Abstract:
Systems and methods for producing micromachined devices, including sensors, actuators, optics, fluidics, and mechanical assemblies, using manufacturing techniques of lead frames, substrates, microelectronic packages, printed circuit boards, flex circuits, and rigid-flex materials. Preferred embodiments comprise using methods from post-semiconductor manufacturing to produce three-dimensional and free-standing structures in non-semiconductor materials. The resulting devices may remain part of the substrate, board or lead frame which can then used as a substrate for further packaging electronic assembly operations. Alternatively, the devices may be used as final components that can be assembled within other devices.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a continuation-in-part of application Ser. No. 11/956,756 filed Dec. 14, 2007, which claims the benefit of provisional application Ser. No. 60/870,354, filed Dec. 15, 2006, which applications are incorporated herein by reference. This application also claims the benefit of provisional application Ser. No. 60/915,310, filed May 1, 2007, which application is incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to methods of manufacturing micromachined devices directly within or on any of the following: lead frames, substrates, microelectronic packages, printed circuit boards, flex circuits, and rigid-flex materials. 
       BACKGROUND 
       [0003]    Microelectrical-mechanical systems (MEMS) are miniature mechanical devices intended to perform non-electronic functions such as sensing or actuation. These devices are typically built from silicon using lithographic techniques borrowed from the semiconductor industry. Some examples of these devices are silicon pressure sensors and silicon accelerometers. Other manufacturing methods have been developed such as microembossing, stamping, microinjection molding, precision machining, and the like. These are typically used to build devices from non-silicon materials such as polymer or metal, for applications where silicon is not an appropriate material. Examples of such devices include microfluidic devices, biochips and optical devices. However, almost all micromachined devices must eventually be placed in a protective housing so that electrical connections can be made to the devices, and to protect the devices. This is troublesome for MEMS devices because they are fragile and so extreme care must be taken to move them from their fabricated substrates (e.g., wafers) to micro-electronic packages. It is well known that 60%-80% of the final cost for a MEMS device is from the costs associated with packaging. 
         [0004]    The use of silicon for MEMS microfabrication has its roots in the successes of the semiconductor industry. Early MEMS designers in the 1980&#39;s looked to the semiconductor industry as a model for building small devices. Other manufacturing industries, such as precision machining, printed circuit board manufacturing, and microelectronic packaging did not have the manufacturing sophistication needed to produce devices with feature sizes in the few microns. In current times, however, these non-semiconductor industries have developed highly sophisticated tooling needed to do high precision manufacturing. These industries are now in an ideal position to take on the job of manufacturing MEMS devices. 
         [0005]    There are at least four major manufacturing steps needed to make a final electronic product. These are: 
         [0006]    1. Semiconductor manufacturing: A semiconductor manufacturer builds microcircuits on semiconductor material such as silicon (“microchips”). 
         [0007]    2. Package base manufacturing: A substrate or lead frame manufacturer builds thin mechanical base structures for the chips. These can be laminate structures (“laminates”) or single precision cut layers of metal foil (“lead frames”). 
         [0008]    3. Packaging: A packaging manufacturer assembles the chips on the base structures, makes electrical attachments, then puts a protective covering on them (“package”). 
         [0009]    4. Printed circuit board manufacturing: A printed circuit board manufacturer makes a multilayer electrical laminate (“printed circuit board”) then takes assemblies and bonds packaged chips on the laminate to produce a final part (“printed circuit”). 
         [0000]    For the purpose of this discussion, we will identify the last three manufacturing steps as “post semiconductor manufacturing” or PSM. 
         [0010]    While MEMS devices have been built using semiconductor manufacturing techniques, little work has been done to demonstrate fabrication of MEMS using the three PSM techniques described above. There are several advantages that could be realized if MEMS devices were built using PSM techniques instead of the semiconductor approach. These are 1. Cheaper manufacturing: Non-semiconductor manufacturing is much cheaper than semiconductor manufacturing. 
         [0011]    2. Better materials selection: Post-semiconductor manufacturing allows many more materials and to be included in the manufacturing process, including low temperature materials such as polymers. 
