Abstract:
Methods for adjusting the bulk material properties of manufactured components, such as resistors, thermistors, varistors, capacitors, resonators, oscillators, and optical components. Adjustment of the resistance of a resistor can be achieved by directing a high energy beam, such as an ultraviolet beam, onto a resistor formed from a matrix component and an embedded conductive component. The high energy beam adjusts the resistivity of the resistor material substantially without ablating the matrix component by affecting the matrix component, the conductive component, or both. Because of the lack of ablation, the material having a property to be adjusted can be a sub-layer in a laminated structure, with the high energy beam being directed through other layers formed thereon

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application is a continuation-in-part application of U.S. patent application Ser. No. 10/689,456, filed Oct. 20, 2003, and entitled “Optically Trimming Electronic Components,” which application claims the benefit of U.S. Provisional Application Ser. No. 60/419,356, filed Oct. 18, 2002, both of which applications are incorporated herein by reference. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. The Field of the Invention  
           [0003]    The present invention generally relates to electronic and optical components. In particular, the present invention relates to a method for selectively modifying specified bulk properties of electronic and optical components, such as are found in integrated circuits and the like.  
           [0004]    2. Related Technology  
           [0005]    The importance of integrated circuits and the products made therefrom cannot be underestimated. Innumerable products featuring electronic components have been incorporated into nearly every facet of modern living. Such electronic products commonly include an integrated circuit (“IC”), which typically comprises a large number of miniaturized electronic components that are mounted on a printed circuit board (“PCB”), in order to provide the needed electronic functionality of the product.  
           [0006]    During IC manufacture, much care is taken by the manufacturer to ensure that the various electronic components that comprise the IC possess operating characteristics that fall within an acceptable specification range. For instance, a resistor should possess a resistance that conforms to a desired specification. Such resistors are typically manufactured as “thin film” or “thick film” components on the PCB. In an untrimmed state, these resistors have tolerances in the range of a few percent for thin film and 5% to 15% for thick film.  
           [0007]    If the IC component as manufactured does not possess the proper characteristics, it may be possible to modify, or tune, its operating characteristics. “Tuning” is generally referred to as the process by which one or more operating characteristics of an electronic component, such as an IC resistor, is modified. In resistors and other IC components, tuning is often accomplished by a method known as “trimming.” Known trimming techniques alter the resistive properties of the resistor, for instance, by removing resistor material therefrom. This removal is typically accomplished by mechanical ablation of a portion of the resistor by a laser device.  
           [0008]    Despite its usefulness, several drawbacks exist with known laser trimming techniques. For example, the material removed from the resistor creates residue, which must be removed from the surface of the PCB after trimming, so as to avoid contamination thereof. This may often require an extra cleaning step during the manufacture of the PCB. Because it is a mechanical process, laser trimming is often limited to the top layer of a multi-layer PCB. Also, the nature of the resistor after treatment with known laser trimming techniques may cause undesired signal reflections from the resistor, as well as electromagnetic interference (“EMI”) from the resistor, during operation of the IC. Further, mechanical laser trimming often requires the use of select-on-test procedures for evaluating the success of the trimming procedure. Select-on-test evaluation is an expensive and slow process, which undesirably increases the time of manufacture for each PCB. As an alternative to mechanical laser trimming, other tuning techniques, such as thermal or electrical tuning, may be used to modify the bulk properties of electronic components. However, these techniques may also be either undesirable or unavailable depending on the type of PCB because of the risk of thermal or electrical damage to sensitive IC components.  
           [0009]    A need therefore exists for a method of modifying the bulk properties of electronic components such as IC resistors without also creating the need for subsequent cleaning operations. A corresponding need also exists for a tuning method that reduces the chances for signal reflection and EMI during operation of the IC. Such a method should also provide for dynamic or active tuning of the electronic component, thus avoiding slower select-on-test circuit evaluation procedures that result in added fabrication/calibration expense. This method would desirably be used to tune components within single or multiple layer PCB structures, as well as non-IC electronic components. Finally, a need exists for a method that also allows for the modification of the bulk properties of optical components as well.  
