Test & Meaurement


Outsourced SAM testing provides a cost-effective solution for expert quality testing and failure analysis


Ultrasonic-based Scanning Acoustic Microscopy (SAM) has long been the method of choice for quality testing and failure analysis of silicon ingots, wafers, integrated circuits, MEMS, and other electronic packages


layers to detect the thinnest of air gaps and delaminations down to a hundredth of a micron. Increasingly, however, manufacturers in the industrial, aerospace and medical sectors are turning to SAM technology to ensure good adhesion and mechanical integrity of devices by examining their internal structures, interfaces, and surfaces. Because potential defects can occur in different layers, more advanced equipment is required to inspect each simultaneously.


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ltrasound can locate voids and disbonds between material layers better than other non- destructive methods because sound waves can look inside the


Many are choosing to outsource SAM services rather than do this quality testing in- house. Outsourcing offers manufacturers key advantages, including capital cost savings on SAM systems, access to specialized expertise in image management and analysis, and the ability to diagnose and isolate material defects.


“Customers typically come to us for SAM testing to address one of three needs,” says Lisa Logan, SAM applications manager, at Sunnyvale, California-based PVA TePla America. The company provides contract services and sales for both PVA TePla Analytical and OKOS, both of which design and manufacture advanced Scanning Acoustic Microscopes. “As part of product R&D, an engineering team may be evaluating welds, bonds, or the effectiveness of an adhesive. When a product is in production, we may be asked to scan trays of parts for quality assurance testing. We may also use SAM testing to investigate why a particular part failed. “Often, when customers come to us, they don’t know what problem they have. If it is relatively easy to solve, investing the time and expense in bringing a SAM system in- house is unnecessary,” she adds.


Contracting SAM services can also be a better match for one-time projects. “The customer’s project may be finite,” Logan says. “They may only need to scan 10,000 parts, and then the project is done. It is much more cost-effective to outsource the work in this case.


“Convenience is a big


factor, too,” Logan adds. “It is just simpler to give parts to a trusted partner to evaluate. Our customers often give us a part to analyse when they can’t isolate the issue and ask us to use our expertise to determine the problem for them.”


Problem solving Newark, California-based California Brazing uses SAM testing to validate and verify processes required by its customers and comply with American Welding Society specifications for brazing of materials such as aluminium, stainless steel and copper. Metals are joined together in the brazing process by melting and flowing a filler material into a joint without melting the workpieces. “Brazing specifications define accepted quality requirements for analysing internal discontinuities using non-destructive testing,” said Jeff Ager, general manager of California Brazing. “In our experience, ultrasound [SAM] gives us the highest resolution images, and they are also easier to interpret than with x- ray technology. “We use the SAM technology to validate and verify that our processes are always in spec. This testing happens initially on a new build of a part, particularly for our aerospace and defence customers, because of their unique requirements. These parts can be all sizes - anywhere from 1 inch by 1 inch to as large as 30 by 30 inches.” He adds: “When we have potential brazing failures to investigate, we first go to Lisa and her team at PVA TePla for testing to pinpoint exactly where it occurred. If necessary, we follow-up with destructive testing too, but


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only after we’ve identified the precise location of the failure using SAM.”


Superior non-destructive testing SAM uses the interaction of acoustic waves with the elastic properties of a specimen to image the interior of an opaque material. A transducer, the heart of a SAM system, directs focused sound at a small point on a target object. The sound hitting the object is either scattered, absorbed, reflected (scattered at 180 degrees), or transmitted (scattered at 0 degrees).


By detecting the direction of scattered pulses and the “time of flight”, the presence of a boundary or object can be determined as well as its distance. To produce an image using SAM, samples are scanned point by point and line by line. Scanning modes range from single-layer views to tray scans and cross-sections. Multi-layer scans can include up to 50 independent layers. The resolution of the microscopic image depends on the acoustic frequency, material properties, and aperture of the transducer. Transducers perform such a critical role that manufacturers like PVA TePla design and manufacture an extensive range of different transducers used in their contracted testing services.


www.pvateplaamerica.com/service/ sam-analytical/


Components in Electronics October 2021 39


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