Laminated foil structure and method of forming the same

Abstract

When forming layer stacks in the presence of solder material, uncontrolled flow of the solder material at the interface of two different layers of the layer stack may significantly be mitigated by providing an area of increased pressure in the material of the overlaying foil layer. For example, the area of increased pressure may be generated during the lamination process by providing a pressure inducing structure, for instance on the underlying foil layer, which laterally surrounds the solder material and therefore, in combination with the material of the overlying foil layer, reliably confines the solder material.

Claims

1. A method of forming a laminated foil layer stack, the method comprising: providing a first foil layer including a layer portion with a contact area having formed thereon a solder material, positioning a second foil layer adjacent to said first foil layer so as to form a layer stack, said second foil layer having an opening extending through the second foil layer and exposing said solder material, defining an area of increased pressure locally in said second foil layer, said area of increased pressure laterally surrounding said opening, and applying pressure and heat to said first and second foil layers so as to build up increased pressure in said area of increased pressure, and laminate said second foil layer to said first foil layer with said area of increased pressure laterally confining said solder material.

2. The method of claim 1, wherein a temperature of said solder material upon applying pressure and heat to said first and second foil layers exceeds a melting temperature of said solder material.

3. The method of claim 1, wherein defining an area of increased pressure locally in said second foil layer comprises providing a pressure inducing structure that has increased thermal and mechanical strength compared to a base material of said second foil layer.

4. The method of claim 3, wherein providing said pressure inducing structure comprises forming said pressure inducing structure by modifying a portion of at least one of said first and second foil layers so as to establish said increased thermal and mechanical strength prior to applying heat and pressure to said first and second foil layers.

5. The method of claim 3, wherein providing said pressure inducing structure comprises positioning said pressure inducing structure in and/or adjacent to said second foil layer.

6. The method of claim 5, wherein said pressure inducing structure is temporarily positioned above said second foil layer and is removed after lamination of said second foil layer to said first foil layer.

7. The method of claim 3, wherein providing said pressure inducing structure comprises positioning said pressure inducing structure on said first foil layer.

8. The method of claim 7, wherein providing said pressure inducing structure comprises commonly forming said pressure inducing structure and a conductor pattern of said layer portion of said first foil layer in a same process.

9. The method of claim 1, further comprising determining in advance a final lateral size and shape of said opening so as to determine lateral dimensions of said solder material after having applied pressure and heat.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) With reference to the accompanying drawings embodiments as discussed above and further additional embodiments will now be described in more detail. In the drawings,

(2) FIG. 1A schematically illustrates an exploded perspective view of two foil layers to be formed into a foil layer stack with improved confinement of a solder material according to illustrative embodiments;

(3) FIG. 1B schematically illustrates a cross-sectional view of the two foil layers to be stacked;

(4) FIG. 1C schematically illustrates the foil layer stack during a process step for applying heat and pressure so as to laminate the first foil layer to the second foil layer while providing for superior confinement of a solder material on the basis of several techniques for implementing an area of increased pressure according to illustrative embodiments;

(5) FIG. 1D schematically illustrates a cross-sectional view of a portion of the first foil layer with a pressure inducing structure according to illustrative embodiments;

(6) FIG. 1E schematically illustrates a perspective view of a portion of a first foil layer having formed thereon a conductor pattern including contact areas with solder material and respective pressure inducing structures according to illustrative embodiments; and

(7) FIG. 2 schematically illustrates a cross-sectional view of a foil layer stack with superior solder material confinement according to still further illustrative embodiments.

DESCRIPTION OF PREFERRED EMBODIMENT

(8) FIG. 1A schematically illustrates an exploded perspective view of foil layer stack 100, which may represent a final product or an intermediate product for forming devices, such as pre-forms of card-type devices, as are typically used for fabricating payment cards, and the like. In other cases the foil layer stack 100 may represent a final product or a pre-form thereof for other sheet-type devices, such as datapages of security documents, labels for any type of products including wireless communication capabilities, such as RFID labels, and the like. In this example, the stack 100 may include a first foil layer 110 having appropriate lateral dimensions as to comply with device specific requirements. The first foil layer may include a layer portion 115, which may have formed thereon or therein a contact area 116, which is to be understood as a conductive area on our within the layer portion 115.

(9) It should be appreciated that although the layer 110 is referred to as a foil layer in the context of this application, this term is meant to also include any embodiments, in which the layer portion 115 represents a specific type of appropriate substrate material, such as a flexible carrier material used for flexible printed circuit boards, and the like, while other portions of the foil layer 110 may represent a different type of material, such as plastic material in the form of PVC, polycarbonate, and the like. Hence, the term foil layer is to be understood as any sheet-type or foil-type material layer, wherein different types of material may be present so as to meet the specific requirements of the layer of the stack 100 under consideration.

