Abstract:
A method for manufacturing an electronic product, comprising providing a flexible, optionally optically substantially transparent or translucent, substrate film, printing a number of conductive traces of conductive ink on the substrate film, said traces defining a number of conductors and conductive contact areas for the contacts of at least one electronic surface-mountable component, disposing the at least one electronic surface-mountable component, such as an integrated circuit, on the substrate film so that the contacts meet the predefined contact areas when they are still wet to establish the electrical connection therebetween, and further securing, optionally overmoulding, the component. Related arrangement and electronic product are presented.

Description:
FIELD OF THE INVENTION 
       [0001]    Generally the present invention concerns manufacturing processes in the context of electronic products. Particularly, however not exclusively, the invention pertains to manufacturing processes involving printed electronics and the usage of conductive inks. 
       BACKGROUND 
       [0002]    Miniaturization is a prevalent trend in the manufacturing of electronic products. Additionally, manufacturing costs should be kept minimum, which implies relatively straightforward, high yield processes with reduced number of process stages and material waste among other factors. 
         [0003]    Although more traditional electronic elements such as PCBs (printed circuit board), conductors, components like SMDs (surface-mount device), etc. have reduced in size, many of them are still relatively bulky compared to printed electronics. Printed electronics have generally shown the way to thin, light, flexible and rapidly manufactured structures but a vast amount of components cannot still be manufactured by printing, not at least economically and reliably enough. 
         [0004]    Accordingly, in many occasions it may sensible to combine several manufacturing technologies to obtain products with desired characteristics, yield and cost. 
         [0005]    A standard way of mounting components such as SMDs on a substrate involves disposing electrically conductive solder paste through a stencil onto the substrate to form a number of small pads whereto the components are positioned when the pads are still wet. A reflow oven may be used to effectuate the attachment. Mechanical or physical connection between the substrate and components thereon may be secured by means of adhesives. Alternatively, instead of solder, conductive epoxy adhesives may be utilized to provide both electrical and physical bond between the substrate and the components. 
         [0006]    However, solder paste and conductive adhesive based solutions have turned out problematic in some use scenarios. 
         [0007]    With particular reference to solder, it has been noticed that certain temperature-sensitive substrate or component materials such as various plastics may not sufficiently withstand the elevated temperatures required by the usage of solder paste, and will thus deteriorate. Yet, solder-applying manufacturing processes tend to have a multitude of different steps considering e.g. the formation of conductors and solder pads, heating, and mechanical strengthening actions such as the usage of epoxies, which renders the overall manufacturing chain rather complicated, time-consuming and costly. 
         [0008]    Meanwhile, electrically conductive adhesives have been found too aggressive, propagating too deep into the adjacent materials due to e.g. capillary action. For example, in connection with thin, potentially transparent or translucent, materials the widely spread, clearly visible traces of adhesive, the coverage or distribution of which is rather hard to predict beforehand, may basically spoil the end product aesthetics and also related optical or electrical functionality. Yet, conductive adhesives such as hardened epoxies may after curing be too hard and brittle, not tolerating substantially any flexing or bending and therefore fracturing very easily in applications where they are subjected to that kind of stress, considering e.g. flexible electronics and associated use cases. Further, even the electrical conductivity of such adhesives is often relatively modest, whereupon they best fit low current, low efficiency applications only. 
       SUMMARY OF THE INVENTION 
       [0009]    The objective of the embodiments of the present invention is to at least alleviate one or more of the aforesaid drawbacks evident in the prior art arrangements in the context of manufacturing of electronic products incorporating flexible substrates, conductors and various electronic components. 
         [0010]    The objective is generally achieved with a method of manufacture and an electronic product obtained therewith. 
