WO2010040399A1

WO2010040399A1 - Method for protecting a condutive material structure provided on a carrier

Info

Publication number: WO2010040399A1
Application number: PCT/EP2008/063475
Authority: WO
Inventors: Ulf Palin; Jerry Nilsson; Elis Hirvonen
Original assignee: Laird Technologies Ab
Priority date: 2008-10-08
Filing date: 2008-10-08
Publication date: 2010-04-15
Also published as: CN102177613A

Abstract

A method for protecting a conductive material structure provided on a carrier comprises the steps of covering (26) the conductive material structure with an environmental protection layer except for in a set of pre-specified areas, where said set of pre-specified areas includes at least one contact area on the conductive material structure; and placing (28) electrical contact enhancing material on the contact area, which placing of electrical contact enhancing material is performed after the conductive material structure has been covered with the environmental protection layer.

Description

METHOD FOR PROTECTING A CONDUCTIVE MATERIAL STRUCTURE

PROVIDED ON A CARRIER

FIELD OF INVENTION The present invention generally relates to conductive material structures on carriers, such as conductors and/or radiating elements on carriers. More particularly, the invention relates to a method for protecting a conductive material structure on a carrier.

BACKGROUND

Patterns or structures of electrically conductive material that are provided on carriers need to be connected to other elements such as other electrically conductive material structures or patterns, circuits, components and elements.

It is known to cover such patterns with protective material in order to protect the pattern against environmental influences such as corrosion, moisture, EMD from other elements etc.

In order to improve an electrical connection to another element it is also often desirable to provide the pattern with contact enhancing material.

US 6,910,636 shows an antenna covered with a dielectric protective layer and a cover layer through which a through hole runs. A contact area is here also provided via the through hole through inserting an external contact pad in this through hole. The protective layer, contact layer and antenna are parts of an IC card. US 2007/0035466 shows a dielectric mask being placed on a conductive pattern. The mask has openings that are used for forming the conductive pattern. The conductive pattern may be an antenna.

US 6,353,420 shows an antenna provided on a substrate. The substrate also has through holes. Electrical connections to the antenna are provided through filling the holes with electrically conductive material. An additional layer may also be applied for protection from environmental conditions and mechanical damage.

US 2002/0094639 shows an antenna and antenna contact leader lines in an RFID circuit. In one embodiment the contact leader lines are covered by an insulating layer having via holes, which are filled with metal for contacting purposes. A transistor structure is then provided on top of the insulating layer.

Contact enhancing materials may be expensive. These materials may furthermore be environmentally undesirable. Consequently it is of interest to limit their use.

This limitation of contact enhancing material should also be performed without providing additional steps in the process of providing a cover and contact enhancing material to the carrier with the conductive material structure in order to keep production costs low. SUMMARY OF THE INVENTION

An object of the present invention is therefore to provide a method for protecting a conductive material structure on a carrier that limits the amount of contact enhancing material used while at the same time avoiding additional process steps.

The invention is based on the realization that an environmental protection layer used for protecting a conductive material structure from the environment can be used as a mask when placing electrical contact enhancing material on the structure.

According to a first aspect of the present invention there is provided a method as defined in claim 1.

Further preferred embodiments are defined in the dependent claims.

The invention provides a method for protecting a conductive material structure on a carrier where the problem of limiting the amount of contact enhancing material used while at the same time avoiding additional process steps is solved through covering the conductive material structure with an environmental protection layer, except for in a set of pre-specified areas including at least one contact area on the conductive material structure, and placing electrical contact enhancing material on the contact area, which placing of electrical contact enhancing material is performed after the conductive material structure has been covered with the environmental protection layer. BRIEF DESCRIPTION OF DRAWINGS

The invention is now described, by way of example, with reference to the accompanying drawings, in which:

fig. 1 shows a top view of a carrier provided with a conductive material structure;

fig. 2 shows a top view of the carrier in fig. 1, where the conductive material structure has been covered by a an environmental protection layer;

fig. 3 shows a top view of the carrier in fig. 2, where contact areas of the conductive material structure have received electrical contact enhancing material;

fig. 4 shows a side view of the carrier in fig. 1;

fig. 5 shows a side view of the carrier in fig. 2;

fig. 6 shows a side view of the carrier in fig. 3; and

fig. 7 shows a flow chart of a number of method steps in a method of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

In the following, a detailed description of preferred embodiments of a method for protecting a conductive material structure provided on a carrier will be given. In the description, for purposes of explanation and not limitation, specific details are set forth, such as particular applications, techniques etc. in order to provide a thorough understanding of the present invention. However, it will be apparent to one skilled in the art that the present invention may be utilized in other embodiments that depart from these specific details. In other instances, detailed descriptions of well-known methods, apparatuses, and circuits are omitted so as not to obscure the description of the present invention with unnecessary details.

