Abstract:
A system and method are provided to measure a total force applied by a device to a device under test on a circuit board.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to testing circuits, and specifically to testing components on a circuit board by applying a proper recommended force.  
           [0003]    2. Description of the Related Art  
           [0004]    Dies, substrates placed on sockets, which are placed on a circuit board, may be tested once force measured is confirmed and verified to be within a specification.  
         SUMMARY OF THE INVENTION  
         [0005]    In a test environment, a test is performed with a die/substrate on automated handlers connected to a test system. In a System Level Test (SLT) environment the die/substrate is tested semi-manually on a printed circuit mother board with a thermal head applying pressure on the die and substrate.  
           [0006]    A die comprises a silicon material, which is sensitive, and also has solder bumps below the die, which are force sensitive. Force on the substrate is also critical because new packages may have either organic and ceramic substrates and require different amounts of force due to warpage, thickness, and solder connect between die and substrate.  
           [0007]    During testing of a die and/or a substrate on a socket in either a test environment or a System Level Test (SLT) environment, it is important to know the proper amount of force to provide the proper conditions for temperature and electrical conductivity. A thermal interface material between the die and a heat sink allows for heat transfer from the die to the heat sink. Such material could be a thermal grease or a carbon-based thermally conductive material. Applying an optimum force and achieving test performance standards in a production setup is desired. With pin lengths and ball diameters for BGA substrates shrinking, along with thinner organic substrates across all types of devices, less force is desired. This desire is amplified when BI-32 or BI-64 systems are used in memory, where 32 or 64 devices are tested simultaneously. In the case of memory chip testing, “BI-32” refers to 32 devices being tested in parallel on a handler. The setup can consist of 1, 8, 16, 32 or 64 devices being tested at a time.  
           [0008]    In accordance with the present invention, a system and method are provided to measure a total force applied by a device, such as a thermal head or some other device, to a device under test (DUT), such as a substrate, die and/or socket. In one embodiment, the force is measured under a printed circuit board or an original equipment manufacturer (OEM) motherboard. The system will advantageously help ensure that proper settings for testing are used and maintained across systems. The system may improve reliability, improve precision, improve accuracy, reduce cost of manufacturing, simplify manufacturing and improve wear characteristic. The system may be used to test microprocessors based upon a measured force on the die/substrate.  
           [0009]    One aspect of the invention relates to a system configured to measure force applied to a device on a circuit board. The system comprises a first stress relief block configured to support a circuit board; a transducer proximate to the first stress relief block, the transducer being configured to measure an amount of force applied to the device on the circuit board; and a second stress relief block proximate to the transducer. The first and second stress relief blocks are configured to position the transducer. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    [0010]FIG. 1 illustrates one embodiment of a system configured to measure force applied to a DUT or socket. 
     
    
     DETAILED DESCRIPTION  
       [0011]    [0011]FIG. 1 illustrates one embodiment of a system  100  configured to measure force applied to a DUT or socket  110 . The system  100  comprises a shaft  104 , a thermal head  102 , a die  106 , a substrate  108 , a socket  110 , a printed circuit board  112 , a force measurement unit (FMU)  114 , a sub-plate  122  and a base plate  124 . The system  100  may comprise other components in addition to or instead of the components shown in FIG. 1.  
         [0012]    The die may comprise a chip set, a processor or some other integrated circuit. The substrate  108  may be organic or ceramic. The sub-plate  122  and a base plate  124  may be made of aluminum or some other suitable material.  
         [0013]    The FMU  114  may replace an aluminum support that would have been placed between the circuit board  112  and the sub-plate  122  in one configuration. In one embodiment, the FMU  114  comprises 3 pieces: a transducer  118 , a stress relief block  116  and a stress relief spacer  120 . The blocks  116 ,  120  may be made of Pomalux (plastic) or some other suitable material. The two blocks  116 ,  120  are used to support the downward force of the thermal head  102  and to position and hold the transducer  118 .  
         [0014]    The thermal head  102  comprises either an aluminum-based or copper-based heat slug attached to a temperature controller for either cooling or heating the die  106  (or metal lid) or substrate  108  to perform testing at a specified temperature.  
         [0015]    In one embodiment, the system  100  may also include a cable  128  and a display  126 , such as a digital display, to display the measured force to a user. In one embodiment, the display  126  displays the measured force in real time.  
         [0016]    In one embodiment, the transducer  118  has a displacement of about 0.003 inches over its full range of about 200 pounds. In one embodiment, the transducer  118  is linear. The transducer  118  allows for measuring force based on either deflection and/or direct force applied on the die  106  and/or substrate  108 . As an example, one specification calls for a load, e.g., heat slug comprising thermo-electric cooler, of about 30 grams per pin. The printed circuit board  112  comes in contact with the socket  110  which has a device, i.e., die  106  and/or substrate  108 , plugged in the socket  110 . If a device (e.g., substrate  108 , socket  110  or printed circuit board  112  comprising electronic components and circuit traces in a multi-layer, which is also known as a mother board) has a total of 462 pins, the total force on the transducer  118  will be about 57.04 pounds or 13,860 grams on the substrate. This means there will be about a (57.04×0.003)/200=0.000856-inch displacement in order for the transducer  118  to take a measurement. Depending on the size of the transducer  118 , the transducer  118  could take measurements, but deflection on printed circuit boards is sensitive because the metal traces could break. Thus, minimum force is preferred, but the force should be sufficient to achieve thermal contact. This deflection from the transducer  118 , although undesired (minimum deflection allowable without breaking the metal traces on the printed circuit board), should not warp the PC board  112  to the point of losing pin contact.  
         [0017]    The above-described embodiments of the present invention are merely meant to be illustrative and not limiting. Various changes and modifications may be made without departing from the invention in its broader aspects. The appended claims encompass such changes and modifications within the spirit and scope of the invention.