Abstract:
A method of manufacturing a hermetic package. In one embodiment, the method includes: (1) forming a plurality of contact-sensitive electronic devices on a device substrate, each of the plurality of devices having an active surface, (2) providing a mounting substrate, (3) forming a grid of dam material between the device substrate and the mounting substrate that is pitched as a function of lateral dimensions of the plurality of devices, (4) bringing the device substrate and the mounting substrate together until the active surface of each of the plurality of devices is proximate, but spaced apart from, the mounting substrate, the mounting substrate and the dam material cooperating to form packages for the plurality of devices and (5) dicing the device substrate to separate the packages.

Description:
TECHNICAL FIELD OF THE INVENTION 
     The present invention is directed, in general, to electronics packaging and, more specifically, to a hermetic package for contact-sensitive electronic devices and methods of manufacturing such package. 
     BACKGROUND OF THE INVENTION 
     Electronic signal processing by means of surface acoustic wave (SAW) devices has been widely adopted by the electronics industry. Such SAW devices can be designed to operate as analog electrical filters that operate over a wide range of frequencies and have several advantages over conventional technologies. One such advantage is that they can be designed to provide complex signal processing in a single unit. Surface acoustic wave devices also benefit from the ability to be mass produced using semiconductor microfabrication techniques which produce highly uniform devices at a substantially reduced cost. SAW devices can be easily integrated into many digital communications systems and designed to operate in high harmonic modes in the gigahertz (GHz) frequency range. 
     Proper operation and containment of the acoustic waves require precise construction. Existing surface acoustic wave device packaging has become well accepted in response to such requirements. Additionally, accurate and reliable performance of surface acoustic wave devices requires hermetic protection of the active surfaces of the devices. However, existing packaging practices often fails to fully and economically passivate the surface acoustic wave device active surface, thereby permitting particulate or contaminants to interfere with the active surface and render the performance of the SAW device inaccurate and unreliable. Such contamination concerns also exist with regard to other contact-sensitive electronic components, including other piezoelectric, pyroelectric, and micro-electromechanical (MEMS) applications. 
     Accordingly, what is needed in the art is a hermetic package for surface acoustic wave devices and other contact-sensitive electronic components, as well as a method of manufacturing such a hermetic package. 
     SUMMARY OF THE INVENTION 
     To address the above-discussed deficiencies of the prior art, the present invention provides a method of manufacturing a hermetic package. In one embodiment, the method includes: (1) forming a plurality of contact-sensitive electronic devices on a device substrate, each of the plurality of devices having an active surface, (2) providing a mounting substrate, (3) forming a grid of dam material between the device substrate and the mounting substrate that is pitched as a function of lateral dimensions of the plurality of devices, (4) bringing the device substrate and the mounting substrate together until the active surface of each of the plurality of devices is proximate, but spaced apart from, the mounting substrate, the mounting substrate and the dam material cooperating to form packages for the plurality of devices and (5) dicing the device substrate to separate the packages. 
     The foregoing has outlined, rather broadly, preferred features of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art should appreciate that they can readily use the disclosed conception and specific embodiment as a basis for designing or modifying other structures for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the invention in its broadest form. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more complete understanding of the present invention, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which: 
     FIG. 1 illustrates a hermetic package for multiple interconnected contact-sensitive electronic devices constructed according to the principles of the present invention; 
     FIG. 2 illustrates a method of manufacturing a hermetic package for multiple interconnected contact-sensitive electronic devices; and 
     FIG. 3 illustrates an alternative method of manufacturing a hermetic package for multiple interconnected contact-sensitive electronic devices. 
    
    
     DETAILED DESCRIPTION 
     Referring initially to FIG. 1, illustrated is a block diagram of a hermetic package  100  constructed according to the principles of the present invention. The hermetic package  100  includes a mounting substrate  130  and a plurality of device substrates  110 , each device substrate  110  being separated from the mounting substrate  130  by one or more electrically conductive spacers  170 . In a preferred embodiment, the spacers  170  separate the active surface  120  of each device substrate  110  from the mounting substrate  130  by approximately 20 microns, but may separate the substrates  110 ,  130  by at most about 40 microns. As is familiar to those skilled in the art, the spacers  170  may be thermosonic gold stud bumps, such as those installed via thermosonic scrubbing. In this manner, the spacers  170  not only separate each device substrate  110  from the mounting substrate  130 , but also electrically connect the mounting substrate  130  to each active surface  120 , such that the electronic devices  105  may be interconnected via conductive traces (not shown) on the mounting substrate  130 . Thus, conductive epoxy or solder or reflow processes are not necessary to connect the active surfaces  120  with the mounting substrate  130 . 
