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MEMS Failure Analysis

Overview

Far outside the realm of typical integrated circuits, there exists a myriad of devices with astonishing properties that are nonetheless fabricated in silicon and other semiconducting materials. Microscopic membranes deflect and deform under fluctuations in atmospheric pressure, creating an electrical signal that can be digitized as sound; an extensive array of silicon springs and plates shift under the influence of external forces, serving as an accelerometer; an infinitesimally small array of metallic mirrors actuated by electrostatic forces can serve as one of the primary components in a theater projector or television. Though these devices have widely divergent purposes, they all have one thing in common: all are Micro-Electro-Mechanical systems (MEMS), and all pose a significant challenge for a failure analyst.

Fundamentals

In addition to the potential issues faced by any integrated circuit - electrical and mechanical stresses, contaminants, and so on - failure analysis of a MEMS is complicated by the fact that these devices are comprised of microscopic moving elements, adding an entirely new dimension to the analysis. For example, a device may fail as a result of “stiction” - an element failing to move properly, perhaps as a result of an incomplete release etch, a foreign particle, electrostatic attraction, or other mechanisms - or from mechanical fatigue, the natural wear and tear of constant motion resulting in a drift in performance over a product’s lifetime. Further complicating matters, many MEMS devices are securely sealed, as a way to protect their fragile elements; to successfully disassemble such a product, an analyst must be familiar with a wide variety of chemical and mechanical preparation methods, always keeping in mind the delicate nature of the sample. Many of an analyst’s tools can be adapted for MEMS work: infrared microscopy can often be used to inspect the MEMS elements for damage or anomalous material without breaking the device seal, as device lids are often made of silicon which is somewhat transparent to short wave infrared light; the focused ion beam can be used to cut windows in the lid of a MEMS to perform a high magnification inspection; and so on.

Sample types

IAL has experience with a wide range of MEMS devices, including extensive work with accelerometers, microphones, and pressure sensors, among others. As long as we can develop a method for replicating a failure on our test bench, chances are good that we can delve into the microscopic beams and gears of your MEMS and come out with the root cause of failure.

Applications

  • Analyzing “dead pixels” on a mirror-based imager array
  • Troubleshooting bad outputs from a silicon accelerometer

Discrete Failure Analysis

Overview

Though perhaps not as glamorous as highly integrated microprocessors or specialized ASICs, discrete components - thin-film resistors, chip capacitors, individual transistors, and so on - are still a vital part of modern electronics. A failing bipolar transistor or shorted capacitor can be just as catastrophic as a malfunctioning IC; fortunately, the tools and techniques of IC failure analysis are equally applicable to FA of discrete components.

Fundamentals

Discrete component failure analysis follows much the same path as an integrated circuit FA; indeed, analysis of a bipolar transistor or power MOSFET uses exactly the same tools, techniques, and procedures as more complex IC FA projects. Analysis of discrete components begins with non-destructive testing, where tools like x-ray imaging and acoustic microscopy are used to examine the device under test for damage or anomalous processing - for example, cracking in a ceramic capacitor, or irregularities in the laser trim on a precision metal film resistor. Next comes fault verification, where an analyst confirms that the reported problem - for example, a short circuit - is still present. After confirming the failure, the analyst applies a variety of different tools to preform fault isolation, identifying the most likely location of the defect. Depending on the type of device and the defect in question, different tools might be used. For example, thermal imaging is commonly used on leaky capacitors or thin film resistors with anomalous values (either too high or too low of a resistance value may be the result of a defect that will emit heat when biased), while photoemission microscopy (PEM) often reveals defects on semiconductor-based discrete devices. Finally, destructive analysis and documentation wraps everything up neatly: protective coatings or passivation layers are stripped away, the defect is photographed in all its glory, and the root cause of the failure is identified.

Sample types

From thermistors to capacitors, LEDs to FETs, and all points between, IAL’s failure analysis expertise extends to all varieties of discrete components. Our suite of test equipment and preparation tools is adaptable across any range of different samples; regardless of your product, be confident that IAL has applicable experience and can successfully identify the source of your troubles.

Applications

  • Determining root cause of insufficient light output of LEDs
  • Analyzing out-of-spec passives to determine lot disposition
  • Post-mortem analysis of power semiconductor devices - MOSFETs, IGBTs, and others

Destructive Physical Analysis

Overview

Ensuring the quality of your product and its constitutent parts - discrete components, circuit boards, ICs, and others - is vital to ensuring reliability. One way to develop a deeper understanding of a device’s construction and thereby determine possible ways to improve it - or, perhaps, to determine whether it has been built to the necessary specification - is to perform a Destructive Physical Analysis, or DPA.