         [0011]    In accordance with one aspect of the present invention a method for manufacturing an electronic product, comprises:
       providing a flexible, optionally optically substantially transparent or translucent, substrate film, optionally a flat substrate film,   printing a number of conductive traces of conductive ink on the substrate film, optionally through screen printing or ink jetting, said traces defining a number of conductors and conductive contact areas, or ‘contact pads’, for the contacts, such as leads, pins or pads, of at least one electronic surface-mountable component,   disposing the at least one electronic surface-mountable component, such as an integrated circuit, on the substrate film such that contacts meet the predefined contact areas when they are still wet to establish the electrical connection between the traces and the at least one component, and   further securing the physical connection between said at least one component and the substrate.       
 
         [0016]    Overmoulding may be utilized so as to at least partly encapsulate the disposed at least one electronic component in the molded material, preferably plastics, to protect and further secure it. In one embodiment, overmoulding incorporates injection moulding. The substrate containing the traces and components may be utilized as an insert therein. 
         [0017]    Alternatively or additionally, adhesive such as surface mount glue may be applied to secure the at least one component physically to the substrate. Further, glop-topping or generally different suitable packaging technologies such as coatings or potting could be selectively exploited to protect and/or secure the components. 
         [0018]    In some embodiments, the substrate film may be thermoformable and thus be optionally thermoformed, prior to or upon moulding, for instance, to produce desired shapes therein. 
         [0019]    In another embodiment, the electrical and/or physical bond between the substrate and the component is secured by means of drying, heating and/or curing using e.g. an oven suitable for the purpose, such as a reflow oven. 
         [0020]    In a further embodiment, a plurality of conductive inks is utilized. For instance, one or more inks may be utilized for printing all or selected conductors whereas one or more other inks may be utilized for printing at least some of the conductive mount locations (contact areas). 
         [0021]    Naturally, a plurality of electronic surface-mountable components may be provided to the substrate as described hereinbefore, not just one. For each such component, the contact pad and conductor areas may be formed on the substrate by the conductive ink. Still, the substrate may optionally comprise a number of electronic and/or other elements electrically/mechanically secured thereto using other means such as clips, anchors, screws, etc. 
         [0022]    In another aspect, a manufacturing arrangement for an electronic product or device, comprises
       printing equipment, optionally screen printing or ink jetting apparatus, to print a number of conductive traces of conductive ink on a flexible, optionally optically substantially transparent or translucent, substrate, said traces defining a number of conductors and conductive contact areas for the contacts of at least one electronic surface-mountable component,   mounting equipment, optionally pick and place machine, to place and align the at least one electronic surface-mountable component, such as an integrated circuit, on the substrate so that the contacts meet the pre-defined contact areas when they are still wet to establish the electrical and physical connection therebetween, and   securing equipment, optionally an injection moulding machine and/or glue dispensing apparatus, to further secure the physical connection between said at least one component and the substrate.       
 
         [0026]    For example, the disposed electronic component may be overmoulded so as to at least partly encapsulate it in the molded material, preferably plastics. 
         [0027]    Yet, the arrangement may comprise a number of additional elements such as drying/heating/curing equipment, cutter, etc. 
         [0028]    One or more elements of the arrangement may be optionally integrated together. For example, printing equipment or mounting equipment may also be configured to provide the adhesive such as surface mount adhesive to the substrate. In extreme case, the arrangement is implemented by equipment that could be considered as a single apparatus. 
         [0029]    In a further aspect, an electronic device comprises a flexible substrate provided with printed conductive traces defining a number of conductors and contact areas thereon, at least one electronic surface-mountable component placed onto the contact areas so as to electrically connect therewith, said component being further physically secured to the substrate by means of e.g. moulded plastic encapsulation layer covering the component and at least part of the substrate and/or by means of adhesive. 
         [0030]    The device may be either substantially planar or three-dimensional. In the latter case, initially optionally planar substrate film may have been provided with components and bent to a target 3d-shape prior to or upon moulding during which the film acted as an insert, for instance. 
         [0031]    The utility of the embodiments of the present invention results from a variety of different issues. The suggested method involves a reduced number of manufacturing steps relative to many prior art alternatives due to the use of conductive ink for establishing both conductor traces and contact pads for the components, thus yielding simple, short and cost-efficient overall process. The conductive ink, which is preferably substantially nonadhesive, tolerates stretching, bending, shaking, etc. better than at least most of the conductive adhesives, and has better conductivity as well. 
