Introduction

Semiconductors are the essential component fueling the growth of industries such as automotive, renewable energy, communications, information technology, defense, and consumer electronics. The rise of their importance began in the late 1950s when Jack Kirby and Robert Noyce invented integrated circuits (IC), which built electronic components and circuits on a common semiconductor base. ICs quickly replaced vacuum tube-based electronic equipment because they were more power efficient, saved space, and more reliable.

Over the past six decades, ICs have advanced significantly and are used in many industries as they are critical components in numerous products and processes. ICs can be multiple discrete components packaged together, such as digital logic circuits, microcontrollers, microprocessors, digital memory storage, analog circuits and amplifiers, radio frequency (RF) / microwave (MW) analog components and circuits, and integrated power circuits. This article focuses on using waveform generators to test various types of ICs.

IC design and test process flow

IC design and testing are complex processes involving precision and expertise to meet required specifications. Engineers engage in iterations, optimizations, and validations to ensure the final IC achieves the desired performance and reliability. In Figure 1, the process begins with software modeling and simulation based on IC specifications. Subsequently, the design is etched onto a photomask and transferred to a silicon wafer during the wafer foundry stage. After wafer testing, the ICs are packaged and undergo functional testing to ensure they function correctly.

Figure 1 The IC design and test process flow including IC design and simulation, wafer processing, parametric testing, lead frame/wire bonding, package testing, and ending with functional test. Source: Keysight

Wafer-level verification testing

During the design or front-end IC manufacturing stage, the ICs tend to be tested at the wafer level. Testing ICs at the upstream wafer-level process can be challenging, especially when using wafer-probing tools. However, it is necessary because the packaging process is costly and complex. Figure 2 shows wafer probing and testing in progress.

Figure 2 Wafer-level IC probing and testing where basic functional verifications can be performed such as catastrophic shorting, leakage, power supply, and general input / output conditions. Source: Keysight

At the wafer level, you can perform tests for basic function verifications such as catastrophic shorting, leakage, power supply, and general input / output conditions. Signal sources can come from programmable DC power supplies, source and measure units, and general-purpose waveform generators.

During the IC design stage, test engineers can perform noise, DC parametric, and S-parameter characterization work at wafer-level probing tests. This process drastically reduces the time to the first measurement and provides accurate and repeatable device and component characterization.

Package testing

After the ICs are placed on lead frames, wire-bonded to their respective leads and encapsulated, they are in their final physical form. Tests are conducted to ensure that the packaged ICs meet packaging expectations, such as no short circuits, open or weak connections, proper electrical isolation between internal circuits, and more.

Waveform generators provide clean signals and controlled frequency and amplitude noise levels for signal integrity and low-frequency noise tests. Figure 3 shows how waveform generators can provide controlled simulated signals into ICs for an oscilloscope to test signal integrity.

Figure 3 The eye diagram of an IC signal integrity test where waveform generators can provide clean signals and controlled frequency and amplitude noise levels. Source: Keysight

Post-packaging functional testing

Post-packaging functional testing, also known as end-of-line testing, is often complex and tedious. This process is the last testing stage, during which the ICs are extensively tested to ensure they meet specified performance and quality standards before they are shipped to customers.

Waveform generators generate complex variable patterns, real-world signals, and even extreme use-case signals to ensure that all ICs shipped meet the required performance specifications and functionality. Modern waveform generators are versatile in generating all kinds of signals, such as digital, analog, complex modulated, low to high frequency, burst, synchronized, and arbitrary waveform signals for all IC applications.

Preferred waveform generator characteristics

Waveform generators on the market have a wide range of specifications. Testing and characterizing ICs requires stringent specifications. IC design engineers need a source that produces a clean, low-distortion, stable, and reliable signal. The signal generated should not vary regardless of frequency or sample rate. Furthermore, certain waveform generator specifications for IC testing are important.

A clean and stable signal source

A clean signal source provides true and unadulterated signals without noise or interference from other foreign signals. The signals are measurable by the purity of a signal void of harmonic distortions and jitter. A clean and stable signal is necessary when testing ICs because engineers want:

• The best product specification: ICs require precise and accurate signals to characterize and validate their functions and performances. The more errors introduced from the signal source, the more degraded the product specification becomes due to measurement uncertainties.
• To avoid false test results: A stable signal source creates a consistent test process. Consequently, the test results can accurately characterize the behavior of the ICs. If the signal source is unstable, problems such as false test results affect downstream tests. Shipping the incorrectly characterized product to customers is the worst-case scenario.
• Repeatable and reliable performance: Clean signals will also provide optimized repeatability test conditions to gauge the true performance of ICs. They will not have unwanted harmonics and noise, rendering test results inaccurate. Furthermore, a test can be made more reliable by replacing a real-world signal with a signal created by a waveform generator.