         [0012]    3. Easier integration: Post-semiconductor manufacturing provides more flexible methods for manufacturing. 
         [0013]    4. More variety: More materials and more manufacturing options yields a greater number of devices that can be designed and developed. Silicon is very limited in its uses. 
         [0014]    5. Easier packaging: Since devices are built in packaging materials, using packaging techniques, packaging is easier to design. 
         [0015]    Although MEMS devices can be built using manufacturing techniques that come from the PSM fields, little work is done in that area today. Thus it is desirable to provide methods for producing 3-D structures and free-standing structures using PSM techniques. 
       SUMMARY 
       [0016]    The various embodiments and examples provided herein are generally directed to systems and methods for producing micromachined devices using manufacturing techniques of lead frames, substrates, microelectronic packages, printed circuit boards, flex circuits, and rigid-flex materials. A micromachined device refers to a small device (less than 5 mm overall size) whose function is not primarily electronic in nature. These include sensors, actuators, optics, fluidics, and mechanical assemblies. 
         [0017]    Preferred embodiments comprise using methods from post-semiconductor manufacturing (PSM) to produce three-dimensional and free-standing structures in non-semiconductor materials. The resulting devices may remain part of the substrate, board or lead frame which can then used as a substrate for further packaging electronic assembly operations. Alternatively, the devices may be used as final components that can be assembled within other devices. 
         [0018]    Several manufacturing embodiments are provided herein. One embodiment is the method of first patterning a microstructure on a carrier, then processing the carrier and microstructure according to normal manufacturing procedures, then removing part of the carrier at the end of the manufacturing process. 
         [0019]    Another embodiment is to use a pick-and-place operation to move an encapsulated microstructure to a surface, or alternatively, to move components on to an embedded microstructure. 
         [0020]    Another embodiment is to create a mold cavity within a laminate structure by creating openings in the laminates and building up the cavity one layer at a time. 
         [0021]    The manufacturing processes provided herein are compatible with existing processes for building these items, so they enable new classes of devices to be built using the same technology. The manufacturing techniques can be applied to the manufacture of micromachined microdevices as stand-alone products, or for building micromachined microdevices that are part of the lead frames, substrates, microelectronic packages, printed circuit boards, flex circuits, and rigid-flex materials. 
         [0022]    Other objects and features of the present invention will become apparent from consideration of the following description taken in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0023]    The details of the invention, both as to its structure and operation, may be gleaned in part by study of the accompanying figures, in which like reference numerals refer to like parts. The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. Moreover, all illustrations are intended to convey concepts, where relative sizes, shapes and other detailed attributes may be illustrated schematically rather than literally or precisely. 
           [0024]      FIG. 1  is an illustration of a manufacturing process using a thin sheet carrier to provide the structural support for subsequent manufacturing steps. 
           [0025]      FIG. 2  is an illustration of a manufacturing process using a thin sheet carrier, where the carrier is pre-etched or otherwise structured to impart additional patterning properties to the microstructure. 
           [0026]      FIG. 3  is an illustration of a manufacturing process using a thin sheet carrier, where both sides of the thin sheet are patterned with microstructures prior to subsequent processing. 
           [0027]      FIG. 4  is an illustration of a manufacturing process using a thin sheet carrier, where a second component is attached to the carrier prior to subsequent processing. 
           [0028]      FIG. 5  is an illustration of a manufacturing process using an encapsulating material to enable a small micromachined device to be physically moved and bonded to a new carrier. This figure also shows that the encapsulating material can protect the device during high stress operations such as lamination and overmolding. 
           [0029]      FIG. 6  is an illustration of a manufacturing process using an encapsulating material to provide enough rigidity in a micromachined device to allow a pick and place operation to place and bond more components on the microdevice, thus increasing the complexity and function of the microdevice. 
           [0030]      FIG. 7  is an illustration of a manufacturing process using several layers of laminating materials to form a hollow mold cavity that can be used for injecting a second material, thus forming a 3-D device. 
           [0031]      FIG. 8  is a diagram showing a process for fabricating a microdevice within a substrate. 