         [0032]    The substrate and other elements are also typically subjected to lower thermal stress than in conjunction with solder-based arrangements, which preserves their advantageous properties and reduces heat-generated artifacts. 
         [0033]    As a result, flexible, three-dimensional (e.g. bent/arced), durable, light and/or thin electronic/plastic products may be manufactured for various uses. Combining surface mount components with bend films becomes feasible, for instance. The obtained structures will find use in consumer electronics, mobile devices such as tablets or smartphones, automotive industry, user interfaces, sensors, embedded electronics, wearable electronics, optics, etc. 
         [0034]    Potentially rather considerable physical fixing characteristics provided by some conventional conductive adhesives are not required in the context of the present invention as fully satisfactory physical attachment may be obtained by utilizing e.g. the combination of traditional non-conductive adhesive, such as epoxy, and e.g. molded plastics to secure the component, such as package or body, to the substrate. Also the (wet) ink may be selected so as to facilitate retaining the component(s) in place at least temporarily prior to subsequent process steps such as heating and/or moulding steps. 
         [0035]    The obtained optical quality of the manufactured device or generally product is high as deteriorations caused by aggressive, penetrative and often colored, conductive adhesives are omitted through use of more passive conductive ink(s) and potential non-conductive, merely physical/mechanical bond—providing adhesives. Formation of internal artifacts, such as air/gas pockets or ‘bubbles’, within the materials such as the moulded plastic commonly caused by conductive adhesives may be avoided or at least reduced. 
         [0036]    The expression “a number of” may herein refer to any positive integer starting from one (1). 
         [0037]    The expression “a plurality of” may refer to any positive integer starting from two (2), respectively. 
         [0038]    Different embodiments of the present invention are also disclosed in the attached dependent claims. 
     
    
     
       BRIEF DESCRIPTION OF THE RELATED DRAWINGS 
         [0039]    Next, the embodiments of the present invention are more closely reviewed with reference to the attached drawings, wherein 
           [0040]      FIG. 1  is a flow diagram disclosing an embodiment of a method in accordance with the present invention. 
           [0041]      FIG. 2  illustrates the overall concept of the present invention via an embodiment thereof. 
       
    
    
     DETAILED DESCRIPTION 
       [0042]    With reference to  FIG. 1 , a flow diagram of one feasible embodiment for manufacturing an electronic product, or device, in accordance with the present invention is shown. 
         [0043]    At  102 , referring to a start-up phase, the necessary preparatory actions such as material, element and tools general selection, acquisition and preprocessing take place. Circuit layout may be defined in the light of product specification and other constraints. Process parameters may be tested, tweaked and optimized. 
         [0044]    Conductive ink(s) is/are acquired. Examples of commonly available conductive inks include e.g. DuPont 5000™ and Asahi SW1600C™. 
         [0045]    Advantageously, the selected inks are passive in contrast to e.g. many conductive adhesives, and bear rheological properties, e.g. viscosity or surface tension, which enable sufficient flow during ejection or squeezing, i.e. ink dispensing/printing, but prevent the ink from spreading too easily into adjacent materials and structures afterwards. Yet, drying characteristics may be optimized. The preferred sheet resistivity of the printed ink may be about 80 mOhm/sq (at about 10 um thickness) or less, for example, more advantageously about 50 mOhm/sq or less. 
         [0046]    Preferably, the conductive ink is selected such that it withstands the necessary amount of strain like stretching so that the traces produced retain their conductivity and potential other desirable properties under stress. The substrate may be subjected to stress during the manufacturing process of the electronic product (considering e.g. shaping) or later during the use thereof. 
         [0047]    The conductive ink may contain conductive particles such as nanoparticles. The particles may be metal particles such as metal nanoparticles, but alternatively or additionally, conductive polymer ink may be utilized. 
         [0048]    The inks may include silver, gold, copper or carbon as a conductive material, for example. Transparent ink may be used in applications wherein e.g. the material moulded over the substrate/component(s) is transparent or translucent and the underlying conductive traces should not be clearly visible. 