(10) In the embodiment shown, the contact area 116 may be covered by a solder material 117, which may represent any appropriate solder material as required for forming the stack 100 and imparting a desired connectivity to the stack 100. In some illustrative embodiments, the solder material 117 may represent a solder material having a relatively low melting temperature, for instance in the range of 150° C. and less, which may frequently be encountered in the manufacturing card-type devices, such as payment cards, and the like, in which the respective electronic modules, sensor elements, and the like may have to be electrically connected with each other, at least partially, on the basis of a respective solder material.

(11) The stack 100 may include a second foil layer 120, which may be positioned “above” or adjacent to the first foil layer 110 and may be laterally aligned to the layer 110 in order to be formed into the stack 100 on the basis of appropriate process conditions, such as applying heat and pressure, as will be described later on in more detail.

(12) The second foil layer 120 may include an opening or hole 121 that extends through the entire layer 120 so as to expose the solder material 117. That is, the lateral size, shape and position are selected such that the solder material 117 is exposed upon connecting the layer 120 to the layer 110. Furthermore, an area of increased pressure 122 is defined in the second layer 120 so as to laterally surround the opening 121 and thus also laterally surrounding the solder material 117 after the first and second layers 110, 120 have been connected to each other.

(13) In this context the term “defining” in the context of the area of increased pressure is to be understood such that a region is determined, in which during the application of pressure to the first and second foil layers when performing a lamination process the area 122 of increased pressure is locally formed, while without applying external pressure to the area 122, for example prior to the lamination process, similar pressure conditions may prevail in the area 122 as in other areas of the second layer 120. As will be described later on in more detail, several techniques may be applied so as to locally, i.e., in the area 122, induce increased pressure within the material of the second foil layer 120 when performing the lamination process by applying heat and pressure to the layers 110, 120.

(14) FIG. 1B schematically illustrates a cross-sectional view of the layer stack 100. As illustrated, the second foil layer 120 is positioned “above” or adjacent to the first foil layer 110 such that the opening 121 is aligned to the contact area 116 having formed thereon the solder material 117. Consequently, upon positioning the second foil layer 120 so as to be in contact with the first foil layer 110 the opening 121 laterally surrounds the solder material 117, and therefore also the area of increased pressure 122 laterally surrounds the contact area 116 and the solder material 117. Regarding the area or zone of increased pressure 122 it is to be noted that although precise boundaries are illustrated in the Figures, the skilled person will understand that the increased pressure in the area 122 actually generated during the actual lamination process pressure may vary laterally and vertically, i.e. along a height direction, which is represented in FIG. 1B as the vertical direction, within the area 122. Therefore, typically a continuous transition of a portion of increased pressure to regions of lower pressure in the vicinity of the area 122 may be observed during the actual lamination process. Moreover, it should be understood that in the state as shown in FIG. 1B the actual pressure conditions may not differ from the pressure conditions in the neighbouring regions of the layer 120 and a respective increase with respect to neighbouring material regions may build up during the actual lamination process.

(15) FIG. 1C schematically illustrates a cross-sectional view of the stack 100 during a process step, in which pressure, as represented by arrows 190, and heat as indicated by arrows 191, is supplied to the first and second foil layers 110, 120, which are positioned so as to be in contact with each other. Hence, as discussed above, the contact area 116 having formed thereon the solder material 117 is positioned within the opening 121 such that the solder material 117 is laterally surrounded by the opening 121, i.e., by inner side walls thereof, which in turn is laterally enclosed by the area of increased pressure 122. Upon applying the external pressure 190 to the layers 110, 120, appropriate means are provided so as to have a higher pressure in the area 122 compared to the area near the side walls of the opening 121, where the material of the layer 120 may more easily deform.

(16) To this end, in some illustrative embodiments, at least a portion of the material within the area 122 may be modified so as to change specific material characteristics, as indicated by material 122A, so that, for example, the modified portion 122A is less compressible when subjected to the external pressure 190 compared to non-modified portions of the layer 120. Consequently, the area 122 may actually act as an area of increased pressure due to the reduced compressibility of the portion 122A, thereby also transferring increased pressure to the interface formed between the layer 110 and the layer 120. Such a modification of the portion 122A may be achieved by surface treatment, irradiation with appropriate particles and/or photons, and the like.