     Each device substrate  110  includes a contact-sensitive electronic device  105  secured to the active surface  120 . The device substrates  110  may be comprised of bismuth germanium oxide, gallium arsenide, lithium borate, lithium niobate, lithium tantalate, langasite, lead zirconium tantalate, quartz, or a combination thereof. The device substrates  110  are lodged within a dam material  140  in a manner that, in conjunction with the spacers  170 , suspends each active surface  120  a predetermined distance away from the mounting substrate  130 . The dam material  140  preferably encompasses a substantial portion of the perimeter of each device substrate  110 , such that each device substrate  110  and the spacers  170  are located inboard of an outboard surface of a corresponding portion of the dam material  140 . The dam material  140  may also extend a short distance into the gap  180  formed by an active surface  120  and the mounting substrate  130 . The dam material  140  may be comprised of epoxy resin, polyimide, benzocyclobutene, silicone or cyanoacrylate, and is preferably a lower viscosity material than previously used to mount contact-sensitive device substrates to mounting substrates. Note, however, that no underfill materials are necessary in package  100  to hermetically seal the active surface  120 , such that the lower viscosity material relied on by prior designs is avoided by the use of the higher viscosity dam material  140  and a hermetic seal  150 . 
     The hermetic seal  150  covers the dam material  140 . The hermetic seal  150  may also cover one or more device substrates  110 , or a portion thereof, and may also cover a portion of the mounting substrate  130 . At a minimum, however, the hermetic seal  150  seals each gap  180  within the dam material  140 , such that particulate and contaminants are precluded from contacting each electronic device  105 . Each gap  180  may also be evacuated, such that each gap  180  may be under a vacuum. By evacuating each gap  180 , and subsequently sealing each gap  180  with the hermetic seal  150 , operation of each electronic device  105  will not be disturbed or otherwise influenced by unwanted particulate or contaminants. In this manner, the unpassivated and contact-sensitive electronic devices  105  may be passivated, thereby ensuring hermeticity and predictable performance of each device  105 . The hermetic seal  150  may be applied to the package  100  by sputtering or otherwise depositing organic or inorganic material over the desired surfaces, and may comprise silicon nitride, silicon carbide, silicon oxide, aluminum nitride, or aluminum oxide. 
     The hermetic package  100  may also include a passivation layer  160  covering all or a portion of the hermetic seal  150 , the dam material  140 , the device substrates  110  and/or the mounting substrate  130 . The passivation layer  160  is primarily utilized to resolve mechanical and handling issues. By protecting the package  100  with the passivation layer  160 , the threat of damage encountered in subsequent manual or automated handling and assembly procedures (e.g., pick-and-place procedures) may be mitigated. The passivation layer  160  may be comprised of a standard encapsulant epoxy resin conventionally used and known to those skilled in the art. The passivation layer  160  may be applied to the package  100  either by injection, transfer molding or liquid disposition. 
     In an alternative embodiment, the dam material  140  and/or the passivation layer  160  may hermetically seal the gap  180  to a degree sufficient for the proper and accurate operation of the electronic device  105  required of a particular application. That is, the dam material  140  and/or the passivation layer  160  may provide sufficient mechanical, environmental and hermetic protection of the electronic device  105  in the absence of a discrete hermetic seal  150 . In such instances, the hermetic seal  150  may be comprised of the portion of the dam material  140  and/or the passivation layer  160  that forms such sufficient hermetic protection, instead of requiring a separate, distinct material or layer. For instance, the portion of the dam material  140  that provides hermetic protection of the electronic device  105  may be outboard of and therefore located over the portion of the dam material  140  not physically functioning to provide sufficient hermetic protection. In this manner, the hermetic seal  150  may still be “located over” the dam material  140  despite actually being the same material as the dam material  140 . 
     Although the package  100  is originally intended to satisfy the hermeticity needs of surface acoustic wave devices, one skilled in the art can foresee other piezoelectric, pyroelectric, micro-electromechanical (MEMS) or mirror device applications that would benefit from the hermetic passivation ensured by this architecture. 
     Turning now to FIG. 2, illustrated is a method  202  of manufacturing an embodiment of a hermetic package  200  containing a plurality of interconnected contact-sensitive electronic devices. In a first manufacturing step  285 , a substantially planar piezoelectric wafer  230 , such as a 4-inch piezoelectric wafer, is provided as a mounting substrate. The piezoelectric wafer  230  may comprise many known or hereinafter discovered piezoelectric materials. However, in one advantageous embodiment of the present invention, the piezoelectric wafer  230  comprises a material selected from the group consisting of bismuth germanium oxide, gallium arsenide, lithium borate, lithium niobate, lithium tantalate, langasite, lead zirconium tantalate, or quartz, or a combination thereof. 
