Abstract:
A signal lead structured to be attached to an electrical device that comprises a signal pad, a spring housing, a spring, and a flexible conduit. The spring is carried in the spring housing, and a portion of the spring extends beyond a surface of the spring housing when the spring is unsprung. The spring is structured to touch the electrical device and carry an electrical signal between the electrical device and the signal pad when the signal lead is attached to the electrical device. The flexible conduit is coupled to the signal pad at an end of the flexible electrical conduit and extends away from the spring housing.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a continuation of, and claims priority to, U.S. patent application Ser. No. 13/724,344, filed on Dec. 21, 2012, which is incorporated here by this reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This disclosure is directed to lead assemblies, and, more particularly, to devices that couple test equipment to devices to be tested through such lead assemblies. 
       BACKGROUND 
       [0003]    Electrical devices are often tested, especially during development, production, or when they are not working properly. Test equipment provides information about the operation of the devices. Test equipment may include meters, probes, logic analyzers, and scopes such as oscilloscopes, for example. 
         [0004]    It is sometimes difficult to accurately measure high frequency signals generated by a device because of, among other reasons, the difficulty in reliably connecting or coupling the device under test to the measuring device. For the best results, the devices should be solidly electrically connected to the test device. For example, a preferred method for measuring test signals having frequencies between 6-10 GHz is to first attach a small solder-in lead to various testing points in the circuit. Then, the lead may be coupled to a probe of a high-frequency testing device and the signals of the device are measured. In practice, the probe may be manually coupled to a number of separate soldered-in leads so that the signals at the testing points may be measured. 
         [0005]    Even though soldering such connections is the best currently available method, it is not without problems. Installation of such devices by soldering the typically small leads is problematic, and can lead to damage to either the lead, the device, or both. Damaging either may be costly, either in equipment or in time lost to fix the damage. Further, solder-in leads tend to be small and are damaged easily, and it is easy to break the fine leads that are typically coupled to coax cable connectors. Costs are another issue, both in device and labor costs, as the leads are expensive and take time to install properly. 
         [0006]    Embodiments of the invention address these and other limitations of the prior art. 
       SUMMARY OF THE INVENTION 
       [0007]    Aspects of the invention include a high bandwidth solder-less lead mountable to an electrical device having land patterns. The lead includes an attachment mechanism to attach the lead to the device, a microspring housing, and at least one microspring carried in the housing. A portion of the microspring extends beyond the microspring housing to electrically couple to one of the land patterns of the electrical device. In some embodiments there may be multiple microsprings coupling different signals from the device to the solder-less lead. The signals may include ground signals. The lead may be attached to a flexible conduit that is readily attachable to a test device, such as through a socket. 
         [0008]    Other aspects include a combination of a solder-less lead having at least one microspring carried in a housing for coupling to an electrical device in which the lead is removably or temporarily coupled to a connector. The connector further includes another microspring carried in another housing. The solder-less lead may be permanently attached to the electrical device, while the connector may be temporarily connected to a first lead, and then connected to a second lead to measure a second set of signals. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a top view of a head of a lead assembly for attaching to a device being tested according to embodiments of the invention. 
           [0010]      FIG. 2  is a is a side view of the lead assembly of  FIG. 1  attached to a connection bracket according to embodiments of the invention. 
           [0011]      FIG. 3  is a side view of an example lead assembly as it is being coupled to a head end of a cable assembly according to embodiments of the invention. 
           [0012]      FIG. 4  is a top view of the head end of the cable assembly according to embodiments of the invention. 
           [0013]      FIG. 5  is a perspective view of a lead assembly for attaching to a device according to other embodiments of the invention. 
           [0014]      FIG. 6  is a perspective view of a head of the lead assembly of  FIG. 5  according to embodiments of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    Embodiments of the invention are now described beginning with reference to  FIGS. 1 and 2 .  FIG. 1  is a top view of a head of a lead assembly for attaching to a device being tested according to embodiments of the invention, and  FIG. 2  is a side view of the same device. 
         [0016]    A head assembly  100 , generally, is structured to physically attach to a device under test (DUT) (not illustrated). Such devices may include those devices that have high-speed RF signals on the board. In many embodiments the device will have an exposed printed circuit (PC) board that terminates in test points or includes particular land patterns. Land patterns are areas for electrical connection, such as for connecting a surface mounted Integrated Circuit (IC) to a particular device. Land patterns may also be used to couple to a testing device, or to a probe or other lead coupled to the testing device. Land patterns are oftentimes used as soldering points to connect the DUT to a soldered lead assembly. Land patterns could be, for example, flat spots of metal or solder-covered metal, or could be raised bumps on a PC board of the DUT. Bumps could be bumps of a Ball Grid Array (BGA), for instance. Of course, the examples described herein are merely examples, and embodiments of the invention may be used in various and multiple ways without deviating from the inventive scope. 
         [0017]    The test lead  100  of  FIG. 1  includes a support bracket  110 , which is more apparent in  FIG. 2 . The support bracket  110  may be formed of metal or other supporting material. 
