Abstract:
Embodiments may include a method and an apparatus for inducing degradation through temperature cycling of a solder joint or a component on a surface mount printed wiring board (SMPWB) coupon. The coupon may include alternating layers of dielectric material and conductive material stacked one upon another and a heating trace mounted on a surface of the SMPWB or between layers of dielectric material. A first value indicative of a temperature of the heating trace may be determined based on a measured electrical resistance of the heating trace. A difference between the first value and a second value indicative of a desired temperature of the heating trace may be determined. A particular current and a particular voltage may be applied to the heating trace based on the determined difference between the first value and the second value.

Description:
BACKGROUND 
     Surface Mounted Technology (SMT) has been increasingly replacing through-hole mounting systems as component size reduction drives technological development. SMT involves use of flat pads on a surface of a printed wiring board (PWB), application of solder paste to the pads via a template, and application of components to the pads, wherein the components have leads which match the pads. The board may then be reflowed and the components soldered to the pads. 
     Most assembly failure occurs at interface points, namely within solder joints. For this reason, testing to determine life expectancy of an assembly has included analysis of thermal cycling on solder joints. As a result of testing involving thermal cycling, an expected lifetime of a device can be determined as well as identification of possible failure modes that may be corrected in order to extend the lifetime of the device. 
     Currently, thermal cycling of SMT solder joints includes immersing a PWB in an environment, such that heat is either absorbed or lost by the PWB. Typically, this is done by using oven-like chambers, which may perform temperature cycling in either a single chamber or dual chambers. In single chamber cycling, air within the chamber is incrementally heated. A rate of heating is known as a ramp rate. Once a desired ambient temperature is reached, the ambient temperature is stabilized while a temperature of the PWB lags due to thermal transference. The temperature within the chamber may then be dropped by applying a coolant or by a lack of heating. 
     In dual chamber thermal cycling, each chamber is regulated at a respective constant temperature and the PWB is physically moved from one chamber to another chamber in a process known as thermal shock. The process of thermal shock may include use of a gas, such as air or nitrogen, or liquids, such as fluoropolymers. 
     The current methods for performing thermal cycling for SMT connections has many disadvantages, such as, for example, cost, size and equipment complexity. Often, each item of equipment must be purchased separately, at great cost, and an end-user must custom design a configuration that meets space requirements and end-user requirements. Such a system tends to be unreliable, resulting in downtime. Although single chamber systems are less complex and more reliable than dual chamber systems, single chamber systems take up considerable space and are expensive to maintain. 
     In addition, both single chamber systems and dual chamber systems operate by heating an intermediate medium, such as air. In order to accommodate various sizes of devices, chambers are built with an excess of volume. Thus, for example, in order to heat a small device for testing, energy must be expended to heat an entire volume of a chamber. 
     SUMMARY 
     This Summary is provided to introduce a selection of concepts in a simplified form that is further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. 
     In embodiments consistent with the subject matter of this disclosure, a surface mount printed wiring board coupon may be provided. The coupon may include alternating layers of dielectric material and conductive material stacked one upon another and a heating trace mounted on a surface of the coupon or between layers of dielectric material. In some embodiments, multiple heating traces may be mounted on the surface of the coupon or between layers of dielectric material, wherein each of the heating traces may be thermally isolated from others of the heating traces. 
     In other embodiments consistent with the subject matter of this disclosure, a method for inducing degradation of solder joints or components on a surface mount printed wiring board coupon may be provided. The coupon may include alternating layers of dielectric material and conductive material stacked one upon another and at least one heating trace mounted on a surface of the surface mount printed wiring board coupon or between layers of dielectric material. In the method, a first value indicative of a temperature of the heating trace may be determined based on a measured electrical resistance of the heating trace. A difference between the first value and a second value indicative of the desired temperature of the heating trace may be determined. A particular current and a particular voltage may be applied to the at least one heating trace based on the determined difference between the first value and the second value. 