         [0049]    As a further example, PTF such as silver-based PTF (Polymer Thick Film) paste type ink could be utilized for (screen) printing the desired circuit design on the film. Also e.g. copper or carbon-based PTF pastes could be used. 
         [0050]    Adhesive properties are not needed from the ink, and in most cases, not even desired as they typically introduce problems in terms of durability and controllability as already reviewed hereinbefore. 
         [0051]    The physical or mechanical bond between the substrate/traces and electronic components is preferably secured by surface mount adhesive designed or at least suitable for the purpose and/or overmoulding the components using suitable plastic material, for example. The adhesive may be non-conductive as electrical connections are at least preferably established by the conductive ink. 
         [0052]    In determining applicable elements and other components/electronics for the method, specific care must be taken that the individual components and material selections work together and survive the selected manufacturing process, which shall be naturally preferably checked up-front on the basis of the manufacturing process vs. element data sheets, or by analyzing the produced prototypes, for example. 
         [0053]    At  104 , substrate such as a flexible and/or flat substrate film, or alternatively a rigid substrate or a multi-layer/film substrate, is obtained and optionally pre-treated such as coated or otherwise (surface-)processed to elevate its adhesion properties and/or for other purposes. Further, also initial shaping and/or cutting operations may be executed at this point. 
         [0054]    The substrate film may comprise e.g. polycarbonate (PC) or polyethylene terephthalate (PET) bearing rather suitable characteristics, such as thermoforming properties and flexibility, in the light of e.g. three-dimensional forming. 
         [0055]    Thickness of the substrate may vary according to properties required from the film, such as material strength, flexibility, elasticity, transparency and/or size required from the final product. The thickness of the substrate may be selected depending on the embodiment. It may be a tenth or few tenths of a millimeter only, or more, several millimeters, for example. 
         [0056]    The substrate/substrate film may contain a number of structures such as recesses, cavities, or holes, for accommodating elements, which may include electronic components, electronic circuits, conductors, component leads, sockets, etc. 
         [0057]    At  106 , conductive traces of conductive ink are printed onto the substrate, typically according to a predetermined schema. The traces define conductor areas and component contact areas, or ‘pads’, which may optionally differ from each other in terms of ink constitution, ink layer thickness, dimensions, etc. It shall be noted, however, that the predefined (schema-following) contact areas do not have to necessarily differ from the conductor areas, regarding e.g. shape or used ink, and these two may appear substantially the same, i.e. uniform or homogenous, at least locally on the substrate. 
         [0058]    Item  107  refers to the preparation of printing equipment. For instance, in connection with screen printing, first a number of film positives may be created in accordance with the desired circuit layout to be manufactured. 
         [0059]    Then the screen(s) are provided with the film image(s) using suitable exposure procedure etc., after which the hardened screen(s) are provided to the printing machine or ‘press’. 
         [0060]    Generally, feasible techniques for printing conductive traces or e.g. graphics include screen-printing, rotary screen printing, gravure printing, flexography, ink-jetting, tampo printing, etc. In some embodiments, multiple printing technologies may be selectively utilized. 
         [0061]    The ink(s) shall be preferably selected in connection with the available printing technique and the film material because different printing techniques require different rheological properties from the used ink, for instance. Further, different printing technologies provide varying amounts of ink per time unit, which often affects the achievable conductivity figures. 
         [0062]    Alternatively, the conductors and/or graphics may be at least partially provided within the film or overall substrate structure. In some embodiments, the aforementioned PTF technology may be utilized to construct multi-layer solutions with multiple, potentially printed, substrate layers of printed electronics stacked together to form multi-layer, aggregate substrates at least locally on an initial substrate. 
         [0063]    At  108 , a number of electronic components such as surface-mountable ICs (integrated circuit) and/or other components, e.g. optoelectronics like light-emitting diodes, are placed onto the substrate. A disposed component may generally be active or passive. The various components to be provided on the substrate may be generally based on surface-mount technology. Additionally, other technologies such as printing technologies could be applied. Also hybrid components are feasible, considering e.g. flip chips that are surface mounted. 