         [0018]    Coupled to the support bracket  110  is a support board, such as a PC board  120 . The PC board  120  may be soldered to the bracket  110  through solder tabs  111  or otherwise attached to the support bracket  110 . The PC board  120  has components mounted thereon. For instance, a set of resistors  140 , or other components, may be mounted between a set of signal pads  130  and a set of probing signal pads  150 . A set of ground pads  132  may also be included. As described below, the set of signal pads  130  may be coupled to the set of land patterns of the DUT, and a set of probing signal pads  150  provides an area for measurement by a probe of a measurement device. The probing signal pads  150  are typically larger than the land patterns on the DUT, which makes it easier to couple to the test probe. The probing signal pads  150  may also be referred to as differential pads because they are typically placed in pairs, and the pair receives differential signals, one on each pad of the pair. 
         [0019]    The ground pads  132  may likewise be coupled to signal grounds of the DUT, as described below. 
         [0020]    As shown in  FIG. 2 , springs  134  may be connected to an under-side of the signal pads  130  and ground pads  132  through a via in the PC board  120 . The springs  134  make an electrical connection between the signal pads  130 , ground pads  132  and their respective land patterns on the DUT. The springs  134  may be metal having a relatively low resistance. The springs  134  may be shaped as microsprings, and capable of carrying high bandwidth signals from the land patterns of the DUT to the signal pads  130  and ground pads  132 , respectively. 
         [0021]    The springs  134  may be supported by an insulated spring housing  136 . The spring housing  136  maybe be a plastic of sufficient strength and stiffness to properly support the springs  134 . The spring housing  136  may be made of thermoplastic polyetherimide such as Ultem plastic available from SABIC, or from any other suitable material. 
         [0022]    The springs  134  may be spaced to exactly match the spacing of the land patterns of the DUT. In some embodiments, multiple test leads  100  may be available, each having different spacing between the springs  134 . In those embodiments, a test engineer selects the proper test lead  100  having the desired spacing. In other embodiments, device manufacturers may develop one or more standard spacings that are based on the widths between the springs  134 . 
         [0023]    The test lead  100  also includes an attachment mechanism  160 , such as adhesive foam, epoxy, or a clamp, so that the test lead  100  may be attached to the DUT. In some embodiments the test lead  100  may be mounted on the DUT permanently. 
         [0024]    In practice, to mount the test lead  100  to the DUT, the adhesive foam  160  is exposed by removing a protective covering. In some embodiments the same or another protective covering also covers and protects the springs  134 , and removing the covering or coverings exposes a bottom portion of the springs. After uncovering the adhesive foam  160 , the test lead  100  is lowered toward the DUT so that the exposed springs  134  touch the land patterns in a mating fashion. Then, the test lead  100  is pressed into place, making a secure connection to the DUT with the adhesive foam  160 , and simultaneously making a secure electrical connection between the land patterns of the DUT and the springs  134 . As described above, the springs  134  make a secure electrical connection between the land patterns and the under-side of the signal pads  130  and ground pads  132  of the test lead  100 . Further, a top side of the signal pads  130  and ground pads  132  may also include surfaces so that wires or other electrical connections may be made to other portions of the DUT. Or, in some embodiments, the test lead  100  may be attached to the DUT by the adhesive foam  160 , or other methods, near the desired land patterns, and the land patterns may be connected to the top of the signal pads  130  and ground pads  132  with soldered wires, and not necessarily through the springs  134 . 
         [0025]    With reference to  FIGS. 3 and 4 , described is a connector assembly  300  that may be matingly and removably coupled to the test lead  200 , which may be an example of the lead  100  of  FIG. 1 . In other words, after the test lead  200  has been attached to the DUT, using the methods described above, a connector assembly  300  may be temporarily attached to test lead  200  and be used to electrically connect it to the measurement device through a cable, such as a pair of coaxial cables  310 , so that measurements of the DUT may be made. In this way, a single probe may be able to easily attach to multiple test leads  200  mounted on a DUT in a serial manner, i.e., first testing a first test lead, then removing it from the first test lead and attaching it to another, etc. After the testing is complete, the test lead  200  may be left attached to the DUT, while the connector assembly  300  may be used to test other devices. 
         [0026]    The test lead  200  of  FIG. 3  differs from the test lead  100  of  FIG. 1  by the position of a bracket  210 . More specifically, the bracket  210  is bent away from the main body of the test lead  200 . As described above, the bracket  210  may be made from a yieldable material, such as a soft metal, that may be relatively easily moved, such as by manual pressure, but remains in place once moved. One benefit to having a positionable bracket  210  is that it allows the connector assembly  300  to be attached to the test lead  200  even though there may be an interfering structure that would otherwise hinder attaching the connector assembly  300 . Because it is unknown in advance what hindrances there may be near a test site of the DUT, having a bracket  210  that is positionable may allow the test lead  200  to be used with more test sites of a DUT than if the bracket were not positionable. 
