Patent Publication Number: US-2023143660-A1

Title: Test socket for semiconductor integrated circuits

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a U.S. National Phase Entry claiming priority to International Patent Application No. PCT/US2021/025913 filed on Apr. 6, 2021, titled Test Socket for Semiconductor Integrated Circuits, which claims priority to U.S. Provisional Patent Application No. 63/006,529, filed on Apr. 7, 2020, titled Test Socket for Semiconductor Integrated Circuits, the entire contents of which are hereby incorporated herein by reference. 
    
    
     FIELD OF INVENTION 
     The field of the disclosure relates generally to a test socket for semiconductor integrated circuits and, more specifically, a test socket with rotational contacts that translate, or “scrub,” on the contact pads of the integrated circuit under test. 
     BACKGROUND 
     Semiconductor integrated circuits (ICs) are produced in various packages, or chip configurations, including, for example, a quad flat no-leads (QFN) package that is common in many IC applications and is produced in large quantities. Production of ICs of any quantity generally includes testing of the ICs in a manner that simulates an end-user&#39;s application of those ICs. One manner of testing ICs is to connect each IC to a printed circuit board (PCB) that exercises the contacts and various functionalities of the IC. That PCB is sometimes referred to as a load board, and can be re-used to test many ICs. A fundamental component of the load board that enables such testing is a test socket for the IC that can be re-used many times to test large quantities of the IC. The test socket connects, both electrically and mechanically, the IC to the load board. The degree to which the test socket can be re-used is quantified by how many “cycles” it can withstand without degrading performance, e.g., signal performance. Each time an IC is inserted, or set, into the test socket is referred to as one cycle. Generally, over the course of many cycles, electrical and mechanical properties of the contacts and structures of the test socket begin to degrade as a result of, for example, oxidation, abrasion, compression, tension, or other forms of wear. Such degradation eventually impacts integrity of the testing itself, at which point the test socket reaches the end of its useful life. Accordingly, test sockets that maintain good electrical and mechanical performance for long life cycles are desired. 
     BRIEF DESCRIPTION 
     In one aspect, a test socket for a flat no-leads semiconductor IC includes a socket body, a rotational contact, and an elastomer retainer. The socket body includes a top surface configured to face the flat no-leads semiconductor IC, and a bottom surface, opposite the top surface, configured to face a load board. The socket body defines a slot extending from the top surface to an aperture in the bottom surface. The rotational contact is positioned in the slot. The rotational contact is configured to translate between a free state and a pre-load state, and to rotate about a rounded section of the elastomer retainer between the pre-load state and a loaded state. The elastomer retainer captures the rotational contact in the socket body. The elastomer retainer is configured to compress under translatory force from the rotational contact when translating from the free state to the pre-load state upon engagement with the load board, and compress under rotational force from the rotational contact when rotating from the pre-load state to the loaded state upon engagement with the flat no-leads semiconductor IC. 
     In another aspect, a test system includes a load board and a test socket. The test socket includes a top surface configured to face the semiconductor IC, and a bottom surface, mounted to the load board. The socket body defines a slot extending from the top surface to an aperture in the bottom surface. The rotational contact is positioned in the slot in a pre-load state. The rotational contact is configured to rotate about a round section of the elastomer retainer between the pre-load state and a loaded state. The elastomer retainer captures the rotational contact in the socket body. The elastomer retainer compresses between a socket frame and the rotational contact, and is configured to further compress under rotational force from the rotational contact when rotating from the pre-load state to the loaded state upon engagement with the semiconductor IC. 
     In yet another aspect, a method of assembling a test system for a semiconductor IC is provided. The method includes positioning a plurality of rotational contacts in corresponding slots of a socket body for a test socket. The method includes positioning an elastomer retainer over the rotational contacts. The method includes mounting a socket frame over the plurality of rotational contacts and the elastomer retainer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a cross-section diagram of an example IC test system; 
         FIG.  2    is a perspective diagram of an example test socket for a QFN IC; 
         FIG.  3    is a cross-section diagram of one embodiment of a rotational contact in the test socket shown in  FIG.  1    in a free state; 
         FIG.  4    is a cross-section diagram of the rotational contact shown in  FIG.  3    in a pre-load state; 
         FIG.  5    is a cross-section diagram of the rotational contact shown in  FIGS.  3  and  4    in a loaded state; 
         FIG.  6    is a perspective diagram of the rotational contact shown in  FIGS.  3 - 6   ; 
         FIG.  7    is a perspective diagram of the rotational contact shown in  FIGS.  3 - 5    in the free state; and 
         FIG.  8    is a flow diagram of a method of assembling a test system for a semiconductor IC. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the test socket described herein provide a rotational contact that, when engaged with a load board and an IC under test, produces scrub on a contact pad of the IC. The described test sockets are configured to receive a flat no-leads IC package, such as a QFN IC, where scrub on the contact pad of the IC is desirable to reduce contact electrical resistance of the electrical connection between the IC and the rotational contact of the test socket. Conversely, the test sockets described herein generally minimize translation, or scrub, by the rotational contact on the PCB contact of the load board. 
