WO2010020709A1

WO2010020709A1 - Connection

Info

Publication number: WO2010020709A1
Application number: PCT/FI2009/050665
Authority: WO
Inventors: Dewei Tian; Mikko Silvennoinen; Esa Muukkonen
Original assignee: Perlos Oyj
Priority date: 2008-08-20
Filing date: 2009-08-18
Publication date: 2010-02-25
Also published as: FIU20080261U0; FI8114U1

Abstract

A connection for connecting at least two pieces having different thermal expansion coefficients to one another. The connection is provided with at least one fastening aperture (3) arranged in a first piece (2) and at least one pin (1) which is arranged in a second piece (8) and which consists of an end (5) which is at least in a longitudinal or lateral direction wider than the fastening aperture, and a shaft (6) which is at least in a longitudinal or lateral direction narrower than the fastening aperture (3). The pin (1 ) is arranged to travel through the fastening aperture (3) of the first piece such that the end (5) of the pin and the second piece (8) reside on opposite sides of the first piece (2) with respect to the fastening aperture (3).

Description

CONNECTION

BACKGROUND OF THE INVENTION

[0001] The invention relates to a connection for connecting at least two pieces having different thermal expansion coefficients to one another. [0002] Injection moulding is widely used when polymer materials are used for making plastic products. The material used in injection moulding is typically fed to a screw of an injection moulding machine, at which it is plasti- cized or heated and by means of which the material is forwarded and injected into a mould cavity. After the mould cavity has been filled, the piece is allowed to cool, after which the piece is removed from the mould cavity. The method is particularly advantageous when manufacturing very large series.

[0003] It has become more and more necessary to connect parts made of another material to plastic material pieces e.g. so as to connect a plastic material piece to other pieces or to coat a piece in order to change its appearance or properties. Typically e.g. in electronics it is also necessary to connect components, such as circuit boards or other electronic components, to plastic material pieces, in which case the plastic material piece may form e.g. the surface, casing or protective shell of a product or a part thereof. The pieces can be connected to one another by conventional assembly methods, but the part to be connected to a plastic material piece may also be inserted into the mould cavity as an "insert" and cast to the plastic by an injection moulding method.

[0004] When pieces made from another material are connected to a plastic material by casting them to the plastic, the problem is, however, that the thermal expansion coefficient of the piece to be connected, such as a circuit board, and that of the plastic piece differ from one another. When pieces having different thermal expansion coefficients are connected to one another by a method wherein the temperature of the connecting phase differs from the normal usage temperature, the pieces expand or contract differently when the pieces that have been connected with one another return to the usage temperature. This causes the connected piece to curve, which is also known as a banana phenomenon. BRIEF DESCRIPTION OF THE INVENTION

[0005] An object of the present invention is to provide a novel and improved connection for connecting at least two pieces having different thermal expansion coefficients to one another. [0006] The connection according to the invention is characterized in that the connection is provided with at least one fastening aperture arranged in a first piece and at least one pin which is arranged in a second piece and which consists of an end which is at least in a longitudinal or lateral direction wider than the fastening aperture, and a shaft which is at least in a longitudinal or lateral direction narrower than the fastening aperture, the pin being arranged to travel through the fastening aperture of the first piece such that the end of the pin and the second piece reside on opposite sides of the first piece with respect to the fastening aperture.

[0007] Other embodiments of the invention are characterized by what has been disclosed in the dependent claims. Inventive embodiments are also set forth in the specification and drawings of this application. The definition of the inventive contents in the application may also differ from that provided in the claims below. The inventive contents may also include several separate inventions, particularly if the invention is considered in the light of ex- pressed or implicit partial tasks or in terms of achieved benefits or beneficial groups. Hence, some definitions contained in the claims below may be redundant as far as separate inventive concepts are concerned. Within the scope of the inventive basic idea, features of the different embodiments of the invention may be applied in connection with other embodiments. [0008] The idea of the invention is that in order to avoid the curling of pieces that have been connected to one another and that have different thermal expansion coefficients when the pieces change from a connecting temperature to a usage temperature, the pieces have to be able to move or slide with respect to one another. [0009] An advantage of the invention is that the pieces may be connected to one another already in connection with injection moulding, thus avoiding disadvantages caused by thermal expansion. This often enables the components of a product to be simplified and the assembly to be made speedier. The invention also enables production costs to be reduced since savings may be achieved in costs regarding e.g. space, machine time, and labour, as well as the quality of the product to be improved and even novel product structures to be made possible.