The present invention is generally directed towards the provision of conductive material structures on carriers, i.e. of material structures that are able to conduct electrical currents. Such structures can be conductors or antenna radiator traces provided on circuit boards, flex films, chassis, covers, casings or middle decks of a piece of electronic equipment. A piece of electronic equipment where such a carrier having a conductive material structure may be provided can be such a thing as a portable electronic device, like a gaming machine or an electronic organizer. Such a portable electronic device may also be a portable communication device such as a cellular phone, a lap top or a desk top computer.

Typically such a conductive material structure on a carrier is provided as a mounting entity, which is to be mounted as one piece in such a piece of electronic equipment. The conductive material structure of the present invention may then be provided on the exterior of this entity, like on the surface of it. This means that the carrier in this case will become an outer surface of such a mounting entity. This also means that the conductive material structure is the subject of environmental hazards such as corrosion and moisture. The conductive material structure will therefore need an environmental protection layer or an environmental protection cover that protects it from this environment, such as protecting it from air, dirt and/or water.

The conductive material structure will furthermore be connected to other entities such as components and circuits in the electronic device. In order to do this it may furthermore be necessary to provide the conductive material structure with contact enhancing material, where such contact enhancing material may act to lower the contact resistance.

The way that such a protection layer and contact enhancing material are provided is in many cases through providing the whole conductive material structure with contact enhancing material and thereafter the conductive material structure is covered with a protection layer. This has the disadvantage in that an excessive amount of contact enhancing material is used. This may be very expensive, especially if the contact enhancing material used is gold.

The present invention is therefore directed towards providing a method for protecting a conductive material structure provided on a carrier that limits the amount of contact enhancing material being used to only what is necessary for ensuring contact at areas of the structure where contact is desired. This is according to the invention furthermore done without performing any additional method steps.

Fig. 1 — 3 shows a top view of a carrier with a conductive material structure being subjected to three separate production steps of the present invention, fig. 4 — 6 shows a side view of the same production steps, and fig. 7 shows a flow chart of the process steps being performed.

The method according to the present invention starts with the provision of a carrier 10 with a conductive material structure. One such exemplifying structure 12 is shown in fig. 1 — 6. This structure 12 is here a radiating element structure or antenna structure 12 that is provided on a carrier 10. Here the antenna structure 12 is furthermore in the form of a Planar Inverted-F multiband antenna (multiband PIFA) . The structure 12 does furthermore include at least one contact area, i.e. an area where the structure is to be connected to another entity, such as for instance to a conductor, to a circuit, to a circuit board, to a component etc. Since the structure according to the present example is a PIFA, two such areas 14 and 16 are provided on this structure 12. Naturally there may be more or fewer such areas for other types of conductive material structures. In the case of PIFA one such area 14 is a signal connection area for connection to a radio circuit and the other 16 is a ground connection area for connection to a ground potential. The connection to the radio circuit and to the ground potential may both be provided via a circuit board provided separately from the carrier 10.

It has to be emphasized that the shown antenna structure 12 is only exemplifying and the present invention can be used on any antenna structure. A conductive material structure may also include more than one antenna. The conductive material structure is actually not limited to antennas at all but may be any conductive material structure provided on a carrier. It may for instance be the conductors and component contact points provided on a printed circuit board

(PCB), i.e. the layout of a PCB. Such a structure may, as was mentioned before, be a conductive structure provided on carrier in the form of a printed circuit board (PCB) or a flex film. In these cases the structure is normally a two-dimensional structure provided on a planar surface of carrier.

It should however be realised that the invention is not limited to these types of carriers and conductive material structures. The carrier with the conductive material structure may have a three-dimensional extension, i.e. both the conductive material structure and the carrier may extend in three dimensions. Here the three-dimensional conductive material structure may be provided on a curved surface of a carrier or on two planar surfaces of a carrier that are provided at an angle to each other, like an exemplifying angle of ninety degrees. Such a surface or surfaces may be the exterior or a part of the exterior of a mounting entity, like for instance a chassis or a middle deck of a portable electronic device. The conductive material structure may be provided on the carrier through Laser Direct Structuring (LDS), where a plastic material that is doped with particles of electrically conductive material, like copper, is irradiated with laser light. This laser light then causes the metal to appear on the surface of the plastic material. It should here be realized that other ways of providing a conductive material structure may also be used such as Moulded Interconnect Device (MID), Two Shot Moulding and Photo Imaging. The electrically conductive material used for the structure is with advantage a metal such as

Copper, Nickel or Silver. However the material is not limited to being metal but may also for instance be a conductive polymer or a conductive glue.