       FIG.  1    is a cross-section diagram of an example IC test system  100  for testing a semiconductor IC  102 . IC  102  is one or more electronic circuits packaged into a single semiconductor chip generally including a plurality of contact pads  104  for conducting signals to and from the circuits within the package. IC test system  100  includes a load board  106  onto which a test socket  108  is mounted. Load board  106  includes PCB contacts  110  that will connect IC  102  to a load circuit, or test circuit (not shown), integrated with load board  106 . Test socket  108  is a re-usable interface for connecting many units of IC  102  to load board  106 .  FIG.  2    is a perspective diagram of test socket  108  for a QFN IC, such as IC  102 . Test socket  108  includes a socket body  112  that defines a receptacle  114  that receives IC  102 . In certain embodiments of test socket  108 , socket body  112  includes guide walls  116  that may be straight or tapered for guiding IC  102  into receptacle  114  to ensure proper alignment of contact pads  104  with PCB contacts  110 . More specifically, guide walls  116  align contact pads  104  with corresponding contacts (not shown) of test socket  108 . The contacts of test socket  108  extend through socket body  112  to electrically connect each contact pad  104  of IC  102  with a corresponding PCB contact  110  on load board  106 . 
       FIG.  3    is a cross-section diagram of one embodiment of a rotational contact  300  in test socket  108  (shown in  FIG.  1   ) in a free state, i.e., before test socket  108  is mounted to load board  106 , and before IC  102  is set.  FIG.  4    is a cross-section diagram of rotational contact  300  in a pre-load state, i.e., test socket  108  is mounted to load board  106 , but IC  102  is not yet set.  FIG.  5    is a cross-section diagram of rotational contact  300  in a loaded state, i.e., test socket  108  is mounted to load board  106  and IC  102  is set into receptacle  114 .  FIG.  6    is a perspective diagram of rotational contact  300  separate from test socket  108 . Rotational contact  300  is composed of an electrically conductive material, such as, for example, copper, copper alloy, aluminum, aluminum alloy, steel, or other conductive metal, or some combination thereof. 
     Rotational contact  300  is positioned in a slot  302  in socket body  112 . Rotational contact  300  extends from receptacle  114  to an aperture  304  in socket body  112  where it protrudes and engages PCB contact  110 . Rotational contact  300  includes a surface  306  and an arm  308  that rest respectively on a surface  310  and a support edge  312  of socket body  112  when rotational contact  300  is in the free state. Rotational contact  300  is captured in slot  302  by an elastomer retainer  314  that holds, or biases, rotational contact  300  against surface  310  and support edge  312 . Elastomer retainer  314  provides force to maintain good connections between rotational contact  300  and contact pads  104  of IC  102 , and between rotational contact  300  and PCB contact  110  of load board  106 . 
     Rotational contact  300  terminates at a first end with a tip  316  that engages and translates, or scrubs, on contact pad  104  of IC  102 , and includes a rounded edge  318  connecting tip  316  to a lower surface of arm  308 . Rotational contact  300  terminates at a second end, opposite tip  316 , with a round nail  320  and a flat  322 . 
     Tip  316  of rotational contact  300  should be pointed, or “sharp,” to enable effective scrubbing on contact pad  104  of IC  102 . For example, in one embodiment, tip  316  is rounded with a radius of about 0.05 millimeters (mm). More generally, tip  316  should be rounded with a radius of no more than 0.10 mm. 
     Rounded edge  318  connecting tip  316  to the lower surface of arm  308  of rotational contact  300  is rounded with a sufficient radius to enable smooth motion during assembly of test socket  108  in the free state, and to enable smooth rotational motion within slot  302 . For example, in one embodiment, rounded edge  318  has a radius of about 0.15 mm. 
     Arm  308  of rotational contact is substantially straight and, in certain embodiments, is narrower at tip  316  than at the opposite end of rotational contact  300 . For example, arm  308  may taper, having a narrow width, W, near tip  316 , to a wider width, W, near the point of contact with PCB contact  110 . The taper of arm  308  enables greater mechanical strength of rotational contact  300  due to the increased width, W. The taper of arm  308  also enables efficient current conduction by avoiding discontinuities in the surfaces of rotational contact  300 . The width, W, of arm  308  also partially defines (with the shape of surface  306 ) where rotational contact  300  rests on socket body  112  at surface  310  and support edge  312 . 
