WO2009142592A1 - Electronic device and component protection during manufacture - Google Patents

Abstract

The invention relates to an electronic device comprising a substrate having a surface and a compartment structure provided on said surface and comprising a frame and a film sealingly covering the frame. There is at least one component provided inside said compartment structure on said surface. The housing structure enclosing the component is embedded in a layer of material. The device can be a smart card.

Description

ELECTRONIC DEVICE AND COMPONENT PROTECTION DURING MANUFACTURE

Technical Field of the Invention The present invention relates to manufacture employing pick-and-place mounting of components in wet environments. In particular it relates to manufacture electronic devices, such as thin functional cards, commonly referred to as smart cards, e.g. credit cards having electronic functionalities. More in particular it relates to provision of push buttons for controlling the functionality of the card using such pick-and-place mounting.

Background of the invention

Modern credit cards and other types of cards for e.g. identification, cards providing access to secure premises and other localities, and other types, commonly require the user to enter a PIN code in order that a transaction be granted or in order that a locked door be opened.

PIN codes must either be remembered by the user, with the apparent risk that one may forget it, or be kept in written form where it can be easily accessed. The latter could mean that the code is kept in a wallet together with the card, with the obvious risks associated therewith.

One solution to the problem discussed above is to provide the card with a display that shows the numbers only upon activation by the user. Such cards are frequently referred to as Advanced Smart Cards with Integrated Displays (ASCID). Activation of the display can be achieved by using biometric means, e.g. to provide the card with a sensor element that can identify the correct users fingerprint.

Only when the microprocessor in the card has identified the fingerprint as belonging to the correct card holder the information is displayed.

However, there is still a need to navigate between different functions in the display, which normally is relatively limited in size, and cannot therefore display all information at one time. To this end there can be provided push buttons for enabling scrolling through menus or between lines of information in the display.

Such push buttons normally comprise a resilient element that when pressed upon will close an electric circuit that triggers a shift from one entry in the display to another. The manufacturing is normally performed using so called "pick-and-place" methods, where components are fed on a transport line to a point of assembly and a robot removes the component from the transport band and places it on the card in the correct position.

Furthermore, during manufacture of the card it is normally required to provide a flat top surface on a card. Such flat surface is commonly made by spreading a low viscosity adhesive or polymer on the substrate on which all components have been assembled, these components obviously exhibiting a topography that cannot be printed on. Of course the components also need a protective layer.

In the process of applying the adhesive or polymer, by virtue of the low viscosity, this material would penetrate into the push button assembly if preventive measures are not made. Thus, in view of the requirement that there must be no contaminating material "inside" the push button assembly, which could insulate the components from each other and prevent the electric circuit to be closed, there is a need to protect the push button during manufacturing of the card.

Similar problems occur in the manufacturing of many other kinds of electronic devices comprising sensitive components. An example is the mounting of a crystal on a printed circuit board, for providing a clocking frequency to drive circuits, where the crystal must be able to oscillate freely, and thus must be protected from coming into contact with adhesives or other liquid materials during manufacturing, which would prevent proper function of the crystal.

Summary of the invention

In view of the above mentioned problem in connection with the manufacture of electronic devices having sensitive components, the object of the present invention is to provide a device comprising a protected component, said device being defined in claim 1. In a further aspect of the invention, there is provided a push button structure for a smart card, and which is defined in claim 1 1.

In a still further aspect of the invention there is provide a smart card comprising a push button. This card is defined in clam 12.

In a further aspect of the invention, there is provided a method of making electronic devices, such as smart cards, that will protect components, such as push buttons, during manufacture, and which is particularly suited for pick- and-place manufacturing in wet environments. The method is defined in claim 13.

Brief Description of the Drawings

Fig. 1 shows a smart card having a display and push buttons according to the invention;

Fig. 2a-b illustrates one step in the manufacturing method according to the invention;

Fig. 3 illustrates a further step in the manufacturing method according to the invention;

Fig. 4a illustrates a push button dome component;

Fig. 4b is a cross section through a push button structure according to the invention;

Fig. 4c illustrates the electric circuitry for the push button structure according to the invention;

Fig. 5 shows an embedded push button structure according to the invention; and Fig. 6 shows a double push button structure according to the invention.

Detailed Description of Preferred Embodiments

The inventive concept will be illustrated by way of examples from two different technical applications, namely so called smart cards and a device requiring an oscillating crystal for providing a clocking frequency.

First the general structure of a smart card comprising push buttons as designed according to the invention will be given.

