FR2845858A1 - Printed circuit open zone filling technique having filling product passing substrate surface and filling surface area accompanied product front air circulation extraction chamber. - Google Patents

Abstract

The open zone (7) filling technique for aspect ratios lower than 1 has a substrate surface (1) and a filling product (2). The filling is accompanied by generation of air circulation in an extraction chamber (8) in front of the filling product.

Description

DEVICE FOR FILLING OPEN AREAS LOCATED IN A HOLLOW RELATIVE TO

A SURFACE

APPLICATION DOMAIN

  The present invention relates to a device for filling areas 5 open or having an aspect ratio of less than 1 and located in hollow relative to a surface, with a viscous product. The aspect ratio is defined by the depth of the area to be filled relative to the surface, divided by the smallest dimension of the opening considered. By way of example, it finds its application for the production of printed circuits. Indeed, there are applications for which substrates 10 comprising conductive tracks for example of copper and having a thickness

  greater than 100 microns (typically of the order of 400 microns) are used. In these applications, it is necessary to fill the inter-track zones with a dielectric product, this filling having to be complete and free of bubbles in order to obtain the optimum electrical characteristics. In addition, the inter-track zones are not closed.

PRIOR STATE OF THE ART

  To carry out this filling, a person skilled in the art uses techniques at his disposal, namely: - roller coating,

  - screen printing using a doctor blade or a closed device.

  The problems with the devices of the prior art are twofold - the first lies in the fact that in certain areas located in the hollow, the air remains trapped and prevents the product from filling them completely (cushion effect). To overcome this problem, it is necessary to make multiple passages in both directions of scraping in order to obtain sufficient filling, obviously these multiple passages

  generate cycle times incompatible with mass production.

  - the second is linked to the fact that the product is entrained by the scraping element, which tends to dig deposits, particularly if they are large or if the

  drawings are parallel to the scraping direction.

  Devices intended to fill blind holes have been proposed in the past, for example in patent application PCT / FROO.03494 from the same inventor. This technique consists in moving two slots on the surface of the substrate to be filled. The first slot is connected to a vacuum generator while the second contains the filling product. The first slot is both distant from the outside and from the second slot by a distance greater than the largest opening present on the substrate, the distance being measured parallel to the direction of movement. In this case, the device must be in sealed contact with the substrate, otherwise the blind hole cannot be filled completely. This technique is only applicable to blind cavities whose perimeter on the surface of

  filling represents a closed area.

DESCRIPTION OF THE INVENTION

  The present invention aims to fill areas located in open hollow or having an aspect ratio, defined by the depth of the area relative to the area divided by the smallest opening dimension, less than 1, such as areas located between copper tracks. The filling of the zones is done by submitting to a vacuum, to the filling product and to a scraping. The difficulty in filling these 15 zones is linked to the fact that it is impossible to ensure a seal between a device in

  relative movement on the surface and the substrate due to the fact that the zones are open.

  According to a first characteristic of the invention, at the front of the filling product, a chamber is formed in which a circulation is generated by extracting the air using a means having a higher flow rate. at the leak rate, the leak rate being the air flow which enters the chamber at the front and on the sides.

  Thus the circulation and the flow differential creates a vacuum in the chamber. Preferably, an extraction device will be chosen having a flow rate at least greater than twice the maximum leakage flow rate. The leakage rate is related to the open section which connects the exterior of the device and the chamber 25 in which the vacuum prevails. For example, to obtain a level of depression of the order of 15% in a room, it is necessary to extract 0.11 liters per second of air from this room per square millimeter of leakage. For electronic card applications of 400 millimeters in length and having tracks of thickness 400 microns, the overall leakage section is typically of the order of 20 mm2. It is therefore essential to create an air circulation using an extraction means at the front of the filling product to compensate for the leakage rate, the means will be chosen.

  extraction so as to favor the flow rather than the high vacuum.

  According to another characteristic, the level of vacuum necessary for proper filling is low. A maximum level of less than 50% depression gives good results. On the other hand, the low vacuum level makes it possible on the one hand to avoid excessive plating of the device on the substrate and therefore to limit the forces necessary in advance of the device and on the other hand to avoid re - suck air at the back of the device according to the direction of advance. Finally this level of depression also allows

  avoid sucking product into the extraction and air circulation means.

  According to another characteristic of the invention, the device comprises a chamber which is connected to a means for circulating air by extraction having a flow rate greater than the flow of air (d) drawn from the outside by this chamber and a tank which contains filling product. A scraping element is located at the rear of the filling product relative to the direction of movement of the device. When the device is moved over the surface of the substrate, the areas to be filled first see the chamber, then the reservoir, then the scraping element. Advantageously, the means for circulating and extracting air consists of an air amplifier. By way of example, an amplifier of the M20C type from the company COVAL makes it possible to obtain a potential extraction flow rate of 700 Nl / min for an actual consumption of around 200 NI / min. The maximum depression thus obtained is 5%. It should be noted that the level of vacuum necessary for proper filling is also a function of the viscosity of the filling product. For this purpose, we will choose a higher level of depression

when the viscosity increases.

  According to another characteristic of the invention, the device can operate in both directions by designing it symmetrically with respect to the reservoir containing the product so that it can be used on a screen printing machine.

  According to another characteristic of the invention, a scraper element is disposed at the rear in the direction of movement so as to scrape off the excess product which is coated on the surface of the product and so as to level the filling product. with the surface of the substrate, avoiding digging deposits. This scraping element can be produced directly by the body of the device, but preferably it is constituted by a polyurethane profile such as those used by screen printers and known to those skilled in the art. To the extreme and to avoid digging deposits in areas of

  large dimension, the scraping element may consist of a metal blade.

