Abstract:
The present invention relates to a socket for testing an integrated circuit utilizing an improved contact pin structure. In the test socket of the present invention, the length of the electrical path between the leads of tested IC and terminals of PCB is minimized and the contact pin may maintain wiping action in a wide area of contact portions. Further, as the contact pin may accommodate the pressure applied by the IC leads with great elasticity and provides sufficient floating suspension when the pressure is removed, the invention may efficiently prevent damages to the leads of IC being tested and extend the life of the contact pin.

Description:
TECHNICAL FIELD 
     The invention relates generally to a socket for testing an integrated circuit package. More particularly, the invention relates to a socket utilizing an improved contact pin structure which is able to reduce the electrical connection length between a to-be tested subject and a PCB to improve the high-frequency characteristic and has capability to maintain good electrical contact and extend the life of the socket. 
     BACKGROUND OF THE INVENTION 
     Generally, an integrated circuit (IC) package is subjected to a test of its electrical characteristic using an open-top type socket for a handler or a manual socket of a Calm type. For this test, the socket is mounted on a printed circuit board (PCB) connected to measurement equipments. The IC circuit package is mounted on the socket. At this time, an electrical connection element, such as a contact pin is required for connecting the leads of the IC package to the terminals of the PCB. 
     In order to design a contact pin performing this function, the following four requirements should be considered. First, it should maintain good contact be with the tested subject. For this, the contact portion of the contact pin should maintain contact with the IC package while performing a wiping action. Second, it is required that the length of the electrical connection between contact points should be short as possible. In particular, when the contact pin is used to perform a high-frequency IC test, a long length of electrical connection may act as an impedance since the inductance of the contact pin becomes larger. Third, the contact pin should not cause any bending of an IC lead during the test. Bending of an IC lead during the test substantially degrades the yield of the IC. Fourth, the contact pin and the elastic members supporting them should have a long life. If any of the contact pins fails, the entire test socket should be replaced. 
     Various structures of contact pins in consideration of these requirements have been developed and used. FIGS.  1 ˜ 3  are cross-sectional views of conventional contact pin structures mounted on a conventional socket according to their respective use. 
     The contact pin shown in FIG. 1 is so called Yamaichi socket pin, which is widely used in integrated circuit tester sockets. The Yamaichi socket pin, however, has the following disadvantages in view of the above four requirements. First, when a lead  12  of an IC  11  is pressed against the contact pin  10 , some degree of wiping action is caused at a potion contacting a PCB terminal  13 . As can be seen clearly from FIG. 1, the rotational radius of the contact portion of the terminal is short since a rotational axis of the contact pin  10  is very near to the PCB. Thus, it is difficult to perform wiping action in a wide area. Second, as the contact points of the integrated circuit lead  12  and the PCB terminal  13  are not aligned in a straight line and they are connected to each other via detouring path, there is a problem that the electrical length becomes longer. Third, when the pressure applied by the lead  12  of the integrated circuit  11 , the floating suspension of the contact pin  10  is relatively small. Thus, when pressure is applied for test, the integrated circuit lead  12  may be bent since a great force is directly applied to the integrated circuit leas  12 . 
     U.S. Pat. No. 4,445,735 was contrived to solve the problem of the Yamaichi socket pin. (see FIG.  2 ). However, this invention also has some limitations. First, it has a long electrical length. When pressure is applied, the integrated circuit lead can be bent since the floating suspension provided by the contact pin  20  when pressure is removed is limited. Thus, this invention achieves little improvement over the Yamaichi socket pin. 