         [0064]    The components including the contacts thereof are located such that they electrically couple to the predefined contact (pad) areas on the substrate provided by the conductive ink. Additionally, physical binding between the substrate and the component may be strengthened or accomplished through the use of the adhesive. The adhesive may be single-part surface mount epoxy, for instance. Alternatively or additionally, multi-component adhesive may be utilized. The adhesive is preferably non-conductive as discussed hereinbefore. 
         [0065]    In some embodiments, a number of additional process phases may next take place. At  109 , ink and optional adhesive may be dried, heated and/or cured. The substrate may be cut or otherwise re-dimensioned for the subsequent processing. 
         [0066]    Indeed, more complex shaping may take place as optionally in some embodiments, a film type substrate may be processed from substantially flat into substantially three-dimensional. This may be effectuated, for instance, by thermoforming, particularly through vacuum forming or pressure forming, for example. Thermoforming as a process may include heating the film to enter the thermoforming window (i.e. in which the material becomes substantially pliable for stretching and shaping), placing the film into a mold, applying vacuum in order to press the film against the mold so that the film mold to the shape of the mold, letting the film cool down while at the same time applying the vacuum and ejecting the cooled down film, which has now adapted the desired shape according to the mold, by releasing the vacuum and/or applying e.g. air ejection for easier removal of the film. Cutting of the film e.g. to a preferred size may be carried out before or after the thermoforming. The heating of the film into the thermoforming window may be optionally performed inside a thermoforming machine e.g. in the mold, or outside the thermoforming machine e.g. in an oven. 
         [0067]    Considering the parameters and set-up of the preferred thermoforming process using vacuum or pressure, few further guidelines can be given as mere examples as being understood by the persons skilled in the art. Few approximate examples for the lower limit of the thermoforming temperature include: PC 150° C., PET 70° C., ABS 88° C.-120° C. The pressure applied on the film obtained either by pressing mechanically air into the mold or by sucking a vacuum into the mold could be roughly over some 100 psi for a single layer film construction and roughly over some 200 psi for laminated structures. The used three-dimensional film and the process parameters shall be preferably selected such that the film does not melt or the components separate therefrom. 
         [0068]    At  110 , the assembly comprising the components attached to the substrate may be placed, depending on the embodiment, as an insert into a mold frame and overmolded by injection molding, for example. The material molded over the substrate is optionally transparent and may comprise polymers such as polycarbonate (PC), polyethylene terephthalate (PET), polymethyl methacrylate (PMMA), polyamide (PA), cyclo olefin copolymer (COC), cyclo olefin polymer (COP), polytetrafluoroethylene (PTFE), polyvinyl chloride (PVC), or a mixture of these. Alternatively or additionally, the material could include e.g. glass. An applicable layer material shall be generally selected such that the desired flexibility, robustness, and other requirements like adhesion and/or optical properties in view of the electronics and the adjacent materials, or e.g. in view of available manufacturing techniques and target use, are met. 
         [0069]    Having regard to the process parameters and set-up, few further guidelines could be given as mere examples as being understood by the skilled persons. When the three-dimensional film is PET and the plastics to be, for example, injection molded thereon is PC, the temperature of the melted PC may be about 280 to 320° C. and mold temperature about 20 to 95° C., e.g. about 80° C. The used three-dimensional film, electronic components and process parameters shall be preferably selected such that the film/components remain substantially static and unharmed during the process. After the injection process the injected material may be kept under a pressure and let to cool down, after which it may be taken out. 
         [0070]    By molding, the desired components and substrate portions may be generally encapsulated and the substrate covered to a desired extent by the molding material, which may thus form protective shell, cover or housing of the manufactured device. 
         [0071]    Yet, the molding material may be configured to establish other functional elements such as transmission medium for light/electromagnetic radiation in case the components include e.g. optoelectronic elements such as light-emissive or -sensitive elements. In-mold labelling or decoration may further be used to exhibit desired, embedded visual appearance to the users of the product. 