[0010] An idea of an embodiment of the invention is that the connection is provided with an immovable "neutral point" away from which the axis of the direction of motion of the connection is directed. In a second embodiment of the invention, the pieces are connected to one another immovably at the neutral point. Further, in a third embodiment of the invention, this neutral point is the centre point of the piece.

[0011] Furthermore, an idea of a fourth embodiment of the invention is that the pieces are connected by at least two sliding connections which are formed by a fastening aperture and a pin and which are positioned symmetrically with respect to the neutral point.

[0012] An idea of a fifth embodiment of the invention is that at least the second piece together with its pins is an injection moulding piece. An idea of a sixth embodiment of the invention is that the first piece is a circuit board, preferably a flexible circuit board.

BRIEF DESCRIPTION OF THE FIGURES

[0013] Some embodiments of the invention are described in closer detail in the accompanying drawings, in which Figures 1 a, 1 b and 1 c schematically show a detail of a single sliding pin connection according to the invention as two side sectional elevations in different directions and as seen from above,

Figure 2 is a schematic top view showing an embodiment according to the invention provided with four sliding pin connections positioned symmetri- cally with respect to a neutral point,

Figures 3, 4, 5 and 6 are schematic top views showing different embodiments of a connection according to the invention,

Figure 7 is a schematic sectional side view showing a part of an electronic device, Figure 8 is a schematic top view of a fastener shown in Figure 7, and

Figure 9 shows the fastener according to Figure 8 as sectioned along line A-A of Figure 8. For the sake of clarity, the figures show some embodiments of the invention in a simplified manner. Like reference numerals identify like elements.

DETAILED DESCRIPTION OF THE INVENTION [0014] When pieces having different thermal expansion coefficients are connected to one another by a manufacturing method wherein the connecting temperature differs from the usage and/or storage temperature, the problem is that the pieces expand and/or contract to a different degree when the temperature changes. When the pieces expand or contract to a different degree, their combination tends to curve, which reduces the dimensional accuracy of the piece, may prevent assembly and, in the worst case, may break the piece or a part thereof. However, for instance in electronics industry, it would be advantageous to be able to connect plastic material pieces, such as covers and casings, to pieces made from another material, such as circuit boards, e.g. in connection with injection moulding in order to simplify e.g. the structures and assembly. In the solution according to the invention, this problem is solved by forming a sliding pin connection between the pieces to enable the pieces to move with respect to one another when the temperature changes, and thus also to enable the pieces to be connected to one another in connection with manufacture, e.g. injection moulding.

[0015] The invention may be well applied e.g. to designing and manufacturing electronic devices. An electronic device may be any portable or fixed device. Examples include a mobile telephone, communicator, palmtop computer, portable computer, game console or controller, playback device for audio and/or visual material, desktop computer or the like.

[0016] Figures 1 a, 1 b and 1 c show a detail of an embodiment of a sliding pin connection according to the invention as seen from different directions: in Figure 1 a as a cross-section as seen from an end of a sliding direction, in Figure 1 b as a cross-section as seen from a side of the sliding direc- tion, and in Figure 1 c as seen from above an aperture. For the sake of clarity, the figures only a pin 1 , a fastening aperture 3, part of a first piece 2, which in this embodiment is a piece to be connected to a plastic material, such as a circuit board, and part of a second piece 8, whose continuum is formed by the described pin 1 and which in this embodiment is a plastic material piece, that are relevant to the invention. Further for the sake of clarity, no second piece 8 is shown in Figure 1 c.

[0017] The circuit board may have a rigid or flexible structure. Similarly, the second piece 8 to be connected to the circuit board may be rigid or flexible. Thus, the pieces to be connected to one another may be e.g. a rigid circuit board and a rigid second piece, a flexible circuit board and a rigid second piece, a rigid circuit board and a flexible second piece, or a flexible circuit board and a flexible second piece.