     Surface  306  of rotational contact  300  rests on surface  310  of socket body  112  when test socket  108  is in the free state, and rises away from surface  310  when in the pre-load or loaded state. Round nail  320  engages elastomer retainer  314  when rotational contact moves into the pre-load state. Round nail  320  is rounded to provide smooth deformation of elastomer retainer  314  and reduces wear on elastomer retainer  314  when deforming. In one embodiment, for example, round nail  320  has a radius of about 0.18 mm. More generally, round nail  320  should have a radius of at least 0.10 mm to enable smooth deformation and to minimize wear on elastomer retainer  314 . 
     When test socket  108  is mounted on load board  106  (i.e., the pre-load state shown in  FIG.  4   ), PCB contact  110  engages rotational contact  300 , and load board  106  engages socket body  112 . Upon engaging rotational contact  300 , PCB contact  110  forces rotational contact  300  upward to compress elastomer retainer  314  against a socket frame  324  of test socket  108 . More specifically, rotational contact  300  translates toward socket frame  324 , compressing and deforming elastomer retainer  314  against a first head  326  and a second head  328  of socket frame  324 . Flat  322  of rotational contact  300  enables smooth translation of rotational contact  300  along a wall of socket body  112  that partially defines slot  302 . Elastomer retainer  314 , upon engagement with load board  106  and compression of elastomer retainer  314 , applies a pre-load force to rotational contact  300 . The pre-load force applied to rotational contact  300  ensures good electrical contact between rotational contact  300  and PCB contact  110 , and must be at least partially overcome by insertion of IC  102  into receptacle  114 . The amount of pre-load force provided by elastomer retainer  314  is customizable for a given application by selecting appropriate properties of elastomer retainer  314 . 
     When IC  102  is inserted, or set, into receptacle  114  of test socket  108 , contact pad  104  engages tip  316  of rotational contact  300 , forcing tip  316  downward into slot  302  in socket body  112 . Downward motion of tip  316  into slot  302  results in rotational motion of rotational contact  300  about elastomer retainer  314 . Support edge  312  of socket body  112  also functions as a fulcrum, or pivot point, transferring downward force of IC  102  into a compressing force, or a contact force, applied by round nail  320  of rotational contact  300  onto elastomer retainer  314 , which further deforms against first head  326  and second head  328  of socket frame  324 . Likewise, PCB contact  110  also operates as a pivot point to transfer downward force of IC  102  to a rotational force to compress elastomer retainer  314 . Because motion of rotational contact  300  is rotational, round nail  320  rotates away from the wall of socket body  112  and, likewise, tip  316  of rotational contact  300  translates, or scrubs, along contact pad  104 . The scrub produced by rotational motion of rotational contact  300  and, more specifically, tip  316  reduces electrical resistance of the connection between contact pad  104  and rotational contact  300 , and ultimately reducing the contact electrical resistance of the electrical connection between contact pad  104  of IC  102  and PCB contact  110  of load board  106 . Rotation about elastomer retainer  314  and across PCB contact  110  enables reduction of scrub on PCB pad  110  of load board  106 . 
     When IC  102  is removed from receptacle  114  of test socket  108 , elastomer retainer  314 , previously deformed under rotational force, returns to the pre-load state and reverses the rotational force on rotational contact  300 , and returns rotational contact  300  to the pre-load state with a return force. 
       FIG.  7    is a perspective diagram of rotational contact  300  (shown in  FIGS.  3 - 6   ) positioned in test socket  108  in the free state.  FIG.  7    illustrates contact pad  104  separate from IC  102 , and illustrates PCB contact  110  separate from load board  106 . Rotational contact  300  is positioned in slot  302  defined in socket body  112 .  FIG.  7    illustrates only the portion of socket body  112  proximate the shown rotational contact  300 . Embodiments of test socket  108  may include any number of rotational contacts  300  packaged in respective slots  302  along one or more dimensions. For example, one embodiment of test socket  108 , shown in  FIG.  2   , is configured for a QFN IC having a plurality of rotational contacts  300  arranged on all four sides of socket body  112 . In such an embodiment, for example, slots  302  are independently defined in socket body  112  to constrain motion of rotational contacts  300  to rotational motion in the plane shown in  FIGS.  3 - 5   . Conversely, in certain embodiments, elastomer retainer  314  and socket frame  324  span multiple rotational contacts  300  positioned in their respective slots  302 . 