     In other embodiments, an apparatus for inducing degradation of solder joints or components on a surface mount printed wiring board coupon may be provided. The coupon may include alternating layers of dielectric material and conductive material stacked one upon another, and at least one heating trace mounted on a surface of the coupon or between layers of dielectric. The apparatus may include a housing surrounding an area for mounting the surface mount printed wiring board coupon, at least one cooling component for cooling the surface mount printed wiring board coupon, and a controller module electrically connected to each of the at least one cooling component. The controller module may be arranged to be electrically connected to a portion of the surface mount printed wiring board coupon. The controller module may be configured to receive information indicative of a target temperature from a processing device, to monitor a value indicative of a temperature of the heating trace on the surface mount printed wiring board coupon, to apply an electrical current to the at least one heating trace of the surface mount printed wiring board coupon when the monitored value and the received information indicate that solder joints or the components of the surface mount printed wiring board coupon have a temperature lower than the target temperature. 
    
    
     
       DRAWINGS 
       In order to describe the manner in which the above-recited and other advantages and features can be obtained, a more particular description is described below and will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings. Understanding that these drawings depict only typical embodiments and are not therefore to be considered to be limiting of its scope, implementations will be described and explained with additional specificity and detail through the use of the accompanying drawings. 
         FIG. 1  illustrates multiple layers that may be included in an exemplary surface mount printed wiring board coupon. 
         FIG. 2  illustrates a top view of an exemplary surface mount printed wiring board coupon. 
         FIG. 3  illustrates an exemplary conductive layer of a surface mount printed wiring board coupon having a flat serpentine-shaped heating trace mounted thereon. 
         FIG. 4  illustrates an exemplary conductive layer of a surface mount printed wiring board coupon having a flat rectangular-shaped heat spreader. 
         FIGS. 5A and 5B  show an exemplary Surface Mount Testing System consistent with the subject matter of this disclosure. 
         FIGS. 6A-6C  show another embodiment of an exemplary Surface Mount Testing System consistent with the subject matter of this disclosure. 
         FIG. 7  illustrates an exemplary processing device and an exemplary Surface Mount Testing System controller, which may be used in embodiments consistent with the subject matter of this disclosure. 
         FIG. 8  shows a more detailed view of the exemplary Surface Mount Testing System controller of  FIG. 7 . 
         FIG. 9  illustrates a functional block diagram of an exemplary processing system, consistent with subject matter of this disclosure. 
         FIG. 10  is a flowchart illustrating an exemplary process that may be performed in embodiments consistent with the subject matter of this disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments are discussed in detail below. While specific implementations are discussed, it should be understood that this is done for illustration purposes only. A person skilled in the relevant art will recognize that other components and configurations may be used without parting from the spirit and scope of the subject matter of this disclosure. 
     Overview 
     Embodiments consistent with the subject matter of this disclosure may include a test coupon having alternating layers of dielectric material and conductive materials stacked one upon another. A heating trace may be mounted on a surface of the test coupon or between layers of dielectric material for heating an area. The heating trace may be constructed of copper in some embodiments. Further, in some embodiments, a second heat spreader or heating trace may be mounted on a surface of the test coupon or between other layers of dielectric material. The two heating traces may be placed such that they are thermally isolated from one another. The heating traces may be of a flat serpentine shape, a flat rectangular shape, or any other flat shape. Other embodiments may include more than two heating traces. 
     A Surface Mount Testing System (SMTS) may include a housing in which one or more test coupons may be placed for testing. A processing device such as, for example, a personal computer, or other processing device may be connected to a controller, which further is arranged to monitor a temperature of the heating trace of the test coupon by measuring an electrical resistance of the heating trace. Upon receiving data from the processing device, via a USB interface, or other interface, the controller may cause a heating trace to become heated when the monitored temperature of the heating trace is less than a desired temperature, as provided by the processing device. In some embodiments, a cooling component such as, for example, a fan, or other cooling component, may be activated when a desired temperature is less than the monitored temperature of the heating trace. 
     By heating the test coupon itself, via one or more heating traces, and cooling the test coupon with forced ventilation, either of ambient air or a cooling medium such as, for example, nitrogen or another medium, an amount of energy required per thermal cycle may be drastically reduced over an amount used by prior art methods. Further, an amount of space required for thermal testing of a test coupon may be greatly reduced. 