[0018] In the pin connection according to the invention shown in Figures 1 a, 1 b and 1 c, the pin 1 consists of a shaft 6 and an end 5, and it is arranged to travel through the fastening aperture 3 arranged in the first piece 2. In order to form a sliding pin connection, the shaft 6 of the pin 1 is at least in the longitudinal or lateral direction narrower than the fastening aperture 3, as is shown in Figure 1 b in particular, and the end 5 of the pin is at least in the longi- tudinal or lateral direction wider than the fastening aperture, as is shown in Figures 1a and 1 c in particular. Such a pin connection thus enables the pieces to move with respect to one another in a direction in which the shaft 6 of the pin 1 is narrower than the fastening aperture 3. In different embodiments of the invention, the shape of the fastening aperture may differ from that shown in Fig- ures 1 a-1 c within the scope of the claim. Some examples of possible shapes of the pin and fastening aperture according to the invention are shown in Figures 3 and 4, wherein the horizontal cross-sections of the shaft 6, the fastening aperture 3 and the end 5 are differently sized circles and ellipses, and in Figures 5 and 6, wherein the horizontal cross-sections thereof are squares or rec- tangles.

[0019] In order to avoid distortions in shape, it is usually advantageous that pieces which have been connected to one another by a method including thermal changes and which have different thermal expansion coefficients are allowed to move with respect to one another in more than one direc- tion. In the solution according to the invention, this may be implemented e.g. by using more than one sliding pin connection to connect the pieces. According to the shape, use and other conditions of the pieces, these pin connections may be arranged in the pieces either symmetrically or asymmetrically. Such a connection may preferably have an immovable "neutral point", in respect of which the sliding directions of the pin connections may be adjusted and in respect of which the changes in thermal expansion are thus allowed to occur. Further, in an embodiment of a solution according to the invention, the pieces may be fastened to one another immovably at the neutral point. Preferably, the neutral point may be the centre point of the piece.

[0020] Figure 2 is a schematic top view showing a detail of a pre- ferred embodiment according to the invention. In this embodiment, the pieces are connected to one another by four pin connections positioned symmetrically with respect to a neutral point 7 such that the sliding direction of the pin connections is directed in the direction of the neutral point. In this case, the neutral point 7 is the centre point of the piece and the sliding directions of the pin con- nections are parallel with the diagonals of a rectangle, but in other embodiments of the invention the neutral point may also be arranged at another, case- specifically more appropriate point in the pieces, and the number and position of fastening points may also be determined freely in each case in the most appropriate manner. [0021] When two pieces having different thermal expansion coefficients are connected to one another by using a method wherein the connecting temperature differs from the usage and/or storage temperature, the dimensional changes caused by a change in the temperature of the pieces differ from one another. An example of such a method is injection moulding, wherein high temperatures are used, whereas the finished products are often used and stored at normal temperatures. If the pieces were connected to one another immovably over their entire surface area, the differently sized dimensional changes taking place during the cooling of the pieces would cause the interconnected entity to curve. Instead, when the pieces are connected to one an- other by a connection according to the invention, for instance in the manner shown in Figure 2, when necessary, the pieces may be connected to one another by forming the pins 1 in connection with injection moulding. When the temperature drops from a high temperature to a low temperature, the size of the pieces with respect to one another changes on account of their different thermal expansion coefficients. When using the connection according to Figure 2, this does not, however, cause curving, since the pins 1 are allowed to slide in the fastening apertures 3 in their sliding directions with respect to the neutral point 7. This sliding pin connection thus enables differences in the thermal expansion of the pieces to be compensated for. [0022] An application of the invention may be e.g. insert injection moulding of an electronic product, wherein a first piece may be connected to a second to be injection-moulded in connection with injection moulding by utilizing the connection according to the invention. In such a case, the first piece may be an "insert" to be inserted in the mould cavity, such as a circuit board. The second piece may be a part or a component to be connected to the insert and to be manufactured from a plastic material by injection moulding, such as a cover structure. The cover structure may then be formed and fastened to the circuit board inserted in the mould cavity in the mould in one work phase by injection moulding.