     U.S. Pat. No. 5,069,629 illustrates improved electrical connection device over the Yamaichi socket pin or U.S. Pat. No. 4,445,735, the cross-sectional view of which is shown in FIG.  3 . As can been seen from FIG. 3, the contact pin  30  of U.S. Pat. No. 5,069,629 has a structure in which contact points are aligned in a straight line to reduce the electrical length between the contact points. However, as the structure of the contact pin has a generally S-shape, it has a significant limitation in reducing the horizontal length of the contact portion. Thus, this structure is not able to minimize the electrical length. Also, as the displacement of the contact point on the side of the lead  32  of an integrated circuit  31  and that of the contact point on the PCB terminal  33  side are symmetric, if the contact point on the integrated circuit lead  31  has a downward displacement, displacement of the contact point on the side of the PCB terminal  33  should be upward. Also, axial axes of respective contact points are not same and have short rotation radius. Thus, although the contact pin structure provides some degree of wiping action, its wiping distance is very short. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide a socket for testing an integrated circuit using a contact pin structure which has a very short electrical length between the contact points, and does not cause bending of an integrated circuit lead during test, and which is able to maintain good contact state with the test subject and extend the life of the device. 
     In order to accomplish the above objects, the present invention proposes a socket for testing an integrated circuit including a plurality of contact pins for electrically connecting leads of an integrated circuit to terminals of a PCB spaced from the leads of the integrated circuit, being characterized by comprising a contact pin housing installed on said PCB for mounting said integrated circuit, said contact pin housing having a flat top surface and a flat bottom surface; a plurality of slots formed on both sides of the contact pin housing to pass through the contact pin housing from the top surface to the bottom surface and having a size adequate to accommodate the contact pins; a first channel and formed on both sides of the contact pin housing and a second channel formed in parallel to said first channel and on the outer side of the respective first channel, the channels being formed from the bottom surface of the contact pin housing and extending to cross all of the slots; a first elastic member and a second elastic member respectively installed within the first channel and the second channel, wherein the contact pins are inserted into the respective slots, and each of the contact pin engages with the first and second elastic members, and each of the contact pins includes a first contact portion protruding over the top surface of the contact pin housing for making contact with a lead of the integrated circuit and a second contact portion for making contact with one of the terminal of the PCB. 
     Also, the contact pin of the present invention is made of a thin and flat metal piece, said contact pin is characterized by including a first elastic member receiving portion having a circular circumferential face which is open toward and engage with the first elastic member when the contact pin is inserted into the slot; a second elastic member receiving portion having a circular circumferential face which is open toward and engage with the second elastic member when the contact pin is inserted into said slot, and said contact pin is further characterized in that the first elastic member receiving portion and the second elastic member receiving portion are formed on a upper side of the contact pin facing said first and second elastic members when the contact pin is inserted into the slot and the second elastic member is formed at a location opposing said first elastic member with respect to the center of the contact pin; and the first contact portion extends from the outer side of the first elastic member receiving portion with respect to the center of the contact pin and extends generally in a upward direction with respect to the upper side of the contact pin; and the second contact portion is formed on a bottom side of the upper side of the contact pin and at a location generally below the center of the contact pin. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The aforementioned aspects and other features of the present invention will be explained in the following description, taken in conjunction with the accompanying drawings, wherein: 
     FIG. 1 illustrates a cross-sectional view of a major part of a conventional socket; 
     FIG. 2 illustrates a cross-sectional view of another conventional socket; 
     FIG. 3 illustrates a cross-sectional view of a still another conventional socket; 
     FIG. 4 is a perspective view of one type of a contact pin to be mounted on a socket according to the present invention; 
     FIG. 5 is a perspective view of another type of a contact pin to be mounted on a socket according to the present invention; 
     FIG. 6 shows a plane view of a contact pin housing used in a socket according to the present invention; 
     FIG. 7 is a cross-sectional view taken along “A-A” of the contact pin housing in FIG. 6; 
     FIG. 8 is a perspective view illustrating a contact pin mounted on a contact pin housing of a socket according to the present invention; 
     FIG. 9 is a cross-sectional view illustrating a state that one type of an integrated circuit is mounted on a socket according to the present invention and the actuator of the socket is closed; and 
     FIG. 10 is a cross-sectional view illustrating a state that another type of an integrated circuit is mounted on a socket according to the present invention and the actuator of the socket is closed. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention will be described in detail by way of a preferred embodiment with reference to accompanying drawings, in which like reference numerals are used to identify the same or similar parts. 