  According to another characteristic, the device according to the invention has a length greater than or equal to the length of the substrate to be filled. Advantageously, the device according to the invention can be adapted on a screen printing machine.

  Other characteristics will appear in the light of the attached figures and their following description.

  Figure 1 shows a first embodiment of the present invention.

  Figure 2 shows a second embodiment of the present invention.

  FIG. 3 represents a type of substrate to be filled. FIG. 4 shows the variations in vacuum inside the device during a filling operation.

  In Figure 1, a device (4) according to the invention is shown in working mode. The device (4) is moved relative to the substrate (1) in the direction (F). As the movement progresses, the zones (7) to be filled are subjected to a vacuum which prevails in the chamber (8) then to the filling product (2) and finally to a scraping element (5). The areas to be filled (7) here consist of the space between copper tracks (3), so the area to be filled can at the same time be in contact with the outside, the chamber (8) and the product of filling (2). The vacuum Pi in front of the viscous filling product (2) is obtained by means of an air circulation and extraction means (6) having a flow rate greater than the leakage flow rate (d). This difference in flow rate makes it possible to obtain a low level of depression which is less than 50% sufficient to allow complete filling of the zones situated in the hollow. This method of obtaining vacuum makes it possible to maintain a relatively stable level of vacuum despite a leakage rate which varies greatly depending on the areas to be filled encountered. When the device advances, the adhesion of the viscous product to the substrate generates an overpressure P2 in the product. It therefore suffices to comply with Pi + P2 greater than P3, P3 30 being the pressure prevailing inside the device to prevent air from being sucked in from the rear of the device. The device is supplied with product as and when

  measurement of consumption, by any means known and not shown.

  In Figure 2 is shown another embodiment of the present invention. In this case, the product is kept apart from the chamber (8) by a wall (9). This arrangement makes supplying the device with product simpler since it is not necessary to maintain a precise level, it suffices to guarantee a minimum volume s of product in the reservoir.

  As can be seen, the devices shown are symmetrical and can therefore operate in the direction (F), but also in the opposite direction.

  FIG. 3 schematically represents a printed circuit (1) on which an operation of filling the zones (7) between the copper tracks (3) must be carried out. It can be seen in the top view at (3a) that the zones (7) are open, which prevents the possibility of sealing between the device and the substrate when said device is moved in the direction F. In the view in section (3b), one can appreciate the extra thickness generated by the copper tracks (3), which is typically of the order of 400 microns for this type of application. The leakage rate at an instant t is proportional to the sum of the areas of the zones (7) between the copper tracks (3)

  encountered by the device at time t.

  FIG. 4 shows how the level of vacuum can vary as a function of the variation in the leakage rate encountered according to the movement F of the device on the substrate. In the case shown, the maximum vacuum attainable by the extraction means 20 when the leak is zero is 10%, the maximum leak encountered on this

  substrate leads to a minimum depression of 5%. The object of the invention is therefore to create a dynamic regime of air circulation in front of the filling product and thanks to the differential between the potential extraction flow rate and the leakage flow rate representing the air admitted into the chamber of the device. a minimum vacuum is maintained in front of said filling product.

  Since the vacuum in the device according to the present invention is low and that the filling product can be very viscous, it is advisable to subject the product to a transfer pressure so as to push the product into the openings of the substrate. This transfer pressure can be generated by pressurizing the filling product by means not shown, or else and preferably it is obtained by imparting an angle of less than 900 to the wall of the device located behind the filling product. relative to the surface of the substrate. To limit the leakage rate and thus obtain a higher level of vacuum for the same air extraction means, it may be advisable to increase the width of the front wall of the device (4). So, we create baffles at the front of the

  device, which generates a pressure drop which reduces leakage (d).

Claims (6)

claims:   1) Method for filling open areas (7) or having an aspect ratio of less than 1 and located in hollow relative to a surface of a substrate (1) with a filling product (2) characterized in that an air circulation is generated in a chamber (8) by extracting the air at the front of the filling product 5 according to the direction of advance and that the extraction rate is greater than the leak rate and qu '' a scraping is carried out on the back of the filling product in the direction of advance of the device (4).   2) A method of filling open areas (7) or having an aspect ratio of less than 1 and located recessed relative to a surface of a substrate (1) 10 with a filling product (2) according to claim 1 , characterized in that the   filling product is subjected to transfer pressure.   3) Device (4) for filling areas (7) which are open or have an aspect ratio of less than 1 and which are recessed relative to a surface of a substrate (1) with a filling product (2), characterized in that it comprises: - at the front of the filling product in the direction of advance of the device, a chamber (8) connected to a means for circulating and extracting air (6) having a flow rate greater than the leakage flow rate between said chamber and the outside, - at the rear of the filling product in the direction of advance of the device, an element scraping (5).   4) Device (4) for filling areas (7) open or having an aspect ratio of less than 1 and located in hollow relative to a surface of a substrate (1) with a filling product (2), according to claim 3, characterized in that a wall (9) is interposed between the chamber (8) in which the depression prevails and   the tank in which is the filling product.   5) Device (4) for filling open areas (7) or having a   aspect ratio less than 1 and located recessed relative to a surface of a substrate (1) with a filling product (2), according to claim 3, characterized in that the device (4) is symmetrical with respect to to the reservoir containing the product (2) so as to be able to operate in both directions and be implemented on a screen printing machine 30.   6) Device (4) for filling areas (7) open or having an aspect ratio of less than 1 and located in a hollow relative to a surface of a substrate   (1) with a filling product (2), according to claim 3, characterized in that the circulation means by air extraction (6) consists of an air amplifier.