Abstract:
Provided is a probe card including: a printed circuit board comprising a ground electrode; at least one dielectric disposed below the ground electrode; and a plurality of needles, each of which comprises: a first end portion contacting a wafer pad of a semiconductor device, a second end portion electrically connected to the printed circuit board, and the remaining portion excepting the first and second end portions surrounded by the at least one dielectric. A metal plate is disposed below the at least one dielectric; and a connecting pin electrically connects the metal plate to the ground electrode and fixes the at least one dielectric and the metal plate to the printed circuit board.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS  
       [0001]     This application claims the benefit of Korean Patent Application No. 10-2005-0008349, filed on Jan. 29, 2005, in the Korean Intellectual Property Office, the contents of which are incorporated herein in their entirety by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a probe card used to detect the electrical characteristics and defects of a semiconductor device, such as an integrated circuit formed on a semiconductor wafer, and more particularly, to a probe card for testing high-frequency digital signals or analog signals.  
         [0004]     2. Description of the Related Art  
         [0005]     Typically, the electrical characteristics of semiconductor devices such as an integrated circuit are tested when semiconductor devices are formed on a wafer. That is, if a semiconductor integrated circuit is found to have detects after being packaged, the packaging process is wasted. Thus, the electrical characteristics of the semiconductor integrated circuit are tested when the semiconductor integrated circuit is disposed on a wafer before chips are cut. In order to test electrical characteristics, first, a needle of a probe card contacts an external contact terminal of an integrated circuit such as a wafer pad; an electric signal is input from an electrical characteristics testing apparatus to the integrated circuit through the needle; and then an output wave signal is received by the electrical characteristics testing apparatus from the integrated circuit.  
         [0006]      FIG. 1  is a schematic diagram of a conventional cantilever probe card.  
         [0007]     Referring to  FIG. 1 , a needle  20  electrically connected to a printed circuit board (PCB)  10  is fixed by an epoxy ring  30 . The needle  20  is composed of tungsten and is electrically connected to a signal line (not shown) formed in the PCB  10  by, for example, soldering. The needle  20  extends 5 mm from the inner circumference of the epoxy ring  30  so that a wafer can be supported by elastic force of the needle  20 .  
         [0008]     Since signal lines in the PCB  10  can be multi-layered, impedance matching can be realized. Therefore, when signals are transferred at high rates, noise generated by, for example, reflection and crosstalk can be removed. However, it is difficult to obtain impedance matching between the signal lines of the PCB  10  and an end of the needle  20 , and thus, electric parasitic inductance occurs. A current signal from the integrated circuit being tested is interrupted by the parasitic inductance of the needle  20  and thus, an increase or decrease of the output of the integrated circuit is delayed. In addition, as a measurement frequency increases, the parasitic inductance further degrades transferring characteristics. The conventional probe card illustrated in  FIG. 1  is suitable for a direct current (DC) test with a frequency of less than 100 MHz, but is not suitable for testing an analog device or logic devices with a frequency greater than 500 MHz. That is, the conventional cantilever probe card is not suitable for testing high speed characteristics of an integrated circuit.  
         [0009]     However, the parasitic inductance can be decreased by reducing the length of the needle  20 , thus decreasing transfer loss. However, the needle  20  must be of at least a standard length or longer. As illustrated in  FIG. 1 , the needle  20  can be divided into three portions  20   a ,  20   b , and  20   c . The portion  20   a  of the needle  20  contacts a wafer pad. The portion  20   b  of the needle  20  is surrounded by the epoxy ring  30  to be attached to the PCB  10 . The portion of  20   c  of the needle  20  is connected to the signal line of the PCB  10 . In this case, a length L 1  of the portion  20   a  cannot be reduced because elastic force must be maintained, a length L 2  of the portion  20   b  cannot be reduced because the needle  20  must be completely fixed in the epoxy ring  30 , and a length L 3  of the portion  20   c  cannot be reduced because adjacent needles  20  can be bridged to each other. Rather, the length of the needle  20  must be increased to test chips on a wafer before cutting them. Therefore, RF devices operating at a range of hundreds of MHz to a few GHz and high speed logic devices cannot be tested before packing, thus decreasing productivity.  
