Device for double-sided exposure of printed circuit boards using masks

The present invention relates to an exposure setup for the light of a printed circuit board, double-sided through cliches.

It is known that, among the operations necessary for the implementation of a printed circuit board, it operates an exposure step, in particular for the definition by photo-conductive tracks. The corresponding system is operable to expose to ultraviolet for a given time the printed circuit covered with a film or a photoresist through a plate to expose the corresponding part of the lacquer or photosensitive film defined by the cliche .

of course we understand, in this operation, a fundamental point is the positioning accuracy of the plate relative to the printed circuit on which you want to achieve sunstroke.

The vast majority of machines of this type only allows ultraviolet exposure of one side of the printed circuit board. However, when the circuit plate is double-sided type, which is increasingly common, the use of such machines is not very suitable since it requires passing the plate twice in the exposure machine , thus requiring particular cliché positioning two operations on his support relative to the PCB.

To overcome this disadvantage, it has already proposed insolation machines for the simultaneous irradiation through snapshots of both sides of the PCB. Such machines are described in particular in US patent 5,337,151 and in European Patent application EP 618 505.

The machine described in the American patent mentioned above is based on the principle of position by mechanical centering the lower support and the upper support plate and to move with the aid of a pair of fingers coupled together cliché relative to the assembly constituted by the lower and upper supports snapshots.

This machine has numerous drawbacks, including the fact that there is not a really accurate positioning of the upper plate relative to the lower plate and in that the displacement of the printed circuit by using two fingers can not be coupled how in the precision requirements, particularly because bending risk moving fingers PCB.

Moreover, this machine does not allow the separate positioning of the upper plate relative to the upper face of the printed circuit and the positioning of the lower plate relative to the underside of the printed circuit. However, such a possibility can be useful in certain situations.

As regards the European patent also mentioned above, it corresponds to an effective machine in so far as displacements of the printed circuit with respect to the lower and upper plates are using two independent fingers and allow good positioning the printed circuit. Furthermore, in the machine described in this patent, it does have a real positioning of the upper plate relative to the lower plate. However, this machine does not allow a separate positioning of the upper plate relative to the upper face of the printed circuit and a positioning of the lower plate relative to the underside of the printed circuit. In addition, there is also in this machine positioning error risks due to the flexion of the fingers for positioning the printed circuit.

To overcome these drawbacks, an object of the present invention is to provide a light exposure of installing a double-sided printed circuit which allows to overcome the drawbacks mentioned above and in particular, where necessary, to achieve a separate positioning relative to the circuit board upper support plate and the lower plate of medium.

To achieve this object, the exhibition facility in the light of a printed circuit board, double-sided through a first and a second plate provided with a register mark which comprises<ul><li>a first and a second fixed frame in a horizontal plane,</li><li>a first and a second support of the first and second plates cooperating respectively with the first and second frames,</li><li>means for arranging said circuit between the first and second artwork supports, said circuit being provided with a marking in tracking position, </li><li>optical means for detecting position errors between said circuit and said first and second supports,</li><li>means for moving perpendicularly to their planes of said support to the other support,</li><li>a light source, and</li><li>optical means for simultaneously towards each plate holding a portion of the light beam emitted by the source beam,</li></ul>    characterized in that it further comprises:<ul><li>means disposed outside of the assembly constituted by said supports and said circuit to maintain fixed in its plane said circuit relative to said frame; and</li><li>means for moving independently said first support with respect to said circuit and said second support with respect to said circuit based on the detected position error.</li></ul>

It is understood that, thanks to the specific provisions of the exposure system, the circuit board is held stationary relative to the frame of the machine, which avoids any risk of inaccurate positioning due to bending displacement of the circuit means printed since these fingers are fixed and, on the other hand, means are provided for independently moving the first support relative to the printed circuit and the second support relative to the printed circuit, thereby thus obtaining independent positioning of the upper plates and lower relative to the printed circuit.

In a first mode of implementation, the means for maintaining fixed the printed circuit comprises first, second and third means forming a centering finger secured in a horizontal plane of the lower frame and traversing freely said lower support and each having one end adapted to into a corresponding hole provided in said tracking circuit, said three holes are not aligned.

