WO2007125178A1

WO2007125178A1 - Method of producing casing provided with circuit board

Info

Publication number: WO2007125178A1
Application number: PCT/FI2007/050238
Authority: WO
Inventors: Mikko Silvennoinen
Original assignee: Perlos Oyj
Priority date: 2006-05-02
Filing date: 2007-04-27
Publication date: 2007-11-08
Also published as: FI20065282L; FI20065282A0

Abstract

A method of producing a casing provided with a circuit board, the method comprising a step of forming a circuit board (PCB) having a first surface and an opposite second surface arranged to receive a display element (4). The method further comprises a first injection moulding step where a first layer of injection moulding material is formed on the first surface of the circuit board (PCB) and a second layer (82) of injection moulding material is formed on the second surface of the circuit board (PCB), an installation step where at least the display element (4) is mounted on the second surface of the circuit board (PCB), a second injection moulding step where a third layer (83) of injection moulding material is formed on the second surface of the circuit board (PCB), the layer being arranged to form an essential part of the casing's front surface. The second injection moulding step is performed after the installation step and comprises integrating at least one of the components mounted on the circuit board (PCB) in the installation step into the casing by forming a connection between the component to be integrated and the third layer of injection moulding material by means of the injection moulding material.

Description

METHOD OF PRODUCING CASING PROVIDED WITH CIRCUIT BOARD

BACKGROUND OF THE INVENTION

[0001] The invention relates to a method according to independent claim 1 for producing a casing provided with a circuit board.

BRIEF DESCRIPTION OF THE INVENTION

[0002] The object of the invention is to provide a method of producing a casing which comprises a circuit board where a display element has been inserted and whose both surfaces are provided with a layer of injection moulding material. The object of the invention is achieved by a method characterized by what is disclosed in independent claim 1. Preferred embodiments of the invention are disclosed in the dependent claims.

[0003] The invention is based on using two injection moulding steps in the production of a casing. In the first step, a first layer of injection moulding material is formed on a first surface of a circuit board, and a second layer of injection moulding material is formed on a second surface, after which an installation step is performed where at least a display element is mounted on the second surface of the circuit board, and finally the second injection moulding step is performed where a third layer of injection moulding material is formed on the second surface of the circuit board, the layer integrating at least one of the components mounted on the circuit board in the installation step into the circuit board and simultaneously forming an essential part of the casing's front surface.

[0004] An advantage of the method according to the invention is that the layer of injection moulding material to be formed on the first surface of the circuit board in the first injection moulding step protects sensitive components mounted on the surface that could, without the material layer, be damaged when pressed against the injection mould during the second injection moulding step. Furthermore, the layer of injection moulding material to be formed on the second surface of the circuit board in the first injection moulding step may be arranged to protect at least one component to be mounted on the second surface of the circuit board in the installation step from excessive heat and/or pressure during the second injection moulding step. BRIEF DESCRIPTION OF THE FIGURES

[0005] The invention will now be described in greater detail by means of preferred embodiments with reference to the accompanying drawings, in which: Figure 1 illustrates a circuit board of a casing according to an embodiment of the invention before a first injection moulding step seen from the direction of a first surface;

Figure 2 illustrates the circuit board of Figure 1 after the first injection moulding step seen from the direction of a second surface; Figure 3 illustrates a casing formed of the circuit board of Figure 2 by means of an installation step and second injection moulding step; and

Figure 4 illustrates a cross section of the casing according to Figure 3.