     Subsequent to providing the piezoelectric wafer  230 , a plurality of electrically conductive spacers  270  may be positioned over the piezoelectric wafer  230 . In a second manufacturing step  287 , the device substrate  210  of each of a plurality of contact-sensitive electronic devices is secured to the piezoelectric wafer  230  via a corresponding one of the plurality of spacers  270 . A preferred embodiment includes the use of a thermosonic scrub (e.g., a gold-to-gold scrub) to secure the device substrates  210  to the piezoelectric wafer  230 , wherein an electrically conductive spacer component (not shown) connected to a terminal of an active surface (not shown) of the device substrate  210  is bonded by temperature and/or vibration (“scrubbing”) to an electrically conductive spacer component (not shown) connected to a terminal (not shown) of the piezoelectric wafer  230 . 
     However, it should be understood by those skilled in the art that many other processes may be used to secure the electronic devices (via device substrates  210 ) to the piezoelectric wafer  230 . Note, however, that no conductive epoxy or solder or additional reflow process is necessarily required to secure the device substrates  210  to the piezoelectric wafer  230 . In securing the plurality of device substrates  210  to the piezoelectric wafer  230  via the electrically conductive spacers  270 , the electronic devices may be interconnected via conductive traces (not shown) on the piezoelectric wafer  230 . 
     Step  287  further secures the device substrates  210  to the piezoelectric wafer  230  such that the spacers  270  may preferably separate the active surfaces (not shown) of each of the plurality of device substrates  210  from the piezoelectric wafer  230  by approximately 20 microns. However, the spacers  270  may separate the active surfaces of each of the plurality of device substrates  210  from the piezoelectric wafer  230  by at most about 40 microns. 
     In a third manufacturing step  289 , a dam material  240  is dispensed around the perimeter of each device substrate  210 . The dam material  240  may be comprised of epoxy resin, polyimide, benzocyclobutene, silicone or cyanoacrylate, and is preferably a lower viscosity material than previously used to mount contact-sensitive device substrates to piezoelectric wafers. Note, however, that no underfill material, such as a material typically of lower viscosity than the dam material  240  used here, is required in any of the present embodiments. The dam material  240  may flow a short distance into the gaps (not shown) formed by the active surfaces of each of the plurality of device substrates  210 , but less of the dam material  240  flows into the gap than in conventional processes. It is because of this lack of flow of the dam material  240  towards the active surfaces of the devices substrates  210  that the conventional use of a window-shaped dam around the device active surface is not necessary. 
     In subsequent manufacturing step  291 , a hermetic seal  250  is formed over the dam material  240  and at least a portion of the piezoelectric wafer  230  and one or more device substrates  210 , thereby forming a hermetic wafer assembly  285 . The hermetic seal  240  ensures that the electronic device will not be disturbed or otherwise influenced by unwanted particulate or contaminants. In this manner, an unpassivated and contact-sensitive electronic device may be passivated, thereby ensuring hermeticity and predictable performance of the electronic device. The hermetic seal  240  may comprise silicon nitride, silicon carbide, silicon oxide, aluminum nitride, or aluminum oxide. 
     Method  202  may also include a manufacturing step  293 , wherein a passivation layer  260  is formed over the hermetic seal  240 . The passivation layer  260  may also be formed over all or a em portion of the dam material  240 , the piezoelectric wafer  230 , and/or one or more device substrates  210 . The passivation layer  260  may also be formed over the entire hermetic wafer assembly  285 . The passivation layer  260  may be formed by injection, transfer molding or liquid dispensing. Note, however, that in an alternative embodiment, the step  293  formation of the passivation layer  260  may be excluded from method  202 . 
     In a final manufacturing step  295 , the hermetic wafer assembly  285  may be separated into the individual hermetic packages  200  containing one or more hermetically sealed electronic devices. In an exemplary embodiment, the hermetic wafer assembly  285  may be separated into the individual hermetic packages  200  using wafer dicing, however, one skilled in the art understands that any compatible separation technique may be used. 
     Turning finally to FIG. 3, illustrated is an alternative method  303  of manufacturing an embodiment of a hermetic package  300  containing a plurality of interconnected contact sensitive electronic devices, which in the present embodiment may be similar to the hermetic package  100  illustrated in FIG.  1 . In a first manufacturing step  385 , a substantially planar piezoelectric wafer  330 , such as a 4-inch piezoelectric wafer, is provided as a mounting substrate. The piezoelectric wafer  330  may comprise many known or hereinafter discovered piezoelectric materials. However, in one advantageous embodiment of the present invention, the piezoelectric wafer  330  comprises a material selected from the group consisting of bismuth germanium oxide, gallium arsenide, lithium borate, lithium niobate, lithium tantalate, langasite, lead zirconium tantalate, or quartz, or a combination thereof. 
