Abstract:
A system and method for fabricating a thermoelectric cooling (TEC) device and a semiconductor device using such a TEC device are described. Adhesive-containing support structures are used to secure, respectively, positively-doped and negatively-doped TEC elements. The elements are intermeshed and an encapsulating material is applied to the intermeshed array. The support structures are then released and the ends of the encapsulated elements are smoothed and electrically coupled together. If desired, panels are secured to the ends of the elements and a heat sink may also be provided. The TEC device may be used to control and/or tune a laser device.

Description:
FIELD OF THE INVENTION  
         [0001]    The invention relates generally to the fabrication of semiconductor devices that include fragile elements. More particularly, the invention is related to a system and a method for smoothing the ends of fragile elements used in heat transfer devices and the semiconductor devices incorporating such heat transfer devices.  
         BACKGROUND  
         [0002]    Known thermoelectric coolers (TECs) for optoelectric semiconductor devices utilize fragile elements formed of bismuth telluride. Bismuth telluride, and other such materials, are susceptible to shear and/or fracture if subjected to physical stress, especially when not properly anchored. In a known method, positively-and negatively-doped elements are restrained by some mechanical means, and then the ends of the elements are smoothed or lapped to the desired size. A disadvantage of the known method is that the doped elements are susceptible to shear and/or fracture during the lapping (smoothing) process. The elements can break, chip or spall.  
         SUMMARY  
         [0003]    The invention relates to an improved method of making a heat transfer device. The heat transfer device may be formed of a plurality of positively-doped and negatively-doped fragile elements. In a preferred embodiment of the invention, the ends of the elements are smoothed to a precise tolerance. The positively-doped elements may be electrically coupled to the negatively-doped elements, and an encapsulating material may be provided to hold the elements in place during the smoothing process.  
           [0004]    The invention also relates to a system for aligning elements of a thermoelectric cooler device. The system includes a first support structure adapted to support a plurality of first elements, a second support structure adapted to support a plurality of second elements, a holding structure for positioning the first elements on the first support structure, and a source of encapsulating material for encapsulating the elements.  
           [0005]    According to an aspect of the invention, a holding structure is used to hold the positively-doped elements and another holding structure is used to hold the negatively-doped elements. Adhesive support structures may be used to support the elements while they are intermeshed, and the elements are encapsulated in a resin or other flowable material after they are intermeshed. The hardened encapsulant material may be used to hold the intermeshed elements in place while their ends are polished or otherwise mechanically finished.  
           [0006]    The invention also provides a method for fabricating a semiconductor device. The method includes the steps of positioning first elements on a first support structure and second elements on a second support structure, intermeshing the first and second elements such that each element contacts each support structure, and subsequently encapsulating the elements within an encapsulating material.  
           [0007]    These and other advantages and features of the invention will be more readily understood from the following detailed description of the invention which is provided in connection with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    [0008]FIG. 1 is a partially broken-away perspective view illustrating the placement of positively-doped heat transfer device elements on a hoop in accordance with an embodiment of the invention.  
         [0009]    [0009]FIG. 2 is another perspective view like FIG. 1 showing the positively-doped elements adhered to the hoop.  
         [0010]    [0010]FIG. 3 is a side view illustrating intermeshing of positively-doped and negatively-doped elements in accordance with an embodiment of the invention.  
         [0011]    [0011]FIG. 4 is a perspective view like FIG. 2 showing intermeshed positively-doped and negatively-doped elements on the hoop.  
         [0012]    [0012]FIG. 5 is a partially broken-away side view showing the elements of FIG. 4 encased in a matrix in accordance with an embodiment of the invention.  
         [0013]    [0013]FIG. 6 is a side view illustrating the smoothing of the elements of FIG. 4.  
         [0014]    [0014]FIG. 7 is a side view of a semiconductor device constructed in accordance with an embodiment of the invention.  
         [0015]    [0015]FIG. 8 illustrates process steps for fabricating a semiconductor heat transfer device in accordance with an embodiment of the invention. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0016]    FIGS.  1 - 8  illustrate various stages of fabricating a heat transfer device according to an exemplary embodiment of the invention. A plurality of positively-doped elements  10  are placed within respective openings  18  of a holding structure, such as a jig  16 , in step  100  (FIG. 8). The jig  16  should be suitable to mechanically maintain the correct positional relationship between a piece of work, here the element  10 , and the jig  16  and/or the correct positional relationship between the elements  10 . The elements  10  are used in heat transfer devices, such as a thermoelectric cooler device  50  (FIG. 7), used in semiconductor packages.  
         [0017]    Each element  10  has opposite ends  12 ,  14 . As shown in FIG. 1, the first ends  12  do not abut any other object. The second ends  14  contact an adhesive surface  26  of an adhesive material  24  at step  105  (FIG. 8). The material  24 , which is preferably a tape, is affixed to a hoop frame  22 . The frame  22  and the material  24  make up a first hoop  20 .  