Fig. 1 shows a top view of a standard format smart card, generally designated 10, and having a so called smart chip 12, a display 14, and two push buttons 15a and 15b. The number of push buttons can vary, and for some applications it may be sufficient with a single button, whereas in other cases three or four buttons, or even more can be provided. There is also shown a biometric sensor 16 for identifying a users fingerprint. The latter is not strictly necessary if user identification is not the key issue for the use of the card.

Now a pick-and-place mounting procedure for mounting components such as push buttons will be described with reference to Fig. 2.

Fig. 2a shows how a transport web 20 carries components 22a-c (only schematically illustrated). The web has a slightly adhesive surface in order that the components 22 not be lost during the transport. When the components arrive at the edge 23 of the web 20 they will release from the web an begin to protrude out from the web as shown for component 22c. at this instant a robot using vacuum suction will pick up the component and carry it to a mounting station where it is placed on e.g. a smart card substrate, as schematically illustrated in Fig. 2b.

If it is desired to provide a flat surface on the final device 30 that is being manufactured, a liquid (low viscosity) material 31 such as an adhesive or a curable polymer is poured over the surface of the substrate 32 with its component 22, as schematically shown in Fig. 3, which is a cross-section of a device during pouring of the liquid. In order to keep the liquid on the surface and so as to not allow the liquid to flow out over the edges of the substrate, there is provided a frame 33 around the substrate 32, which is removed when the adhesive or polymer has cured.

Now a push button as used in the present invention will be described with reference to Fig. 4a.

The button 40 is essentially dome shaped 41 as seen in Fig. 4a and made of a flexible and resilient material, such as steel. The dome is suitably coated with an electrically conductive layer on the side facing the substrate, or the conductivity of the material itself can be used. It has four corners 42 (see Fig. 4b) forming points of contact with the substrate surface 43 of e.g. a card on which it is mounted. At the apex of the dome 41 there is a small indentation 44a forming small protrusion 44b. This protrusion will form a contact member and when the dome 41 is pressed downwards by someone using the card the protrusion is brought into contact with a corresponding contact pad 45 on the substrate located just under the dome apex. Thereby an electric circuit will become closed and electricity can be supplied via said conductive layer from the pads 42' and to e.g. the display so as to activate it. The electrical coupling is schematically shown in Fig. 4c.

Thus, as is easily understood, if the dome 41 is attached with its corners 42 at the corresponding points 42' in Fig. 4c, electrical current will flow from the battery 46 via the conductive coating on the dome and to the pad 45 and further to the display (not shown), when the protrusion 44b contacts the pad 45.

Instead of providing a conductive coating on the dome 51 it is possible to just provide metallization strips interconnecting the corners 42 and the protrusion 44b.

Now, if the dome 41 were to be mounted to the substrate 43 without any precautions having been made it is obvious that a liquid polymer or adhesive provided on the substrate, as described above, would flow in under the dome 41 and block any possibility of operating the push button. Therefore, according to the present invention the dome 41 will be protected in a way that will be described with reference to fig. 5.

The inventive idea is to provide a frame 50 on the surface 54 of a substrate 53 around the component 52 to be protected, in Fig. 5 exemplified with a dome 51 (like the one shown in Fig. 4 and forming a push button), and to cover the frame 50 with a very thin film 52, suitably less than 20 μm thick. The film has a layer of adhesive on at least one side, so as to stick to the frame 50 when applied, and also so as to adhere to the dome 51. The assembling sequence is suitably to locate the dome 51 on a transport line, and subsequently to place the frame 50 around the dome. Then, the film 52 is supplied form a web of film on a supply roll and suitably rolled out over the frame 50 and dome 51, and when it is provided in adhering contact with frame /dome assembly it is cut from the web resulting in the structure shown in Fig. 5. Thus, the dome will be hanging freely from the film 52 but the adhesive on the film is selected such that the dome safely can be lifted off from the transport line in the pick-and-place operation.

The frame 50 can comprise a plastic material and suitably exhibits a thickness of about 0,30 - 0,40 mm. Suitable materials can be selected among the frame comprises silicone rubber, polyethylenetereftalate (PET), polycarbonate (PC), polyurethane, polyethylene, PEN, or combinations thereof. However, the exact design of the frame is not critical, and it could instead comprise a thin plastic spacer and a double sided adhesive in a composite structure as long as the thickness is large enoug to accommodate the dome.

The film 52 is suitably made of poly-ester or poly-carbonate and the adhesive provide thereon is suitably selected from adhesives of the type Epoxy, Polyurethane, Acrylate or Thiolene.

In fig. 5 there is also shown an embedding layer 55 of a (suitably) transparent material.

For many applications it may well be sufficient to provide a single push button of the type disclosed above. However, if it is required to be able to navigate, e.g. to scroll up and down in the display window, at least two buttons will be required. If an "ENTER" or "OK" function is desirable even three buttons could be required. For submenu selections one might want to have four buttons, and so on. The only limitation is essentially only the space available on the card.