It is understood that, according to this implementation mode of the invention, the centering fingers which are fixed and integral with the lower frame allow a very precise and stable positioning of the printed circuit with respect to the machine frame and thus with respect to upper and lower plates.

According to a second embodiment, the means for maintaining fixed the printed circuit comprises a first and a second set of nip, each nip assembly comprising

a first pinching member integral with the first frame and passing freely through the first support and a second pinching member integral with the second frame and passing freely through the second support, said pinching members facing one another in the vertical direction, and means for relatively moving the first and second clamping members towards one another to pinch the printed circuit.

It is understood that, in this embodiment, the PCB is gripped between two gripping members secured respectively to the upper and lower frame. Thus, a very precise and stable positioning of the printed circuit to the frame of the exposure installation. From this particular position of the printed circuit, it is possible, with the aid of displacement means, to separately position the upper artwork support and the lower plate support.

Other characteristics and advantages of the invention appear better on reading the following description of several embodiments of the invention given by way of non-limiting example.

The description refers to the appended figures in which:<ul><li>1a is a schematic top view of the lower portion of the exposure system showing the main bodies of this lower portion;</li><li>1b is a simplified view in vertical section of the installation;</li><li>Figure 2 is a partial view of the installation showing a clamping device for fixing the printed circuit;</li><li>Figure 3 is a detail view showing the installation of the fastening means of the printed circuit using fingers;</li><li>Figure 4 is a detailed view showing the end of the immobilisation finger of Figure 3; </li><li>Figure 5 is an elevational view of securing means of the artwork supports relative to the frame;</li><li>Figure 6 is a detailed view showing the supporting means of the artwork support by the frame; and</li><li>Figure 7 is a detail view showing one embodiment of the displacement motors of the lower support or the upper support plate relative to the fixed racks.</li></ul>

In this type of installation, it is well known that, at first, there is provided a pre-positioning of the circuit board relative to plate support with retractable positioning fingers. A part of this pre-positioning of the circuit board relative to the upper and lower plate support is carried out by optical means a measure of the positioning errors of these three parts. From these positional error measurements, control travel motors to achieve the final positioning of which must correspond to a positioning error of less than 10 microns. The present invention relates to the part of the plant to obtain the final positioning from measuring the error corresponding to the pre-positioning.

Optically detecting the positioning error has been described in detail in European patent application 618 505. For this part of the installation, reference is therefore made to the description of this patent application to be considered as integral part of the present application. We simply specify in certain modes of implementation of the embodiments and use of the optical pre-positioning error detection system.

With reference initially to Figures 1a and 1b, we will describe the different parts of the installation and, specifically, the lower portion of this facility to support the lower plate and, somehow, the circuit printed.

In Figure 1, there can be seen the lower fixed frame of the machine referenced 10 and the lower plate support 12. The lower support 12 is constituted by a rectangular metal frame 14 on which is fixed a mirror 16, on ice which actually rests below the plate.

Preferably, in the exposure system, the lower plate support 12 rests directly on the upper face of the frame 10. To enable movement of the support 12, the latter is resting on the frame 10 via systems ball schematically at 18. in the particular example, the Bracketing is done through four balls arranged on four sides of the frame 14. This ball system to be described later in more detail allows to mechanically support all the lower support by the frame while ensuring Bracketing with an extremely reduced friction. We understand that with this arrangement, the effort that will be required to move the lower bracket 14 will be very reduced, which will reduce accordingly the power and therefore the size of the motors used for making the trip.

In this figure, there is also shown schematically the devices 20 and 22 moving respectively in X and XY of the lower support 12. As already explained, the displacement tables which are integral with the frame 10 do not conduct according to Bracketing and simply used to move the holder relative to the frame, being added that the friction between these two parts being very reduced and due to the presence of the beads, the energy required is reduced. Figure la, there is also shown schematically electromagnetic brakes or similar braking system 24. The braking system 24 regularly distributed over the frame 14 for ensuring the immobilization of the frame 14 and therefore of the whole of the bottom support plate 12 with respect to frame 10 when correct positioning has been achieved. These braking devices 24 are made necessary due to the frictionless connection between the frame and the lower support and the fact of the very low engine power used to achieve the displacement tables 20 and 22.