         BRIEF SUMMARY OF THE INVENTION  
         [0010]    Embodiments disclosed herein relate to methods for optically modifying the bulk properties of electronic and optical components. These components may comprise a portion of an integrated circuit (“IC”), or of any other suitable apparatus that employs such components. Examples, of such components are multichip modules (“MCMs”), multilayer hybrids such as low temperature cofired ceramic (“LTCC”) and multilayer glass substrates (“MGS”), which is the subject of another related patent on MGS and low temperature bonding. Also disclosed herein are methods for tuning the bulk properties of electronic and optical components in a dynamic or active fashion, thereby saving manufacturing time and resulting in a more efficient fabrication process of the IC or associated apparatus. These methods also allow for the bulk property modification of these electrical components without creating the need for cleaning the surface of the printed circuit board (“PCB”) or electronic substrate supporting the IC after the tuning is performed. Further, multi-layer PCB&#39;s and similar substrates may be tuned using these methods. The operating characteristics of the particular electronic component, such as a resistor, can be improved by reducing signal reflection by the component as well as reducing electromagnetic interference (“EMI”), which in turn helps eliminate circuit variations that may degrade the performance of the IC. The eye diagram of electronic components optically trimmed may be substantially improved.  
           [0011]    In one embodiment, the component having a bulk material property to be adjusted is a resistor formed from a matrix component and a conductive component. The adjustment can be performed in response to a determination that the resistance of the resistor does not meet specifications. In a first example, the matrix component is a cross-linkable polymer, while the conductive component is formed from carbon particles embedded in the matrix component. The resistivity of the material that forms the resistor and, consequently, the resistance of the resistor, can be reduced by directing a high energy beam, such as an ultraviolet beam, onto the resistor. The matrix component shrinks and brings the carbon particles closer together, thereby reducing resistivity of the material and the resistance of the resistor.  
           [0012]    In a second embodiment, the conductive component is introduced into the matrix component, whereby the conductivity of the conductive component is directly changed by exposure to the appropriate wavelength of light. Advantageously, this embodiment does not rely on a physical size change and internal movement of the matrix component.  
           [0013]    In a third embodiment, the matrix component can be caused to react with the conductive component. For example, the matrix component can be formed from a sol-gel, while the conductive component is formed from a suboxide material, such as a silicon suboxide or a titanium suboxide. In this case, the high energy beam directed onto the resistor causes oxygen in the sol-gel material to react with the suboxide material, thereby increasing resistivity of the material and the resistance of the resistor.  
           [0014]    In any of these cases, substantially no ablation occurs. These and other advantages and features of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    To further clarify the above and other advantages and features of the present invention, a more particular description of the invention will be rendered by reference to specific embodiments thereof that are illustrated in the appended drawings. It is appreciated that these drawings depict only typical embodiments of the invention and are therefore not to be considered limiting of its scope. The invention will be described and explained with additional specificity and detail through the use of the accompanying drawings in which:  
         [0016]    [0016]FIG. 1 is a perspective view of a portion of a printed circuit board having disposed thereon various electronic components, and a high energy beam source directed toward a selected electronic component in accordance with an embodiment of the present invention;  
         [0017]    [0017]FIG. 2A is a top close-up view of a portion of a resistor disposed on a printed circuit board, showing the relative distribution of conductive particles within the resistor material;  
         [0018]    [0018]FIG. 2B is a top close-up view of the resistor portion of FIG. 2A, showing the relative decrease in distance between conductive particles within the resistive material that results from application of one embodiment of the present method; and  
         [0019]    [0019]FIG. 3 is a top view of a resistor disposed on a printed circuit board, showing a graded resistive material resulting from application of one embodiment of the present method.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0020]    Reference will now be made to figures wherein like structures will be provided with like reference designations. It is understood that the drawings are diagrammatic and schematic representations of presently preferred embodiments of the invention, and are not limiting of the present invention nor are they necessarily drawn to scale.  