     Elastomer retainer  314  provides force to maintain good, or “tight,” connections between rotational contact  300  and contact pads  104  of IC  102 , and between rotational contact  300  and PCB contact  110  of load board  106 . Elastomer retainer  314  includes a round section  702  that engages rotational contact  300  to produce the pre-load force. Elastomer retainer  314  includes a quadrangle section  704  that deforms when rotational contact  300  transitions to the loaded state, under a contact force from IC  102 , and pushes rotational contact  300 , with a return force, back to the pre-load state when IC  102  is removed from receptacle  114  of test socket  108 . First head  326  of socket frame  324  is positioned to align with an apex, or tip, of nail  320 . Likewise, second head  328  of socket frame  324  is positioned to align with a centerline of round section  702  of elastomer retainer 
       FIG.  8    is a flow diagram for a method  800  of assembling test socket  108  shown in  FIGS.  3 - 5  and  7   . Rotational contacts  300  are positioned  802  in corresponding slots  302  of a socket body  112 . Each rotational contact  300  is positioned on a surface  310  and a support edge  312 . Elastomer retainer  314  is then positioned  804  over rotational contacts  300  to capture rotational contacts  300  between elastomer retainer  314  and socket body  112 . Socket frame  324  is mounted  806  over rotational contacts  300  and elastomer retainer  314 , which holds both elastomer retainer  314  and rotational contacts  300  in place. Elastomer retainer  314  is uncompressed when rotational contacts  300  are in the free state, i.e., before test socket  108  is mounted onto a load board. Test socket  108  is then mounted  808  onto load board  106  to transition rotational contacts  300  from the free state to the pre-load state. Rotational contacts  300  translate toward socket frame  324  into the pre-load state, compressing elastomer retainer  314  against socket frame  324 . More specifically, elastomer retainer  314  compresses and deforms against first head  326  and second head  328  of socket frame  324 . 
     Semiconductor IC  102  is set  810  into test socket  108  to transition rotational contacts  300  from the pre-load state to the loaded state. Rotational contacts  300  rotate about elastomer retainer  314 , rotating nail  320  of each rotational contact  300  into elastomer retainer  314  to compress elastomer retainer  314  against socket frame  324 . Tip  316  of each rotational contact  300  translates across a corresponding contact pad  104  of semiconductor IC  102 . 
     When semiconductor IC  102  is removed from test socket  108 , rotational contacts  300  rotate back to the pre-load state. When transitioning from the loaded state back to the pre-load state, elastomer retainer  314  releases and rotates nail  320  back toward surface  310  of socket body  112 , thereby rotating tip  316  back toward socket frame  324 . 
     The technical effects of the systems and apparatuses described herein may include: (a) providing customizable pre-load force via an elastomer retainer; (b) enabling scrub across semiconductor IC contact pads when setting the IC into the test socket; (c) reducing contact electrical resistance between test socket and IC by introducing scrub when setting the IC in the test socket; and (d) reducing scrub across the PCB contact of the load board by the rotational contact. 
     In the foregoing specification and the claims that follow, a number of terms are referenced that have the following meanings. 
     As used herein, an element or step recited in the singular and preceded with the word “a” or “an” should be understood as not excluding plural elements or steps, unless such exclusion is explicitly recited. Furthermore, references to “example implementation” or “one implementation” of the present disclosure are not intended to be interpreted as excluding the existence of additional implementations that also incorporate the recited features. 
     “Optional” or “optionally” means that the subsequently described event or circumstance may or may not occur, and that the description includes instances where the event occurs and instances where it does not. 
     Approximating language, as used herein throughout the specification and claims, may be applied to modify any quantitative representation that could permissibly vary without resulting in a change in the basic function to which it is related. Accordingly, a value modified by a term or terms, such as “about,” “approximately,” and “substantially,” are not to be limited to the precise value specified. In at least some instances, the approximating language may correspond to the precision of an instrument for measuring the value. Here, and throughout the specification and claims, range limitations may be combined or interchanged. Such ranges are identified and include all the sub-ranges contained therein unless context or language indicates otherwise. 
     Disjunctive language such as the phrase “at least one of X, Y, or Z,” unless specifically stated otherwise, is generally understood within the context as used to state that an item, term, etc., may be either X, Y, or Z, or any combination thereof (e.g., X, Y, and/or Z). Thus, such disjunctive language is not generally intended to, and should not, imply that certain embodiments require at least one of X, at least one of Y, or at least one of Z to each be present. Additionally, conjunctive language such as the phrase “at least one of X, Y, and Z,” unless specifically stated otherwise, should also be understood to mean X, Y, Z, or any combination thereof, including “X, Y, and/or Z.” 
     The systems and methods described herein are not limited to the specific embodiments described herein, but rather, components of the systems and/or steps of the methods may be utilized independently and separately from other components and/or steps described herein. 
     Although specific features of various embodiments of the disclosure may be shown in some drawings and not in others, this is for convenience only. In accordance with the principles of the disclosure, any feature of a drawing may be referenced and/or claimed in combination with any feature of any other drawing. 
     This written description uses examples to provide details on the disclosure, including the best mode, and also to enable any person skilled in the art to practice the disclosure, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the disclosure is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.