(17) As previously discussed, in many cases, the melting temperature of the solder material 117 may be relatively low, instance 150° C. and less, while the heat energy 191 applied to the layer stack 100 may have to be selected so as to create a temperature above the melting temperature, thereby causing the melting of the solder material 117. Therefore, a liquid solder material 117 may spread out into the neighbouring areas at the interface between the first and second layers 110, 120, which may finally result in unacceptable characteristics of the layer stack 100. In particular, since the external pressure 190 may typically be transferred with unavoidable process variations, in particular when a plurality of layer stacks 100 have to be processed at the same time, respective flow paths at the interface between the layers 110, 120 may significantly depend on the local pressure induced by the external pressure 190.

(18) According to the area of increased pressure 122 such typical pressure variations caused by during application of the external pressure 190 may be less relevant, since increased pressure is transferred to the interface between the layers 110, 120 at or in the vicinity of the area 122, thereby providing for increased contact force and, thus, superior sealing effect. Therefore, any potential flow paths that might otherwise be taken by the liquid solder material 117 may be blocked. Since the area of increased pressure 122 is immediately effective as soon as the external pressure 190 is applied, the associated efficient sealing effect is effective from the beginning of the lamination process and thus is effective prior to melting the solder material 117 and transforming it into a relatively low viscosity state.

(19) In other illustrative embodiments, in addition or alternatively to providing the modified material 122A within the zone 122 a material portion of increased mechanical strength 122B may be provided locally within the area 122, thereby also using the reduced compressibility of this portion 122B within the area 122, thereby generating increased pressure and thus obtaining a superior sealing effect, as discussed above. For example, the portion of material 122B having the increased strength may be provided in the form of a metal component, such as a wire that is embedded into the layer 120 at any appropriate manufacturing stage, while in other cases, the material of reduced compressibility may be provided in the form of a plastic material.

(20) In still other illustrative embodiments, in addition to or alternatively to the material or portions 122A, 12AB, excess material 122C may be provided at or in the vicinity of the area 122, thereby also creating increased pressure and thus superior sealing effect upon applying the external pressure 190. The excess material 122C may be provided as substantially the same material as is used in the rest of the second foil layer 120 and may be formed on the basis of any appropriate process technique upon manufacturing the foil 120 or at any other appropriate manufacturing stage. In other cases, an appropriate structure of any appropriate material may be added to the foil 120 after having manufactured the foil layer 120 and may be permanently connected to the layer 120 by appropriate adhesive agents, lamination, and the like. For example, metal materials, other plastic materials of higher density, and the like may be used for structure 122C.

(21) In still other illustrative embodiments in addition to or alternatively to the techniques described above with respect to portions or structures 122A, 122B and 122C a pressure applying apparatus itself may be modified so as to generate the increased pressure in the area 122. For example, the pressure 190 may be applied on the basis of a “pressure plate” 180, in combination with an appropriate counterpart 181, wherein the pressure plate 180 may have an appropriate structure 182, that is, a protruding structure 182, which, when coming into contact with the foil layer 120, will generate the increased pressure in the area 122. It should be appreciated that the structure 182 may thus represent a structure that is temporarily applied so as to induce the increased pressure in the area 122, since after removing the pressure plate 180, also the structure 182 may be removed.

(22) In other illustrative embodiments, the structure 182 may be configured so as to be connected to the pressure plate 180 and be removable therefrom. In this case, the structure 181 may react with the material of the foil layer 120 upon applying heat 191 and the pressure 190, wherein the structure 182 connect to the layer 120 and may remain within the layer 120 upon removal of the pressure plate 180. In this case, the structure 182 may play the role of the excess material 122C, however, without being firmly associated to the layer 120 prior to the actual lamination process.

(23) Consequently, at least one of the structures 122A, 122B, 122C and 182 may act as a pressure inducing structure in order to generate the increased pressure within the area 122, thereby obtaining the superior sealing effect, as discussed above.

(24) FIG. 1D schematically illustrates a cross-sectional view of a part of the layer 110 including the layer portion 115. As illustrated, the contact area 116 and the solder material 117 formed thereon are provided with appropriate lateral dimensions, as indicated by 116D, for instance having dimensions of several hundred μm (micrometer) to several mm (millimeter), depending on the device specific requirements. Similarly, a thickness of the contact area 116 that is formed of any appropriate conductive material, such as copper, aluminium, copper alloys, and the like, may be selected in accordance with device and process requirements. For example, typically a thickness of 10 μm to several ten μm may be selected.

