Electricity: conductors and insulators – Boxes and housings – With grounding means
Reexamination Certificate
1998-08-31
2001-02-13
Kincaid, Kristine (Department: 2831)
Electricity: conductors and insulators
Boxes and housings
With grounding means
C361S752000, C361S753000
Reexamination Certificate
active
06188019
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a plastic housing for receiving an electrical printed circuit board according to the preamble of patent claim
1
and a procedure for mounting an electronic subassembly on a carrier body according to patent claim
5
.
Increasingly, electronic subassemblies are being made with plastic housings, especially in the automotive industry, since these are considerably lighter, in particular, as well as being relatively easy and cheap to manufacture, which in turn reduces fuel consumption. To attach the plastic housing to a metal carrier body, the plastic housing generally includes a mounting flange with an opening. However, as the plastic housing is very susceptible to damage in the area of the opening as a result of the forces arising during the mounting operation as when tightening screws or riveting, a hole-strengthening metal insert is employed, as can be seen, for example, from German patent DE 90 07 621 U1 (hollow rivet
4
in FIG.
1
).
However, plastic housings have the disadvantage of not being able to provide electrical connection to a metal carrier body, as is used in the automotive industry, in particular, for connecting to chassis ground. A purely friction-grip connection, provided, for example, by screwing the printed circuit board to the metal housing carrier body, does not satisfy the safety requirements of the automotive industry, as the printed circuit board cannot be totally enclosed by the plastic housing and also because a friction-grip connection such as this cannot guarantee electrical contact over the service life of the product. More particularly, the printed circuit board displays a tendency to warp slightly over time in the area of the friction-grip connection and the large contact surface required for providing electrical contact eventually disappears. Cables passed through and welded inside the plastic housing, as can be seen from German patent DE 43 30 977 C2, for example, are extremely susceptible to breakage.
For this reason, electrical wiring to the chassis is currently guided through a plug construction in the plastic housing together with the other wiring for the printed circuit board and from there connected at the screw fastening point to the metal carrier body, and thus to chassis ground, during mounting by means of a cable clamp or similar device. A plastic housing of this type with a state-of-the-art connection to chassis ground via a plug device is shown at FIG.
2
. Housing
1
contains printed circuit board
2
, which has an electrical connection
14
to plug device
15
. In plug device
15
a grounding pin not further explained is connected to a lead
11
outside plastic housing
1
and led to flange
10
and mechanical connecting means
12
(shown as a screw). However, the cost of having a separate grounding pin such as this in the plug device, in particular the cost of the parts, and of the mounting operation, including that for lead
11
outside housing
1
, is considerable. German patent DE 297 09 904 U1 describes a solution similar to this. Additional contact springs for grounding purposes are described in German patent DE 91 14 287 U1.
SUMMARY OF THE INVENTION
A plastic housing for making a simple electrical connection between a printed circuit board and a metal carrier body is disclosed.
The basic idea is to employ the metal insert, hitherto used solely for mechanically stabilizing the mounting flange, as an electrical conductor and to connect it electrically with an electrical terminal on the printed circuit board. The economic benefits gained by the saving in plug device cost can be of decisive market importance. Particularly advantageously, the necessary electrical connection between the metal insert and the electrical printed circuit board terminal can be realized by running an electrical lead such as a metal or wire element bent according to the shape of the plastic housing within the plastic housing material from the printed circuit board terminal to the metal insert. An electrical connecting device such as this is, for example, co-molded directly with the plastic material during manufacture of the plastic housing. It may also be joined to the metal insert or be an inherent part of it.
Equally advantageous is the second method of providing electrical connection to the printed circuit board terminal by way of an electrically conducting layer on the surface of the plastic housing, preferably on the inner side. As is commonly known, deposition of a corresponding metallization path is very easy to accomplish.
Generally speaking, electrical connection between the metal insert and the printed circuit board can also be made by means of a metal part inside the plastic housing such as a screening plate or a metal part of the inherently plastic housing.
In describes a preferred development of the invention the electrical lead is run along the inside surface of the plastic housing to a metal interference-fit pin that on assembly is pressed into an at least partially metallized opening in the plastic housing on the one hand and into an opening located in the electrical printed circuit board terminal on the other and retained on both sides.
In a procedure for mounting an electrical subassembly having a metal insert in the mounting flange, an additional snap-in means being provided on the underside of the plastic housing and an associated snap-in opening on the carrier body, by means of which the subassembly is initially locked in place and then aligned by rotating the subassembly with respect to the snap-in connection so that the metal insert in the subassembly housing mounting flange comes to rest over a second opening in the carrier body, where the subassembly is retained by a mechanical connecting means such as a screw or a rivet. It is particularly advantageous to determine by testing the conductivity of the electrical connection between printed circuit board and metal carrier body whether the mounting operation has been successfully completed and a corresponding electrical connection made. The process monitoring of the chassis ground is of particular importance, especially for safety-relevant subassemblies, as in the automotive industry, for example.
REFERENCES:
patent: 5053923 (1991-10-01), Niemetz
patent: 5286920 (1994-02-01), Fassel et al.
patent: 5644474 (1997-07-01), Jang
patent: 5872332 (1999-02-01), Verma
patent: 9114287 (1993-04-01), None
patent: 9007621 (1993-05-01), None
patent: 4329083A1 (1995-03-01), None
patent: 4330977C2 (1995-03-01), None
patent: 297 09 904 U 1 (1997-09-01), None
patent: 2 269 946 (1994-02-01), None
Baur Richard
Fendt Gunter
Kincaid Kristine
Kunitz Norman N.
Ngo Hung V
TEMIC Telefunken microelectronic GmbH
Venable
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