Meeting the Challenges of 5G RF Production Test Services
Based on the 4G mobile network’s unit volume metrics, the confidence levels on achieving the unit volumes in Figure 1 and total addressable market (TAM) with 5G standards definition appear to be high.
图1：Strong growth is predicted for 5G products.Source: IoT Business News。
There are plenty of similar plots showing such volumes from worldwide geographies developing products to 5G specifications. Higher 5G RF unit volumes are expected to result in higher unit volumes at test. Infrastructure developments and deployments are expected to precede the user equipment introductions. As shown in Figure 2, a typical cellphone application includes a base station with cellphone towers, each of which supports multiple users’ cellphones in the coverage area.
图2：Key ingredients of a two-way RF communication block diagram include an application processor (AP), baseband integrated circuit (IC), and radiofrequency integrated circuit (RFIC).
Since base stations have a coverage area to support multiple user equipment, the RF power requirement is higher relative to the user equipment. Base stations are powered by plug-in power, while the user equipment is designed to be power efficient because they are mobile and battery-powered. Since the magnitude of data downloaded on a typical cellphone is a couple of orders of magnitude higher than the data uploaded, the number of receive channels is typically larger than the number of transmit channels. Concepts like multiple-input, multiple-output (MIMO), and carrier aggregation (CA)  are employed at a protocol layer to increase the effective bandwidth. Receive channels employ diversity  to improve spatial performance. Even though these concepts are not the direct focus of this article, product architecture and design do have an impact on test requirements and test methodology. WiFi technology-based applications are typically within the home/office. Their maximum RF power is limited, yet the dynamic range is not, and their bandwidth is typically higher relative to cellphones.
The recent introduction of the 5G 3GPP standard , identifies carrier frequencies in two separate carrier frequency spectrums. As shown in Figure 3, FR1 carrier frequencies are in the 410 MHz to 7.125 GHz range and the FR2 carrier frequencies are in the 24 GHz to 52 GHz range. The allowable bandwidths exceed 100 MHz up to 2 GHz. The sub-carrier spacing is compacting and hence the need for tighter constraints for phase noise and gain flatness.
Figure 3:The 5G carrier frequencies are defined in the 3GPP specifications .
5G New Radio (NR) Modulation Schemes
There are two 5G NR signal modulation schemes – cyclic prefix orthogonal frequency division multiplexing (CP-OFDM) and discrete Fourier transform spread orthogonal frequency division multiplexing (DFT-S-OFDM)  (Figure 4).
Figure 4:A 256 quadrature amplitude modulation (256-QAM) 5G NR constellation plot captured on an Advantest V93K.
CP-OFDM用于下行链路（D / L），具有正交相移键控（QPSK），16-QAM，64-QAM和256-QAM。它具有高光谱效率，并与MIMO和4G LTE定义兼容。DFT-S-OFDM用于上行链路（U / L），具有π/ 2-二进制相移键控（BPSK），16-QAM，64-QAM和256-QAM。它具有更复杂的实现，并且与CP-OFDM相比具有更少灵活的资源分配，并且它不与MIMO结合使用。5G NR的五个子载波间距在15kHz至240kHz之间。图4显示了256 QAM图。
5G RF Products & RFIO
Modern direct and heterodyne converter architectures  have digital baseband I/O. The digital baseband feeds the data to a digital-to-analog converter (DAC) that creates the analog in-phase and quadrature (I/Q) waveforms. These waveforms, when mixed with a local oscillator (LO) signal, up-convert the data to produce the modulated intermediate frequency (IF) or RF signal that is transmitted to the receiver (Rx). The signal transmission occurs over a coaxial shielded cable or over the air. Prior to transmission, especially when it is over the air, the signal may require signal amplification. Also, the receiver may require the received signal to be amplified prior to supplying the signal for down-conversion. The down-converted signal is fed to an analog-to-digital converter (ADC) that converts the signal to digital baseband for processing by the application processor. Figure 5 shows these steps.
Figure 5:Simplified transmitter (Tx) and Rx RF chain blocks.
Integrated device manufacturer (IDM) customers bring a variety of RF products for assembly and test services. This includes, and is not limited to transceivers, low-noise amplifiers (LNA), power amplifiers (PA), digital step attenuators (DSA), filters, and mixers. Depending on the target application, the number of RF input and output channels may be different. Bandwidth, phase noise, intermodulation distortion (IMD), phase and amplitude resolution/accuracy, and other test requirements may vary as well.