(25) Moreover, a pressure inducing structure 112 is formed on the layer portion 115 so as to laterally around the contact area 116, wherein the lateral dimension of the structure 112, indicated by 112D, may be selected in accordance with overall device and process requirements. For example, the lateral extension 112D may range from several ten μm to several hundred μm. Appropriate values for the thickness and the lateral dimension 112D may be selected on the basis of experiments, and the like, so as to obtain the desired sealing effect in combination with the layer 120, as discussed above in the context of FIGS. 1A to 1C.

(26) In some embodiments, the pressure inducing structure 112 may be formed of the same material as the contact area 116, thereby enabling application of the contact area 116 and the pressure inducing structure 112 in one and the same process step. For example, the layer portion 115 may include an appropriate carrier material that may be coated by a conductive material of appropriate thickness and conductivity, such as copper, and the like, and the respective layer may be patterned on the basis of lithography and etch techniques or by any other patterning techniques. In other cases, one or more appropriate precursor materials may be deposited in a selective manner, for instance by any type of printing techniques, and the actual conductive material, such as copper, may be deposited by electrochemical selective deposition techniques, and the like. Hence, upon forming the pressure inducing structure 112 together with the contact area 116 no additional process steps are required and therefore a highly efficient overall manufacturing process may be accomplished.

(27) In other illustrative embodiments the pressure inducing structure 112 may be formed as a separate component and may be attached to the layer portion 115 at any appropriate manufacturing stage. For example, a metal material, a plastic material of reduced compressibility or increased density, and the like may be pre-processed so as to obtain the structure 112 having the appropriate lateral size and shape and may be connected to the portion 115 immediately prior to the lamination process or at any other appropriate phase of the manufacturing process prior to performing the lamination process.

(28) FIG. 1E schematically illustrates a perspective view of the layer portion 115 according to further illustrative embodiments. As shown, the layer portion 115 may include a plurality of contact areas (not shown) in combination with the solder material 117 and a conductor pattern 118 that provides for the electrical connection to the contact areas (not shown) and, thus, to the respective solder materials 117. The number of contact areas and portions of solder materials 117 and the structure of the conductor pattern 118 depend on the overall configuration of the respective device and are, therefore, selected so as to comply with the connectivity requirements for incorporating any electronic component into the corresponding foil layer stack. Furthermore, in the embodiment shown the respective pressure inducing structures 112 are provided for each of the respective solder materials 117 in the form of ring-type structures that surround the respective solder material 117. It should be appreciated that a part of the conductor pattern 118 connecting to the contact area and thus the solder material 117 may be considered as part of the pressure inducing structure 112, thereby providing for a non-interrupted pressure inducing structure, which may also be referred to herein as a seal structure. From another point of view, the connection from the contact area 116 to the remainder of the conductor pattern 118 may be considered as an interrupt region of the structure 112. In any rate, the function of providing increased pressure and thus superior sealing at the pressure inducing structure 112 is still intact.

(29) It should be appreciated that the pressure inducing structure 112 is illustrated as a ring-type structure in order to laterally surround the solder material 117, which in turn may also typically be provided in the form of solder bump formed on a circular contact area, as for instance shown in the context of FIG. 1A. It should be appreciated, however, that the pressure inducing structure 112, and also the pressure inducing structures 122A, 1226, 122C and 182, as described in the context of FIG. 1C, may have any appropriate geometric configuration, as long as efficient lateral enclosure of the respective contact area is achieved. The same holds true for the contact area, which may also be provided in the form of any appropriate geometric configuration. For example, the respective pressure inducing structures may have the shape of a triangle, a rectangle, a square, polygon, and the like. The geometric configuration of the contact area 116 and of the associated pressure inducing structure or seal structure 112, 1226, 122C, 182 may be different. For example, a circular contact area may laterally be enclosed by a triangular, a rectangular, square-like, polygon-like structure, and vice versa.

(30) FIG. 2 schematically illustrates a cross-sectional view of a foil layer stack 200 according to further illustrative embodiments. As shown, the foil layer stack 200 may include a first foil layer 210 having incorporated therein a layer portion 215, on which may be formed a contact area 216, which in turn may have formed thereon a solder material 217. With respect to the characteristics of the first foil layer 210 it is also referred to the embodiments as discussed above. That is, for example the layer portion 215 may represent a flexible carrier material for forming thereon or therein an appropriate conductor pattern including the contact area 216 as required by design criteria of the layer stack 200. The remaining portion of foil layer 210 may be provided in the form of any appropriate plastic material, such as PVC, polycarbonate, and the like.

(31) The layer portion 215 may include a pressure inducing structure 212, for instance provided in the form of the conductive material having the same characteristics as the material used for forming the contact area 216.