DETAILED DESCRIPTION OF THE INVENTION [0006] Figure 1 illustrates a printed circuit board PCB for a mobile station seen from the direction of its first surface before a first injection moulding step. In the first injection moulding step, a first layer of injection moulding material is formed on the first surface, the layer covering active and passive components mounted on the first surface. [0007] As illustrated by a broken line in Figure 1 , the first layer of injection moulding material extends further in the radial direction than the printed circuit board PCB, i.e. the vertical and horizontal dimensions of the first layer of injection moulding material are larger than the corresponding dimensions of the printed circuit board PCB when seen from the direction of the first surface. Seen from the direction of the first surface, the first layer of injection moulding material totally covers the PCB and the active and passive components mounted on it. The first layer of injection moulding material forms a substantially smooth surface whose plane is substantially parallel with the first surface of the printed circuit board PCB. [0008] Figure 2 illustrates the printed circuit board PCB of Figure 1 after the first injection moulding step seen from the opposite direction, i.e. from the direction of the second surface of the printed circuit board PCB. In the first injection moulding step, a second layer 82 of injection moulding material is formed on the second surface of the printed circuit board PCB, the material layer comprising a frame element 6 extending in the display-receiving area. The display-receiving area is arranged to receive a display element and comprises a connector element 85 arranged for transmitting electric power and data into the display element.

[0009] The outer edge of the frame element 6 is rectangular and its upper edge extends slightly further than the upper edge of the printed circuit board PCB, and its both side edges extend slightly further than the corresponding side edge of the printed circuit board PCB. The lower edge of the second injection moulding material layer 82 is at a short distance from the upper edge of a key switch assembly 92. The outer edge of the first layer 81 of injection moulding material surrounds the side edges of the printed circuit board PCB downwards from the frame element 6 and the lower edge of the printed circuit board PCB.

[0010] The inner edge of the frame element 6 is rectangular and extends within the rectangle defining the outer edge. The frame element 6 thus has the shape of the difference between the rectangle defining the outer edge and the rectangle defining the inner edge. Inside the inner edge of the frame element 6, there is a connector element 85, which is not covered by injection moulding material.

[0011] The key switch assembly 92 comprises eighteen key switches 93 arranged in three substantially vertical rows. In a finished mobile phone, each key switch 93 of the key switch assembly 92 is arranged to transmit information on a key press by a mobile station user to the data processing means of the circuit board.

[0012] After the first injection moulding step, an installation step is performed where a display element is mounted in the display receiving area on the second surface of the printed circuit board PCB so that the connector element in the display element connects to the connector element 85 on the printed circuit board PCB. Furthermore, a transparent rectangular window element is placed on top of the display element, the window element covering the whole display surface of the display element and extending radially further than the display surface and also further than the inner edge of the frame element 6. After the installation step, the outer edge of the window element is against the frame element 6, in which case the distance of the lower surface of the window element from the surface of the printed circuit board PCB is the same as the thickness of the frame element 6. [0013] Figure 3 illustrates a casing formed from the circuit board of Figure 2 by means of the installation step and second injection moulding step. A third layer 83 of injection moulding material is formed on the second surface of the printed circuit board PCB after the installation step by the second injec- tion moulding step. The third layer 83 of injection moulding material is arranged to form an essential part of the front surface of the casing of a mobile phone, and it extends over a larger area in the radial direction than the first and the second layer of injection moulding material formed in the first injection moulding step. [0014] Figure 4 illustrates a lateral cross section of the casing of

Figure 3 at the lower part of the frame element 6. It can be seen in Figure 4 that in the depth direction, i.e. perpendicular to the plane of the printed circuit board PCB, the third layer 83 of injection moulding material extends substantially further than the first surface of the printed circuit board. Thus side walls are also formed for the casing in the second injection moulding step, the side walls being substantially perpendicular to the printed circuit board PCB. It can further be seen in Figure 4 how the injection moulding material surrounds the printed circuit board PCB in each direction after the first injection moulding step, i.e. from the direction of the first and the second surface and from the direction of the edges of the printed circuit board PCB.

[0015] If the first layer 81 of injection moulding material had not been formed in the first injection moulding step, the components placed on the first surface of the printed circuit board PCB would be pressed against the inner surface of the injection mould in the second injection moulding step, in which case they could be damaged. The first layer 81 of injection moulding material thus protects the components mounted on the first surface of the printed circuit board PCB during the second injection moulding step.

