CS213532B1 - A method of casting electronic components in a casting mold or housing - Google Patents

Abstract

The invention relates to a method of potting electronic components and circuits in a mold or casing and solves the problem of using electrically insulating lacquers for potting these components. The essence of the invention is to fill the casing (casing) or casting mold with glass microspheres or thermoplastic granules so that the created cavities have a maximum dimension smaller than the thickness of the boundary gap for the polymerization of the lacquer and this space is filled with electrically insulating lacquer, which is subsequently hardened.

Description

The invention relates to a method for potting electronically, in particular semiconductor components, in a mold or a housing.

Light-current components and circuits, especially semiconductors such as transistors, diodes, thyristors, bridge circuits, thin-film circuits, integrated resets and the like. are very often encapsulated in plastics, generally epoxy, silicone, epoxy silicone, phenolformaldohydride, polyurethane, and others, which are processed as casting / salivaol / molding or molding materials for these facials. Many materials are suitable for large-scale products of smaller, simpler shape or circuitry, and have therefore achieved considerable use in the manufacture of, for example, integrated circuits. Due to their composition, the molding and casting materials have adhered to each other not to differ the molding compositions, since they usually contained the filler content and therefore the moldings have a lower linear expansion compared to the castings. Casting materials have better adhesion to metal outlets and the like because they do not contain an internal separator contained in the molding materials for easy removal of the moldings from the mold while for the molding materials and only uses an external eeparator eg silicone paste applied to the mold surface. ee the mold does not become an integral part of the casting · This is the so-called encapsulation by sheath casting »the token of the final product and its dimensions also correspond to the dimensions of the product. Depending on the component type, the outer skin may be made of different materials, may be metal, molded from thermoplastic, or thermosetting plastic, and the like. The advantage of the casing casting over the conventional casting method is that the outer shape of the parts so produced is more perfect. One of the problems in encapsulation by casting from the sheath is sometimes poor adhesion of the resin to the sheath. It is necessary to carry out the watering under vacuum in order to remove bubbles and fumes in the casting, using the centrifugal casting technique. Typically, the poured mixture is degassed before casting and then after casting in the form or after casting. in a coat. E.g. The epoxy resins are generally treated at a pressure of less than 13 cc. Problems with encapsulation in the compositions arise from the admixture of the individual components, since they are usually multi-component systems, so that they are difficult to measure with the homogenization of the mixture because, for example, some fillers tend to dissipate in the mixture.

Similar compositions and properties · such as make-up or silicone compositions 1 have some electro-insulating varnishes, e.g. molding epoxides, like silicones, polyurothanes, phenol formaldehydes and tp. Sometimes due to various modifications and combinations of different polymer components, ee preferably achieves properties of e.g. better adhesion, better flexibility, lower shrinkage, better elongated properties and the like. However, they are not usable for the production of castings, either because they are solvent system and evaporation of solvent and polymerization would disproportionately increase cure times, or because the two-component solvent-free paints release large exothermic heat with the polymerol, so that it can be used to apply thin protective layers e.g. for PCB protection.

The present invention overcomes these disadvantages and solves the problem essentially by having the liol form adherent. the casing is filled with glass microspheres, the cavities therebetween having a dimension smaller than the thickness of the boundary layer for the polymerization of the electroinsulating varnish. The cavities thus formed are coated with an electrolytic lacquer which is cured.

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An advantage of the method of embedding the electronic components in the casting mold or sleeve according to the invention is, in particular, that there are no problems with the evacuation of the casting mixtures and their homogenization! the castings produced in the above manner are sufficiently homogeneous and free of bubbles and pores. There are 1 systems which do not require elevated polymerization temperatures, but polymerize in a controlled manner only at lower temperatures and in thin layers.

To fill the lychee mold or sleeve, glass microspheres (glass beads) and / or glass beads are used. the thermoplastic granules of suitable size optionally select the ratio of the microspheres of different diameters. Then it is possible to reach the ninetieth. percent filled space. The backfill is filled with a suitable electrolytic lacquer to fill the cavities.

The curing time and temperature and the casting pressure depend on the nature of the lacquer and the casting height. Coatings capable of being polymerized in a layer, e.g., 1 mm thick, can be used to produce single-cast castings having a height of approximately 10 times larger, i.e., 1 cm.

Components or circuits 2 to 3 m high, and most of them in practice, can be encapsulated in two to three pots.

When using thermoplastic granules as a filler, it is sometimes advantageous to use solvent type lacquers with a solvent which, prior to evaporation and polymerization of the lacquer, etch the surface of the thermoplastic granules so as to form a compact assembly of thermoplastic and lacquer; it is in fact an encapsulation of a thermoplastic and a lacquer of a thermoplastic lacquer.

example 1

The inner space of the semiconductor bridging circuit formed by a 2 cm high epoxy resin molding and attached eg with an epoxy adhesive to a metal base is filled halfway with 0.125 nm glass microspheres and sealed with a solution of acrylic lacquer in toluene to fill all cavities between mlkrokuličkami.

After evaporating toluene and curing the lacquer, which lasts at 20 ° C for 24 hours, the whole process is repeated.

Example 2

The interior of the housing of the semiconductor bridging circuit is filled with granules of thermoplastic, for example polypropylene, and sealed with a solution of sillconacoxylate lacquer in toluene. After evaporating the toluene and polymerizing the lacquer, the casing is topped up with the lacquer.

Example 3

The interior of the housing of the semiconductor bridging circuit is filled with glass microspheres and sealed with a solution of acrylic lacquer in toluene. The component is then placed in a vacuum oven at a pressure of 13.3 kPa and at 60 DEG C. the lacquer has cured in 6 hours.

Claims (3)

A method for casting electronic components in a casting mold or casing, characterized in that the casting mold or casing is filled with glass microspheres, wherein the cavities therebetween have a maximum dimension less than the thickness of the boundary layer for the polymerization of the electro-insulating lacquer. after which the electro-insulating varnish cures. 2. Method of embedding of electronic components according to claim 1, characterized by t The casting mold, if any, is filled with thermoplastic granules. Method for potting electronic components according to Claims 1 and 2, characterized in that the cavities between the glass microspheres or granules of thermoplastic with an electroinsulating lacquer in at least two portions. 4. Method of potting of electronic components according to claim 3, characterized in that after the cavities are filled with each batch of electroinsulating varnish, the varnish is hardened.