         [0018]    The positively-doped elements  10  may be placed in the jig  16  (step  100 ) before the elements  10  are brought into contact with the adhesive surface  26  (step  105 ). Alternatively, the elements  10  may be located within the openings  18  after the jig  16  is brought into contact with the adhesive surface  26 . After the elements  10  are adhered to the hoop  20  (step  105 ), the jig  16  is removed, leaving the elements  10  free-standing on the adhesive surface  26  (FIG. 2). The adhesive surface  26  contains sufficient adhesive properties to securely hold, and to inhibit tipping of, the elements  10 . The adhesive material  24  may be temperature sensitive. Specifically, with the application of heat to a certain predetermined temperature the adhesive properties of the adhesive surface  26  diminish, allowing a loss of adhesion between the elements  10  and the hoop  20 .  
         [0019]    A similar operation may be undertaken to adhere negatively-doped elements  11  to an adhesive surface  26 ′. Specifically, a holding structure, like the jig  16 , is used to collect a plurality of the elements  11  (step  100 ). The elements  11  have opposite ends  13 ,  15 . An adhesive material  24 ′ is lowered onto the jig with the elements  11  such that the adhesive surface  26 ′ contacts the ends  15  (step  105 ). The adhesive material  24 ′ is affixed to a hoop frame  22 ′, with the frame  22 ′ and the material  24 ′ making up a second hoop  20 ′.  
         [0020]    As shown in FIG. 3, the hoop  20 ′ is lowered and/or the hoop  20  is elevated to interdigitate or intermesh the elements  10  and  11  at step  110  (FIG. 8). Specifically, the hoops  20 ,  20 ′ are placed near enough to each other to allow each of the ends  12 - 15  to contact one of the adhesive surfaces  26 ,  26 ′. The flexibility of the materials  24 ,  24 ′ may be advantageous in ensuring that all of the element ends  12 - 15  are adhered to the surfaces  26 ,  26 ′. Further, the flexibility of the materials  24 ,  24 ′ may be advantageous during intermeshing to allow any needed slight angular realignments of the elements  10 ,  11  to avoid breakage or damage.  
         [0021]    At step  115  (FIG. 8), an encapsulating material  30  may be flowed onto and around the elements  10 ,  11  (FIG. 5). Alternatively, one of the hoops  20 ,  20 ′ may be removed at step  120  (FIG. 8) and then the encapsulating material  30  may be flowed around and between the elements  10 ,  11  (step  115 ). A mold  31  (FIG. 4) may be utilized to assist the encapsulating material  30  to surround the elements  10 ,  11 . The encapsulating material  30  is preferably a viscous fluid that hardens over a short period of time, either with no outside stimulus or with a temperature change. Most preferably, the material  30  is a dielectric material such as epoxy or an elastomer such as rubber. Upon hardening, the encapsulating material  30  creates a solid matrix around the elements  10 ,  11  which prevents tipping.  
         [0022]    Utilizing the temperature sensitivity of the adhesive material  24 ′, heat from a heat source  35  (FIG. 4) is directed at the adhesive surface  26 ′ to release the hoop  20 ′ from the ends  12 ,  15  at step  120  (FIG. 8). As an alternative, it is equally possible to heat the adhesive surface  26  to release the hoop  20  and leave the elements  10 ,  11  adhered to the hoop  20 ′.  
         [0023]    After the material  30  has hardened, the remaining hoop  20  can be released in the same manner as the hoop  20 ′ (step  120 ). Next, at step  125  (FIG. 8) the ends  12 - 15  of the elements  10 ,  11  are smoothed or polished. Referring to FIG. 6, a lapping machine  40  may be used to precisely smooth or lap first the ends  12  and  15  and then the ends  13  and  14  so that each of the elements  10 ,  11  are linearly aligned with one another and to provide smooth surfaces for electrical connectivity. The lapping process may also be used to create a precise height size of the elements  10 ,  11  such that the ends  12 ,  15  and the ends  13 ,  14  are respectively within the same planes. The encapsulating material  30  provides lateral restraint during the lapping process so that the positively-doped and negatively-doped elements  10 ,  11  do not become misaligned. The elements  10 ,  11  could be damaged by the lapping machine  40  if they were misaligned.  
         [0024]    The presence of the material  30  provides an anchoring mechanism  30  for the elements  10 ,  11  during the lapping or polishing process. This anchoring mechanism  30  inhibits shearing and/or fracturing of the elements  10 ,  11  during the finishing process. Further, the material  30  assists in maintaining accurate alignment of the elements  10 ,  11 .  
         [0025]    After lapping of the ends  12 - 15 , the elements  10 ,  11  are electrically coupled together and attached to a panels  52 ,  54 . Solder balls  51  may be provided to the desired electrical connections. The assembly is coupled to a heat sink  56  at step  130  (FIG. 8) to create a thermoelectric cooler device  50  (FIG. 7). If desired, a semiconductor device (such as a laser device)  58  is thermally coupled to one of the panels  52 ,  54  to create a semiconductor device  60 .  
         [0026]    While the invention has been described in detail in connection with the preferred embodiments known at the time, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.