(32) Furthermore, the layer stack 200 may include a second foil layer 220 provided in the form of any appropriate material, such as PVC, polycarbonate, and the like. As previously discussed, in some illustrative embodiments, it is advantageous to provide polycarbonate or similar polymer materials that require a relatively high temperature during a lamination process, which may exceed the melting temperature of the solder material 217.

(33) The second foil layer 220 may include an opening 221 so as to expose the solder material 217, as also discussed above.

(34) As shown, a lateral dimension 221D of the opening 221 is selected so as to expose the solder material 217 and thus the dimension 221D is selected to be larger than the corresponding dimension of the contact area 216 and the solder material 217 prior to the reflowing of the material 217. On the other hand, the dimension 221D is selected such that a certain overlap portion 225 is provided in combination with the pressure inducing structure 212.

(35) Moreover, in the example shown, a further foil layer 230 may be positioned “below” the first foil layer 210 and may be provided in the form of any appropriate material. Moreover, a further foil layer 240 made of any appropriate material may be formed “above” the second foil layer 220. In the embodiment shown, a thickness or height 220T of the second foil layer is selected so as to be equal to an initial height of the solder material 217 or slightly greater so as to avoid generation of increased pressure on the solder material 217 during a lamination process.

(36) Upon applying heat and external pressure to the stack 200 an area of increased pressure 222, the basic shape and position may be defined by the pressure inducing structure 212, may be created and therefore the material of the second foil layer 220 within the area 222 may be compressed with increased pressure compared to the surrounding material of the layer 220, thereby also forming a portion of increased material density in the area 222. However, at the interface between the layer portion 215 and the layer 220, in particular at the interface between the pressure inducing structure 212 and the material of the layer 220, i.e. the area 222, a sealing effect is achieved due to the increased contact force in this region. Therefore a potential flow path of melted solder material 217 may efficiently be blocked by the superior sealing effect. Furthermore, due to the overlapping portion 225 a respective lateral confinement for the melted solder material 217 may be achieved. Consequently, a respective solder bump may be obtained, the lateral size and shape of which may substantially be defined by the final lateral size and shape of the opening 221.

(37) It should be appreciated that the final lateral dimension 221D of the opening 221 may depend on the process conditions and the material characteristics, since typically during the lamination process the material of the layer 220 may undergo a certain lateral “flow” so that the lateral dimension 221D at the end of the lamination process may differ from a respective lateral dimension at the beginning of the lamination process. Any such changes of lateral dimensions, however, may readily be determined in advance, for instance by experiment, and the like, and may be taken into consideration upon forming the opening 221 in the layer 220. Therefore, the lateral size and shape of the solder material 217 after reflowing during the lamination process may be defined with a high degree of repeatability for any number of contact elements and also across a plurality of layer stacks 200, which are typically processed during a common lamination process.

(38) In the example shown, the layers 230, 240 are illustrated as additional foil layers, which are also subjected to the lamination process in combination with the first and second foil layers 210, 220. In other cases, one or both of these layers may represent a “pressure plate”, as previously discussed. For example, the layer 240 may represent a pressure plate so that the solder material 217 may be confined by the layer portion 215, the opening 221, i.e., by the inner side walls thereof, and the pressure plate, wherein, if considered appropriate, the top of the solder material 217 may be covered by solder plastic material, such as freefilm, hotmelt, thermoplastic, and the like. Furthermore, any of the techniques described above in the context of FIGS. 1A to 1E with respect to obtaining the superior sealing effect on the basis of the area of increased pressure 222 may also be applied additionally or alternatively to the usage of the pressure inducing structure 212.

(39) Consequently, after completion of the lamination process the area of increased pressure 222 is formed into a high-density portion, i.e., a portion of increased density of the material compared to material outside of this area, such as the material corresponding to the overlap portion 225. Therefore, even if providing the area of increased pressure 222 on the basis of a temporarily used pressure inducing structure, as for instance discussed the context of FIG. 1C the increased pressure in the area 222 may nevertheless result in an increased local material density and in a superior sealing effect, even if the pressure inducing structure 212 is omitted, thereby leaving the area 222 as a portion of increased density.

(40) As a result, the present invention provides methods and foil layer stacks, in which flow paths of a liquefied solder material during the lamination process may efficiently be blocked by forming a “seal” in combination with material of the overlaying foil layer that laterally confines the melted solder material. Therefore, increases flexibility may be achieved in combining solder materials with foil layer materials, since the lamination process is no longer restricted to temperatures that are below the melting temperature of the solder material.