Procedure for Manufacturing a Radio Telephone Chassis and a Chassis Manufactured According to This Procedure

The present invention relates to a procedure for manufacturing a chassis for a radio telephone, for attaching circuit boards on the chassis, and a chassis made according to this procedure.

Various radio telephone chassis are known in the art on which the circuit boards of the radio telephone are attached. Such chassis are usually cast or pressed chassis of aluminium provided with thicker points, or `towers`, in which a threaded hole has been made for fixing the circuit board thereon with a screw or threaded bolt to form a screw joint. Similarly, the chassis are provided with `towers` on which the shell components of the apparatus are likewise fixed applying by means of a screw joint, when assembling the radio telephone. The fixing can be carried out self-tapping screws.

Chassis of the type known in the art are subject to certain drawbacks. The aluminium chassis is rather expensive to manufacture, in particular when a cast chassis is used. Drilling and threading the holes for the fixing screws add work steps and consequently, costs. Fixing RF shielding covers and achieving good sealing is also problematic. A radio telephone chassis of the kind known in the art constitutes an entity together with the outer shell intended to be affixed thereto. This implies that since the fixing is done with screw joints, the chassis on which the circuit boards have been attached and the shell must be mutually consistent at the fixing points. Hence, it follows that a particular shell only can be used with a given chassis. Said feature restricts the number of the external modifications of the apparatus. Whenever one desires to produce a radio telephone of novel appearance, it becomes necessary to design a new chassis to go with it.

In the present invention a procedure has been provided for manufacturing a chassis for a radio telephone, the chassis produced according to this procedure being relieved of the above drawbacks. The invention is characterized in that the chassis is punched out of a sheet or board blank in such a manner that strip-like parts and a plurality of tongues are created. The strip-like parts and marginal areas of the board blank are bent 90.degree. to form a box-like chassis with the strip-like parts on the bottom. A first circuit board is supported by the strip-like part and a second circuit board is supported about the first by the tongues.

The present invention results in a chassis having low manufacturing costs and upon which the circuit boards can be attached without screw joints, even though screw joints may be employed if desired. The chassis can be enclosed in a plastic outer shell which has been designed so that in the final assembly of the radio telephone not a single screw is necessarily used.

The plastic shell may be variable appearance, while the body part to which the circuit boards have been attached is always the same. Producing new modifications is hereby restricted merely to mechanical designing of the plastic shells. This substantially reduces the manufacturing costs because with different shells one and the same electronics assembly can be used, which assembly may have already been tested functionally and has its RF shielding in order.

The invention is described more in detail with the aid of the figures attached, in which:

FIG. 1 illustrates sheet blank from which a chassis according to the invention is made by die cutting and bending.

FIG. 2 shows a detail of the attachment of a circuit board to the chassis, and

FIG. 3 is an exploded view of the radio telephone.

In FIG. 1, reference numeral 1 refers to a board blank which in the present instance is a rectangular, thin metal sheet. The corners 2 are removed from the board blank 1 by die cutting. From the region which, after bending marginal parts 3 and 4 will constitute the bottom part of the chassis, the areas 9 are similarly removed by die cutting (only one area indicated). Likewise, requisite areas 6 are removed from one margin of the board 1. Similarly an appropriate number of punchings 8 are made and tongues 7 are cut in the remaining marginal parts 3 and 4 close to the edges of the board, their purpose being described later. In FIG. 1, the areas to be removed are shown with diagonally hatched lines. The main bending lines are shown with interrupted lines. After the die cutting is completed, the end parts 4 and side parts 3 forming the side walls of the future chassis, and the bottom part confined by these are visible in the board blank 1. From the bottom part the greater part of the board material has been removed, as can be seen in FIG. 1, so that only fairly narrow strip-like parts 5 remain. The shape of the strip-like parts 5 is very important. First, their breadth is the same or slightly larger than the height of the piece component extending farthest from the surface of the circuit board. Secondly, those points where the strip-like parts join one another and the side parts 3 and end parts 4 have been cut to such shape that the strip-like parts can be bent 90 degrees about their longitudinal axis. When the board blank has been die cut in one or several work steps, the bending step follows. Bending takes place such that e.g., in the plane of FIG. 1 the marginal parts 3 and 4 of the board blank are bent along the interrupted main bending lines 90.degree. upward from the picture plane and the strip-like parts. Hereby, a rectangular box, is formed with `a rib system` 5 on the bottom part, and the longitudinal sides are composed of the side parts 3 and the end short sides of the parts 4. One short side 4 is provided with one or several notches 6 at its outermost edge. The above-mentioned strip-like parts 5 in the bottom part are bent 90 degrees about their longitudinal axis towards the box interior. In this manner a rib system in the bottom part of the box is formed, the breadth of each rib being equal to the material thickness of the metal forming board blank 1 and its height being equal to the breadth of the strip-like part 5 produced in the die cutting step. One edge of the rib system is located on the same level as the edge of the parts 3 and 4 after bending.