           [0032]      FIG. 9  is a diagram showing a process of fabricating a microdevice with an electret and with an all-air gap. 
           [0033]      FIG. 10  is a diagram showing a second process for creating free-standing structure in laminate. 
           [0034]      FIG. 11  is a diagram showing a third process for creating free-standing structure in laminate. 
           [0035]      FIG. 12  is a diagram showing a process fabricating a microdevice with an electret and an all-air gap. 
           [0036]      FIG. 13  is a diagram showing a process for fabricating a microdevice on a lead frame. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0037]    Each of the additional features and teachings disclosed below can be utilized separately or in conjunction with other features and teachings to accomplish post-semiconductor manufacturing techniques that can result in three-dimensional structures and freestanding devices. Representative examples of the present invention, which examples utilize many of these additional features and teachings both separately and in combination, will now be described in further detail with reference to the attached drawings. This detailed description is merely intended to teach a person of skill in the art further details for practicing preferred aspects of the present teachings and is not intended to limit the scope of the invention. Therefore, combinations of features and steps disclosed in the following detail description may not be necessary to practice the invention in the broadest sense, and are instead taught merely to particularly describe representative examples of the present teachings. 
         [0038]    Moreover, the various features of the representative examples and the dependent claims may be combined in ways that are not specifically and explicitly enumerated in order to provide additional useful embodiments of the present teachings. In addition, it is expressly noted that all features disclosed in the description and/or the claims are intended to be disclosed separately and independently from each other for the purpose of original disclosure, as well as for the purpose of restricting the claimed subject matter independent of the compositions of the features in the embodiments and/or the claims. It is also expressly noted that all value ranges or indications of groups of entities disclose every possible intermediate value or intermediate entity for the purpose of original disclosure, as well as for the purpose of restricting the claimed subject matter. 
         [0039]    The following descriptions are of basic manufacturing processes that can be deployed in the manufacture of microdevices. These processes are all typically available in post-semiconductor manufacturing. Microdevices are built using one or more of these processes, as will be described later. 
         [0040]    Lamination: Layering thin sheets or films of material and bonding together using pressure, heat or adhesives, or any combination of these. 
         [0041]    Lithography: Patterning a light sensitive material by selectively exposing it to light, as through a mask or through the movement of a thin beam of light. 
         [0042]    Deposition: Placement of material on a surface through any means, including spraying, dipping, spinning, dry film laminating, painting. 
         [0043]    Vapor deposition: Placement of material on a surface through the vapor phase, such as by vapor film growth, evaporation, sputtering and the like. 
         [0044]    Etch: Selective removal of material using a chemical reaction or physical erosion to dissolve or breakdown the material. Chemical reaction can take place in the liquid or gas/vapor phase. 
         [0045]    Electroplating: Use of electrolytic reactions to put material, usually metal, on a surface. 
         [0046]    Electrodeposition: Use of electric fields to place a material, usually a polymer, on a surface. 
         [0047]    Stenciling: Placement of material at selected regions on a surface by using a physical stencil to obstruct certain regions. Also, the use of a stencil to protect certain regions from etch. 
         [0048]    Laser machining: Use of a laser to remove material through melting, vaporizing or ablation. Also, laser machining may mean the use of a laser to assist in other processes such as laser assisted etch. 
         [0049]    Machining: Use of a sharp tool to remove a material from a surface. This includes common operations such as sawing, drilling, milling, lathing, reaming, tapping, and the like. 
         [0050]    EDM: Electron discharge machining, the use of an electrical current to etch or cut materials. 
         [0051]    Water jet machining: Use of a high pressure water jet, sometimes filled with abrasive materials, to cut or etch materials. 
         [0052]    Sandblasting: Use of abrasives blown at high velocity to etch a surface. 
         [0053]    Dispensing: Placement of flowable material on a surface by pushing through a nozzle or ejecting from a reservoir. 
         [0054]    Ink-jet printing: Placement of liquid material on a surface by ejecting through a nozzle. 
         [0055]    Offset printing: Placement of liquid material on a second surface by placing the material on a first surface, then bringing that surface in contact with the second surface. 
