GB2074475A - Process of coating an electric component built into a casing, with a sealing coating - Google Patents

Abstract

A relay built into a casing (2,4) has two rows of electric terminals (5) projecting, which are covered by two adhesive tapes (17) during dipping the relay into a liquid covering material to seal the casing particularly where the terminals (5) pass through the casing. The tape is used in a continuous process and is removed afterwards. <IMAGE>

Description

SPECIFICATION Process of coating an electric component built into a casing, with a sealing coating The invention relates to a process of coating an electric component built into a casing and comprising at least one row of electric terminals projecting out of the casing, with a sealing coating by way of being dipped into the liquid coating material.

For mechanical protection purposes, an electric component is in many cases built into a casing from which the electric terminals project in at least one row. To these, there belong in particular electromechanical components, such as relays. Such components are mostly soldered directly into the holes of a printed circuit board, with not only the printed conductor boards themselves, but also the individual components being dipped at least partially into soldering and cleansing baths. In so doing, there is a certain danger that liquid or gaseous substances enter into the interiorthrough holes or gaps in the casing where they are likely to have detrimental effects upon the built-in electric component.

Thus, for example, in the case of relays, the contacting points are likely to become contaminated. The contaminations enter either through the gaps between the individual parts of a multi-part casing or else at the points where the electric terminals are led through the bottom of the casing where, owing to the different thermal expansion coefficient of the casing material and of the material of the terminals, there are often formed fine interspaces.

By taking various steps, it has already been tried to make such electric components wash-proof.

Thus, for example, attempts have been made to close the leakage points by way of a thermoplastic deformation of the casing parts with the aid of ultrasonic waves or heated plugs. It has also already been tried to encapsulate the casing in a plastics compound. These conventional processes, however, involve a considerable investment in working time and material.

It is also already known to place a thermoplastic body of insulating material in the form of either a foil or a trough with tight-fitting recesses on to the terminal pins (DE-AS 2 129 918). The foils placed thereon, however, become deformed owing to temperature effects, and do not result in a sufficient sealing.

Finally, an absorptive covering layer has also already been placed on to the electric terminals, with the latter having been saturated with a thinly liquid sealing compound (DE-AS 2 616 299).

This conventional process, however, not only required the use of an additional material apart from the sealing compound, but the covering layer must also be cut exactly to size and results in an enlargement of the dimensions of the component.

Actually, a wash proof sealing of the casings of electric components can be obtained in a simple way in that the casing is coated with a thin layer of a sealing compound, such as a lacquer. In the most simple way, such a coating is obtained by dipping the casing into the liquid coating material. This actually simple and effective process, however, has the disadvantage that the coating material also is applied to the terminals of the component from which it has to be removed again. Removal of the coating material from the electric terminals, however, is so expensive that the simple dipping process has hitherto not been used in practice.

According to the present invention, there is provided a process of coating an electric component built into a casing and comprising at least one row of electric terminals projecting out of the casing, comprising dipping the component into a liquid coating material to provide a sealing coating, wherein prior to dipping the electric terminals are covered with an easily removable covering means.

Preferably, as an easily removable covering means there is used a tape provided with an adhesive layer, which is pressed on to the terminals prior to the dipping process, and is removed from the terminals afterthe dipping process has been carried out.

It is of particular advantage to enclose the electric terminals as arranged in one row, on both sides by two oppositely arranged adhesive tapes.

In order to obtain a good sealing around the terminals which may be designed either as round metal pins or wires but also as such ones having a square or rectangular cross section, the adhesive tapes are appropriately pressed against the terminals with the aid of rollers made of a flexible material. In this way it is safeguarded that no interspace remains free between the adhesive tapes and the terminals, into which the coating material would be likely to penetrate.

In order to ensure in any case that the terminals are completely surrounded by the adhesive tapes, it is of advantage to choose the adhesive layer to have such a thickness as to correspond at least to half the diameter of the terminals. Relative thereto, the adhesive tapes do not need to be completely pressed around the terminals, because these are alone embedded in the thick adhesive layer.

Preferably, there are used adhesive tapes with a width greater than the length of the electricterminals of the component, so that the adhesive tapes completely enclose the free ends of the terminals.

In the case of electric components whose terminals are partly exposed by lateral recesses in the bottom of the casing, the adhesive tapes can be arranged in such a way as to come close to the bottom of the casing, thus maing sure that the terminals are reliably covered up to the bottom (bearing surface) of the casing. By the lacquer penetrating into the recesses in the casing, the openings for the terminals are reliably sealed in a washproof manner.

The invention will now be explained in greater detail with reference to Figs. 1 to 6 of the accompanying drawings, in which: Fig. 1 schematically shows the application of the adhesive tapes for covering the electric terminals, Fig. 2 is a top view on to a component according to Fig. 1 shows the covered terminals, Fig. 3 is a side view and, Fig. 4 is a view from below showing electric components whose terminals are covered according to the invention, Fig. 5 shows one component with lateral recesses for the terminals in the casing, in a side view, and Fig. 6 is a section taken on line A-B of Fig. 5.