         [0010]     Although probe cards not including needles have been developed to test RF devices operating at a range of hundreds of MHz to a few GHz, or high speed logic devices, the manufacturing process is complex, long, and expensive. For example, the manufacturing costs for probe cards not including needles are tens times higher than the manufacturing costs for probe cards including tungsten needles. In addition, the repair of probe cards during mass production requires a long time. Therefore, it is difficult to achieve the development and mass production of a probe card not including needles.  
         [0011]     In addition, a portion of the needle can be surrounded by an insulating material and a metallic structure to thus form a coaxial cable so that the inductance of the needle can be decreased. In this case, however, the manufacturing costs are high because holes in which the needle and the insulating material are filled must be made in the metallic structure.  
       SUMMARY OF THE INVENTION  
       [0012]     The present invention provides a probe card used to precisely measure a signal of an integrated circuit operating at a high frequency.  
         [0013]     The present invention also provides a method of manufacturing the probe card.  
         [0014]     According to an aspect of the present invention, there is provided a probe card including: a printed circuit board comprising a ground electrode; at least one dielectric disposed below the ground electrode; and a plurality of needles, each of which comprises: a first end portion contacting a wafer pad of a semiconductor device, a second end portion electrically connected to the printed circuit board, and a remaining portion excepting the first and second end portions surrounded by the at least one dielectric. A metal plate is disposed below the at least one dielectric; and a connecting pin electrically connects the metal plate to the ground electrode and fixes the at least one dielectric and the metal plate to the printed circuit board.  
         [0015]     In one embodiment, the at least one dielectric comprises an upper dielectric layer and a lower dielectric layer and the needles are disposed between the upper dielectric layer and the lower dielectric layer. The upper dielectric layer and the lower dielectric layer can have the same thicknesses. In one embodiment, the probe card further comprises an adhesive filling spaces between the needles interposed between the upper and lower dielectric layers. Spaces formed between the upper and lower dielectric layers and the needles can be filled with the adhesive, and the adhesive can contain epoxy.  
         [0016]     In one embodiment, the at least one dielectric is a bulky hexahedron and has through holes through which the needles are passed. The through holes can pass through the center of the at least one dielectric. The through holes can be parallel to the printed circuit board.  
         [0017]     In one embodiment, the at least one dielectric is Teflon. In one embodiment, the metal plate is composed of Cu or Al.  
         [0018]     In one embodiment, the ground electrode, the at least one dielectric, and the metal plate have the same areas.  
         [0019]     In one embodiment, the connecting pins are disposed at corners of the metal plate.  
         [0020]     In one embodiment, each of the connecting pins comprises: a bolt passing through the metal plate, the at least one dielectric, and the ground electrode; and a nut into which the bolt is threaded on the printed circuit board.  
         [0021]     In one embodiment, each of the connecting pins comprises: a bolt, which is attached to the metal plate and passes through the at least one dielectric and the ground electrode; and a nut into which the bolt is threaded on the printed circuit board.  
         [0022]     In one embodiment, the semiconductor device is an RF device and the second end portions of the needles through which the ground and the signal are supplied to the RF device are shorter than other needles.  
         [0023]     In one embodiment, the printed circuit board comprises an opening and four ground electrodes extending radially from the opening, and each of the ground electrodes are respectively disposed above the dielectrics and the metal plates.  
         [0024]     According to another aspect of the present invention, there is provided a method of forming a probe card, the method including: passing a plurality of needles through an upper dielectric layer and a lower dielectric layer such that first end portions and second end portions of the needles protrude from the upper and lower dielectric layers, and then fixing the needles with an adhesive; placing a metal plate below the lower dielectric layer; arranging the upper dielectric layer such that the upper dielectric layer faces a ground electrode formed in a printed circuit board; fixing the upper and lower dielectric layers and the metal plate to the printed circuit board using connecting pins such that the metal plate is electrically connected to the ground electrode; and bending the first end portion to contact a wafer pad of a semiconductor device and electrically connecting the second end portion to the printed circuit board.  
