Advances in X-ray Inspection for Electronics, Part 1: Tubes

March 22, 2016

Origin Story

The “open” transmission X-ray tube was a major step forward for x-ray inspection. This technology itself is  almost 55 years old, but was adopted for X-ray inspection for electronics in 1982 when the German company Feinfocus introduced the first open Microfocus tube. Most  modern high technology electronics systems use Open Tubes.

Figure 1. Open transmission x-ray tube

Open Microfocus tubes (a stainless steel tube that can be opened anytime for cleaning and maintenance, and is evacuated prior to each use) are used in high-resolution applications of electronics assembly and packaging. Such tubes can provide a spatial resolution of less than 1μm, with geometrical magnifications of as much as several thousand times.

In the past, some companies were wary of such systems because the tube can be opened, which generated concerns about maintenance. These have been addressed by the leading manufacturers of open tubes:

  • Pre-vacuum pumps are maintenance free
  • Vacuum inside the tube is higher improving feature recognition
  • Filament lifetime has been extended up to four times longer than previous generations
  • Exchanging the filament is faster due to a pre-adjusted quick change unit that can be clicked in place

All in all, the benefits of the open tube technology outweigh the need for maintenance:

  1. No limited lifetime
  2. Best “as new” performance after exchange of the filament
  3. Higher target powers provide higher image intensity
  4. The option to customize inspection objectives to meet the needs of specific applications
    1. High Power Target
    2. High Resolution Power target
    3. Conical target

New Technologies for Smaller and Denser Electronic Components

The trend toward smaller and more densely populated electronics components, as well as the emergence of MEMS (micro-electro-mechanical systems) and MOEMS (micro-opto-electromechanical systems), led to the development of nanofocus X-ray technology, a differnt type of non-destructive X-ray inspection.

Nanofocus technology is defined as having a focal spot of less than 1 mm in diameter, which enables the level of detail and resolution needed for the inspection of low-density structures and ultra-small features common in today’s electronics components. The technology is an integration of tube and sophisticated software for controlling performance aspects such as short- and long-term stability, image contrast, brightness, and amount of radiation.

Figure 2: A Nanofocus X-ray

Another development was True X-ray Intensity (TXI) control. Unlike technologies that attempt to measure and control the input level of the high voltage and current to the X-ray tube, TXI control ensures controlled and stable output X-ray intensity. The result is a consistent and sharp X-ray image each time inspections are carried out. TXI ensures repeatability during automated analysis routines, a capability that is of particular interest in the production environment.

Figure 3: X-ray Image Quality without True X-ray Intensity (TXI) Control.

Due to the varying X-ray intensity output over the duration of the inspection process, the image contrast and brightness vary considerably over a 24-hour period.

Figure 4: X-ray Image Quality with True X-ray Intensity (TXI) Control.

Due to the constant long-term stability of the output X-ray intensity, the image contrast and brightness is 100% consistent, even over a long period of time.

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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