     FIG. 4 is an enlarged perspective view of one type of a contact pin to be mounted on a socket according to the present invention. FIG. 5 is an enlarged perspective view of another type of a contact pin to be mounted on a socket according to the present invention. FIG. 6 shows a plane view of a contact pin housing used in a socket according to the present invention. FIG. 7 is a cross-sectional view taken along “A-A” of the contact pin housing in FIG.  6 . FIG. 8 is a perspective view illustrating a contact pin mounted on a contact pin housing of a socket according to the present invention. FIG. 9 is a cross-sectional view illustrating a state that one type of an integrated circuit is mounted on a socket according to the present invention and the actuator of the socket is closed. FIG. 10 is a cross-sectional view illustrating a state that another type of an integrated circuit is mounted on a socket according to the present invention and the actuator of the socket is closed. 
     As shown particularly in FIGS. 4 and 5, a contact pin  40 ,  50  includes a first elastic member receiving portion  41 ,  51  having a circular circumferential face, which is formed on one side (right side in FIGS. 4 and 5) of a thin and flat metal piece  45 ,  55 . The first elastic member receiving portion  41 ,  51  is open toward the upward direction to engage with a first elastic member  84  as illustrated particularly in FIGS. 8 to  10 . The contact pin  40 ,  50  further includes a first contact portion  42 ,  52  which extends generally in an upward direction from an outer side of the contact pin, and particularly from the outer side of the first elastic member receiving portion  41 ,  51 . The first contact portion  42 ,  52  has a generally tapered shape and extends higher than the tip of the thin and flat metal piece  45 ,  55 . The contact pin  50  in FIG. 5 differs from the contact pin  40  in FIG. 4 in that its first contact portion  52  is wider than that of the contact pin in FIG.  4 . The width of the first contact portion may be adequately adjusted according the purpose of use within the principle of the present invention. As shown in FIGS. 9 and 10, the first contact portion makes contact with a contact lead  61 ,  71  of an integrated circuit  60 ,  70  when the integrated circuit is mounted on the socket. 
     The contact pin  40 ,  50  also includes a second elastic member receiving portion  44 ,  54  which is formed on the upper side on the contact pin and on a side (left side in FIGS. 4 and 5) opposing the first elastic member receiving portion  41 ,  51 . A metal piece  45 ,  55  located between the first and the second elastic member receiving portions and at a location generally over the center of the contact pin. On the bottom side of the contact pin, a second contact portion  43 ,  53  is formed at a location generally below the thin and flat metal piece  45 ,  55 . As shown in FIGS. 810, the second contact portion  43 ,  53  contacts a terminal of a PCB terminal  81  when the contact pin is installed in the socket. 
     Further, the upper tip of the first contact portion  42 ,  52  of the contact pin  40 ,  50  extends higher than the upper side of the contact pin where the first and the second elastic member receiving portions are formed. The first elastic member receiving portion  41 ,  51  has a shape gradually widening toward the upper direction. The second contact portion  43 ,  53  have a curved shape protruding downward to perform a wiping action with the PCB terminal  81  in a wide area. 
     A first and a second elastic members  84 ,  85  are respectively inserted in a first channel  88  and a second channels  89  of a contact pin housing  82  shown in FIG.  7 . When mounting a contact pin in the housing  82 , as shown in FIGS. 8 to  10 , the first elastic member  84  is inserted into the first elastic member receiving portion  41 ,  51  and the second elastic member  85  is inserted into the second elastic member receiving portion  44 ,  54 , respectively. In this state, the first contact portion  42 ,  52  of the contact pins  40 ,  50  protrudes out of the top  86  of the contact pin housing  82  and the second contact portion  43 ,  53  is biased toward the bottom  87  of the contact pin housing  82  due to the elastic force applied by the elastic members. Thus, the first and the second contact portions can easily contact the lead  61 ,  71  of the integrated circuits  60 ,  70  and the PCB terminal  81 , respectively. Then, the first and second elastic member receiving portions are formed to have a circular shape greater than a half semicircle so that they may not be easily disengaged from the first and second elastic members  84 ,  85  when they are once engaged with each other. 