         [0056]    Electrostatic printing: Placement of charged material on a surface by charging the surface in specific regions, then allowing the charged materials to move and settle on the charged regions. 
         [0057]    Assembly: Mechanical placement of components on a material. 
         [0058]    Joining: Physical connection of two materials. 
         [0059]    Bonding: Physical connection of two materials in such a way as to make the connection permanent or semi-permanent, such as through adhesives, welding, diffusion, or the use of mechanical joining structures. 
         [0060]    Molding: Forming a shape by pushing a flowable material into a predefined cavity. 
         [0061]    Embossing: Forming a shape by pressing a predefined cavity against a flowable material. 
         [0062]    Encapsulation: Covering one material with a flowable second material. 
         [0063]    Turning to the figures, a plurality of methods for building 3-D structures and free-standing structures using these basic processes will be described. 
         [0064]    Free Standing Structure Using a Thin Sheet Carrier. 
         [0065]    Referring to  FIG. 1  a manufacturing process is depicted as using a thin sheet carrier to provide the structural support for subsequent manufacturing steps. The process includes preparing a thin sheet carrier  102  preferably from copper foil. A photosensitive material (photoresist) (not shown) is then deposited on the surface of the thin sheet carrier  102  and patterned using lithography. A second material  104 , preferably a second metal, is then deposited on the surface of the thin sheet carrier  102 , preferably by electroplating through the openings in the photoresist. Alternatively, the second material  104  can be deposited prior to lithography, then etched through the openings in the photoresist. Following either of the photoresist is stripped. The patterned second material (patterned microstructure)  104  is left on the thin sheet carrier  102 . The thin sheet carrier  102  acts as a structural support for subsequent manufacturing steps. The process may be repeated to produce further microstructures  106  on the thin sheet carrier  102 . 
         [0066]    The foil  102  may be bonded against another material  108 , if desired, using any convenient process including lamination, molding, deposition, or processes listed above. The layers  108  may contain openings  110  and/or structures, or may have openings and structures machined into it. Various manufacturing steps may be performed on the foil  102  including laminating another material  112  to foil  102 , joining, bending, cutting, drilling, and the like as listed above. 
         [0067]    After subsequent manufacturing, parts of the thin sheet carrier  102  are etched away to reveal a freestanding structure  114 . Etching may be performed from either side of the thin sheet carrier  102 , or both sides, depending on the specific need of the final device, and depending on manufacturing convenience. If etching must occur through the top side of the carrier  102 , then holes may be patterned in the patterned microstructures  104  and  106  to allow etching to occur under the patterned microstructures  104  and  106 . 
         [0068]    Alternatively, the thin sheet carrier  102  may be a laminate comprising more than one sheet  102 ,  108 . 
         [0069]    In other alternatives, the patterned microstructures  104 ,  106  may be formed from multiple layers of material; may be formed from multiple layers of material where each layer is patterned differently; may be made from photosensitive material formed by lithography, may be made from a material formed by depositing through a stencil; may be made from a material formed by deposition and subsequent cutting or etching by other means, such as by laser, sandblasting, EDM, waterjet, milling, and the like as listed above; or may be made from a material formed by selective deposition such as by nozzle-based dispensing or by printing (ink-jet or offset), as listed above. 
         [0070]    Referring to  FIG. 2  a manufacturing process is depicted as using a thin sheet carrier, where the carrier is pre-etched or otherwise structured to impart additional patterning properties to the microstructure. The patterned microstructure may be made more functional by performing mechanical shaping or pre-etching of the thin sheet carrier  202  to form a pre-shaped region  204 . The process may proceed as before, by bonding against one or more materials  208  and machining the materials to form, e.g., an opening  210 . Deposition of the microstructure  212  over the pre-shaped region  204  of the thin sheet carrier  202  causes it to conform to the shape of the pre-shaped region  212 . After etching of the thin sheet carrier  202 , the microstructure  212  is released having shapes that are defined by the pre-shaped region  204 . 