         [0025]     According to yet another aspect of the present invention, there is provided a method of forming a probe card, the method including: passing a plurality of needles through a plurality of through holes formed in a bulky hexahedral dielectric such that first end portions and second end portions of the needles protrude from the dielectric; placing a metal plate below the dielectric; arranging the dielectric such that an upper surface of the dielectric opposite the metal plate faces a ground electrode formed in a printed circuit board; fixing the dielectric and the metal plate to the printed circuit board using connecting pins such that the metal plate is electrically connected to the ground electrode; and bending the first end portion to contact a wafer pad of a semiconductor device and electrically connecting the second end portion to the printed circuit board.  
         [0026]     In one embodiment, passing the needles through the through holes comprises: forming the bulky hexahedral dielectric; forming the through holes through the dielectric; and passing the needles through the through holes such that the first end portions and second end portions of the needles protrude from the dielectric. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0027]     The foregoing and other objects, features and advantages of the invention will be apparent from the more particular description of preferred aspects of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention.  
         [0028]      FIG. 1  is a schematic view of a conventional cantilever probe card including a needle, which is electrically connected to a printed circuit board and fixed by an epoxy ring.  
         [0029]      FIG. 2  is a view of a bottom surface of a probe card according to a first embodiment of the present invention.  
         [0030]      FIG. 3A  is a sectional view taken along line a-a′ of  FIG. 2 .  
         [0031]      FIG. 3B  is a sectional view taken along line b-b′ of  FIG. 2 .  
         [0032]      FIG. 3C  is a sectional view taken along line c-c′ of  FIG. 2 .  
         [0033]      FIG. 4  is an exploded view illustrating a method of manufacturing the probe card according to the first embodiment of the present invention.  
         [0034]      FIG. 5A  is a sectional view of the probe card according to a second embodiment of the present invention corresponding to the sectional view taken along line a-a′ of  FIG. 2 .  
         [0035]      FIG. 5B  is a sectional view of a probe card according to the second embodiment of the present invention corresponding to the sectional view taken along line b-b′ of  FIG. 2 .  
         [0036]      FIG. 6A  is a sectional view of a probe card according to a third embodiment of the present invention corresponding to the sectional view taken along line a-a′ of  FIG. 2 .  
         [0037]      FIG. 6B  is a sectional view of the probe card according to the third embodiment of the present invention corresponding to the sectional view taken along line b-b′ of  FIG. 2 .  
         [0038]      FIG. 6C  is a sectional view of the probe card according to the third embodiment of the present invention corresponding to the sectional view taken along line c-c′ of  FIG. 2 .  
         [0039]      FIGS. 7A  to  7 C are perspective views illustrating a method of forming the probe card according to the third embodiment of the present invention, in particular, a method of passing needles through a dielectric.  
         [0040]      FIG. 8A  is a sectional view of the probe card according to a fourth embodiment of the present invention corresponding to the sectional view taken along line a-a′ of  FIG. 2 .  
         [0041]      FIG. 8B  is a sectional view of the probe card according to the fourth embodiment of the present invention corresponding to the sectional view taken along line b-b′ of  FIG. 2 .  
         [0042]      FIG. 9  is a graph of insertion loss with respect to frequency for a probe card according to an embodiment of the present invention and a conventional probe card.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0043]     According to the present invention, an epoxy ring of a conventional cantilever probe card is substituted by a structure similar to a coaxial cable, thus decreasing transfer loss. That is, a needle is surrounded with a dielectric and a metal plate instead of the epoxy ring so that the inductance of all but an elastic portion of the needle can be minimized. However, the coaxial structure of the present invention is different from a conventional coaxial structure in that the metal plate is electrically connected to a ground electrode of a printed circuit board and the middle portion of the needle is surrounded by the dielectric layer interposed between ground conductances. Accordingly, the impedance of the middle portion of the needle is determined by the thickness and dielectricity of the dielectric. That is, a desired impedance can be obtained by choosing a dielectric material with a predetermined dielectricity and adjusting the thickness of the dielectric material. For example, the impedance of the middle portion of the needle can be matched at 50 Ω.  