         [0021]    Various details of embodiments of the present invention are shown in FIGS. 1-3. Briefly summarized, embodiments of the present invention are directed to a method for optically modifying the bulk properties of electronic and optical components. These components may comprise a portion of an integrated circuit (“IC”), or of any other suitable apparatus that employs such optical and/or electronic components. Embodiments of the present invention further allow for the tuning of the bulk properties of electronic and/or optical components in a dynamic or active fashion, thereby saving manufacturing time and resulting in a more efficient fabrication process of the IC or associated apparatus.  
         [0022]    These methods also allow for the bulk property modification of electrical components without creating the need for cleaning the surface of the printed circuit board (“PCB”) or electronic substrate supporting the IC after the tuning is performed. In addition, optical and/or electronic components embedded within a multilayer stack of substrates can be tuned. Preferably, the substrate material, or, in particular, the path to the optical and/or electronic component, is sufficiently transparent to the tuning wavelength. Further, multi-layer PCB&#39;s and similar substrates may be tuned using this method. Advantageously, embodiments of the present invention improve the operating characteristics of the particular electrical component, such as a resistor, or optical component by reducing signal reflection by the electrical and/or optical component as well as reducing electromagnetic interference (“EMI”), which in turn helps eliminate circuit variations that may degrade the performance of the IC. Desirably, the eye diagram of electronic components optically trimmed may be substantially improved.  
         [0023]    Reference is first made to FIG. 1, which illustrates in a general fashion the various components employed in one exemplary embodiment of the present invention. As explained above, specified bulk properties of an electronic and/or optical component can be modified using the methods disclosed herein. Specifically, the electrical and/or optical component is optically trimmed by a high energy beam, such as a beam of ultraviolet light. “Trimming” as used herein, is understood to mean the modification of a selected bulk property of an electronic or optical component.  
         [0024]    [0024]FIG. 1 shows a printed circuit board, or PCB, designated generally at  10 . The PCB  10  includes an integrated circuit  12  comprising a plurality of electronic components  14 . FIG. 1 also illustrates a high energy beam source  16  emitting a high energy beam  18 . In preferred embodiments, the high energy beam  18  substantially comprises ultraviolet light. However, it is understood that the high energy beam  18  could comprise electromagnetic radiation having a wavelength distinct from that of ultraviolet radiation, or even energetic particles. Examples of such other beams  18  include electron, x-ray, gamma ray, and particle beams. Indeed, it is appreciated that a variety of beams having sufficiently high energy may be advantageously employed in the method of the present invention.  
         [0025]    The high energy beam source  16  is shown in FIG. 1 directing the high energy beam  18  toward a resistor  20 . Resistor  20  is only one type of electronic or optical component that may benefit from the practice of the methods disclosed herein. Indeed, and as will be further described below, various electronic and optical components may be modified in their bulk properties by practice of the present invention. Therefore, even though the following discussion concentrates on the optical trimming of the resistor  20 , an electronic component, it is understood that this is merely exemplary of the present method, and is not limiting of the scope of the present invention.  
         [0026]    The specified electronic component  14  is affected by the high energy beam  18  produced by the beam source  16  such that the desired bulk property of the component is altered. As seen in FIG. 1, the resistor  20  has incident upon it the high energy beam  18 . In one embodiment, this enables the high energy beam  18  to modify the resistive properties of the resistor  20 . This alteration of the resistivity of the material that forms the resistor and, consequently, the alteration of the resistance of the resistor, may be desirable, for example, if a proper level of resistance was not achieved during initial fabrication of the resistor  20 . Thus, it is seen that a major advantage of the present methods for optically trimming electronic or optical components is the ability to bring into specification those optical and/or electrical components that, for one reason or another, were not manufactured according to desired specifications. As already noted, these methods are not limited to the modification of resistors; indeed, various electronic and optical components may be improved by the present invention. For instance, the dielectric constant of a capacitor disposed in an IC may be altered so as to give the capacitor a desired capacitance. More details concerning components that may benefit from the present invention are discussed further below.  
         [0027]    The operating characteristics of the high energy beam  18 , such as the energy and time of exposure, are dependent upon several factors, including the extent to which the bulk property electronic of the component  14  requires modification, the type of material comprising the electronic component, etc. In one embodiment, deep ultraviolet light is employed as the high energy beam  18 , preferably having a wavelength range of from about 60-300 nm.  