         [0071]    Referring to  FIG. 3  a manufacturing process is depicted as using a thin sheet carrier, where both sides of the thin sheet are patterned with microstructures prior to subsequent processing. The patterned microstructure may be made more functional by preparing the thin carrier sheet  302  and micropatterning structures  304 ,  306  on both sides of the carrier sheet  302 . The process may proceed as before, by bonding against one or more materials  310  and processing the materials  310  to form, e.g., openings  312  therein. Other materials layers may be added by lamination, molding, lithography, etc. After etching of the thin sheet carrier  302 , the microstructure  314  is released having freestanding microstructures separated by the thickness of the thin carrier sheet  302 . 
         [0072]    Referring to  FIG. 4  a manufacturing process is depicted as using a thin sheet carrier, where a second component is attached to the carrier prior to subsequent processing. Alternatively, the patterned microstructure  404  may be made by a separate process, then transferred to the surface of the thin sheet carrier  402  and assembled on the surface of the thin sheet carrier surface  402 , then bonded  406  to the surface. Other material layers  408  may be added by lamination, molding, lithography, etc. After etching of the thin sheet carrier  402 , the microstructure is released having freestanding microstructures  410 . 
         [0073]    Free Standing Structure Using Pick and Place, Method 1. 
         [0074]    Referring to  FIG. 5  a manufacturing process is depicted as using an encapsulating material to enable a small micromaehined device to be physically moved and bonded to a new carrier. This figure also shows that the encapsulating material can protect the device during high stress operations such as lamination and overmolding. A microstructure  504  is created on a carrier material  502  using any available means. In the preferred embodiment, the microsctructure  504  is defined using lithographic methods. The carrier material  502  may be any convenient material, such as a silicon wafer, glass plate, etc. A second material  506  is used to cover and encapsulate most of the microstructure. Part of the microstructure  504  is not covered, preferably the part of the microstructure  504  already attached to the carrier surface  502 . The encapsulating material  506  may be applied in flowable form, or may be rigid. Furthermore, the encapsulating material  506  may be applied during the construction of the microstructure  504  as part of its natural method of manufacture. 
         [0075]    The second material  506  may be further processed, for example to put holes  508  in it or to create functional structures on it. Processing may be by any means, including laser etch and lithography. If attached to the carrier surface  502 , the microstructure  504 , securely held within the encapsulant  506 , is released from the carrier surface  502  by etching the carrier surface  502 . For some surfaces, the adhesion between the carrier  502  and the microstructure  504  may be low, so that it can be readily removed by pulling it off. The microstructure  504 , still within its encapsulant  506 , is moved and further processed. The microsctructure encapsulate  504  is moved to a new carrier  512  using precision pick and place machinery. The microsctructure encapsulate  504  is bonded to the surface of the new carrier  512 , for example using solder or adhesive  514 . The encapsulant  506  may be removed by etching or stripping leaving an unencapsulated microstructure  516 . The microsctructure  516  may be further released by etching or removing part of the new carrier surface  512 . Alternatively, the microstructure  516  may be made from multiple materials. The encapsulant material  506  may also contain other materials or structures to make the encapsulating structure more useful or functional. Multiple microstructures may be encapsulated at once. Alternatively, the encapsulated device may be further encapsulated with a second encapsulating material  518 . An opening  520  is made through the second material  518  or the bottom carrier  512  to provide access to the microsctructure encapsulate. The first encapsulate or sacrificial material is removed by liquid or vapor etch, leaving a freestanding part within a cavity  522 . 
         [0076]    Free Standing Structure Using Pick and Place, Method 2. 
         [0077]    Referring to  FIG. 6  a manufacturing process is depicted as using an encapsulating material to provide enough rigidity in a micromachined device to allow a pick and place operation to place and bond more components on the microdevice, thus increasing the complexity and function of the microdevice. The process includes creating a microstructure  604  is created on a carrier  602  using any conventional means. The microstructure remains encapsulated in its sacrificial material  606  and is not freestanding. A second component  610  is mechanically placed on the first microstructure to add functionality to the first microstructure. Placement may be performed by any convenient means, such as by pick and place machinery  608 . Since the first microstructure  604  remains embedded within its sacrificial material  606 , it can survive the forces associated with the pick and place operation. The second component  610  is bonded to the first microstructure  604 . After all subsequent operations, including the optional placement of other components on the microstructure  604 , the microstructure  604  is released by selective removal or etch of the sacrificial material  606 . The result is a freestanding microstructure  612  containing components that are bonded to it which would normally not be possible to bond to a micromachined device. 
