x-ray inspection and applications

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Introduction to X-Ray Inspection


10 Basic Principles of X-Ray Inspection

Safety Operating X-Ray Cabinet SystemsSize and Weight of X-Ray Inspection SystemsHow do we image the X-rays?MagnificationResolutionField of ViewX-Ray Inspection AreaPower of X-Ray TubeX-Ray SensorSample Positioning


Safety Operating X-Ray Cabinet Systems

The Food and Drug Administration regulates all cabinet x-ray systems:

Redundant interlocks

Warning lights Maximum radiation allowed.

FDA 21 CFR 1020.40(c)(1)(i) specifies “radiation emitted from the cabinet x-ray system shall not exceed an exposure of 0.5 mR/h at 5cm from the external surface” Operators can safely work on the x-ray inspection system in a full time capacity with no danger to their health.


Size and Weight of X-Ray Inspection Systems

• The size of the x-ray cabinet is a direct function to the maximum sample size that can be inspected and the amount of manipulation that can be achieved.

• The weight of the x-ray cabinet is also a function of the size of the cabinet. Larger cabinets often weight more than smaller cabinets.

• Another important parameter that determines the weight of a cabinet is the maximum power of the x-ray source. More powerful x-ray sources need more shielding material – lead and steel – to keep radiation inside the cabinet. As a result, systems with very powerful x-ray sources tend to be very heavy.


Introduction to X-rays

Why use microfocus X-ray sources?Microfocus means that the size of the X-ray source is only a few microns across

(1 micron or 1µm is 1/1000th of one millimeter).

Using a small X-ray source means that we can magnify the X-ray images on to the detector and thus see more detail.

Microfocus source(~33µm to 5µm)

Typical medicalX-ray source(~1mm)

Large sharp imageLarge blurred image

Object


How do we image the X-rays?

When X-rays hit certain materials, they cause them to fluoresce. In this process, the

energy of the X-ray is absorbed and re-emitted as visible light. Usually this light is very

faint and needs to be amplified, else very sensitive detectors need to be used.

Flat Panel Detector standard in all TruView X-Ray inspection systems. Photo by Teledyne Technologies.

Image intensifier available for TruView X-Ray inspection systems. Photo by Hamamatsu Corporation


How do we get a magnified image?

10

Just like light, X-rays travel in straight lines.Unlike light, we cannot use a lens, so we use geometric magnification.The magnification is increased by moving the sample closer to the X-ray source (and vice versa).


Resolution

The X-ray source size can be measured with a resolution test pattern, as shown here

Electron microscopy image of test pattern

5µm

1µm

Outer bar width = 5 mmInner bar width = 1 mm

Thickness 1 mm gold


Field of View

The electron beam generated by the cathode is rapidly accelerated against the anode. Upon colliding with the anode, a cone-shaped beam of x-rays is generatedAs the x-ray beam moves farther from the anode target, the diameter of the beam increases proportionally. The angle of the x-ray cone beam, α, is determined by the angle of the anode targetDiameter of the x-ray beam increases as it moves away from the sourceMagnification is a function of the distances between source, sample, and detector


X-Ray Inspection Area

Inspection area is the total size of the x-ray chamber. In other words, the size of the largest object that can be placed inside the x-ray machine. Viewable area, on the other hand, accounts for the maximum area of the object that can be seen in the x-ray machine.

TruView Prime

TruView Elite


Power of the x-ray tube

The power of the x-ray tube is composed of two parameters: voltage (rated in kilovolts, or kV) and current (rated in milliamperes, or mA). The voltage determines the maximum energy of the x-ray photon produced by the source. Higher energies have more penetrating power, so x-ray sources with higher kV can penetrate denser materials. The proper determination of how many kV you need for your application is critical: price goes up fast with kVs! The current of the source is a measure of how many x-ray photons are being produced in a certain amount of time. As a result, increasing the current of the x-ray source produces a brighter image – at the same penetration level.


Sample positioning

Modern x-ray inspection systems have migrated to semi or fully automated manipulation of samples inside the cabinet.With these systems the user can safely manipulate the sample inside the machine without a direct contact with the sample. Multiple degrees of freedom are available to allow the user to image the sample.


Applications include…

• Semiconductor and passive electronics component Inspection

• Surface mount and through hole PCB solder joint Inspection

• Ball Grid Array (BGA) inspection

• IC Wire bond and Die Attach inspection

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Identification of defects in soldered components – excess voiding or excess solder

PCB – Sample Image 1

At a medium magnification it is useful to look for PCB level quality. This PCB shows good via to pad registration. It is a useful image to look for die attach level quality issues.


Higher magnification to expose the large BGA part under the heavy heat sink. Even with the heavy heat sink, the high definition flat panel camera show details of each ball to assess potential shorts and opens under the BGA.


This image shows some excess voiding on the pads of this surface mount component. This is a possible indication of manufacturing issues.

PCB(– Sample(Image(4

Higher magnification shows inner details of several components, allowing us to verify any processing potential problems like wrong temperature cycles and defective stencils.

A high magnification image of surface mount devices allow us to inspect the quality of solders and other voiding.

It would be possible to see lifted pins, shorts, opens, and misplaced parts. The detail of the imaging system allows us to see the details inside the parts, including the wire bonds inside this SMT component.


Inspection of wirebonds

TruView’s resolution allows for inspection

of metal layers on the ASIC

Inspection of PCBs with EMI shields, when optical is no longer an option – TV, cell phones, RF boxes

FAIL: Short on SMD part

Detail

Quality Control

Defect inspection of BGA and QFN

Damaged balls during assembly

Close up of wire bonds

Quality control of medical temperature sensors

FAIL: Electrodes are too close, which may lead to a catastrophic fail during use in a critical medical monitoring application

Inspection of microwire connections inside components

x-ray inspection and applications

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