Background of the Invention Microcircuits within electronic devices must be protected against static electricity because electrostatic discharges (ESD) may damage them.

Protection is particularly important, because the potentials required to cause damage are very low compared to the potentials a human being is able to create as frictional electricity. As frictional electricity, a human being easily creates potentials in the thousands of volts range (a human being is able to sense discharges that are in the range of at least 3000 volts) whereas dis- charges in the range of as little as ten volts may destroy the most sensitive circuits.

The damages caused by a discharge are difficult to repair because they are not perceptible to the eye and they do not necessarily show even when the microcircuit is tested. Consequently, the financial losses caused by electrostatic discharges are not limited to the cost of new components, but include the costs related to the locating and repairing of the damages. It has been estimated that the ESD damages to electronic devices, if assessed as above, are as high as 25 milliard Finnish marks per year.

Products that control and prevent electric discharges are based e. g. on charge prevention, use of protection (Faraday's shield), or grounding. As the present invention relates to how grounding is arranged, the following only examines grounding.

Grounding only works with electric conductors. When grounding is employed, all conductors are connected to a common point, which is in prac- tice constituted by the body of the rack, shelf, subrack or cabinet in which the circuit boards are located. One of the conductors to be grounded is the human body.

In practice, the best tool for grounding the human body when work is done in ESD sensitive areas is a wrist grounding strap. According to the pres- ent-day ESD recommendations, a dedicated and clearly marked connection

point for the wrist grounding strap must be arranged in the protected area. The connection must additionally be such that the connector used does not fit into any other connector system. Further, the connector must stay in place as securely as possible so that the chances of the wrist strap unintentionally disconnecting can be minimized. For the above reasons, the wrist grounding straps and electronic devices nowadays utilize mating snap connectors.

Figure 1 illustrates a wrist grounding strap and its use. The wrist grounding strap comprises a wrist part 11 which is placed on a worker's wrist, and whose inner part, at least, is of conductive material. The wrist part com- prises e. g. a snap connector part 12 by means of which a connecting lead 13 can securely be attached to the wrist part, the free end of the connecting lead further comprising a connector 14 for connecting it to the grounding point. The wrist straps additionally comprise a high-impedance (in the 1 megohm range) resistor placed e. g. inside the snap connector part. As the present invention does not relate to the structure of the wrist part and as the wrist part may be implemented as in prior art, the wrist part is not described in any greater detail here. Readers interested in various types of wrist parts are referred to U. S.

Patents 5,036,423 or 4,402,560 for a more detailed description.

As mentioned in the above, the connector at the free end of the con- necting lead is nowadays usually a (female) mating snap connector. This con- nector is attached to the mating connector part at the cartridge, rack, subrack or a similar body of an electronic device.

Figure 1 shows, as an electronic device of a part thereof, a telecom- munications device subrack to whose body part GB has been arranged a connector part 15 for the mating snap connector of the wrist grounding strap.

The subrack comprises, as in prior art, parallel card units BU containing inte- grated circuits IC. For the sake of simplicity, the figure only shows one card unit with its front connector FC.

The manufacturers of electronic devices make provisions for a wrist grounding strap provided with a mating snap connector by implementing the connector part 15 as in Figure 2, i. e. by attaching a separate (mating) metallic counterpart 20 of the snap connector 14, located at the free end of the con- necting lead 13, to the device body by means of a suitable attaching means such as a clench nail or a screw 21 (and nut 22). The body can also have threads for the screw fastening. One of the disadvantages of such grounding

connections is that they easily become loose, which results in that they cannot provide an efficient grounding.

A dedicated connection point made for the wrist grounding strap in the body of an electronic device will, for its part, produce additional steps to the assembly and additional load to the material management at the assembly stage.

Summary of the Invention It is an object of the present invention to eliminate the drawbacks de- scribed above and to obtain a grounding arrangement by means of which a proper grounding point for personal grounding can be implemented into an electronic device in a simpler and more economical way than previously.

This object is achieved with solutions disclosed in the independent claims.

The idea of the invention is to design a formed part to the body structure of the electronic device to act directly as the counterpart (i. e. the mating connector part) for the connector at the end of the connecting lead of the wrist grounding strap, without there being any need to attach a separate counterpart (connector) to the body structure. The formed part is thus inte- grated into the body structure and it protrudes from the plane of the body part either inward or outward (it may thus be either male or female). The formed part may also be made in a protruding part attached to the body part.

The solution according to the present invention provides the advan- tage that it is possible to simplify the material management related to assembly of electronic devices because parts required for grounding at the working stage can be omitted. This consequently leads to a smaller number of steps at the assembly stage of the devices, which results in a shorter assembly time.

Brief Description of the Drawings In the following, the invention and its preferred embodiments are de- scribed in closer detail with reference to Figures 3 and 4 in the examples of the attached drawings, in which Figure 1 illustrates use of the grounding wrist strap, Figure 2 illustrates the prior art grounding connection,

Figure 3 illustrates the grounding connection according to the present inven- tion, and Figure 4 illustrates an alternative grounding connection.

Detailed Description of the Invention According to the inventive solution, the use of the personal wrist grounding strap or another personal grounding means is taken into account by designing an integrated formed part 30 according to Figure 3 to the body part GB of an electronic device, the formed part 30 constituting a counterpart for the snap connector 14 at the free end of the connecting lead 13 so that the snap connector can be pressed directly into the formed part by means of the snap connection. Thus, the counterpart of the snap connector 14 is designed by shaping the basic material of the body part so that a shape corresponding to the counterpart and protruding from the plane of the body part is created to the body part. The formed part may thus be made e. g. by die-cutting it directly to the body part.

In the exemplary case of Figure 3, the formed part is a male con- nector and, as to its cross-section, it is substantially round in plane A of the body part.

However, the shape of the connector on the connecting lead and the formed part is not essential to the invention. The only significant issue is that their shapes match one another so that the connector 14 can be pressed to the formed part 30 sufficiently tightly by way of the snap connection. For ex- ample, the formed part and the snap connector need not be round or even symmetrical, but they may be square or triangle. Further, the shape of the mating surfaces, used to create the snapping effect, may vary.

The formed part may also extend inward from the body part surface (female connector) if the mating snap connector has a matching male con- nector.

The body parts of electronic devices may also be such that they have not enough free surface to which the connector part could be formed. If this is the case, the body parts nowadays incorporate a separate metal lobe or a protruding part to which the grounding connection is formed, as shown by Figure 2, by using a separate counterpart 20 and fixing means. When the solution according to the invention is applied to such a device, the formed part 30 is integrated into the metal lobe in the same manner as into the actual body

part. Such an alternative is shown in Figure 4, in which reference number 40 denotes the metal lobe or protruding part. The body part must therefore be understood to also comprise such additional parts that are connected to the actual body part for grounding.

Although the invention is in the above described with reference to the accompanying drawings, it is obvious that the invention is not restricted thereto but may vary within the inventive idea set forth in the attached claims.

For example, the structure of the wrist part and its connecting lead may vary in many ways. The wrist part can also be used e. g. around the ankle, or another type of personal grounding means may be used instead of the wrist part.