging circuit 57 of this same capacitor is constituted by a DC source 58, a resistor 59 and a switch 60 connected in series across the capacitor. The trigger of the thyristor 51 is connected to an electronic circuit for switching on and off 61, known per se, itself controlled by a push button 62. The circuit 61 thus makes it possible to precisely control the conduction time thyristor 51 and therefore the electrical energy actually discharged between the electrodes to destroy the conductor 24. Furthermore, an electronic circuit 63 for checking the charge voltage of the capacitor 50 is connected to the latter. The circuit 63 is associated with any display means 64, making it possible to assess whether the charge of the capacitor 50 is sufficient. This circuit 63 may also include a control output 65 connected to a disable input 66 of the control circuit 61 to prevent ignition of the thyristor 51 if the charge of the capacitor 50 is not sufficient. The circuit 54 can also include a control output 67 connected in a similar manner to the input 66 to prevent actuation of the thyristor 51 if the electrical contact between the electrodes, via the circuit elements of the substrate 14, does not is not properly performed.

 Referring now to FIG. 9, in which the elements identical to those of FIG. 5 are designated by the same reference, a lifting and lowering device associated with each pair of electrodes, comprises a lever arm 71, d axis 72, one end 73 of which is articulated to the body of electrodes 40 by means of a fork joint 74. As in the embodiment shown in FIG. 5, the cylindrical body 40 of each electrode (for example the 'electrode 18a) is guided in two coaxial sleeves 41 and 42. On the other end 75 of the lever 71, bears the lower end of the core 76 of an electromagnet 80, the coil 77 of which is connected to a source of electric current 47b by means of a switch 47a. There is shown at 78 a sleeve for guiding the core 76 secured to the housing 17 and at 79 two stops acting on either side of the sleeve 78. The device for lifting each pair of electrodes comprises a spring R2 constituting a means intended to urge this pair of electrodes upwards when the lowering device is not controlled by means of the switch 47a. To do this, in the example illustrated in FIG. 9, the spring R2 is disposed between the upper end of the core 76 of the electromagnet 80 and the housing 17.

In the lowering device illustrated, a spring
R1, connected between the housing 17 and the part 84 of the arm 71, biases the pair of electrodes downwards.

 This lifting and lowering device operates as follows. When the electromagnet 80 is energized, using the switch # 47a, the core 76 rises, thus compressing the spring R2 to cancel its action. The lever 71 then switches under the action of the spring R1 and puts the assembly comprising the electrode bodies 40 and the contact points of the contact. When the current is cut in the electromagnet 80, the core 76 of the latter descends, the spring R2 relaxes, the lever 71 pivots by tensioning the spring R1, and the assembly comprising the electrode bodies 40 and the contact tips 45 goes up. A pressure-limiting damping device is interposed between the lower part of the cylindrical body of electrodes 40 and the contact tip 45. it includes two spring blades 82 joined at their ends by two spacer pieces 85. A first rod 81 joins one of the bracing pieces 85 to the lower part of the electrode body 40. The contact tip 45 is in turn fixed to a second rod 83 secured to the other piece of bracing 85 of said device. The spring blades 82 thus limit the pressure of the contact tips 45 on the pads to a predetermined value by the choice of the force of the spring blades 82, while maintaining the trajectory of the contact tips.

 The operation of the device which has just been described is> LrsshDes and follows clearly from the above description. The substrate 14 is first placed on the support 15. After checking the orientation of the latter and possible angular compensation, the movement of the XY table 16 is controlled so as to bring the pads 22 and 23 joined by the conductor 24 which it is desired to remove, vertically from the contact points of one of the pairs of electrodes 18 or 19, depending on the orientation of the conductors to be removed. Then the electrodes are lowered either by simply cutting the supply of the corresponding electromagnets 46 in accordance with the first embodiment shown in FIG. 5, or by exciting the electromagnets 80 meters in accordance with the second embodiment represented in FIG. 9. After checking the continuity of the discharge circuit of the capacitor 50 between the electrodes and of the charge of this capacitor, the actuation of the thyristor is controlled, which results in significant heating between the pads 22 and 23 and a cutting of the condu factors 24.

 Of course, the invention is in no way limited to the procedure defined above or to the embodiment of the apparatus described, it includes all the technical equivalents of the means used if these are in the context of the claims that follow.

