Advances in X-ray Inspection for Electronics, Part 2: Which Tube?

June 09, 2016

The Tube Is The Heart of the System

Within the realm of X-ray inspection for electronics there are a wide range of applications, so a single type of X-ray tube is not a "one-size-fits-all" solution. To address the demands of industries such as electronics manufacturing, better X-ray system manufacturers offer various non-destructive test solutions based on the power, kV and feature recognition capabilities electronics producers need. Having a choice of tubes and features allow the makers of chips, boards, circuits and compontents to obtain the images they need to resolve their production issues quickly and accurately.

Multifocus vs. Nanofocus

A need exists for both microfocus and nanofocus tubes for real-time X-ray inspection. This is of particular interest to contract manufacturers for whom inspection requirements can vary. It's also important for electronics producers who have microfocus applications that demand high X-ray output as well as nanofocus applications that demand high magnification and high resolution. Multifocus X-ray tubes are ideal for this. They incorporate a high-power mode (>15W target power) for dense structures that require high intensities for inspection. For example, one of the challenging applications is the insulated-gate bipolar transistor (IGBT). Without high target power it becomes hard to get meaningful information for analysis.

Figure 1. X-ray Image of IGBT, 130 kV, 61µA

High-power mode can deliver added value, too, if an inspection of the end product is required--especially if the ROI (region of interest) is hidden in the high density case. For an example of this, Figure 2 shows an image taken with a Multifocus tube in Microfocus mode. Some information is missing due to the lack of intensity. Figure 3 shows the same ROI but the image is taken with High-Power Mode.

Figure2. X-ray Image of IC inside of end product, Microfocus mode, 160kV, 55 µA

Figure3. X-ray Image of IC inside of end product, High Power mode, 160kV, 54 µA

Typical microfocus X-ray devices don’t necessarily meet the unique inspection challenges posed by complex electronic devices, such as MEMS (micro-electromechanical systems) and MOEMS (micro-opto-electromechanical systems). The emergence of MEMS and MOEMS was a driving force behind the development of nanofocus X-ray technology, as we mentioned in a previous post. With a focal spot of less than 1 µm in diameter, nanofocus X-ray inspection systems can provide the detail and resolution required to inspect ultra-small components.

Besides inspections of MEMS and MOEMS devices, nanofocus systems are used to examine sub-micron components, circuitry, and assemblies in wafer-level packaging. In these applications, nanofocus tube design and system technology is the only inspection option that provides the resolution and sharpness required to detect defects in solder bumps and interconnects.

Figure 4. X-ray Image of a solder crack in 50μm Cu pillar, Sample size: 300mm wafer

Nanofocus technology is also used to inspect packages with non-filled die attach material, including the thermal  adhesive that holds microchips in place. A nanofocus tube is needed to detect the slight difference in contrast attributable to the adhesive. In addition, nanofocus tubes can be used to check the silver particle loading in electrically conductive adhesives. This ensures that the material is homogeneous and filled with sufficient particles to achieve the desired conductivity.

Nanofocus systems can also check:

  • Package delamination that can go “unseen” by microfocus X-ray systems;
  • Sub-micron cracks and flaws in silicon packaging and fine bonding wires (under 25 µm);
  • Orientation of the fibers in polymer materials

Think you know what today's X-ray inspection for electronics can do? Read the full white paper on this topic, a free PDF download:

"Recent Advances in X-ray Inspection for Electronics Manufacturing"

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