Noise additive

Besides having clean signals to characterize the performance of IC devices, adding noise to test signals simulates real-world noisy transmission, crosstalk, and EMI. Instead of getting the best product performance specifications, adding noise stresses the IC under test and determines the robustness of the products.

Suitable waveform generators can produce variable noise bandwidth to control the frequency content of the test signal. Figure 4 illustrates that this approach enables controlled stress testing of the ICs under test.

Figure 4 Adding controlled noise into a test signal (top image) results in a noisy ECG signal (bottom image). Source: Keysight

Mixed signals

Many applications require mixed-signal ICs, which are essentially ICs with digital and analog circuits built-in and packaged together. Applications that use mixed-signal ICs include analog-to-digital converters, digital-to-analog converters, power management circuits, microcontroller circuits, and physical parameter sensing measurements such as temperature, humidity, and pressure. Waveform generators can simulate both digital and analog signals to test mixed-signal ICs.

Arbitrary waveform signals created by software

Modern waveform generators can generate arbitrary waveforms to simulate real IC test applications. These generators usually come with software applications that create arbitrary waveforms.

Importing simulated or real signals

The most direct method for importing signals is digitizing a real-world test signal using an oscilloscope, saving it in a format that is readable with your software application, digitally manipulating or conditioning the test signal, and then transferring it to a waveform generator to regenerate the signal.

Another common method is to use waveform builder software to generate custom arbitrary waveforms and combining them into the desired simulated test signal. Some IC design engineers may want to generate the waveforms directly in MATLAB or Python programming and transfer those waveforms to the waveform generators. For example, Figure 5 shows how MATLAB understands the plotting of a complex waveform. The waveform is a simulation of a section of an electrocardiograph (ECG) heart signal showing part of the PQRST points. In fact, this waveform shows only the RST points for the purpose of creating a T-wave rejection test waveform. MATLAB can model waveforms using math equations and translate all these points into a complex ECG test signal.

Figure 5 Using math equations, assembling into a simulated cardio ECG test signal in MATLAB. Source: Keysight

Figure 6 shows the output of a cardio ECG test signal generated from MATLAB. The MATLAB software application offers options to send waveform points as a binary block to an arbitrary waveform function generator. The reason for sending a waveform as binary data rather than ASCII data is simple—the binary data is much smaller than the equivalent ASCII data.

Figure 6 MATLAB can transfer the above-simulated cardio ECG test signal into a waveform generator. Source: Keysight

These methods enable engineers to create the desired test signals for cataloging and storing in digital waveform libraries. This approach enables consistent and organized testing for many types of IC test applications.

Creating waveforms in playlist test sequences

Most modern waveform generators can play various segments of waveforms in sequence. Design engineers can build a playlist of test sequences with waveforms of incremental changes or good or bad signals to test the IC responses. Depending on your waveform generator’s capabilities, you can combine individual arbitrary waveform segments into user-defined lists or sequences to form longer, more complex waveforms.

The need for waveform generators

Waveform generators are versatile test instruments essential throughout IC design and manufacturing processes. They can generate all kinds of signals, such as digital, analog, complex modulated, low to high frequency, burst, synchronized, and arbitrary waveform signals, for many types of IC applications.

Designers can take advantage of the powerful capabilities of waveform generators to create clean and stable signals as well as to control IC stress testing by adding incremental noise content to the test signals. Waveform generators can also generate all kinds of arbitrary waveforms to simulate real IC test applications, this is critical as ICs are getting smaller and integrate more complex functions.

Bernard Ang has been with Keysight Technologies (previously Hewlett Packard and Agilent Technologies) for more than 30 years. Bernard held roles in manufacturing test engineering, product engineering, product line management, product development management, product support management, and product marketing. He is currently a product marketer focusing on data acquisition systems, digital multimeters, and education product solutions. Bernard received his Bachelor of Electrical Engineering from Southern Illinois University, Carbondale, Illinois. 

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