测试设备(DUT)发射机水资源teristic specifications for production testing includes transmitting power and RF spectrum emissions (occupied bandwidth, out of band emissions, adjacent channel leakage ratio (ACLR), and IMD). DUTs Receiver characteristic specifications for production testing include receiving sensitivity, maximum input levels, adjacent channel selectivity, blocking, spurious response, and IMD .
Advantest, Teradyne, National Instruments, and Cohu have recently publicly released an upgrade path for their mature ATE offerings. Amkor utilizes ATE’s RF sub-systems hardware and software instrumentation infrastructures to test customer products in production factories.
ATE vendors typically architect a universal superset configuration of instrument resources for customer test application development. The number of arbitrary waveform generators (AWGs), digitizers (DGTs), LOs, filters, amplifiers, tone combiners, transmit signal splitters, receive signal switches and their wide bandwidth and dynamic range of operation present trade-offs that must be considered for every new 5G RF application for each customer. Phase noise at application-specific frequencies and amplitudes from the instrument design has a direct impact on the error vector magnitude (EVM) test. Phase noise of -110 dBc/Hz at an offset of 100 kHz and -10 dB or better is acceptable (typical) at 5G range of continuous wave (CW) frequencies. In typical broadband customer product applications, there is a need to switch frequencies and amplitudes. Switching times impact the overall test list execution times. Testers with the smallest switching times are the most efficient in production testing. Figure 6 shows an ATE block diagram.
Figure 6:A simplified ATE block diagram.
Custom tooling (probe cards and/or load boards) must be developed to help route tester resources to devices, pins, or bumps. For wafer probe services, probe card vendors deliver probe pin technologies. For 5G RF carrier frequencies that are above 50 GHz, the challenges include impedance matching and pin to pin and site to site signal isolation. For packaged parts, load board, socket, and socket-pin technology vendors deliver pin technologies. For 5G RF carrier frequencies, challenges are similar to the ones described for probe pins. Acceptable levels of insertion loss (S-parameter S21) at these frequencies are typically no more than -10 dB and return losses (S11) over the frequency range are typically better than -10 dB. Acceptable levels of pin-to-pin isolation for typical applications are better than -45 dB over the range of frequencies.
供应商保证RF性能和精度规范，以测试头信号传送界面。测试仪供应商开发和提供校准系统（硬件和软件）以在记录的规格中进行校准，验证和诊断性能。RF Instruments的精度规格对温度波动敏感。在大多数情况下，温度±5°C（或更紧密）的温度变化触发了仪器的自校准程序。电源，信号（数字，模拟/ rf）和时钟需要将校准平面从测试头移动到设备引脚。该路径包括探针卡或装载板上的迹线。我们具有采用去嵌入技术和使用环回或定制短路，打开，负载，通过（SOLT）结构的独特优势，以帮助将所需的RF信号精度提供给所测试的设备。在大多数情况下开发定制标准进行校准需要额外的努力，但是，随着内部包装设计，大道确实存在。在大多数情况下，Golden Loopback DUT技术足以实现所需的准确性。
Our Assembly and Test divisions work closely to enable 5G RF engineering development followed by production testing. The benefit is a complete assembly and test turnkey solution offered from the same factory location. 5G packages offering antenna in package and antenna on package (AiP/AoP) SIP were first produced by Amkor in July 2018 and announced in a public press release in 2019 .
With the recent advancements in assembly and packaging technologies, RFICs, like 5G transceivers and RF Front End (RFFE) devices, may have antennas embedded within the package. Similarly, System in Package (SiP) devices have integrated relevant components like processor, memory, RFIC peripherals, discrete components including power amplifiers, low noise amplifiers, phase arrays, and antenna structures within the IC package . The antenna forms the critical component of the front-end and requires tuning for the specific frequency band of operation. The 5G NR FR2 compliant customer products being designed today have their performance-tuned in specific operating bands, as defined in the 3GPP specification . Data-intensive applications may warrant packing multiple radios within the package and hence the need for multiple antennas tuned per frequency band of operation.