Fundamentals

A Destructive Physical Analysis is a rigorous series of tests that are designed to generate a comprehensive set of qualitative and quantitative characteristics of a given device type. Depending on the type of sample, the battery of tests may include physical stress tests (e.g. wire pull, die shear, Young’s modulus, etc.), device teardown (e.g. decapsulation, cross-section, etc.), high resolution imaging (either optically or with the electron microscope), and other methods of inspection. Integrated circuits, for example, might be decapsulated and delayered to gather measurements on metal thinning and step coverage; ceramic capacitors, on the other hand, might be cross-sectioned to measure dielectric thicknesses. Generally, the quantitative data generated will be compared to specifications or prints to determine compliance to the design or other spec sheet; variation of a process outside specified parameters may have negative implications for device reliability and functionality.

Sample types

Practically any electronic device or assembly can be subjected to destructive physical analysis in order to characterize a process or product lot. Whether your product is a simple discrete like a resistor or a complex, densely-routed circuit board, a DPA can produce valuable information. Depending on your needs, IAL can either work to a standard procedure (as in a MIL-STD DPA) or develop a custom testing schedule based on a set of desired data provided at the start of the project.

Applications

  • Comparing the quality of product ordered from multiple subcontractors
  • Verifying that a mature product remains within specifications
  • Qualifying a new product, subcontractor, process, etc.

PCB Quality Auditing

Overview

Looking to qualify a new process, or check up on one that has been turning out questionable product? Concerned that a subcontractor may have made a change in their materials, reflow process, or any of a countless number of variables that might spell disaster for your product reliability? A PCB quality audit can help uncover these sorts of issues and bring you peace of mind - or, in the worst case, leverage with which to implement corrective action.

Fundamentals

A PCB quality audit can be limited only to non-destructive analysis. An optical inspection may reveal process indicators, as those specified by IPC-A-600 and IPC-A-610, which may be sufficient to determine whether a product has been produced to acceptable standards. Such an inspection can identify a wide range of defects and anomalies that could potentially be reliability pitfalls, such as incomplete solder mask coverage or via and thru-hole misregistration. This inspection can be augmented by elemental analysis techniques like energy dispersive spectroscopy (EDS) or x-ray fluorescence (XRF) to characterize whether a change in materials has been made (for example, if a lead-free solder has been substituted for leaded solder). X-ray imaging can also identify issues internal to the board - misaligned blind vias, cracked traces, and so on.

Should non-destructive testing be insufficient, destructive physical analysis provides additional data for consideration. A cross-section can reveal information on plating thicknesses, the integrity of the board lamination, and more; other techniques like dye penetrant testing can reveal information about solder integrity.

Sample types

PCBs or PCAs of any size, unpopulated or populated, can be inspected for quality control. Some tests are only applicable to certain types of devices; IAL will advise you of our recommended methodology at the time of quotation.

Applications

  • Continuous monitoring of an established process
  • Qualification of a new device or process
  • Comparative analysis of product produced by multiple subcontractors

Services at Insight Analytical Labs

At Insight Analytical Labs, our goal is to turn your failing electronics into sources of learning and continuous improvement. Whether you’re faced with a one-of-a-kind defect or a systemic reliability issue, IAL will dive in headfirst to determine the root cause of failure and provide you with actionable data to effectively resolve your problem. We provide more than just a mix-and-match list of tests and techniques; we pride ourselves in providing world class failure analysis by telling the whole story of a defect, going beyond the results of any individual test to provide a comprehensive view of the root cause of failure at a highly detailed level.

Of course, all the experience gained from exploring the minutiae of the microelectronics world can be applied elsewhere, as well, and IAL offers services that complement our core failure analysis focus. Our extensive experience with failure analysis provides insight into the ways that devices might fail, which we apply to a wide variety of preventative inspection and screening services to preemptively identify quality issues before they impact your end users. We use industry accepted best practices and procedures, to include MIL-STD and IPC specifications, to generate a complete picture of the quality of a submitted process.

In addition, our extensive experience with the composition of microelectronics devices gives a unique vantage from which to analyze their construction. IAL offers teardown and reverse engineering services supporting clients interested in protecting their intellectual property, recreating obsolete parts, or other competitive analysis endeavors. To support these services, IAL works with a network of circuit extractors and subject matter experts that can be made available to further strengthen your analysis.

One of our greatest strengths at IAL is our adaptability; if you don’t see a specific test you’re interested in, or are faced with a problem whose solution doesn’t seem to be published in our list of services, please feel free to contact us. We are constantly working to expand our list of tools and techniques, and a conversation with one of our engineers may give you exactly the information you need in order to entrust us with your request.