The invention concerns an audio processing device with an electronic component such as a chip, which has been encapsulated. Such an encapsulation is common and serves the purpose of protecting sensitive components against light and other environmental exposures. The encapsulation is usually achieved in an injection moulding process, wherein the chip and PCB substrate is enclosed in a mould and the encapsulation material is injected into the mould cavity around the electronic component and caused to solidify in the closed mould, where after the electronic component with the solid encapsulation material is removed from the mould cavity. Other ways of moulding the encapsulation are known, such as dispensing material onto and around the electronic component, and subsequently solidifying the material.
In audio devices such as hearing aids and headsets where small size is very important, it is desirable that the PCB remains as small as possible. Also the encapsulation should take up as little volume as possible. Further mounting area for further electronic parts like capacitors, contacts and antennas should remain as small as possible in order to minimize the volume of the PCB.
The invention provides an audio device with at least one encapsulated electronic component. The encapsulated component is mounted and electrically connected to a substrate and further electric components are mounted for connection with the encapsulated component through the substrate. The encapsulated component is protected by an encapsulation material moulded onto the substrate. According to the invention at least one metal layer is deposited on a surface part of the encapsulation material. The metal layer provides a very dense and effective light protection, and as such may allow a very thin layer of encapsulation material to be used. The encapsulated component, possibly a chip may be accompanied by one or several other electric components, all of which are embedded in the encapsulation material.
In a further embodiment the metal layer on the encapsulation material is provided as conductive metal traces and electric components are formed onto or mounted onto the surface of the encapsulation such that the components are connected with the leads in the substrate through the metal traces. By having electric components on the surface of the encapsulation material more space becomes available for mounting purposes as components like capacitors and resistors are mountable on top of the chip and the metal traces will provide the connection between the components and the PCB.
In a further embodiment the metal layers or traces form capacitors, coils, antennas or other active or passive devices on the encapsulation material. This allows such components to be generated in a very space saving manner.
In a further embodiment the encapsulation material comprise cavities or other surface structures, serving as part of, or receiving elements for individual components. Such surface structures are provided simply by providing mirror images thereof in the mould used for the moulding of the encapsulation. The provision of metal traces can be caused to follow possible cavities or raised areas on the surface of the material. The individual component mounted in or on cavities or other surface structures may comprise microphone or receiver parts or other transducer elements.
The invention further comprise a method for producing an amplifier for an audio device whereby an electronic component is mounted on and electrically connected to a PCB and where an encapsulation material is provided to protect the electronic component wherein further a metal layer is generated at least on a surface area of the encapsulation material. Preferably the encapsulated component comprises a semiconductor chip.
In an embodiment of the method the metal layer is deposited by an electrochemical deposition method. Such methods are known in connection with MID techniques developed in recent years. Here, the surface material of the encapsulation must have special properties, which allows the deposition of a metal layer. This is achieved by the addition to the encapsulation material of a compound comprising an organic metal complex which is activated in the areas where the metal is to be deposited. The activation step may be performed by treatment with laser light, and this allows electrically conductive, thin traces to be deposited on the surface. The compound comprising the organic metal complex can be provided as part of the encapsulation material in only the areas wherein the metal is to be deposited. Here a two component moulding technique could be used.
In a further embodiment of the method according to the invention, the metal layer is deposited through a nozzle directly onto the surface of the chip encapsulation material. In this procedure an aerosol stream is focused, deposited, and patterned onto the surface of the encapsulation material. The surface need not be planar to perform this process. After deposition of the material thermal annealing or photochemical annealing using laser decomposition is performed in order to achieve physical and/or electrical properties near that of the bulk material.
Other ways to deposit metal layers on top of the encapsulation material may be used according to the invention. The entire surface may be electroplated and later the metal may be stripped off by burning in the areas where no metal is desired.
After metallization, components 8,9,10 are mounted followed by reflow soldering. In this case the remaining components are SMD's 8 and a membrane chip 9. The membrane chip 9 constitutes part of a microphone such that when it is added on top of the cavity 5 a silicon microphone is created. Further an ASIC 10 for preamplification and signal processing is shown in
In
In
The embodiment in
In
Following this step, metal traces 6 are formed on the encapsulation material 2 and as shown in the example of
The entire PCB board 4 is then run through a pick and place automat wherein electric components 8 are mounted on the pads 26 on the encapsulation surface. Hereafter the PCB is run through a soldering tunnel, causing the components to be fastened to the surface and electrically connected to the pads. The resulting array of devices with the mounted components is seen in
The audio devices are then singularized, preferably by sawing the PCB, whereafter they are ready for use in hearing aids or other audio processing equipment. In the description above each device contain only one chip, but multi chip devices are easily provided by chip-on-chip mounting or by mounting chips side by side on the same PCB.
Two ways of generating the metal on top of the encapsulation material is described in more detail in the following. The first way comprises electrochemical deposition of metal in traces or covering larger surfaces. Here the surface of the chip encapsulation material is activated to provide catalytic sites for the metal deposition. The activation results in inclusion of precious metal ions (Pd, Pt, Au, etc.) in the surface of the encapsulation. The inclusion of the metal ions in the surface is obtained either by photochemical dissociation of an organic metal complex, which has been added to the encapsulation material and which contains the precious metal, or by sequentially treating the surface in dedicated micro-etch, pre-activator and activator solutions. Here the later provides the precious metal ions. In the photochemical dissociation the organic metal complex in the chip encapsulation material is cracked open by a focused laser beam and the metal atoms are broken off from organic ligands. The metal atoms then act as nuclei for reduction of metal ions during a subsequent electrochemical deposition process. The laser activation is performed in traces to provide electric connection to discrete components as disclosed above or along larger areas to allow protective layers of metal to be formed on selected areas.
After surface activation metal is electrochemically deposited either by electroless plating or by electroplating. In situations where the electrochemically deposited metal is not allowed to be deposited elsewhere on the PCB, the metallic pads for wirebonding, solder bump bonding, etc. must be protected/masked during metal deposition. This is done by covering the pads with a layer of polyimide, which is later ablated by a laser in order to re-open the pads.
A second way of providing metal layers on the encapsulation material is Maskless Mesoscale Materials Deposition, also known as M3D technology. This process is promoted by Optomec, www.optomec.com. Here aerodynamic focusing is used in a maskless deposition of chemical precursor solutions and colloidal suspensions. An aerosol stream is focused, deposited, and patterned onto the surface of the encapsulation material. Also un-even surfaces with cavities as disclosed above are provided with metal layering. A thermal annealing or photochemical (laser decomposition) process to achieve physical and/or electrical properties near that of the bulk material follows the deposition.
Number | Date | Country | Kind |
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PA 2004 01385 | Sep 2004 | DK | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/EP05/54355 | 9/5/2005 | WO | 3/27/2007 |