Implementation of a Cellular Phone Automotive Grade Validation

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"The solution implemented respected the automotive requirement for device validation and reduced test time."

- Paolo Bertoldo, SEICA

The Challenge:
Validating the cellular phones produced to certify their automotive grade by testing the units in different temperature environments (-40 °C, +85 °C, +25 °C) in a multidevice-under-test solution (up to 50 units).

The Solution:
Combining different hardware solutions: the hardware for electric testing and signal simulation is made by Seica, while the RF analysis is perfomed using five NI vector signal transceivers (NI PXIe-5644R) in parallel matching an RF switcher for the 50 units under test (UUTs). A climatic chamber was selected to simulate the temperature profile. Everthing is then controlled using the LabVIEW and TestStand capabilities.

Author(s):
Paolo Bertoldo - SEICA
Marco Marigo - SEICA

Founded in 1986, Seica S.p.A. is a global supplier of automatic test equipment and selective soldering systems with an installed base of more than 1,500 systems on four different continents. Seica offers a complete line of proprietary test solutions as well as integrated solutions. The company has established strong partenerships with leaders of manufacturing and inspection systems to enlarge the portfolio of solutions across the whole production line. In a time of continuous changes, where globalization challenges competitiveness, Seica drives its strategy with local direct presence in Italy, France, Germany, USA, and China in addition to best service and support quality with a local, strong, and professional team.

Electronics devices are a relevant part of the automotive architecture. Cellular phones are following this trend and are increasingly used inside vehicles. Multiple applications can be identified, starting from black boxes for ecall and insurance purposes to complex infotainment units providing connectivity to the onboard systems.

The Requirements

Telit Wireless Solution, a market leader in the M2M segment, requested Seica to study the implementation of the validation process of a set of wireless products to respect the automotive specification. The analysis was jointly conducted and resulted in the definition of two steps: (1) a burn-in station to stress the UUT for four hours at 85 °C and (2) the implementation of a functional test (with the necessary RF performance analysis) in three different challenging temperatures (-40 °C, +85 °C, and +25 °C). The second is the solution we describe here.
The defined test requires a long time for execution, so to respect the production cycle time, we defined a minimum set of 50 to run simoultaneously inside the temperature chamber.

Critical Aspects

Multiple aspects are critical for the above implementation, including:
• The management of a multidevice testing solution with up to 50 devices under test (DUTs)
• The implementation of a tray solution to hold the DUTs inside the temperature chamber
• The proper communication link with the UUTs
• The RF signal routing and connection characterization
• The selection of a proper climatic chamber

The Implementation

Different subsystems can be identified in the solution implemented and are represented in the following block diagram. We describe them in the following sections.
The Controller
The overall system is controlled by an industrial PC (i7 core) that can handle all the interfaces to the different system blocks, the multiple communication link to the DUTs, and the necessary computing power to manage the relevant data analysis. For example, we could manage the need for 50 serial ports with all RS232 interfaces to the DUTs implemented using serial port expansion modules. The communication with the selected NI PXI rack hardware was implementd using a PCI-MXI interface.

Interface to DUTs

All the resources integrated in the system are made available for the application using a standard Seica fixture interface. We designed the solution based on the long-time experience that Seica has proven in the functional environment (including in-circuit knowledge) and includes the reliable connections made with a combination of Harting and ODU type of solution.
We carefully selected a second key element, the RF cables, based on certified vendors and components to avoid problems in the signal analysis and routing. For the same reason, cable length is identical for all DUTs and the path loss is accurately measured and calibrated using the NI VST functionalities.
The final part of the project to interface the DUTs is the design of the specific burn-in boards, which hosts them while in the climatic chambers. Not only should those boards survive the multiple temperature cycle, but the performance of the boards also should not degrade at all so the test results to all the DUTs will  remain homogeneous.
The burn-in board design included:

  • Definition of the DUT sockets (10 per board) in terms of easy insertion and optimal contacting (the final solution is a customer choice based on previous project experience)
  • All signal and power controlling (overcurrent condition) to avoid damaging the device
  • The heat dissipation after a temperature cycle (including avoiding condensation)
  • The optimal RF signal routing to guarantee identical path loss between the different positions

Temperature Chamber

To certify the automotive grade of a device, it is necessary to measure the functional performance in the extreme temperature condition: -40 °C and +85 °C. With the range so wide, the selection of the climatic chamber was also based on the requirement of a relevant temperature variation speed, always with the aim to reduce the total process time. This temperature ramp has been defined with a 15 °C/minute value, which can be considered a good compromise between temperature speed and DUT thermal stress. In fact, a bigger value could lead to device damages.
Among the different vendors evaluated, the solution is supplied by the company ATT.

Electric Test Hardware

The requirement for signal monitoring is accomplished using the Seica prorietary hardware. Seica has a full set of solutions for in-circuit and functional test, so that the implemented resources are used for the DUT controlling. In particular, all power supply, DUT-enabled signals, and current consumption control are realized with the ACL  measuring card and switching matrix (Seica proprietary hardware solution), which allows future expansion capabilities.

RF Testing

The most relevant part of the functional testing activity is related to the RF simulation and testing of the DUT wireless characteristics. Following the 3GPP standard, the initial requirement was to measure the DUT performance in all the different GSM and WCDMA bands for the basic functionalities: BER, trasmitted and received power, frequency analysis, and so on. For this reason, the selection of the RF instrument was a key factor.
We then selected the solution offered by the NI PXIe-5644R VST, because of its versatility and proven testing speed. The NI PXIe-5644R VST combines a vector signal generator and vector signal analyzer with FPGA-based real-time signal processing and control. It combines the fast measurement speed and small form factor of a production test box with flexibility. We can use the VST to test a variety of cellular and wireless standards with a range of 65 MHz to 6 GHz frequency range.
The requirement of testing 50 UUTs leads to the integration of five VSTs in the same PXI rack for the first time, thus guaranteeing the maximum system production capability. The final PXI rack was then realized as follows:

  • NI PXIe-1075 chassis (1x)
  • NI PXIe-5644R VST (5x)
  • NI PXIe-PCIe8381 MXI-Express interface(1x)

With the above configuration, we could test five UUTs simultaneously. Connecting then a proper 1-to-10 RF switcher, the solution was then finally completed.

Software

The overall solution is managed using the LV/TS functionalities. In fact, all used instruments (including Seica proprietary hardware and climatic chambers) are controlled via dedicated VIs. Among the others, the application is focusing the software architecture on the the multithread capability. This is a key native feature in the NI software that allowed the complete parallel management of all 50 DUTs using the TestStand batch model synchronization. Nevertheless, the basic functionalities of variant management and the resources sharing are extensively used in the test sequence development.
Considering that this is a production solution, we developed a specific customer interface to help the operator with easy indication on the test progress/result.

Results

The solution implemented respected the automotive requirement for device validation and reduced test time by making it possible to handle 50 UUTs with a full test parallel of five UUTs.

Author Information:
Paolo Bertoldo
SEICA

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