For a dual button configuration it may be necessary to design the frame to account for the larger area that the film has to cover. Thus, as can be seen in Fig. 6, the frame 60 surrounds two buttons 61a and 61b. Between the two buttons the frame in the shown embodiment has two additional frame portions 62a and 62b, respectively, extending inwards but leaving a small opening between the two compartments formed. These frame portions are provided to help support the thin covering film that is to be attached on top of the push button assembly. The reason for not providing a partition wall extending across the entire frame width is to provide pressure levelling between the compartments when one of the buttons is pressed down. Of course the additional supporting frame portions are not strictly necessary, but will be the preferred embodiment.

After mounting the components on the substrate, they are embedded in a layer of material to provide a flat surface to render it printable. The material for embedding is suitably selected from transparent or semi-transparent materials such as polyethylenetereftalate (PET) or polycarbonate (PC). Any other material suitable for printing can be used.

In another application of the inventive method and principle, a component such as a crystal for providing a clocking frequency is mounted in a similar way as described above.

In a preferred embodiment the process is very similar to the one described above with reference to Figs. 2-3. Thus, the crystal is placed on a transport web, whereupon a frame is positioned so as to surround the crystal. Then, an adhesive film is applied to cover the frame and crystal, whereby the crystal sticks to the adhesive surface of the film. The assembly of crystal, frame and film is then lifted e.g. by a suitable vacuum device and moved to substrate on the surface of which it the assembly is placed. The frame having an adhesive provide on its lower surface will adhere to the surface and form a sealed protective cavity for the crystal.

Claims

CLAIMS:

1. An electronic device comprising

a substrate (53) having a surface (54);

a compartment structure provided on said surface and comprising a frame (50) and a film (52) sealingly covering the frame (50);

at least one component (51) provided inside said compartment structure on said surface; wherein

said housing structure enclosing the component is embedded in a layer of material (55).

2. The device as claimed in claim 1 , wherein the compartment structure has a thickness of 0,2 - 1 mm.

3. The device as claimed in claim 1 , wherein the frame comprises silicone rubber, polyethylenetereftalate (PET), polycarbonate (PC), polyurethane, polyethylene, PEN, or combinations thereof.

4. The device as claimed in claim 1 , wherein the film is made of polyester

5. The device as claimed in claim 4, wherein the film is less than 20 μm thick.

6. The device as claimed in claim 1 , wherein the component is a micro switch/push button.

7. The device as claimed in claim 1 , wherein the material layer embedding the compartment structure has an essentially flat surface to render it printable.

8. The device as claimed in claim 7, wherein the material of the embedding layer is polyethylenetereftalate (PET) or polycarbonate (PC).

9. The device as claimed in any preceding claim 1-7, which is a smart card.

10. The device as claimed in claim 1 , wherein the component is a crystal.

1 1. Push button structure comprising:

a substrate surface having a plurality of contact pads provided thereon;

an essentially dome shaped flexible member having an upper surface and an under surface, and being located over a first one of said contact pads, and having a contact member on its surface mating with said contact pad to close an electric circuit when the flexible dome is pressed downwards by exerting a force on said upper surface;

the dome shaped member having at least one support structure in contact with at least a second one of said contact pads on said substrate surface;

an electrically conductive material provided on the dome shaped flexible member so as to form an electrically conductive path between said first and second contact pads when the flexible dome is pressed down;

a frame surrounding said dome member; and

a film covering said frame forming a sealed compartment containing/ housing said dome shaped member.

12. A smart card comprising a push button structure as claimed in claim 1 1.

13. A method usable in/for the manufacture of electronic devices comprising at least one component on said device that needs to be protected from manufacturing steps involving a wet environment, the method comprising

at an assembly station, providing a component to be mounted on a substrate surface of the device; providing a frame and placing the frame so as to surround said component;

attaching to the frame a thin film having adhesive provided thereon to cover the component whereby also the component is attached to the film so as to form a unit comprising frame, film and component;

picking/ lifting/ moving the unit comprising frame, film and component from the assembly station and mounting/ placing the unit on a substrate surface of said device to form a sealing housing structure around the component on the substrate surface; and

performing further steps of manufacture involving a wet environment, whereby the component is protected form being contaminated by the wet environment by the frame and film.

14. The method as claimed in claim 13, wherein the further step involving a wet environment comprises applying a curable low viscosity material over the substrate covering the housing, and curing said low viscosity material so as to provide a protective layer on said substrate.

15. The method as claimed in claim 13, wherein said protective layer is essentially flat to render it printable.