     Test Coupon 
       FIG. 1  illustrates a side view of an exemplary test coupon  100 , which may be used in embodiments consistent with the subject matter of this disclosure. Test coupon  100  may include alternating layers of dielectric material and conductive material stacked one upon another. For example, test coupon  100  may include conductive layers  102 ,  106 ,  110 , and  114  and dielectric layers  104 ,  108  and  112 . In one embodiment, the conductive layers may include copper, or other conductive material, and may have a thickness of about 35 microns. The dielectric material may include epoxy, ceramic polyimide, a glass resin substrate, or other insulating material, and in one embodiment may have a thickness of about 450 microns. 
       FIG. 2  illustrates a top view of test coupon  100 , showing conductive layer  102  having rectangular areas, where various components may be soldered. 
       FIG. 3  illustrates a conductive layer, such as, for example, layer  106  or  110  having a flat serpentine-shaped heating trace mounted thereon. In one embodiment, the heating trace may be made from a conductive material such as, for example, copper, or other conductive material. In some embodiments, a heating trace or heat spreader may have a flat rectangular shape, or other flat shape. Further, some embodiments may have one heating trace and other embodiments may have two or more heating traces, each of which may be mounted on a surface of a test coupon or between layers of dielectric material of the test coupon. 
       FIG. 4  illustrates a bottom conductive layer, such as layer  114 , of a test coupon having a flat rectangular-shaped heating element  402  mounted thereon. As previously mentioned, in other embodiments, a heating element may have a flat serpentine shape, or another flat shape, and may include copper or another conductive material. 
     Surface Mount Testing System 
       FIGS. 5A and 5B  illustrate an exemplary Surface Mount Testing System (SMTS)  500 . SMTS  500  may include a housing  502  and a removable housing lid  504 , which may be removed for placing test coupons within the housing and removing test coupons from the housing. Housing lid  504  may include multiple vent openings  506  for cooling components such as, for example, fans or other cooling components. A bottom portion of housing  502  may also include multiple vent openings (not shown) for cooling components. 
       FIG. 5B  illustrates a surface mount printed wiring board  510  which may be mounted within housing  502 . Surface mount printed wiring board  510  may be mounted within an area surrounded by housing  502  of SMTS  500  via a number of techniques including, but not limited to, standoffs, edge card guides, wedge locks, or edge clamps. Fan  512  may be included in a cooling assembly located below vent openings  506  of housing lid  504  for blowing cold air toward surface mount printed wiring board  5   10 . Fan  514  may be included in a cooling assembly located above the vent openings (not shown) at a bottom portion of housing  502  for blowing air out of housing  502 . 
     SMTS  500  is an exemplary embodiment. In other embodiments, multiple surface mount printed wiring boards may be mounted within a housing. For example, in one embodiment, six surface mount printed wiring boards may be mounted in two rows of three boards each. A cooling assembly may be positioned above and below each of the surface mount printed wiring boards to cool respective surface mount printed wiring boards. In other embodiments, other configurations may be implemented. 
       FIGS. 6A-6C  illustrate a second exemplary SMTS  600 . SMTS  600  may include a housing  602 , which may have an arced end  604  and a vented end  606  having intake vents  608  and outgoing vents  610 . Housing  602  may be constructed of a plastic material in some embodiments and may have a low height. SMTS  600  may include a front portion  612  which may be opened or removed for inserting or removing a surface mount printed wiring board for testing. Although exemplary housing  602  includes arced end  604 , in other embodiments, housing  604  may have an arced end internally and may not have an arced shape externally. 
       FIG. 6B  shows a portion of SMTS  600  without housing  602  so that internal components may be viewed. SMTS  600  may include a fan  620 , a printed circuit board  622 , an evaporator  624 , and a rotating deflector  626 , which may be electrically controlled in some embodiments. 