[0023] In the disclosed figures, the pieces have not been shown to scale, but it is apparent to those skilled in the art that, for material and manufacture related technical reasons, the thickness of the material and other characteristics of a plastic material piece substantially affect the dimensions of the pin 1 and the aperture 3 in a widely known manner. When using the connection according to the invention in connection with an injection moulding method, the manufacturing method further sets requirements previously known per se also for the selection of material and for the connection surface of the first piece, i.e. the piece to be connected to the plastic material piece. To enable the sliding pin connection, the materials are to be selected such that they do not become fixedly attached to one another in connection with injection moulding. The connection surface of the first piece, in turn, has to be smooth enough so that when injection moulding the second piece against the first piece, no unevenness is formed on the surface of the pieces to prevent the pieces from sliding with respect to one another within the limits allowed by the connection when the temperature changes. [0024] Figure 7 shows a part of an electronic device 9 including a circuit board 10 and a part 11 which has been cast in connection with the circuit board and made from a thermoplastic elastomer or plastic. Preferably, the circuit board 10 is flexible.

[0025] The electronic device 9 may be any portable of fixed device. Examples include a mobile telephone and a computer. The cast part 11 may serve e.g. as a case, cover of the electronic device 9 and/or as protection for the circuit board 9. The cast part 11 may be rigid or flexible, made e.g. from a thermoplastic elastomer or plastic. Examples of the materials for the cast part 11 include polyethene PE, polyvinyl chloride PVC, acrylonitrile-butadiene- styrene ABS, and polypropylene PP. [0026] The surface of the circuit board 10 is provided with fasteners 12. Preferably, the fasteners are fastened to the circuit board 10 with a soldering material 13. The fasteners 12 are thus soldered in the circuit board 10 by using a surface mounting technique; of course, the fastening may be carried out using e.g. glue or the like.

[0027] Next, the circuit board 10 provided with the fasteners 12 is arranged in an injection mould and the thermoplastic elastomer or plastic material is cast in connection with the circuit board. Insert casting is thus used in the manufacture of the electronic device. The material in question to be cast flows around the fasteners 12, providing a mechanical connection between the material to be cast and the fasteners 12. Consequently, the material to be cast becomes extremely well attached to the circuit board 10.

[0028] Figure 8 shows a fastener 12. The fastener 12 is formed from a metal sheet by punching. Thus the fastener 12 preferably includes a bottom plate 15 and and a tip 14 punched therefrom. The material of the fastener 12 may be e.g. stailess steel.

[0029] The tip 14 is elevated from the bottom plate 15, as is illustrated in Figure 9. The fastener 12 can be simply and reliably soldered to the circuit board 2 from the bottom plate 15. The tip 14 penetrates into the material to be cast, providing a reliable mechanical connection between the fastener 12 and the cast material in question.

[0030] In some cases the features disclosed in this application may be used as such, irrespective of other features. On the other hand, when necessary, the features disclosed in this application may be combined in order to form different combinations.

[0031] The drawings and the related description are only intended to illustrate the idea of the invention. The details of the invention may vary within the scope of the claims.

Claims

1. A connection for connecting at least two pieces having different thermal expansion coefficients to one another, characterized in that the connection is provided with at least one fastening aperture (3) arranged in a first piece (2) and at least one pin (1) which is arranged in a second piece (8) and which consists of an end (5) which is at least in a longitudinal or lateral direction wider than the fastening aperture, and a shaft (6) which is at least in a longitudinal or lateral direction narrower than the fastening aperture (3), the pin being arranged to travel through the fastening aperture (3) of the first piece such that the end (5) of the pin and the second piece (8) reside on opposite sides of the first piece (2) with respect to the fastening aperture (3).

2. A connection as claimed in claim ^ characterized in that the connection has a neutral point (7) in the direction of which a sliding direction of the connection is directed.

3. A connection as claimed in claim 2, characterized in that the pieces are connected to one another immovably at the neutral point (7).

4. A connection as claimed in claim 2 or 3, characterized in that the neutral point (7) is a centre point of the piece.

5. A connection as claimed in any one of the preceding claims, characterized in that the pieces are connected to one another by at least two connections formed by the fastening aperture (3) and the pin (1) and positioned symmetrically with respect to the neutral point (7).

6. A connection as claimed in any one of the preceding claims, characterized in that at least the second piece together with its pins is an injection moulding piece.

7. A connection as claimed in claim 6, characterized in that the first piece is a circuit board.

8. A connection as claimed in claim 7, characterized in that the circuit board is flexible.

9. A connection as claimed in any one of the preceding claims, characterized in that the second piece (8) is flexible.