         [0027]    The connector assembly of  FIGS. 3 and 4  includes a pair of springs  370  that are used to electrically connect to the probing signal pads  250  of the lead  200 . Recall from above that the probing signal pads  250  are coupled through the lead  200  to land patterns of the DUT. The pair of springs  370  then connect the probing signal pads  250  to a pair of coaxial cables  310 , which conveys the signals from land patterns of the DUT to a probe of the measurement device (not illustrated) so that the DUT may be measured. Ground signals may be carried by the bracket  210 , or may be coupled to ground pads  314  in another manner. The coaxial cables  310  may be skew matched for better signal integrity. 
         [0028]    The springs  370  may be the same or similar to the springs  134  of  FIG. 2 , except the springs  370  are positioned to project from the connector assembly  300  directly opposite the coaxial cables  310 . The springs  370  are held in a spring housing  360 . The housing  360  maybe be a plastic of sufficient strength and stiffness to properly support the springs  370 . Similar to the spring housing  136  described above, the spring housing  360  may be made of thermoplastic polyetherimide. The spring housing  360  may have a shape at one end to facilitate the springs  370  to contact the probing signal pads  250  no matter what position the bracket  210  is in. For example the spring housing  360  may have an angled shape as illustrated in  FIG. 3 , or the spring housing  360  may be rounded. Other shapes may function in another manner to produce an acceptable result. A substance or structure  380  may cover much of the connector  300  to provide strain relief of the connector  300 . 
         [0029]    A PC board  340  provides a physical support and electrical connections to signal processing circuits  350 . The processing circuits  350  process the signals from the DUT before they are passed through the coaxial cables  310  to the measuring device. 
         [0030]    With reference to  FIG. 4 , test signals from the DUT are passed from the springs  370 , through the processing circuits  350 , to a conductor  316  of the coaxial cable  310 . Similarly, ground connections  314  are coupled to another conductor of the coaxial cable  310 . The connector  300  of  FIG. 4  is symmetric about the longitudinal axis, with a first signal being carried on one of the coaxial cables  310 , and a second differential signal carried on the other, as is known in the art. In other embodiments the connector  300  may only include a single signal path and convey only a single test signal. 
         [0031]    With reference back to  FIG. 3 , to couple the connector  300  to the test lead  200 , a user moves the connector toward the bracket  210  to mate with a spring latch  304  that includes a projection  308 . When inserted, the projection  308  is received and captured in a receiver, such as a depression or hole  212  in the bracket  210  to create a secure physical connection between the connector  300  and the test lead  200 . The secure physical connection also ensures that there is a secure electrical connection between the springs  370  and the probing signal pads  250 . 
         [0032]      FIG. 5  illustrates another device to couple a measurement device with a DUT. In  FIG. 5 , a connector  500  includes a head end  510  and a tail end  520 . The head end  510  attaches to the DUT in a similar fashion as the test leads  100 ,  200 , described above, and is described in more detail below. A strap  502  carries electrical signals from the head end  510  to the tail end  520 , ending in a set of terminals  522 . The tail end  520  in this embodiment is structured to be inserted into a zero insertion force (ZIF) socket  526 , where the terminals  522  make an electrical connection with terminals within the ZIF socket  526 . In this embodiment, the test device, which is coupled to the ZIF socket  526 , may be connected to various different connectors  500  simply by removing the tail end  520  from a first connector and inserting a tail end from another connector. In practice the connector  500  may be left attached to the DUT, even after testing is completed. Of course, the tail end  520  may differ depending on implementation details. 
         [0033]      FIG. 6  illustrates more details of the head end  510  of the connector  500 . The head end  510  of the connector  500  includes many of the same components as described in the test lead  200  and connector  300  described above, except the components are combined into a single unit. 
         [0034]    More specifically, the connector  500  includes a strap  502 , which may be a flexible plastic that has conductive paths running through it. Signal pads  530  and ground pads  532  operate like their counterparts  130 ,  132  described above with reference to  FIG. 1 . Further, the connector  500  may be connected to the DUT using microsprings (not pictured) below the signal pads  530 ,  532  and the other attachment mechanism, as described above. 
         [0035]    A substrate, such as a PC board  504  provides physical support and electrical connections for the components  540 ,  542 , mounted thereon. These components may vary depending on the particular signals being measured, but could include, for instance, resistors, capacitors, etc. An integrated circuit  546  modifies the signal before being measured, similar to the processing circuits  350  described above. Further, the connector  500  may include an identification device  550 , such as a memory device like an EPROM or EEPROM that may identify the particular connector  500  to the test device. Optionally, a tab  506 , which may be made of plastic or other material, may be attached to the connector  500 . The tab  506  allows the connector  500  to be more easily handled when attaching or, less likely, removing, the connector to the DUT. The tab  506  also provides physical protection for any delicate features that may be mounted on the connector  500 , such as the small connection wires  547 . 
         [0036]    It will be appreciated from the forgoing discussion that the present invention represents a significant advance in the field of test and measurement. Although specific embodiments of the invention have been illustrated and described for purposes of illustration, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, the invention should not be limited except as by the appended claims.