While absorption contrast X-ray imaging is a very powerful inspection technique, it does not exploit all of the information present within the X-ray beam transmitted through a sample. A new technology has been recently developed that, instead of simply measuring the total absorption of the X-ray beam, also enables changes in the beam energy to be resolved. This allows the effects of thickness and density to be decoupled, enabling both to be determined. This quantitative composition and thickness information can then be used to provide new levels of insight in PCB and semiconductor inspection, potentially leading the way to a new generation of X-ray inspection technology.
It is quite straightforward to accommodate this technology in an existing 2D X-ray (2DX) inspection system. Advanced software algorithms need to be incorporated and an intuitive user interface is provided.
We present an overview of this new technology and give examples of other industries where this technology is being adopted, as well as example applications for the PCB and semiconductor industries.
INTRODUCTION
The need to inspect electronic components and assemblies non-destructively is the main driver behind the development and advancement of the X-ray inspection technology for the electronics industry. In many cases, X-Ray inspection (2D and 3D) provides the only non-destructive techniques to inspect optically hidden components and solder joints such as BGA, POP, QFN, flip chips, through holes, TSVs, microbumps, copper pillars, etc.
All X-ray inspection systems (2D and 3D) rely on absorption contrast imaging, where the contrast is generated by the stopping power of the sample. As such, higher density and/or thicker regions of a sample produce darker regions in a grey-scale image. X-ray inspection systems use this method to image features such as wire bonds and ball grid arrays down to a feature recognition size of 100 nm (0.1 μm).
While contrast imaging is a very powerful and widely used technique, there is significantly more information present within the X-ray beam, which, until now, has not been exploited in electronics inspection. Instead of simply measuring the total absorption of the X-ray beam, a physical structure known as a multi absorption plate (MAP) can be placed in the beam path. This, coupled with machine learning algorithms, enables material type and thickness information to be acquired alongside the standard grey-scale image.
Quantitative composition and thickness information can then be used to provide more detailed diagnostics in PCB and semiconductor inspection. Applications include, but are not limited to, analysis of solder types, track thickness measurements, and conformance to quality standards.
An overview of the theory behind the operation of the MAP is given below, as well as some simple examples showing the benefits of using the MAP technology to add additional capabilities to 2D X-Ray inspection. MAP technology also has applications in the security, medical and food processing industries. Nordson Dage has partnered with IBEX to bring the benefits of this technology to the electronics inspection, including inspection of PCBs and semiconductor devices. A range of examples is presented and the authors aim to start active discussions that would generate new needs and ideas for use of the technology for non-destructive inspection of electronics systems and components.