Finally, Figure 1a shows schematically two sets of immobilization of the printed circuit relative to the lower frame 10. These sets are referenced 26 and 28.

The upper part of the machine is constituted in exactly the same manner except that the lower frame 10 is stationary, both in a horizontal and in a vertical plane, while, of course, the upper frame is stationary in a horizontal plane but mobile in a vertical plane to allow the application of the upper plate on the circuit board and the bottom plate. so we do not describe in detail the upper part of the machine.

1b shows in vertical section and schematically the entire exposure system. Include the fixed lower frame 10 on which the lower support 12 for receiving the lower plate 12a. This figure also shows the upper frame 30 which is supported through mechanisms such as 32 rack and pinion systems to raise and lower the entire upper frame 30. Furthermore, it is well built 30 on fixed in a horizontal plane. On the upper frame 30, is mounted the upper support 32 identical to the lower support 12, for receiving the upper plate 32a. In Figure 1b shows schematically the displacement motors in X and XY referenced 34 and 36 which control the movement of the support 32 relative to the upper frame 30.

now we understand the general operation of the exposure apparatus of the invention:

At first, the upper frame 30 being removed and plates 12a and 32a being set up, we just have between supports 12 and 32 to expose the PCB. The circuit board is present before using immobilization devices 26 and 28. Using the unrepresented optical systems are measured pre-positioning errors of the lower support 12 and the upper support 32 relative to the printed circuit . The remaining stationary printed circuit, is controlled by means of motors 20, 22 and 34, 36 suitable movements of the upper support 32 and lower support 12 in order to obtain alignment of the three elements or, as appropriate, an alignment the upper support 32 with the upper side of the PCB and the lower support 12 with the underside of the printed circuit.

Referring now to Figure 2, there will be described a first embodiment of the immobilizer, for example, the device 26. In this first embodiment, the immobilization is performed by pinching-off of an edge 40a the printed circuit board 40. the clamping device consists essentially of a first part 42 which is integral with the lower frame 10 and by a second part 44 which is integral with the upper frame 30. the parts 42 and 44 are movable vertically relative to the frames respectively 10 and 30. the parts 42 and 44 terminate in a planar clamping face 46 and 47 intended to be applied on the faces of the circuit board 40. the lower part 42 is provided with a rod 49 movable in vertical translation, which ends in a tip 48. in the rest position, the tip 48 is recessed relative to the face 46, but, with the aid of a displacement system 50, the tip 48 can protrude from the face 46.

When the positioning phase of the upper and lower supports of the exposure system, the tip 48 protrudes out of the room 42. After positioning of the printed circuit 40 by reference to pre-defined markers, the workpiece 44 is lowered so that the edge 40a of the circuit board 40 is caught between the face 47 of the part 44 and the tip 48. Thus, the printed circuit is perfectly immobilized at this point and over a very small area corresponding to the tip 48 . in addition, the tip 48 projecting from the surface 46 which is flush with the upper face of the crystal 16, the circuit board is raised at least at its periphery, allowing the displacement of crystal 16 in relation to printed circuit board. Of course, to allow the effective clamping of the circuit board 40, the ends of parts 42 and 44 pass through holes 52 and 54 formed respectively in the lower 16 and upper wipers 16 '. These orifices 52 and 54 have a sufficient diameter to allow the movement of the supports 14 and 14 'in order to achieve alignment. The cooperation of the two fastening devices 26 and 28 helps maintain rigorously in place the printed circuit board 40 relative to the installation frame.

Referring now to Figures 3 and 4, we shall describe a second embodiment of the fixing device which then carries the reference 26 '. This immobilizer is based on introducing into a hole 60 of the printed circuit 40 with an immobilization finger 62. The finger 62 is mounted displaceable in the vertical direction with respect to a part 64 integral with the lower frame 10. the immobilizing pin 62 is thus movable vertically but immovable in a horizontal plane. By penetration of the end of finger 62 in the hole 60, is therefore obtained immobilization of the corresponding portion of the circuit board 40 relative to the lower frame. For the motion of the circuit, it is necessary to lay along the edge 40a of the printed three immobilizers circuit, such as 26 ', these three devices are not aligned.

