FR2683087A1 - Method of producing a capacitor with non-encapsulated layers - Google Patents

Abstract

The invention relates to a method of producing capacitors with non-encapsulated layers fabricated by cutting out a parent capacitor produced by stacking metallised plastic films, the said method including the deposition of a protective layer on the faces of cuttings (8) for the said capacitors, characterised in that the protective layer is deposited with the aid of a pad (3). The invention applies to capacitors intended for surface mounting.

Description

METHOD FOR PRODUCING NON-LAYERED CAPACITOR
ENCAPSULE.

 The present invention relates to a non-encapsulated layer capacitor. This capacitor is in the form of a chip and is intended to be used for surface mounting.

 The manufacture of capacitors with non-encapsulated layers from metallized plastic films is known.

 Plastic films are generally used comprising a metallized zone and a non-metallized lateral margin.

 Two films are superimposed, their non-metallized lateral margins being on opposite sides in order to obtain a pair of films consisting of a film of even rank and a film of odd rank. At least one pair of metallized films is wound on a large diameter wheel according to a determined number of turns. A capacitive strip is thus obtained comprising layers of alternating even and odd rank, called mother capacitor. Each side of the capacitive strip is then covered with a metal (or alloy) in order to produce outlet reinforcements.

Each outlet reinforcement makes it possible to mechanically and electrically link together the metallizations of the layers of the same rank. This operation, carried out by spraying molten metal, is known under the name of shooping. Finally, we cut the capacitive ribbon or mother capacitor into elementary capacitors. Each of the elementary capacitors thus manufactured constitutes a non-encapsulated layer capacitor.

 These capacitors are intended to be used for surface mounting on circuits.

 During this assembly, the capacitors are, first of all, immersed in an aggressive flow in order to clean the shooping surface before passing to the wave. Secondly, the wave soldering operation takes place during which the capacitors are immersed in a bath of molten metal at 260 ° C. for approximately 10 seconds. For such an operation, the dielectric used to produce the plastic films constituting the capacitors must therefore have thermo-mechanical characteristics allowing it to withstand, for ten seconds, the temperature of 260 "C without deterioration.

 The dielectric used can therefore be, for example, polyethylene naphthalene (PEN).

 During these operations, there may be a surface deterioration of the films on the cutting faces of the capacitors if these are not protected.

 On the one hand, the aggressive flux can penetrate between the metallized sheets constituting the capacitor and thus corrode the metal covering the plastic films; on the other hand, the molten metal at 260 "C in which the capacitors are immersed can come to hang on the cutting faces, thus creating an electrical contact between sheets intended to be brought to different potentials.

 In order to overcome these drawbacks, it is known to those skilled in the art various techniques for protecting the cutting faces.

 One of the techniques used is, for example, the deposition of resin on these faces. This resin must not deteriorate at 260 "C. It can be either an epoxy resin, an acrylate resin, or a mixture of epoxy resin and polyurethane. It can be polymerized by ultraviolet flash or thermally. Flash polymerization ultraviolet is preferable because it is very fast.

 According to the European patent published under No. 0 355 182 A1, the capacitors are immersed, after the saw cutting operation, in epoxy resin liquid at high temperature.

 With this method, once the resin has hardened, it is necessary to remove by various mechanical or chemical means the layer of resin which is deposited on the armatures of the capacitors.

 The invention does not have this drawback.

 The present invention relates to a method of depositing a protective layer on the cutting faces of capacitors with non-encapsulated layers, characterized in that the protective layer is deposited by pad printing.

 An advantage of the invention therefore lies in the fact that the protective layer is applied only to the places where it is necessary to apply it.

Other characteristics and advantages of the invention will appear on reading a preferred embodiment, made with reference to the attached figures in which:
- Figure 1 describes the method according to the invention.

 - Figure 2 shows a perspective view of a capacitor according to the invention.

 In the two figures, the same references designate the same elements.

 FIG. 1 describes the method according to the invention. This process makes it possible to deposit a protective substance simultaneously on the cutting faces of N capacitors.

 A matrix 1 consists of N cells 2, each of which contains the substance intended to produce the protective layer. According to the preferred embodiment, this substance is a resin, for example one of those mentioned above. However, a varnish could just as easily be used.

 In Figure 1, only 4 cells have been shown for convenience. The number N can actually reach the value 1000.

The opening of each cell, square or rectangular, has dimensions identical to those of the cutting faces of the capacitors.

 A Schmid pad 3 is brought into contact with the matrix 1 so that its resin impregnation takes place in well-defined zones. The pad 3 is then applied to one half of the cutting faces 8 of N capacitors.

 The N capacitors are arranged in a mold 4. The arrangement of the capacitors is identical to that occupied by the cells 2 of the matrix 1. Thus, by bringing the pad impregnated with resin into contact with the cutting faces of the capacitors can we deposit resin exactly on the cutting faces. To this end, the guiding of the buffer between the die 1 and the mold 2 must be carried out with precision.

 An advantage of the invention lies in the fact that the resin cannot overflow either on the frames or on the other 2 faces perpendicular to the cutting faces, which makes it possible to avoid having to clean said frames and said faces.

 The resin is then polymerized either by ultraviolet flash, or thermally.

 A stroke of the pad results in a resin thickness of the order of 0.05 mm.

 Another advantage of the invention is to be able to control the thickness of the resin deposited. It then suffices to repeat the operation described above until the desired thickness is obtained.

 According to the preferred embodiment of the invention, the capacitors can be arranged in the mold 4 so that the cutting faces open out on either side of said mold.

 Thus, once half of the cutting faces have been treated, the other half can be covered with resin after having rotated the mold 4 from 1800 with respect to the horizontal.

 The same operations are repeated as above until the desired deposit is obtained before proceeding to another mold.

 Figure 2 shows a perspective view of a capacitor according to the present invention.

 The capacitor 5 has two cutting faces 8 covered with a protective layer 7, for example resin.

 Perpendicular to the cutting faces are the metal frames 6.

Claims (8)

 1. Method for producing capacitors with non-encapsulated layers (5) produced from the cutting of a mother capacitor produced by stacking metallized plastic films, said method comprising the deposition of a protective layer (7) on the faces cutting (8) of said capacitors, characterized in that the protective layer is deposited using a pad (3).  2. Method according to claim 1, characterized in that the pad (3) is brought into contact with a matrix (1) comprising cells (2) filled with the substance intended to produce the protective layer (7) so that the impregnation of said buffer takes place in well-defined zones.  3. Method according to claim 2, characterized in that each impregnation zone of the buffer (3) comes to be applied entirely and exactly on a cutting face (8) of the capacitor.  4. Method according to any one of the preceding claims, characterized in that the protective layer (7) is a resin.  5. Method according to claim 4, characterized in that the resin is an epoxy resin, an acrylate resin or a mixture of epoxy resin and polyurethane.  6. Method according to any one of claims 1 to 3, characterized in that the protective layer (7) is a varnish.  7. Non-encapsulated layer capacitor (5), characterized in that it is obtained by a method according to any one of the preceding claims.  8. Capacitor according to claim 7, characterized in that the dielectric constituting the metallized plastic film is polyethylene naphthalene (PEN).