The box produced after the bending is coated with tin on both sides. This coating may equally be performed prior to bending. It is also possible to use pre-tinned sheet material. A thin tin coating protects the sheet metal from corrosion and is useful when the corner parts of the box are soldered and when the circuit boards are soldered to the box as will be described further below.

After producing the box structure, the circuit boards 10 and 11 (FIG. 3) upon which the requisite components of the radio telephone are fixed are attached. The components include the audio frequency processing unit, a logic unit, a synthesizer producing the radio frequencies, a transmitter, a receiver and a power supply. All of the component parts of the radio telephone are positioned on these two circuit boards. The circuit boards 10 and 11 are interconnected electrically with connectors some of which are in part visible in FIG. 3. The circuit board 11 is first installed on the bottom of the box constituting the chassis so that the piece components of the radio frequency sections are in the front, and the components of the other parts and the connectors remain inside the box. The dimensions of the circuit board 11 conform to the inner dimensions of the box. Laterally the circuit board 11 is supported by the side walls 3 and 4 of the box formed by side parts 3 and end parts 4, and vertically it is supported by the bent strip like parts 5 so that the breadth of the strip like part 5 touching the circuit board is the same as the thickness of the board blank 1. Thereafter the circuit board is soldered, either partially or completely, to the strip-like parts 5 and to the sides of the box forming the chassis.

In the same work step the adjacent marginal parts 3 and 4 which after being bent form the sides of the box are soldered together along the corner formed by said sides.

In the next step, the cooling fin 12 (FIG. 3) required for cooling the power stage of the telephone is fixed on the outer surface of one of side parts 3 of the box forming the chassis. An antenna connector has heretofore been attached to the cooling fin.

Thereafter the circuit board 10 is mounted. As was mentioned before, protrusions 8 have been punched in the die cutting phase. The protrusions are made such that when the board blank 1 is bent into box form, the protrusions 8 remain inside the box. The circuit board 10, its dimensions equivalent to the inner dimensions of the box constituting the chassis, is placed on said protrusions with the component side, toward the earlier installed circuit board 11. The connectors of the circuit board 10 become at the same time connected to the respective connectors of the circuit board 11 placed earlier on the bottom of the box, whereby the circuit boards are electrically interconnected. Thereafter, the tongues 7 cut on the marginal parts 3 and 4 are bent toward the interior of the box, whereby a reliable fixing of the circuit board 10 to the chassis structure is formed, as shown in FIG. 2. The notches 6 in one of the end parts 4 are intended for various connectors and shafts of such controls and switches as may be required. These may be power, mic, ear and, perhaps, handset connectors.

In the next step, metallic shield covers 13 and 14 which provide protection against electromagnetic interference are attached. The shielding of the circuit board 11 may comprise several smaller covers 13, whereas the shield cover 14 positioned on the side of the circuit board 10 covers as an integral plate the entire circuit board 10. The shield covers are known in themselves in the art as to their design. They are sheets with bent edges, that cling in position by the action of these elastic bonds. In the present instance they attach to the side walls 3 and 4 of the box-like chassis and/or to the strip-like parts 5. All functional circuit components requiring radio frequency shielding are located on the circuit board 11, the RF shielding of the various functional blocks on the circuit board being composed of the ground foil of the circuit board 11, of the strip-like part 5 and the shield cover 13.

Testing the radio telephone can be carried out part by part both before and after attaching the shield covers 13 and 14. After the shield covers have been mounted, the radio telephone is a fully functional module, around which the plastic shell intended for the particular product can be mounted.

The chassis of the invention affords a number of advantages in comparison with the designs known in the art. Being made of tinned sheet metal, it is inexpensive in comparison with an aluminium chassis: its cost is only about one tenth of the price of an aluminium chassis. While the board blank 1 is being processed in the punching press, all requisite elements are fixed to the circuit boards. The completed circuit boards are rapidly mounted on the chassis, using no screws whatsoever. After the circuit boards have been attached to the chassis, a fully operative radio telephone has been created, which can be used as a module for various radio telephones which differ in their external design. The circuit boards serve as walls of the module, and the sheet metal chassis constitutes the other walls. The structure is light and rigid at the same time.