     In designing a contact pin of the above structure, the following requirements should be considered. 
     First, when an integrated circuit is mounted so that the leads  61 ,  71  of the integrated circuit contact with the first contact portion  42 ,  52  of the contact pins  40 ,  50  and pressure is applied to the leads  61 ,  71  by means of an actuator of a socket, the contact pins  40 ,  50  are rotated centering around the centers of the first and second elastic member receiving portions  42 ,  52 ,  43 ,  53 , which allows the first contact portion  42 ,  52  and the second contact portion  43 ,  53  respectively make contact with the leads  61 , 71  of the integrated circuit and the PCB terminal  81  making a greater wiping action. As such, the present invention uses two rotational axes of the contact pins  40 ,  50  to maximize distance between the rotational axes and the contact portions and to secure sufficient wiping action of the contact portions. 
     Second, the present invention adopts a structure in which the electrical path between the first contact portion  42 ,  52  and the second contact portion  43 ,  53  is formed in a generally straight line and a horizontal and vertical distance between the contact portions is reduced as much as possible. Thus, the electrical length between the contact portions is minimized. Thus, the contact pin structure according to the present invention is suitable for a socket for high-frequency test of an integrated circuit. 
     Third, the free floating suspension of the contact pins  40 ,  50  when the pressure applied to the contact pins by the actuator is removed need to be sufficient in order to minimize the bending of the semiconductor leads  61 ,  71  during test. The present invention adopts a structure in which elasticity of the second elastic member  85  can be directly transferred to the contact portion by rotating the contact pin  40 ,  50  to secure a great free floating suspension of the socket. 
     Fourth, the present invention adopts a structure in which elasticity is applied to the contact pin  40 ,  50  while the contact pin rotates around the respective axes of the first elastic member receiving portion  41 ,  51  and the second elastic member receiving portion  44 ,  54 . Thus the torsion that may deform the contact pin  40 ,  50  during repetitive tests is minimized. This structure not only extends the life of the contact pins  40 ,  50  but also extends the life of the socket. 
     FIG.  6  and FIG. 7 are a plane view and a cross-sectional view of the major parts of the contact pin housing  82  into which a plurality of the contact pins  40 ,  50  are accommodated. As can be seen from the drawing, the housing  82  has at least one slot into which the contact pin  40 ,  50  is inserted. Each slot penetrates from the top surface  86  to the bottom surface  87  of the housing  82 . An aperture (hereinafter referred to ‘channel’) into which the first elastic member  84  and the second elastic member  85  are inserted is formed from the bottom surface  87  surface of the housing in a vertical direction. The channel extends through all of the slots  83 , and the cross-section of the first second channels  88 ,  89  taken along the vertical direction has a generally  shape, as shown in FIG.  7 . Also, the depth of the of the first and second channels  88 ,  89  is made so that the first contact portion  42 ,  52  and the second contact portion  43 ,  53  of the contact pins  40 ,  50  adequately protrudes from of the top surface  86  and the bottom surface  87  of the housing, when the first elastic member  84  and the second elastic member  85  are respectively inserted into the first and second channels  88 ,  89  and the contact pins  40 ,  50  are installed in the housing as show in FIG.  8 . Preferably, the second channel  89  is formed deeper than the first channel  88  so that they correspond to shapes of the first elastic member receiving portion  41 ,  51  and the second elastic member receiving portion  44 ,  54  of the contact pin  40 ,  50 . 