所有生产测试的所有RF器件的生产测试都是导电的。来自DUT的RF I / O与电缆上的阻抗控制路径电连接，并屏蔽印刷电路板（PCB）微迹线到测试仪的RF仪表。如上所述，所有ATE供应商开发5G RF测试溶液包括导电RF同轴互连。为了使具有嵌入式天线的封装的高批量生产测试，测试方法需要具有最小和受控信号损耗的互连，其可以发送或接收RF能量。天线传输理论，需要最小的发射器和接收器之间的空间分离。这种分离取决于载波频率。RF I / O通道的数量和多站点测试要求增加了生产测试复杂性。目前正在探索的测试选项包括补丁和喇叭天线，波束成形IC（BFICS），嵌入式定向耦合器和波导。这些解决方案都不是高批量制造友好，也不是随着天线的数量增加而可扩展的。这主要是由于测试器接口处理程序中的物理空间要求。
IDMs have been architecting design structures that allow loopback Design for Excellence (DfX) modes on transceivers to help simplify and make production test equipment requirements economical. While an antenna embedded within the package offers added miniaturization and overall integration, it does take away the flexibility of final performance tuning of the application for the new 5G NR operating band of carrier frequencies. The company continues to partner with suppliers and customers to solve the over-the-air (OTA) test challenges for production testing.
在高级别上,有两个主要生产test operating models. The first one has customers take complete control of test content, including consigning the selected 5G RF test equipment and using Amkor to execute production runs. The second test operating model has customer request engineering services to enable production testing. In this case, our test development teams work closely with customers and cater to the custom needs of each customer’s test development engineering (TDE) requirements. Examples of value-add TDE services include but are not limited to:
- Selecting the matching 5G enabled testers,
- Selecting the matching probers and/or handlers,
- Designing the matching 5G test tooling (probe cards, load boards) to enable appropriate tester resource allocation, especially for multi-site production testing,
- Product qualification,
- 产量优化、低屈服失效分析,一个d product design feedback. (Failure analysis may, for example, require X-ray or de-lamination to determine the root causes of fabrication and assembly packaging defects.),
- Custom back-end flows that enable efficient handling of finished goods as well.
The RF test development engineering group has significant experience developing test solutions and test content for previous and present generations of RF technologies and continues to build upon this expertise to solve 5G test challenges described here. The group is actively engaged in creating and proposing test solutions for base station and mobile 5G RF products in both FR1 and FR2 RF spectrum. These test solutions make use of the 3GPP standard-compliant ATE hardware and software test tools described above.
Internal production test processes have matured over the years and allow the implementation of design for manufacturing (DFM) rules to 5G RF production testing. Collecting, analyzing, and retaining manufacturing test results of 5G RF production tests is vital for incremental improvements to test methods, flows, and content. In specific cases, test engineers provide valuable feedback to the IC design and fabrication process engineers. Established statistical bin limits (SBL) for 5G RF test results for multisite across the test equipment fleet can help identify systemic equipment-related false failures and help with the elimination of such factors. This ensures optimal test equipment utilization and improves the overall production throughput.
A good portion of customers have products with critical time-to-market (TTM) goals and are sensitive to intellectual property (IP) contamination and security. Mature systems and processes are in place to handle all such customer concerns.
Amkor production test has been preparing to test the large number of 5G products that are expected in the coming years. This includes the 5G base station and infrastructure equipment that is expected to precede user equipment (mobile devices) growth.
The 5G RF production test business is substantial in size and growing rapidly. Our production test teams have been working closely with assembly packaging, ATE suppliers, and customers to ensure that holistic 5G RFproduction test servicesare made available to meet and exceed all test capability and capacity challenges.
- 3GPPTS 38.101-1 V16.1.0 (2019-09).
- Wide Band RF Architecture options – Peter Delos,Analog Devices。
- Amkor Device Packages
- Antenna In Package/Antenna On Package
- Amkor Antenna in Package –Article。
- Amkor Packages – Press Release 2019
- 菲涅耳远远地区orAntenna Theory
About the Author
Vineet Pancholi，SR Director Test技术，Amkor Technol狗万注册地址ogy，Inc。在坦佩，AZ。Vineet于2019年1月加入了Amkor，目前为5G RF和高速数字生产测试方法提供了测试技术开发。在加入Amkor之前，Vineet在Microchip技术进行了测试开发中。此前，他在英特尔在英特尔度过了19年的一系列测试角色，包括测试仪供应商管理，测试技术开发（烧坏，最终和系统级测试）和RF测试仪建筑师。Vineet持有半导体器件测试人员专利，并在亚利桑狗万滚球官网那州立大学赢得了硕士学位的物理和电气工程学位。