         [0044]     Probe cards according to embodiments of the present invention and methods of manufacturing the same will now be described.  
       Embodiment 1  
       [0045]      FIG. 2  is a view of a bottom of a probe card  100  according to a first embodiment of the present invention.  
         [0046]      FIG. 3A  is a sectional view taken along line a-a′ of  FIG. 2 ,  FIG. 3B  is a sectional view taken along line b-b′ of  FIG. 2 , and  FIG. 3C  is a sectional view taken along line c-c′ of  FIG. 2 .  
         [0047]     Referring to  FIG. 2 , a printed circuit board (PCB)  50  of the probe card  100  has an opening  51 , and four ground electrodes  40  extend radially outside the opening  51 . Each of the ground electrodes  40  is disposed above a dielectric  60 , needles  70  and  70 ′, and a metal plate  80 , and connecting pins  90  pass through the ground electrode  40 , the dielectric  60 , the needles  70  and  70 ′, and the metal plate  80 . The probe card  100  is used to test an RF device, and a ground and a signal are applied to the RF device through the needle  70 , and the needle  70 ′ acts as a digital line or a power line.  
         [0048]     Referring to  FIGS. 3A through 3C , the PCB  50  of the probe card  100  includes the ground electrode  40 . The dielectric  60  is formed below the ground electrode  40 , and the needles  70  and  70 ′ are surrounded by the dielectric  60 . Each of the needles  70  and  70 ′ has a first end portion  70   a  for contacting a wafer pad (not shown) of a semiconductor device and a second end portion  70   c  electrically connected to the PCB  50 . Portions  70   b , that is, residual portions of the needles  70  and  70 ′ not including the first and second end portions  70   a  and  70   c , are surrounded by the dielectric  60 . The metal plate  80  is disposed below the dielectric  60  surrounding the needles  70  and  70 ′. The connecting pins  90  electrically connect the metal plate  80  to the ground electrode  40  and fix the dielectric  60  and the metal plate  80  to the PCB  50 .  
         [0049]     The dielectric  60  includes dielectric layers  60   a  and  60   b . The dielectric layer  60   a  is disposed above the needles  70  and  70 ′, and the dielectric layer  60   b  is disposed below the needles  70  and  70 ′. The dielectric layers  60   a  and  60   b  may have the same thicknesses. An adhesive  65 , such as an epoxy-containing adhesive, fills a space between the needles  70  and  70 ′ disposed between dielectric layers  60   a  and  60   b , and a space between the dielectric layers  60   a  and  60   b  and the needles  70  and  70 ′. The adhesive  65  may spread such that the needles  70  and  70 ′ are disposed in the center of the dielectric  60 .  
         [0050]     When the dielectric  60  is composed of a material with a low dielectric constant, the dielectric  60  can be formed to a small thickness. The material with a low dielectric constant may be, for example, Teflon. The metal plate  80  may be composed of Cu or Al. As illustrated in  FIGS. 3A  to  3 C, the ground electrode  40 , the dielectric  60 , and the metal plate  80  may have the same areas. However, the dielectric  60  may have a larger area than the ground electrode  40  and the metal plate  80 , respectively, or the metal plate  80  may have a larger area than the ground electrode  40  and the dielectric  60 , respectively. The connecting pins  90  can be disposed at corners of the metal plate  80 . In the present embodiment, the connecting pins  90  are composed of bolts  90   a  and nuts  90   b , and the bolts  90   a  are attached to the metal plate  80 , pass through the dielectric  60  and the ground electrode  40 , and are threaded into the nuts  90   b  on the PCB  50 .  