     Subsequent to providing the piezoelectric wafer  330 , a plurality of electrically conductive spacers  370  may be positioned over the piezoelectric wafer  330 . The spacers  370  may be positioned over the piezoelectric wafer  330  by many processes known to those skilled in the art, but are preferably positioned using the thermosonic scrub process described above in reference to FIG.  2 . 
     In a second manufacturing step  387 , a dam material  340  is arranged on the piezoelectric wafer  330  in a pattern configured to receive a substantial portion of a perimeter of each device substrate  310  of a plurality of interconnected contact-sensitive electronic devices. The dam material  340  may also be comprised of epoxy resin, polyimide, benzocyclobutene, silicone or cyanoacrylate, and is preferably a material of lower viscosity than previously used to mount contact-sensitive device substrates to piezoelectric wafers. Note, however, that no underfill material, such as a material typically of lower viscosity than the dam material used here, is required in any of the present embodiments. 
     In a third manufacturing step  389 , the plurality of device substrates  310  are lodged within the dam material  340  arranged in step  387 . In this step  389 , the dam material  340  may flow a short distance into the gaps (not shown) formed by the active surfaces of each of the plurality of device substrates  310 , but because the dam material  340  is of higher viscosity than that conventionally used, less of the dam material  340  flows into the gap than in conventional processes. It is because of this lack of flow of the dam material  340  towards the active surfaces of the device substrates  310  that the conventional use of a window-shaped dam around the device active surface is not necessary. 
     Manufacturing step  389  also preferably includes the use of the thermosonic scrub process described above in reference to FIG. 2 to secure the device substrate  310  of each of the plurality of contact-sensitive electronic devices to the piezoelectric wafer  330  via a corresponding one of the plurality of spacers  370 . However, it should be understood by those skilled in the art that many other processes may be used to secure the electronic devices (via device substrates  210 ) to the piezoelectric wafer  330 . Note, however, that no conductive epoxy or solder or additional reflow process is necessarily required to secure the device substrates  310  to the piezoelectric wafer  330 . In securing  4 , the plurality of device substrates  310  to the piezoelectric wafer  330  via the electrically conductive spacers  370 , the electronic devices may be interconnected via conductive traces (not shown) on the piezoelectric wafer  330 . 
     Step  389  further secures the device substrates  310  to the piezoelectric wafer  330  such that the spacers  370  may preferably separate the active surfaces (not shown) of each of the plurality of device substrates  310  from the piezoelectric wafer  330  by approximately 20 microns. However, the spacers  370  may separate the active surfaces of each of the plurality of device substrates  310  from the piezoelectric wafer  330  by at most about 40 microns. 
     In subsequent manufacturing step  391 , a hermetic seal  350  is formed over the dam material  340  and at least a portion of piezoelectric wafer  330  and one or more device substrates  310 , thereby forming a hermetic wafer assembly  385 . Alternatively, the hermetic seal  350  may be formed over the entire piezoelectric wafer  330 . The hermetic seal  350  ensures that the electronic device will not be disturbed or otherwise influenced by unwanted particulate or contaminants. In this manner, an unpassivated and contact-sensitive electronic device may be passivated, thereby ensuring hermeticity and predictable performance of the electronic device. The hermetic seal  350  may comprise silicon nitride, silicon carbide, silicon oxide, aluminum nitride, or aluminum oxide. 
     Method  303  may also include a manufacturing step  393 , wherein a passivation layer  360  is formed over the hermetic seal  350 . If the hermetic seal  350  has not been formed over the entire piezoelectric wafer  330 , the passivation layer  360  may also be formed over all or a portion of the dam material  340 , the piezoelectric wafer  330 , and/or one or more device substrates  310 . The passivation layer  360  may be formed by injection, transfer molding or liquid dispensing. Note, however, that in an alternative embodiment, the step  393  formation of the passivation layer  360  may be excluded from method  303 . 
     In a final manufacturing step  395 , the hermetic wafer assembly  385  may be separated into the individual hermetic packages  300  containing one or more hermetically sealed electronic devices. In an exemplary embodiment, the hermetic wafer assembly  385  may be seperated into the individual hermetic packages  300  using wafer dicing, however, one skilled in the art understands that compatible seperation techniques may be used. 
     Although the present invention has been described in detail, those skilled in the art should understand that they can make various changes, substitutions and alterations herein without departing from the spirit and scope of the invention in its broadest form.