With reference now being made also to fig. 7, the invention starts with providing a carrier 10 with a conductive material structure that is here an antenna radiator structure 12, step 24. Then the radiator structure is covered with an environmental protection layer or protective cover 18 except for in a set of areas including at least one contact area and here the two contact areas 14 and 16, step 26. This protective cover 18 is here furthermore provided onto the side of this conductive material structure 12 that faces away from the carrier 10. This means that a protective layer is provided over the parts of the structure that are to be insulated and not areas to be used for contacting other devices or for performing other activities, such as probe areas for testing. Here it is possible that a mask of protective material may be sprayed over these areas. It is also possible to use various types of printing for instance ink-jet printing, screen printing or pad printing. In this embodiment the protection layer 18 is printed over the radiator structure 12 except for in the contact areas. The printing is here furthermore with advantage pad printing. The material may here be a plastic material. It may also in some cases be a metal such as gold, silver or nickel that does not corrode easily. However an electrically insulating material, like a plastic material may be advantageous for cost reasons. This material may be an acrylic lacquer or polyester. The mask is here selected so that it protects the underlying structure from environmental hazards such as corrosion and/or moisture. The use of plastic has another advantage. It will provide electrostatic discharge (ESD) protection from other components in the device. If the structure is an antenna the influence on the antenna efficiency and the radio frequency (RF) properties will then be limited.

The use of pad printing is of special interest in case the structure is provided onto a curved carrier surface, since pad printing uses a pad that receives material according to a desired structure on a pad, which is then pressed onto a surface that can have any shape. The pad here adapts its shape to the shape of carrier, which means that a conductive material structure provided on a curved carrier surface may be covered. Such a position of a conductive material structure may be of advantage in many portable electronic devices that need to be kept small. This therefore means that the volume in the interior of such a device, like a cellular phone, is used more efficiently.

It should here be realised that it is also possible to use a masking technique such as for instance to deposit the protective material over all the structure, provide a mask over the parts that are to retain the protective material, remove the protective material from the non-masked areas and then remove the mask material.

After the structure 12 has been covered with the protective layer 18, electrical contact enhancing material 20, 22 is placed in the uncovered contact areas 14 and 16 of the structure 12, step 28. The placing of electrical contact enhancing material is thus performed after the conductive material structure 12 has been covered with the environmental protection layer 18. The material may be placed in these contact areas through plating. It should be realized that this plating may be electroless plating or electroplating. In this step of placing electrical contact enhancing material, the protective layer 18 acts as a mask that stops the other parts of the structure from receiving contact enhancing material. The contact enhancing material may here be a metal such as gold, silver, nickel or tin or a combination of such metals such as a combination of gold and nickel.

It should here be realised that other techniques than plating may be used, such as for instance sputtering or chemical vapour deposition.

In this way the cover that is used for protecting the structure in the end product that is to be mounted in an electronic device acts as a mask when providing contact enhancing material. This means that the amount of contact enhancing material used is reduced. This is also done without using additional process steps.

The printed environmental protection layer has a further advantage. It can be used for providing an aesthetically interesting surface on the carrier. The surface may through this printing be provided with a graphical design, such as a company logotype, a figure or some other type of design. It can also be used for providing characters such as text and numbers and can therefore provide written and/or graphical messages.

As mentioned above the set of areas that are to be excluded from being covered by the protective layer includes electrical contact areas for connection to other entities in the electronic equipment. However, this set may include also other areas such as probing areas that are to be used for testing the contact material structure. Such probing areas may or may not receive contact enhancing material.

Preferred variations of a method for protecting a carrier with a conductive material structure according to the invention have been described. However, it will be appreciated that these can be varied within the scope of the appended claims. Therefore the present invention is only to be limited by the following claims.

Claims

1. A method for protecting a conductive material structure (12) provided on a carrier (10) comprising the steps of:

covering (26) the conductive material structure (12) with an environmental protection layer (18) except for in a set of pre-specified areas (14, 16), where said set of pre-specified areas includes at least one contact area (14, 16) on the conductive material structure (12); and

placing (28) electrical contact enhancing material (20, 22) on said contact area (14, 16), which placing of electrical contact enhancing material is performed after the conductive material structure has been covered with the environmental protection layer.

2. The method according to claim 1, wherein the step of covering comprises printing the protection layer onto the conductive material structure.

3. The method according to claim 2, wherein said printing is pad printing.

4. The method according to any previous claim, wherein the step of placing electrical contact enhancing material comprises plating electrical contact enhancing material onto said contact area while using the environmental protection layer as a mask.

5. The method according to any previous claim, wherein the conductive material structure defines at least one antenna radiator.

6. The method according to any previous claim, wherein the environmental protection layer protects the structure from air.

7. The method according to any previous claim, wherein the environmental protection layer is of an electrically insulating material.

8. The method according to any previous claim, wherein the step of covering the conductive material structure with an environmental protection layer comprises applying the environmental protection layer (18) on a side of the conductive material structure (12) that faces away from the carrier (10).

9. The method according to any previous claim, wherein the carrier and the conductive material structure have a three-dimensional extension.

10. The method according to any previous claim, wherein the carrier is a mounting entity for being mounted in a piece of electronic equipment and the conductive material structure is provided on at least one exterior surface of said mounting entity.

11. The method according to claim 10, wherein said piece of electronic equipment is a portable electronic device.

12. The method according to claim 11, wherein the portable electronic device is a portable radio communication device.

13. The method according to claim 12, wherein the portable radio communication device is a cellular phone.