Metal working – Method of mechanical manufacture – Electrical device making
Reexamination Certificate
1997-10-20
2001-02-27
Young, Lee (Department: 3729)
Metal working
Method of mechanical manufacture
Electrical device making
C029S841000, C174S034000, C361S816000
Reexamination Certificate
active
06192577
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an apparatus and a method for shielding electronic components on an assembly base.
STATE OF THE ART
According to the prior art, electronic components, also called components, attached to an assembly base in e.g. radio receivers, television apparatuses, com-puters, transceivers (transmitters) and telephones in many cases need to be shielded from the environment in order to prevent undesirable radiation from the electronic compo-nents. Examples of such radiation can be radio frequency radiation, so-called RF-radiation (Radio Frequency radiation). Electronic components can also in certain cases be shielded in order to be protected against the influence of e.g. static electricity, so-called ESD (Electro Static Discharge).
Examples of electronic components are resistors, capacitors, coils or transistors, and integrated circuits. The assembly base ban be printed circuit board.
Such electronic components comprise two or more contact connections, so-called poles. The function of the poles is different for different components. For example, a pole on a component can be connected to a common earth connection on the assembly base.
A method according to the prior art for shielding electronic components on an assembly base is to mount a capsule, a so-called shielding box, around the electronic components which need to be shielded. The shielding boxes are manufactured of a suitable solderable metal.
The shielding boxes can be mounted automatically to the assembly base over the intended electronic components with a so-called “pick and place” machine. Such a machine is a robot which picks up components, rolled up on a roll or placed on a tray, from the roll resp. the tray, and places the components in the desired place on the assembly base.
A disadvantage of the method above is that the shielding boxes can be displaced or placed askew during the automatic mounting of the box over the components, whereby the shielding box can come into contact with the components which are placed near to its inner side. This can led to that the components placed near to the inner surfaces of the shielding boxes are shortcircuited against its inner side.
Different methods are used to fix the shielding boxes to the assembly base, for example with the help of bolted or clamping joints.
A disadvantage of screwed or clamped joints is that they can be complicated to manipulate and that they are expensive.
Another method is to solder the shielding box onto the assembly base in a so-called surface mounting process, also called SMD-process (Surface Mount Device-process).
The SMD-process is a process where components are soldered to contact surfaces on the assembly base. The components are positioned with a robot on the desired contact surfaces, which surfaces are provided with solder. Subsequently, the assembly base is heated in an oven, whereby the solder melts which leads to the components being fixed to the base.
A disadvantage when shielding boxes are soldered to the assembly base is that the solder, with which the shielding boxes are fixed to the assembly base, can come into contact with a component situated near the inner side of the shielding box, whereby the component is shortcircuited with the solder.
In order to prevent shortcircuiting as above, according to the prior art the shielding box is made sufficiently large so that a safe distance is obtained between the inner surfaces of the shielding box and the electronic components enclosed in the shielding box. A disadvantage is that the box thereby takes up a large place on the assembly base.
Another method according to the prior art for obtaining a reasonably exact positioning of the shielding box on the assembly base is to use guide holes in the assembly base and guide pins on the shielding box. A disadvantage of this method is that it requires a great precision during the positioning of the box on the assembly base, and furthermore the opposite side of the assembly base cannot be used for mounting of components in the case that the guide holes go all the way through.
In the patent document GB A 2 226 187 a shield with walls is described, which walls are placed in an arrangement on a circuit board over the electronic components which are to be shielded. The device comprises projecting elastic finger-shaped supports which are arranged as a U-shaped channel.
In the patent document JP A
07-142906
a shield is described with projecting brackets which brackets are mounted in soldering recesses intended for them in a circuit. The brackets are fixed in the soldering holes by soldering.
DISCLOSURE OF THE INVENTION
A problem which the invention solves is to prevent emissions from electronic components on an assembly base.
Another problem is to prevent shortcircuiting between a shielding unit and the electronic components situated closest to the shielding unit during automatic mounting of the shielding unit over the electronic components on the assembly base. The electronic components can thereby be enclosed in the shielding unit or can be situated outside it.
Yet another problem is to prevent shortcircuiting between the solder with which the shielding unit is fixed to the assembly base, and the electronic components situated closest to the shielding unit.
Yet another problem is to minimize the space which the shielding unit needs on the assembly base in order to shield said electronic components.
An object of the present invention is consequently to, with a reliable and simple method and with a reliable and simple device, shield intended electronic components on an assembly base with a shielding unit, whereby the shielding unit takes up a small place on the assembly base, and to prevent shortcircuiting between the shielding unit respectively the solder with which the shielding unit is fixed to the base, and the enclosed electronic components situated closest to the shielding unit, when the shielding unit is automatically mounted on the assembly base.
Another object of the present invention is to prevent shortcircuiting between the shielding unit respectively the solder, and the electronic components situated closest to the shielding unit, which electronic components are mounted on the assembly base outside the shielding unit when the shielding unit is automatically mounted onto the assembly base.
In order to bring about this, the present invention uses the placement of a certain number of the mounted components enclosed in the shielding unit, which components have a pole which can be connected to a common earth connection on the assembly base. These poles are then turned towards an inner side surface of the shielding unit and connected to said earth connection.
According to an advantageous embodiment of the method, said enclosed compo-ents are placed at least a certain distance from the other components enclosed in the shielding unit.
According to a modified method, a certain number of possible components, situated outside the shielding unit which comprise a pole connectable to said earth connection, can be turned with their respective poles towards an outer side surface of the shielding unit, wherein these poles are connected to said earth connection.
In more detail, the method is arranged so that the intended electronic components on the assembly base are shielded with the shielding unit. A certain number of the shielded electronic components, which comprise a pole connectable to said earth connection, are laced before said shielding on the assembly base so that these poles are facing out towards the periphery of he part of the assembly base which is to be shielded, the so-called shielded part of the assembly base, wherein they are connected to said earth connection.
The method according to the invention is not limited to connecting said poles to an earth connection but a constant potential V≠0 can also be used, wherein the shielding unit and said poles are connected to the constant potential V.
Said shielded electrical components are also placed on the assembly base so that the side of the components which faces
Burns Doane Swecker & Mathis L.L.P.
Telefonaktiebolaget LM Ericsson
Trinh Minh
Young Lee
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