         [0051]     In this structure, the portions  70   b  of the needles  70  and  70 ′ form a structure analogous to a coaxial cable with the dielectric  60 , the ground electrode  40 , and the metal plate  80 . The metal plate  80  is electrically connected to the ground electrode  40  by the connecting pins  90 , thus being grounded. Accordingly, the impedance of the portions  70   b  is determined by the thickness and dielectric constant of the dielectric  60 .  
         [0052]     In addition, in order to decrease a transfer loss, the lengths of the needles  70  and  70 ′ can be decreased. However, a length L 1  of the first end portion  70   a  contacting the wafer pad (not shown) of the semiconductor device cannot be decreased because the elastic power must be maintained, and a length L 2  of the portion  70   b  cannot be decreased because the portion  70   b  must be fixed to the PCB  50 . Therefore, a length L 3  of the second end portion  70   c  electrically connected to the PCB  50  may be decreased. In this case, as illustrated in  FIG. 2 , the second end portion  70   c  of the needle  70  through which a ground and a signal are applied to a RF device may be shorter than the second end portion  70   c  of the needle  70 ′ so that the formation of a bridge between adjacent needles  70  and  70 ′ can be prevented.  
         [0053]     In this structure, inductance of the portions  70   b  of the needles  70  and  70 ′ can be decreased, and a high speed wave signal generated by a high speed integrated circuit can be transferred to a measuring apparatus without distortion. As a result, an operation test for a high speed integrated circuit can be carried out.  
         [0054]      FIG. 4  is an exploded view illustrating a method of manufacturing the probe card  100  illustrated in  FIG. 2 .  
         [0055]     Referring to  FIG. 4 , the needles  70  and  70 ′ are fixed between the dielectric layers  60   a  and  60   b  using the adhesive  65  such that the first end portions  70   a  and second end portions  70   c  of the needles  70  and  70 ′ protrude from the dielectric layers  60   a  and  60   b . The metal plate  80  is placed below the dielectric layer  60   b , which is disposed below the dielectric layer  60   a . Then, the first dielectric layer  60   a  is arranged to face the ground electrode  40  of the PCB  50 , and then the dielectric layers  60   a  and  60   b  and the metal plate  80  are fixed and electrically connected to the PCB  50  by using the connecting pins  90 . In the present embodiment, the connecting pins  90  are composed of the bolts  90   a  and the nuts  90   b . The bolts  90   a  are attached to the upper surface of the metal plate  80  and threaded into the nut  90   b  on the PCB  50 . Then, the first end portions  70   a  of the needles  70  and  70 ′ are bent to contact the wafer pad of the semiconductor device and the second end portion  70   c  of the needles  70  and  70 ′ are electrically connected to the PCB  50 . In addition, holes O through which the bolts  90   a  pass are made in the dielectric layers  60   a  and  60   b  and the PCB  50  including the ground electrode  40  so that connections between the bolts  90   a  and the nuts  90   b  can be made.  
         [0056]     In a conventional method of forming a portion of a needle in a coaxial cable, a hole is formed in a metal structure and then a needle surrounded by an insulating material is passed through the hole. However, in the present embodiment, the dielectric layers  60   a  and  60   b  and the metal plate  80  are fixed to the PCB  50  using the connecting pins  90 . That is, the method according to the present embodiment is readily accomplished, and if repairs are required, the needle can be easily replaced because the connecting pins  90  can be easily removed.  
       Second Embodiment  
       [0057]      FIG. 5A  is a sectional view of a probe card  101  according to a second embodiment of the present invention corresponding to the sectional view taken along line a-a′ of  FIG. 2 , and  FIG. 5B  is a sectional view of the probe card  101  corresponding to the sectional view taken along line b-b′ of  FIG. 2 .  