Claims (16)

 1. - Method for cutting conductors on the surface of a substrate, in particular screen-printed connections on said substrate, characterized in that it consists in positioning said substrate opposite two electrodes, in applying each electrode in electrical contact with Ig conductor which it is desired to cut and on either side of the location where it is desired to see said cutoff appear and to apply an electrical voltage between said electrodes,, until destroying at least part of said conductor comprised between contact points of the two electrodes.  2. - Method according to claim 1, characterized in that the application of said electrical voltage is carried out by connecting a charged capacitor between the two electrodes.  3. - Apparatus for selectively cutting conductors supported in an adhesive manner by a substrate, characterized in that it comprises an electrode support carrying at least two electrodes having their free ends close to one another and a support for said substrate located opposite said electrodes, in that one of said supports or a part thereof is coupled to a mechanism for translation and / or rotation in a plane, preferably horizontal, in that at least part of the 'one of said supports, possibly the same, is coupled to a translation mechanism in a direction substantially perpendicular to said plane, preferably vertical, and in that it further comprises a source of electrical energy whose terminals are connected to said electrodes via a switching means.  4. - Apparatus according to claim 3, characterized in that said support of said substrate is mounted on an XY table moving said substrate in a substantially horizontal plane and that said electrode support comprises four parallel electrodes, movable substantially vertically in means of guidance and likely to come down substantially freely by the action of their own weight until coming into contact with said substrate mounted on said support, in that a first pair of electrodes has its electrodes which admit a plane of symmetry substantially parallel to one of the directions of movement of said table XY and that a second pair of electrodes has its electrodes which admit a plane of symmetry substantially parallel to the other direction of movement of this same table XY, and in that each pair is associated with a respective lifting device, acting simultaneously on the two corresponding electrodes to keep them above it t substrate. 5. - Apparatus according to claim 4, characterized in that each lifting device comprises at least one electromagnet magnetically coupled with the electrodes of the corresponding pair, a source of electric current being connected to the coil of said electromagnet by l 'via a control switch.  6. - Apparatus according to claim 3, characterized in that said support of said substrate is mounted on an XY table moving said substrate in a substantially horizontal plane and that said electrode support comprises four parallel electrodes, movable substantially vertically in means of guidance, in that a first pair of electrodes has its electrodes which admit a plane of symmetry substantially parallel to one of the directions of movement of said XY table and that a second pair of electrodes has its electrodes which admit a plane of symmetry substantially parallel to the other direction of movement of this same table XY, in that each pair of 6LectS is associated with a respective descent device, acting simultaneously on the two corresponding electrodes to bring them into contact with said substrate mounted on said support, and in that each pair of ## 2ectro.desest is associated with respective lifting tif, acting simultaneously on the two corresponding electrodes to hold them above said substrate.  7. - Apparatus according to claim 6, characterized in that each descent device comprises at least one electromagnet cooperating with a first end of a lever arm, the second end of said arm being articulated to the electrodes of the corresponding pair , and a source of electric current connected to the coil of said electromagnet by means of a control switch.  8. - Apparatus according to claim 7, characterized in that each lifting device comprises means urging said pair of electrodes upwards when the lowering device is not controlled by means of said switch. 9. - Apparatus according to claim 8, characterized in that, dCqzs cmuediwiitif descent, the electro-elder cancels the action of the corresponding lifting device, and in that a means biases said pair of electrodes down . 10. - Apparatus according to one of claims 4 to 9, characterized in that each elec # trode comprises a cylindrical body guided without play in at least one sleeve of corresponding diameter, for example in Teflon, that this body laterally has a projection extending longitudinally with two flat and parallel surfaces and that. two rollers mounted in free rotation on a fixed part of said electrode support are respectively in contact with said planar surfaces; to prevent any possibility of rotation of said electrodes in said sleeves, the contact points of the electrodes of each pair not being located in the extension of said corresponding cylindrical bodies but close to each other to ensure a predetermined relative spacing. 11. - Apparatus according to one of claims 7 to 10, characterized in that the other end of the aforementioned lever arm is articulated to the aforementioned cylindrical bodies of the electrodes of each pair.  12. - Apparatus according to one of claims 3 to 11, characterized in that each of the electrodes comprises a cylindrical body and a contact tip, and in that a damping system is interposed enlrelaffle contact tip and said cylindrical body the electrode.  13. - Apparatus according to one of claims 3 to 12, characterized in that said electrode support having substantially the shape of a bracket, the base of this bracket has a telescopic structure with controlled elongation to allow the release of said electrodes and thus facilitate the establishment of said substrate.  14. - Apparatus according to one of claims 3 to 13, characterized in that the aforementioned electrical energy source consists of a capacitor, that a charging circuit of said capacitor comprising a direct current source is connected to the terminals of this capacitor, preferably by means of a switch and that a discharge circuit of said capacitor comprises at least two aforementioned electrodes and a switch means.  15. - Apparatus according to claim 14, characterized in that said switch means is a thyristor and that an electronic ignition and extinction circuit, known per se, is connected to the trigger of said thyristor, to control the time of conduction of the latter and therefore the electrical energy discharged between electrodes by the capacitor.  16. - Apparatus according to claim 14 or 15, characterized in that a polarity reversing circuit is interposed in the discharge circuit, between the capacitor and said electrodes.