         [0072]    At  112 , the method execution is ended. Further actions such as element regulation, quality control, surface treatment and/or finishing or furbishing may take place next. The dashed loop-back arrows depict the potentially repetitive nature of method items, wherein printing, component placing and/or other activities may occur in phases. 
         [0073]    The use of advantageously flexible materials enables at least some of the method items to be carried out by roll-to-roll or ‘reel-to-reel’ methods, which may provide additional benefits time-, cost- and even space-wise considering e.g. transportation and storage. 
         [0074]    Accordingly,  FIG. 2  illustrates the concept of the present invention by few simplistic sketches in relation to the potential corresponding method steps. 
         [0075]    At  202 , a substrate  210 , such as a flat, thin and/or flexible substrate film, optionally of plastic material, is provided with printed conductive (ink) traces defining a plurality of conductors  212  and contact areas  214  (which may have different shapes and may be, but do not have to be, visually distinguishable from conductor traces), or ‘pads’, for electronic components such as surface mountable ICs or other surface mountable elements. Contact areas  214  may define optionally larger diameter extensions for the conductors  212 , which is the case shown in the figure, or connect different elongated conductor portions together, for example. 
         [0076]    Additionally, printable electronic components, e.g. printable OLED (organic LED), may be constructed onto the substrate. 
         [0077]    As item  216  alludes, screen/screen printing may be applied for producing the traces among other options such as ink-jetting, already listed hereinbefore. Yet, adhesive(s) for mechanical fixing may be provided onto the substrate, optionally also by printing. 
         [0078]    At  204 , the substrate  210  receives the electronic components  218  such as various surface mountable components. Mounting including aligning to the printed contact areas may be executed using suitable placement technology  216   b  for the purpose, e.g. a suitable pick and place machine or bonder. 
         [0079]    Adhesive(s) for securing mechanical attachments of components may be provided by the same or dedicated equipment, e.g. a glue dispenser, prior to or upon placing the electronic components, optionally with the components. Drops of adhesive may be provided on the substrate to the locations of the electronic components  218  prior to mounting those, for instance. Adhesive(s) may also be printed as mentioned above. 
         [0080]    In addition to electronic components, in connection with the present invention also other elements could be located onto the substrate or within the molded material considering e.g. various embodiments of in-mould labelling/decoration. 
         [0081]    At  206 , it is indicated that the substrate and components may be subjected to various treatments. The substrate may be heated/dried/cured by suitable equipment  216   c  to dry the ink, strengthen the mechanical bond/cure the adhesive, etc. Alternatively or additionally, remainder substrate may be cut away, desired shaping (e.g. 3D) may take place, etc. 
         [0082]    At  208 , the substrate is shown with a layer or element  220  of preferably plastic material overmoulded thereon using e.g. injection moulding through the utilization of applicable hardware  216   d , wherein the substrate could have been applied as an insert, to further secure the attachment of components, enhance protection to external conditions such as hermetic isolation, shock and impact protection, exhibit desired optical properties and geometry (dimensions), etc. Overmoulding is, however, not necessary in all embodiments, as the physical connection to the substrate and/or protection may be sufficiently attained by e.g. adhesive, glop-topping, various other packaging technologies, etc. 
         [0083]    The shown arched shape of moulded cover  220  is merely exemplary, but such curved shapes, or alternatively edgy shapes, may indeed generally be obtained for the moulded element  220  depending on the target design. Recalling the fact that the substrate  210  may itself be non-flat or three dimensional (shaping may take place prior to moulding as described hereinbefore), also the manufactured overall product may bear even rather complex 3d-shape, not just the moulded element  220 . 
         [0084]    The scope of the invention is determined by the attached claims together with the equivalents thereof. The skilled persons will again appreciate the fact that the disclosed embodiments were constructed for illustrative purposes only, and the innovative fulcrum reviewed herein will cover further embodiments, embodiment combinations, variations and equivalents that better suit each particular use case of the invention.