         [0078]    Free Standing Structure Using Laminated Mold Cavity, Method 1. 
         [0079]    Referring to  FIG. 7  a manufacturing process depicted as using several layers of laminating materials to form a hollow mold cavity that can be used for injecting a second material, thus forming a 3-D device. The process includes preparing layers of laminate sheets  702  are prepared on a carrier material  704 . Openings are cut into the laminate sheets  702  either prior to lamination or after lamination. Sheets  702  are laminated together to produce a layered structure. Openings  706  in sheets  702  overlap to form a cavity. Material  708  is formed in the cavity by flowing material, electroplating, or other means. Portions of the laminate adjacent to the cavities are etched away to reveal a freestanding part  710 . Some laminate layers  702  may be made of different materials that are not etched away at the end of the process, or may leave parts embedded within the freestanding part. 
         [0080]    Some laminate layers  702  may consist of multiple layers themselves, prepared in advance in order to embed a microstructure in the mold part. Local fiducials and targets may be added to the laminate to guide the cutting tool and ensure high precision overlap from layer to layer. Cutting or etching may be performed through a mask or stencil, where the mask or stencil is aligned with the laminate surface prior to cutting. 
         [0081]    The following describes different methods for building a microdevice within a laminate. In the first embodiment, shown in  FIG. 8 , two halves of the laminate are prepared in advance. The top half contains a laminate layer  142  and a first metal foil  144 , such as copper, bonded to the laminate layer  142 . A second metal foil  146 , such as gold, is patterned over the first metal foil  144 . The second metal is chosen for good mechanical and electrical properties, and because it is resistant to chemicals that would ordinarily etch the first metal. The second laminate layer  145  consists of laminate material that has a cavity  148  within it. The cavity  148  can be created using etching, cutting, ablation, drilling or other methods. Beneath the cavity  148  is a third metal foil  150 , such as copper. The two halves  142  and  145  are bonded together to place the patterned metal over the cavity  148 . An opening  152  is cut into the top layer  142  to expose the first metal foil  144 . The opening  152  can be created using etching, cutting, ablation, drilling or other methods. The opening  152  may be created at any time, such as before the first foil  144  is bonded to the top laminate  142 . Finally, a chemical etchant is introduced into the opening to etch the first metal foil ( 144 ). In the preferred embodiment, the etchant may be ammonium persulfate or ferric chloride which efficiently etch copper but which do not etch gold. The etching process removes the first metal layer  144  but does not affect the second patterned metal  146 . This “release etch” leaves a freestanding movable structure  156  which can be used as the acoustic element. Electrical acoustic of the movable structure can occur at the third metal layer  150  that monitors the change in capacitance through the cavity  148  and laminate material  158 . 
         [0082]    A variation of this embodiment may be realized by substituting the second layer with a laminate containing a charged electret, as seen in  FIG. 9A . In this device, the freestanding structure  162  is suspended over a cavity  164  which is created in a laminate layer  166  and which also contains a charged electret material  168 . A still different embodiment can be accomplished if the design requires an all-air gap between the two conductive layers. In this embodiment, a cavity  170  is created that passes through the laminate to the third metal foil  172 . If the third metal foil  172  is made from a suitably different metal than the first metal foil  176 , the release etching will not harm this metal layer. Alternatively, layer  174  comprised of a fourth metal may be patterned over the third metal foil  172 . This metal is selected to be resistant to the etchant used to remove the first metal foil. The bottom layer  172  of metal is protected during the release etch. This leaves two metals  174  and  178  separated by an air gap at the completion of etching. 