[0016] Different injection moulding materials may be used in the first and in the second injection moulding step. In some embodiments, the material to be injection moulded in the first injection moulding step is not visible at all in the finished devices, which allows selecting the material to be used in the first injection moulding step totally according to the necessary physical properties, such as elasticity and thermostability.

[0017] The third layer 83 of injection moulding material covers a circumferential area at the outer edge of the frame element 6. The outer edge of the window element is covered by the third layer 83 of injection moulding material, in which case injection moulding material integrates the window element into the third injection moulding material layer and also into the whole casing. Since the display element 4 is between the window element and the printed circuit board PCB, the third layer 83 of injection moulding material also integrates the display element into the casing 4.

[0018] Since the window element is integrated into the casing by the second injection moulding step, the above-mentioned mounting of the window element on top of the display element means that the window element is placed on top of the display element without attaching it in any way to the dis- play element. The window element may also be placed at a short distance from the display element, in which case only the frame element supports the window element after the installation step. If the window element is not attached anywhere during the installation step, other measures have to be taken to ensure that the window element stays in place both during the installation step and the second injection moulding step.

[0019] It can be seen in Figure 3 that, after the second injection moulding step, there is a circumferential area of the printed circuit board PCB around the display element 4, no injection moulding material layer being formed in the circumferential area. The circumferential area is surrounded by an inner edge portion of the frame element 6, which can also be seen through the window element like the circumferential area. As described above, the outer edge portion of the frame element 6 is covered by the third layer 83 of injection moulding material.

[0020] The printed circuit board PCB and/or frame element 6 parts can be prevented from being seen through the window element either by darkening the edges of the window element or by installing a separate cover plate covering the edges of the window element in the casing. The separate cover plate may be made of metal or plastic, for instance, and it may be attached to the casing in the second injection moulding step or after it. [0021] During the second injection moulding step, the display element 4 is in a cooled and/or substantially pressureless auxiliary chamber, which is separate from the actual mould to protect the display element from excessive heat and/or pressure.

[0022] Since a substantially smooth first layer of injection moulding material is formed on the first surface of the circuit board PCB, a first auxiliary chamber member, which forms the first half of the auxiliary chamber and is connected to the first layer of injection moulding material from the direction of the first surface during the first injection moulding step, may comprise a cooled planar surface whose projection on the surface of the printed circuit board PCB covers at least the same area as the projection of the display element on the opposite side of the printed circuit board PCB.

[0023] An auxiliary chamber member, which is connected from the direction of the second surface and forms the second half of the auxiliary chamber, may comprise a tubular member, with thin walls and a rectangular cross section. When the casing according to Figure 3 is formed, the outer edge of the tubular element included in the second auxiliary chamber member may define the inner edge of the portion of the third layer 83 of injection moulding material surrounding the display element 4. The tubular member is pressed against the window element during the second injection moulding step so that the projection of the tubular element is at the frame element 6. The thickness of the wall of the tubular element is such that the inner edge of the tubular element does not extend further inwards than the inner edge of the frame element 6.

[0024] In the embodiment of Figure 3, the frame element surrounds the display element 4 circumferentially so that it forms part of the auxiliary chamber during the second injection moulding step. The frame element 6 thus prevents the injection moulding material from accessing the auxiliary chamber where the display element 4 is during the second injection moulding step.

[0025] Both the first auxiliary chamber member and the second auxiliary chamber member may comprise a cooling system provided with a cooling agent circuit. The cooling system prevents transmission of the high temperature into the auxiliary chamber during the injection moulding step.

[0026] During the second injection moulding step, there may be other sensitive components in the cooled and/or substantially pressureless auxiliary chamber in addition to the display element. One or more of these sensitive components may be in the same auxiliary chamber as the display element, or one or more auxiliary chambers may be provided for these other sensitive components.