     Fan  620  may be a cross flow fan to create a wide, uniform flow of air or other cooling medium. Printed circuit board  622  may be mounted within housing  602  of SMTS  600  via a number of techniques including, but not limited to, standoffs, edge card guides, wedge locks, or edge clamps. Deflector  626  is shown in an open position in  FIG. 6B  to encourage maximum flow of air or other cooling medium through vents  608  and  610 . Deflector  626  may be in a closed position ( FIG. 6C ) when cooling solder joints or components of printed circuit board  622  are below room temperature. In the closed position, deflector  626  may block off vents  608  and  610  and may recirculate the cooling medium. As shown in  FIG. 6B , in this embodiment, the air or other cooling medium may flow laterally across printed circuit board  622 , in one direction above printed circuit board  622 , and laterally in another direction below printed circuit board  622 . 
     Although not explicitly shown, a controller may be electrically connected to one or more heating traces on a test coupon, such as, for example, surface mount printed wiring board  510  mounted within housing  502 , or surface mount printed wiring board  622  mounted within housing  602 , such that the controller may cause an electrical current to be passed through the one or more heating traces to heat the one or more heating traces. An electrical resistance of the one or more heating traces may be measured to provide an indication of temperature. In embodiments consistent with the subject matter of this disclosure, an electrical resistance of the one or more heating traces may be in a range of 40-60 ohms at a temperature of 20° C. 
       FIG. 7  illustrates a processing device  702  and an SMTS controller  704  of an SMTS, such as, for example, SMTS  500  or  600 . Processing device  702  may be a server, a desktop personal computer, a notebook personal computer, a handheld processing device, or other processing device. Controller  704  may be a controller for monitoring electrical resistance of one or more heating traces on a surface mount printed wiring board test coupon and for sending an electrical current to the one or more heating traces to cause the one or more heating traces to heat up. 
       FIG. 8  illustrates an exemplary controller  802 , which may be used in embodiments consistent with the subject matter of this disclosure. Controller  802  may include an analog-to-digital (A/D) converter  804 , a resistance measurer  806  a digital-to-analog (D/A) converter  808 , a comparer  810 , and an inverter  812 . 
     D/A converter  808  may receive a signal from a processing device such as, for example, processing device  702 , indicative of a desired temperature. In some embodiments, the signal may represent an electrical resistance value. An analog version of the signal may be provided to comparer  810 . Resistance measurer  806  may cause an electrical current to be passed through at least one heating trace of a test coupon, such that an electrical resistance of the at least one heating trace may be determined. An indication of the electrical resistance may be provided to comparer  810  and to A/D converter  804 , which may provide a digital version of the measured electrical resistance to processing device  702 . Comparer  810  may compare values representing the measured electrical resistance and the desired temperature (or electrical resistance) and may provide a value representing a difference of the compared values to a heater  816 , which in some embodiments may be the one or more heating traces. The value representing the difference of the compared values may also be provided to an inverter  812  which may provide the inverted difference to a cooling component  814 , which in some embodiments may be one or more fans, or other cooling components. 
     In one embodiment consistent with the subject matter of this disclosure, controller  802  may be powered by an alternating current source. In such an embodiment, when a current is to be applied to one or more heating traces, or to one or more cooling components, the current may be applied only during a positive portion of a sinusoidal period of the provided electrical current. When a current is to be applied to the one or more heating traces in order to monitor electrical resistance, the current may be applied to the one or more heating traces and the electrical resistance determined only during a negative portion of the sinusoidal period of the provided electrical current. 
     Exemplary Processing System 
       FIG. 9  illustrates a functional block diagram of an exemplary processing device  900 , which may be used to implement embodiments consistent with the subject matter of this disclosure. In one embodiment, processing device  900  may be used to implement processing device  702 . Processing device  900  may include a bus  910 , a processor  920 , a memory  930 , a read only memory (ROM)  940 , a storage device  950 , an input device  960 , an output device  970 , and a communication interface  980 . 