         [0058]     The present embodiment is the same as the first embodiment except that, referring to  FIGS. 5A and 5B , connecting pins  91  are composed of bolts  91   a  and nuts  91   b , and the bolts  91  a pass through a metal plate  80 , a dielectric  60 , and a ground electrode  40  and are threaded into the nuts  91   b  on a PCB  50 . In this case, the metal plate  80  may have a hole for the bolts  91   a.    
       Third embodiment  
       [0059]      FIG. 6A  is a sectional view of a probe card  102  according to a third embodiment of the present invention corresponding to the sectional view taken along line a-a′ of  FIG. 2 ,  FIG. 6B  is a sectional view of the probe card  102  corresponding to the sectional view taken along line b-b′ of  FIG. 2 , and  FIG. 6C  is a sectional view of the probe card  102  corresponding to the sectional view taken along line c-c′ of  FIG. 2 .  
         [0060]     The present embodiment is the same as the first embodiment, except for the following points.  
         [0061]     Referring to  FIGS. 6A and 6C , a plurality of needles  70  and  70 ′ are surrounded by a dielectric  61 . The dielectric  61  forms a bulky hexahedron, and has through holes  62  through which needles  70  and  70 ′ are passed. The through holes  62  may be formed in the center of the dielectric  61 , and parallel to a PCB  50 . The dielectric  61  is composed of Teflon, which has a low dielectric constant, so that the dielectric  61  can be formed to a small thickness.  
         [0062]     In the present embodiment, the needles  70  and  70 ′ are passed through the through holes  62  of the bulky hexahedral dielectric  61  such that first and second end portions  70   a  and  70   c  of the needles  70  and  70 ′ protrude from the dielectric  61 . The dielectric  61  and a metal plate  80  may be fixed to the PCB  50  by bolts  90   a  and nuts  90   b  in the same manner as in the first embodiment.  
         [0063]     A method of passing the needles  70  and  70 ′ through the dielectric  61  will now be described.  
         [0064]      FIGS. 7A  to  7 C are perspective view illustrating a method of passing the needles  70  and  70 ′ through the dielectric  61 .  
         [0065]     First, referring to  FIG. 7A , the bulky hexahedral dielectric  61  is formed.  
         [0066]     Then, referring to  FIG. 7B , the through holes  62  are formed through the dielectric  61 .  
         [0067]     Then, referring to  FIG. 7C , the needles  70  and  70 ′ are passed through the through holes  62 .  
         [0068]     Alternately, the needles  70  and  70 ′ can be arranged in a mold used to form the hexahedral bulky dielectric  61 , and then a dielectric material is injected into the mold, hardened, and separated from the mold.  
       Fourth Embodiment  
       [0069]      FIG. 8A  is a sectional view of a probe card  103  according to a fourth embodiment of the present invention corresponding to the sectional view taken along line a-a′ of  FIG. 2 , and  FIG. 8B  is a sectional view of the probe card  103  corresponding to the sectional view taken along line b-b′ of  FIG. 2 .  
         [0070]     The present embodiment is the same as the third embodiment except that, referring to  FIGS. 8A and 8B , connecting pins  91  are composed of bolts  91   a  and nuts  91   b , and the bolts  91   a  pass through a metal plate  80 , a dielectric  60 , and a ground electrode  40  and are threaded into the nuts  91   b  on a PCB  50 .  
         [0000]     Simulation  
         [0071]      FIG. 9  is a graph of insertion loss with respect to frequency for a probe card according to an embodiment of the present invention and a conventional probe card. The conventional probe card exhibits a loss of −3 dB at 500 MHz, and the probe card according to an embodiment of the present invention exhibits a loss of −2 dB at 3 GHz.  
         [0072]     The probe card according to the present invention can be used at high frequencies due to a low insertion loss.  
         [0073]     According to the present invention, a delay time due to signal conversion can be substantially decreased by minimizing the inductance of a needle. As a result, frequency signals in the few GHz to hundreds of GHz band can be measured. In addition, a conventional manufacturing process can be used so that the manufacturing process is simple, short, and inexpensive.  
         [0074]     While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.