[0027] In the embodiment of Figure 3, the third layer 83 of injection moulding material is provided with three openings at the key switch assembly 92. Each of these openings is at the respective substantially vertical row ^; formed by the key switches 93 so that none of the key switches 93 is covered by injection moulding material. The openings arranged for the key switches in the third layer of injection moulding material may be formed by means of respective auxiliary chambers.

[0028] In an alternative embodiment of the invention, a domesheet, light guide element and external key element to be integrated into the casing in the second injection moulding step are mounted on top of the key switch assembly. These components may be integrated into the casing in the second injection moulding step by covering the outer surface of the topmost component, i.e. the external key element, with injection moulding material. [0029] The light guide element is arranged to provide the keypad with background light. The external key element is arranged to form an external surface which the user may press when using the keypad.

[0030] Harmful electric phenomena, such as generation of static electricity, may occur during an injection moulding step and damage the most sensitive components. Components inside the auxiliary chamber may be protected, in addition to heat and pressure, from harmful electric phenomena by forming the auxiliary chamber as a Faraday cage.

[0031] The casing provided with a circuit board according to the invention may be a casing for a mobile phone, palmtop computer, mp3 player, camera or another electronic device. Here the casing generally refers to a component arranged to form at least part of the surface of a device arranged therein. The casing may be fixed or replaceable. Here the replaceable casing refers to a casing arranged to be replaced by the users themselves. The fixed casing, on the other hand, refers to a casing not designed to be replaced by the user.

[0032] It will be obvious to a person skilled in the art that the inventive concept may be implemented in various ways. The invention and its embodiments are thus not limited to the examples described above but may vary within the scope of the claims.

Claims

1. A method of producing a casing provided with a circuit board, the method comprising a step of forming a circuit board (PCB) having a first surface and an opposite second surface arranged to receive a display element (4), characterized in that the method further comprises a first injection moulding step where a first layer of injection moulding material is formed on the first surface of the circuit board (PCB) and a second layer (82) of injection moulding material is formed on the second surface of the circuit board (PCB), an installation step where at least the display element (4) is mounted on the second surface of the circuit board (PCB), a second injection moulding step where a third layer (83) of injection moulding material is formed on the second surface of the circuit board (PCB), the layer being arranged to form an essential part of the casing's front surface, whereby the second injection moulding step is performed after the installation step and comprises integrating at least one of the components mounted on the circuit board (PCB) in the installation step into the casing by forming a connection between the component to be integrated and the third layer of injection moulding material by means of the injection moulding material.

2. A method according to claim 1 , characterized in that during the second injection moulding step, at least one of the components mounted on the circuit board (PCB) in the installation step is in a cooled and/or substan- tially pressureless auxiliary chamber, which is separated from the actual mould to protect the component from excessive heat and/or pressure.

3. A method according to claim 2, characterized in that the second layer of injection moulding material comprises a frame element (6) which extends circumferentially around at least one component installed in the installation step and forms part of the wall of the auxiliary chamber protecting the component during the second injection moulding step.

4. A method according to claim 3, characterized in that the frame element (6) extends circumferentially around the display element (4).

5. A method according to any one of the preceding claims, charac- terized in that in the installation step, a transparent window element is placed on top of the display element (4) and integrated into the casing in the second injection moulding step by forming a joint between the window element and the third layer of injection moulding material by means of the injection moulding material.

6. A method according to any one of the preceding claims, characterized in that in the installation step, one or more keypad components are mounted on the second surface of the circuit board (PCB), the keypad components being selected from the following: an external key element, a key contact element, and a light guide element.

7. A method according to any one of the preceding claims, characterized in that the third layer (83) of injection moulding material is formed partly on top of the second layer (82) of injection moulding material.

8. A casing provided with a circuit board, characterized in that it is manufactured by the method according to any one of claims 1 to 7.