     Bus  910  may permit communication among components of processing system  900 . Processor  920  may include at least one conventional processor or microprocessor that interprets and executes instructions. Memory  930  may be a random access memory (RAM) or another type of dynamic storage device that stores information and instructions for execution by processor  920 . Memory  1330  may also store temporary variables or other intermediate information used during execution of instructions by processor  920 . ROM  940  may include a conventional ROM device or another type of static storage device that stores static information and instructions for processor  920 . Storage device  950  may include any type of media, such as, for example, flash memory, Non-Volatile Random Access Memory (NVRAM), magnetic or optical recording media and its corresponding drive or port. 
     Input device  960  may include one or more conventional mechanisms that permit a user to input information to processing system  900 , such as a keyboard, a mouse, a pen, a stylus, a voice recognition device, a microphone, a headset, etc. Output device  970  may include one or more conventional mechanisms that output information to the user, including a display, a printer, one or more speakers, a headset, etc. Communication interface  980  may include any transceiver-like mechanism that enables processing system  900  to communicate with other devices or networks. In one embodiment, communication interface  980  may communicate to a controller via a USB interface. In other embodiments, another type of interface may be employed. 
     Processing system  900  may perform such functions in response to processor  920  executing sequences of instructions contained in a tangible machine-readable medium, such as, for example, memory  930 , a magnetic disk, an optical disk, or other medium. Such instructions may be read into memory  930  from another machine-readable medium, such as storage device  950 , or from a separate device via communication interface  980 . 
     Exemplary Processing 
       FIG. 10  is a flowchart illustrating an exemplary process that may be performed in embodiments consistent with subject matter of this disclosure. The process may begin with a processing device such as, for example, processing device  900 , obtaining a value indicative of a desired temperature (act  1002 ). The value may be included as data in an executing program of processing device  900 , or the data may be provided from a database, or from another input source. In some embodiments, the value may be an electrical resistance value, which may be indicative of the desired temperature. Next, processing device  900  may send a signal, indicative of the desired temperature, to D/A converter  808  (act  1004 ). 
     After resistance measurer  806  measures the electrical resistance from the at least one heating trace, the measured electrical resistance may be provided to A/D converter  804 , which may further provide a digital version of the measured electrical resistance to processing device  900 . Thus, processing device  900  obtains a value indicative of a temperature of the at least one heating trace (act  1006 ). Processing device  900  may then examine the received value indicative of the temperature and may determine whether a failure occurred (act  1008 ). In one implementation a failure may be determined when the received value indicative of the temperature is an unexpected value. If processing device  900  determines that a failure occurred, then processing device  900  may provide an indication of the failure (act  1010 ). The indication of the failure may be provided in a number of different ways including, but not limited to, sounding an alarm, displaying a message, sending an e-mail or other communication to a designated party, or other notification means. 
     Next, if processing device  900  determined that a failure did not occur, then processing device  900  may determine whether the obtained value indicative of the temperature indicates that the temperature is the desired temperature (act  1012 ). If the temperature is not the desired temperature, then processing device  900  may repeat acts  1006  through  1012 . If processing device  900  determined that the temperature is the desired temperature, in act  1012 , then processing device  900  may determine whether there are any additional steps to be performed during thermal cycle stress testing (act  1014 ). If additional steps are to be performed, then processing device  900  may repeat acts  1002  through  1014 , thereby causing a temperature change based on an obtained value indicative of a desired temperature and a measured value indicative of the temperature. 
     By heating and monitoring the temperature of at least one heating trace of the surface mount printed wiring board test coupon, such that the heat is applied at a programmed rate, a SMTS may control a ramp rate of heating while applying a voltage to one or more heating traces. Further, the SMTS may be used to maintain the surface mount printed wiring board test coupon at a constant temperature while monitoring for an occurrence of a failure. 
     CONCLUSION 
     Although the subject matter has been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms for implementing the claims. 
     Although the above description may contain specific details, they should not be construed as limiting the claims in any way. Other configurations of the described embodiments are part of the scope of this disclosure. Further, implementations consistent with the subject matter of this disclosure may have more or fewer acts than as described, or may implement acts in a different order than as shown. Accordingly, the appended claims and their legal equivalents should only define the invention, rather than any specific examples given.