Figure 4 shows a preferred embodiment of the finger 62 of immobilization. The body of the finger 62 is extended by an expandable portion 64 by deforming the set of expandable portions 64 forming the tip of the immobilizing finger. In addition, the shoulder 62a allows the temporary lifting of the edge of the printed circuit to permit movement of the lower support. Inside the finger 62 can be moved an expansion rod 66 which terminates in a head 68. When the head 68 is in the upper position, is carried out the expansion of the end portions 64 of the finger and therefore a rigorous immobilization this part of the printed circuit, even if the orifice 60 of immobilization is not perfectly calibrated.

It is understood that the embodiments of the immobilization means of Figures 2 and 3 can produce the same result. However, in the case of Figure 2, since it is not necessary to provide a close orifice edge of the printed circuit, the non-useful lateral region of the printed circuit can be reduced to a dimension of the order 8 mm. In contrast, in the case of the embodiment of Figure 3, due to the presence of the orifice, this not useful lateral zone is necessarily somewhat larger.

It must be added that through these systems restraining the printed circuit, positioning the circuit is maintained rigorously during phases of displacement of the lower support 12. Indeed, both the immobilization fingers 62 that parts pinch 42 and 44 are themselves motionless, no bending stress can be induced them not.

Referring now to Figure 5, there will be described an embodiment of the device 24 for securing the lower frame 10 with the frame 14 of the lower support 12. Identical devices would be useful in making the attachment of the upper support 32 with the frame top 30. the immobilizer system consists essentially of an electromagnetic head 70 which, when activated, interacts with a ferromagnetic plate 72 secured to the underside of the frame 14 of the lower bracket 12. by activating the magnetic head 70, a fastening is obtained between the lower frame 10 and the lower support 12. the electromagnetic head 70 is mounted via an elastic system 74 and a ball 76. These fastening devices system can maintain the rigorous positioning upper and lower supports during lowering of the upper support for making contact between the two plates and the faces of the printed circuit 40.

Electromagnetic devices which have just been described are advantageous securing means. However, for the securing of the support on the frame, could also be used in pressure systems or of systems of art suction.

Referring now to Figure 6, we will describe one embodiment beads Bracketing Bracketing or 18 for the sustenance of the support relative to the respectively upper and lower frames. 6 illustrates a lifting device 18 connecting the frame 14 'of the upper bracket 12 at the upper frame 30. The ball bearing device is essentially constituted by a metal ball 80 can swivel mounted in a cage 82. The cage 82 is connected by a caliper 84 system 14 'of the upper bracket. For this, the arms 86 and 88 of the bracket through the frame 30 through holes such as 90. To ensure better working and thus further reduce friction, the ball 80 engages a bearing surface 92 secured to the upper face the frame 30.

Bracketing in the case of the frame of the lower support by the frame, we have the same system ball but whose axis is inverted so that the cage 82 of the ball 80 is secured to the lower frame 10 and the ball cooperates with the underside of the frame 14 of the lower support 12. the Bracketing the scope of artwork support could also be performed by devices by air cushion.

Referring now to Figure 7, we will describe a preferred embodiment of the moving devices 20 and 22 or 34 and 36 for the final positioning of each support relative to the corresponding frame. In FIG 7, there is for example shown the displacement device 22 allowing movement in X and Y of the lower holder 12. Similar movement systems are used in association with the upper frame 30. The system 32 has a displacement housing 100 which is integral with the frame 10. for each displacement in X or Y, there is a motor, for example 102 secured to the frame 100. This engine has its shaft 104 which terminates in a cam 106 for moving a first table 108 in direction X. a second table 110 cooperating with the first and associated with a second motor, secured to the first table and not shown in the figure, controls the movement in the direction Y. as a mechanical reference 112, 114, combined displacement in X and Y is applied to the part 18 that defines a gauged vertical bore 118a. A vertical pin 116 secured to the frame 14 penetrates freely into the bore 118 in the vertical direction but in the horizontal plane, the play between the parts is very small but loosely. Could also be provided that the pin is integral with the second table and the vertical bore is made in the frame 14 of the support.