For tightly sealing the terminals of the component there are used preferably, as shown in Fig. 1, two adhesive tapes 6 and 9 of which each one consists of a baseband 7 or 10 and of an adhesive layer 8 or 11 respectively.

The base band may consist of paper or plastics material. The electric component, such as a relay, has a casing consisting of two halves 2 and 3, with the electric terminals 5 projecting therefrom in the shape of two parallel rows on the bottom of the casing. The adhesive tapes 6 and 7 are pulled off cor- responding supply reels and are guided, if necessary, by suitable pulleys. The two adhesive tapes 6 and 9 are then led between the two rollers 12 and 13 which are made of elastic material, such as rubber.

In addition thereto, the shafts 14 and 15 of the two rollers may be supported resiliently in such a way that the rollers are being pressed against one another. The one row of terminals 5, as in the case of Fig. 1, is now introduced from left to right, between the two adhesive tapes 6 and 9. By a suitable drive, the two rollers 12 and 13 are rotated in the direction as indicated by the arrows, in the course of which the adhesive tapes 6 and 7 are pressed against each other and stuck around the terminals 5. At the same time, and likewise in the case of Fig. 1, the component is further transported from left to right The two adhesive layers 8 and 11 are connected to one another on the right-hand side of the rollers 12 and 15 by enclosing the terminals between the double tape 17.

In the same way, the other row of terminals 5, i.e.

in the case of Fig. 1, the lower row, is enclosed between two adhesive tapes. By way of dipping, the component is now provided with a suitable coating of lacquer, and thereafter, the adhesive tapes are removed from the terminals by being pulled apart. In this simple way, electric components built into a casing, can be sealed in a completely washproof man ner without their dimensions being enlarged in any noteworthy manner. In the course of this, the sealing compound enters into the gaps between the two halves 2 and 3 of the casing, as well as into the interspaces which are likely to have been formed at the point between the terminal 5 and the casing. The viscosity of the dipping lacquer can be easily adjusted to make sure that the lacquer is prevented from entering into the interior of the casing.

Fig. 2 is a side view of the component with the terminals being covered. The casing consisting of two parts, of which the one half2 is shown in Fig. 2, is covered on the top side by a cover 4. Also the gap between the halves of the casing and the cover must be sealed. The terminals 5 are completely inserted between a double tape 17, i.e. in such a way that also the free ends of the terminals 5 are completely embedded in the double tape 17. This is accomp lished in that the adhesive tapes have a width grea terthanthe length of the terminals 5.

Of course, not only individual components are subjected to the covering process but, between the adhesive tapes, there are successively in the course of a continuous process, embedded the terminals of a great number of components. Thus, not only the embedding of the terminals of a great number of components can be carried out continuously, but also the dipping into the sealing compound and the removal of the adhesive tapesafterthe setting of the compound can be carried out in the course of a continuous process.

Fig. 3, in a side view, shows several components 1 whose terminals 5 are enclosed by a double tape 17.

Fig. 4 shows the same arrangement as is shown in Fig. 3 from below, with it being-evidentthattheter- minals of the components 1 are ensfosed between thetwo double tapes 17 and 1g.

Fig. 5 is the side view of a component whose cas ing.is provided with lateral recesses t9 at the points where the terminals 5 emerge.

Fig. 6 is a section taken throughsthe component on line A-D of Fig. 5. In the case of such components the terminals 5 can be covered completely. upto the bottom (bearing surface) of the casing, because the sealing compound, on account of the recesses 19, still effecta tight sealing at the points where the terminals emerge from the casing. No ridges of lacquer are caused to result on the bottom of the component around the terminals 5, so that no difficulties will be encountered even when the terminals have to be soldered into very thin printed circuit boards.

Claims (10)

1. Process of coating an electric component built into a casing and comprising at least one row of electric terminals projecting out of the casing, comprising dipping the component into a liquid coating material to provide a sealing coating, wherein prior to dipping the electric terminals are covered with an easily removable covering means.

2. A process as claimed in claim 1, wherein a tape provided with an adhesive layer is used as the covering means.

3. A process as claimed in claim 2, wherein said terminals are included between two oppositely arranged adhesive tapes.

4.. A process as claimed in claiin 3, wherein said adhesive tapes are pressed against said terminals with the aid of rollers of elastic material.

5. A Aprocess as claimed in any one of claims 2 to 4, wherein tapes with an adhesive layer are used, with the thickness of said adhesive layer correspond ihg to at least half the diameter of said terminals.

6. A process asolaimed.in any one of claims 2 to 5, wherein adhesive tapes are used whose width is greaterthan the length of the portions of the terminals of the components, as projecting out of the cas ing.

7. A process as claimed in any one of claims 2 to 6, wherein that in the case of electric components - whose terminals are partly exposed by a lateral recess on the bottom of the casing, the adhesive tapes are arranged in such a way as to come to lie close to the bottom of the casing.

8. A process as claimed in claim 2 or any claim as appended thereto, wherein the tape is used to carry several components sequentially through the dip ping process as a continuous manufacturing pro cess.

9. Aprocessofcoating an electric component substantially as hereinbefore described with reference to the accompanying drawings.

10. An electric component built into a casing and coated by a process according to any preceding claims.