         [0083]    Another embodiment of the manufacturing process is shown in  FIG. 10 . Here a metal foil  182 , preferably copper, is prepared as usual on the surface of a laminate layer  188 . A second metal  184 , preferably gold, is patterned on top of the first metal foil, having different etch properties from the first. A new laminate layer  185  containing an opening  186  is bonded to the first layers  188  to complete the laminate structure  180 . The first metal  182  is etched using an appropriate chemical to leave a thin open cavity  190  below the second patterned metal  184 , thus releasing the metal and yielding a free-standing structure. Etchant chemical may access the metal foil through openings in the patterned metal. The first layer  188  may be a dielectric or may contain charged elements making the device an electret. If the layer  188  is non-conductive, then acoustic of the acoustic element can occur at conductive layers below the non-conductive layer. 
         [0084]    Another embodiment of the manufacturing process is shown in  FIG. 11 . In this embodiment, a top laminate layer  203  is prepared having an opening  201  in it. A metal foil  205 , preferably copper, is prepared with a second metal  207  patterned on its top side and a third metal  209  patterned on its bottom side. The patterned metal is preferably gold. A second laminate layer  211  is also prepared. The two layers are bonded together with the patterned metal foil to form a single laminate construction  213 . Etchant is introduced through the opening in the second patterned metal. The patterned metal should be resistant to the etchant, whereas the foil should be attacked by the etchant. Possible etchants are ammonium persulfate or ferric chloride which will etch copper but will not etch gold. Etching chemical can reach the foil through openings in the top patterned metal layer. After etching, only the patterned metal remains, leaving a free standing structure which is the acoustic element  215 . 
         [0085]    A variation on this embodiment is shown in  FIG. 12 . In this version, a charged dielectric  217  is placed under the patterned metal. After etching the metal foil, the freestanding metal is positioned over an air gap  219  and an electret, forming a microphone. 
         [0086]    Similar embodiments can be envisioned on substrates that do not have laminate structure, but are still used for packaging, for instance metal lead frames. A metal lead frame is often used for mounting microelectronic chips and providing electrical connections to the chip. The lead frame is first cut from a single sheet of metal into its desired shape. Following this, microelectronic chips and other electrical components are attached to the surface of the lead frame, then electrical connections are made between the chip and the lead frame using techniques such as wire bonding, flip chip bonding, surface mount soldering, and the like. Finally, the circuitry is embedded within a mold compound which protects the electronics and forms the shape of the final packaged product. No MEMS device can survive this process. 
         [0087]    The following describes a method for building a microacoustic element that can be packaged on a lead frame. The basic procedure is illustrated in  FIG. 13 . First, a lead frame  222  is created using standard methods, such as cutting. The lead frame  222  should have small holes or openings in it to allow access to the acoustic section. Second, a metal laminate structure  224  is prepared consisting of a first metal film, with a second metal patterned on top, and a third metal film bonded to the top. The first and third metals are constructed of a metal, preferably copper, that is different from the middle metal, preferably gold or aluminum. This metal laminate  224  is bonded to the top of the lead frame  226 . Electrical connections  228  between the lead frame and the metal sandwich structure are made by any method, such as soldering or metal welding. Following this, the lead frame is used for mounting further microelectronic parts such as chips and passive components. Parts  230  are mounted and electrically connected using industry standard methods, such as pick-and-place, wire bonding, flip chip bonding, surface mount soldering, and the like. The assembly is then encapsulated in protective material  232  such as epoxy using normal packaging methods. After encapsulation, etchant is allowed to penetrate through the access holes in the lead frame to etch the metal laminate structure. The etchant is selected to etch only the first and third metal foils, and not the middle patterned metal. After etching, a free standing structure  234  is left that can be used as an acoustic device. Alternative embodiments are readily imagined by injection molding vents and acoustic ports into the encapsulant. 
         [0088]    These embodiments are meant to be illustrative examples and not exhaustive of the types of post-semiconductor manufacturing that can result in 3-D microstructures and freestanding parts. 
         [0089]    While the invention is susceptible to various modifications, and alternative forms, specific examples thereof have been shown in the drawings and are herein described in detail. It should be understood, however, that the invention is not to be limited to the particular forms or methods disclosed, but to the contrary, the invention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the appended claims.