     FIG. 8 is a partial perspective view and a partial cross-sectional view of a socket where a contact pin  40 , a first elastic member  84  and a second elastic member  85  are installed in a contact pin housing  82 , and the contact pin housing is mounted on a PCB. As can be seen from the drawing, in the contact pin housing  82 , the first elastic member  84  is first installed into the first channel  88  and the second elastic member  85  is installed into the second channel  89 . Then, the contact pin  40  is pushed from the bottom  87  to the top  86  of the slot  83 , so that the first and second elastic member receiving portions  41 ,  42  of the contact pin  40  respectively engage with the first and second elastic members  84 ,  85 . 
     Referring now to FIG.  9  and FIG. 10, a detailed operation of the contact pin  40  when the integrated circuit is mounted on the socket according to the present invention and the actuator of the socket is closed will be explained below. 
     FIG.  9  and FIG. 10 show a cover  90 ,  91  of the socket attached to an actuator (not shown). Inside the cover  90 ,  91 , a cushion  90 ′,  91 ′ is attached to the cover. When the cover is closed over the socket, the cushions  91 ′,  92  directly press the lead  61  of the integrated circuit  60  as shown in FIG. 9 or indirectly press the integrated circuit  70  as shown in FIG.  10 . If the integrated circuit is mounted to the contact pin housing  82  and the actuator is closed to press the leads  61 ,  71  of the integrated circuits  60 ,  70  by means of the cushions  90 ,  91  of the actuator, moments in the vertical direction and in the horizontal direction are applied to the first contact  42  of the contact pin  40 . Their combined moment serves as a rotational force rotating the contact pin around the centers of the first and second elastic members  84 ,  85 . As the first contact portion  42  rotates, it makes a good contact with the bottom of a lead  61 ,  71  of the integrated circuits  60 ,  70 . At the same time, the first contact portion performs a good wiping action with the bottom of the lead  61 ,  71 . Also, the second contact portion  43  of the contact pin  40  performs a wiping action with respect to the PCB terminal  81  while rotating. As the contact surface of the second contact portion  43  is curved, wiping action at a wide area can be obtained during rotation. 
     If pressure is applied to the first contact portion  42  of the contact pin  40 , the second elastic member receiving portion  44  of the contact pin  40  also applies a pressure to and deforms the second elastic member  85  during the rotation of the contact pin. Thus, the first contact portion may accommodate the pressure applied by the IC leads with elasticity. Thus, deformation or bending of the IC leads can be prevented during test. The present invention is further characterized in that the force required to restore the position of the contact pin  40  after removing the pressure of the actuator is largely obtained from the elasticity of the second elastic member  85 . In other words, the first elastic member  84  can be made of a material having a relatively small elasticity. The first elastic member  84  with relatively small elasticity may be used as the rotation axis of the contact pin  40  and a support member as well. Meanwhile, the second elastic member  85  may be made of a material having a relatively great elasticity. The second elastic member  85  is not only used as the rotation axis of the contact pin  40  and a support member but also as an element for providing the elastic force required to restore the position of the contact pin  40  after its rotation movement by means of pressure of the actuator. Therefore, the second elastic member  85  is made of a material with the same length as the first elastic member  84  and having a greater elasticity than the first elastic member  84 . For example, the second elastic member  85  may be made of a material such as rubber having an excellent elasticity. 
     As described above, the present invention has outstanding effects that it can improve a contact quality and reduce inductance of a contact pin. Also, the present invention can reduce the bending of an IC lead that may be caused during testing the integrated circuit. At the same time, present invention effectively extends the life of the contact pin and the entire socket. 
     The present invention has been described with reference to a particular embodiment in connection with a particular application. Those having ordinary skill in the art and access to the teachings of the present invention will recognize additional modifications and applications within the scope thereof. It is therefore intended by the appended claims to cover any and all such applications, modifications, and embodiments within the scope of the present invention.