         [0028]    Attention is now directed to FIGS. 2A and 2B, which show top views of the surface of the resistor  20  shown in FIG. 1. As has been discussed, according to one embodiment of the present invention, the resistor  20  may be optically trimmed so as to modify the resistance of the material comprising the resistor. In order for the high energy beam  18  to appropriately modify the resistor  20 , the resistor should be formed from a resistive material  22  that is susceptible to change when the high energy beam is incident upon it. An example of the resistive material  22  is shown in FIGS. 2A and 2B. In one embodiment, the resistive material  22  comprises a matrix component  24  and a conductive component  26 . Though the matrix component  24  and the conductive component  26  may comprise a variety of combinations, in the present embodiment, the matrix component  24  comprises a cross-linkable polymer, such as a methacrylate or vinyl polymer, combined in matrix form with cetyltrimethyl ammonium bromide (“CTAB”). The conductive component  26  is embedded within the matrix component  24  and comprises carbon particles in the present embodiment, though any other appropriate substance having the desired resistive characteristics may also be employed.  
         [0029]    According to one embodiment of the present invention, the resistive material  22  is formed by known fabrication procedures and incorporated into the resistor  20 . At least a portion of the resistor  20  after formation is then exposed to the high energy beam  18  of the beam source  16 , as shown in FIG. 1. FIG. 2A shows the resistive material  22  before treatment by the high energy beam  18 . As can be seen in FIG. 2A, the carbon particles comprising the conductive component  26  are spaced relatively far apart from one another. The exposure of the high energy beam  18  upon the resistive material  22  of the resistor  20  causes the matrix component  24  of the resistive material  22  to shrink, as is seen in FIG. 2B. The shrinkage of the matrix component  24  causes the average spacing of the embedded carbon particles of the conductive component  26  to decrease. The net result of the shrinkage of the resistive material  22 , then, is a net decrease in the resistance of the resistive material  22 , given the now decreased relative inter-particle distance of the carbon particles.  
         [0030]    Thus, the present method for optical trimming can alter the bulk property of an electronic and/or optical component, in this case the resistance of the resistor  20 . Advantageously, this modification of the resistance of the resistor  20  is accomplished optically and not mechanically, as is the case with known laser trimming techniques. Thus, no ablated material is created, thereby precluding the need for cleaning the surface of the PCB  10  after trimming. Further, because no ablation material is created, the present method may be used to alter electronic and/or optical components that reside one or more layers below the surface of the PCB  10  or other substrate. It should also be understood that, though the present discussion focuses on the trimming of electronic and optical components disposed in an IC, non-IC components may also be modified as may be appreciated by one skilled in the art.  
         [0031]    In another embodiment, the conductive component, instead of the matrix component, is altered in some manner by exposure to the appropriate wavelength of light or other energy source. Advantageously, this embodiment does not rely on a physical size change and internal movement of the matrix component.  
         [0032]    In yet another embodiment, the matrix component can be caused to react with the conductive component so that the bulk property of the optical and/or electrical component is altered. In an example, a matrix component  24  comprises sol-gel having embedded therein a conductive component  26  comprising a conductive suboxide, such as silicon suboxide or titanium suboxide. In this case, the conductive suboxide comprising the conductive component  26  induces the attraction of additional oxygen to combine with the suboxide when the resistive material  22  is exposed to the high energy beam  18  of ultraviolet light. The gathering of oxygen by the conductive suboxide in this case results in a net increase of the resistance of the conductive component of the resistive material  22 , thus raising the bulk property resistance of the resistor  20 .  
         [0033]    The matrix component comprising sol-gel having a conductive component embedded therein is one example of using an oxidation/reduction (redox) reaction to change the bulk properties of the optical and/or electrical component. In this embodiment, the conductive component includes metal oxides whose oxidation state, which determines the conductivity, can be changed by photo-induced redox reactions. This method centers around the idea that the conductive component, and possibly the matrix itself, form a redox pair such that the oxidation-reduction reaction can be thermally or photo catalytically induced by a laser or other means.  
         [0034]    Thus, the bulk properties of the optical and/or electrical component can be modified in at least the following ways: (1) the matrix component may be modified, generally by cross linking, so that the size of the matrix component can be altered; (2) the nature of the conductive component may be modified; or (3) the matrix component and conductive component can be caused to react together to change the bulk property of the material.  
         [0035]    In addition to optically trimming resistors, other embodiments of the present invention are able to modify the bulk properties of other electronic components  14 . As mentioned above, the dielectric constant of a capacitor may be modified in accordance with desired specifications. The rate constant of thermistors, the threshold of varistors, and the magnetic susceptibility of ferrite materials are some examples of materials properties that may be trimmed by these methods. Likewise, electronic components such as resonators or oscillators may be modified so as to yield desired characteristics with respect to Young&#39;s modulus. The bulk physical dimensions of an electronic component may be modified or aligned in situ. Or, more generally, the bulk chemical properties of an electronic component may be altered using the optical trimming procedures outlined herein. Thus, the examples given above are merely exemplary of the type of bulk property modification that is possible with the present invention, and thus are not limiting of its scope.  
         [0036]    The bulk properties of optical components may also be modified by the present invention. Examples of this include the modification of the bulk refractive index of an optical component, or the alteration of the crystalline, matrix size, and opacity of an optical component. Further, photonic crystals may be advantageously improved in terms of their bulk properties by employing the methods disclosed herein.  
         [0037]    Reference is now made to FIG. 3, which illustrates a top view of a resistor  30  comprising a portion of an integrated circuit  12 . The resistor  30  is at least partially comprised of a resistive material  32  that has been modified in its resistance according to the present invention. As can be seen from the figure, the resistor  30  is electrically connected to the rest of the integrated circuit  12  by traces  33 A and  33 B, as is well known in the art. The resistive material  32  has been treated in accordance with the principles of the present invention by a high energy beam  18  such that the resistance of the resistor  30  varies as a function of position along the length of the resistor body. Treatment of the resistive material  32  by the high energy beam  18  has been accomplished so as to create a relatively higher resistance region in a middle portion  35  of the resistor  30 . The resistance of the resistor  30  progressively diminishes toward each of the traces  33 A and  33 B such that the resistance of the resistive material  32  near ends  37 A and  37 B of the resistor  30  is lowest.  
         [0038]    Thus, FIG. 3 shows a resistor with graded impedance terminations to the traces. The resistance of the interior, middle portion is significantly greater than the portion near the traces. The resistor  30  is treated by the high energy beam  18  comparatively more at the middle portion  35  of the resistor than near the end portions of  37 A and  37 B in order to achieve this desired resistance. FIG. 3 shows this relative resistance differential by varying shades. The treatment of the resistor  30  to have the graded resistance described above is desirable in several respects. First, such a resistive grading reduces abrupt resistive transitions in or near the resistor  30 , which helps reduce signal reflection. Second, EMI is reduced, thereby reducing interference with adjacent electronic components disposed on the PCB  10 .  
         [0039]    It is appreciated that the high energy beam source  16  may be employed to alter a selected bulk property of the electronic component  14  not only in a homogenous manner, as shown in FIGS. 2A and 2B, but also in a graded pattern, as shown in FIG. 3, or in some combination of these patterns. Thus the electronic component  14  may be altered as may suit the particular application in which the device will function.  
         [0040]    In another embodiment of the present invention, optical trimming may be used to alter the dielectric constant of material surrounding a trace on the PCB  10 . This alteration modifies the phase delay of the electric signal passing through the trace. Thus precise tuning of the phase delay through the trace is possible. Additionally, coupled transmission lines may be similarly tuned. Advantageously, the optical and/or electrical components can be trimmed during a functional test after the PCB like structure has been assembled, thus eliminating guesswork, select-on-test, or other expensive and time consuming manufacturing techniques designed to narrow the distribution of a critical parameter. In one aspect, the present disclosure describes some methods for dramatically narrowing the distribution of certain electrical and optical parameters either stand alone or in relation to other parameters of a manufactured device.  
         [0041]    The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative, not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes that come within the meaning and range of equivalency of the claims are to be embraced within their scope.