Revolution in the soldering processes
07 January 2007
EM&T looked at one application of X-ray 'nanotechnology' and went on to examine what the term actually means.
CEM Aspect Assembly, based in Stoke-on-Trent, has installed a Revolution x-ray inspection system manufactured by X-Tek. Aspect Managing Director, Dean Wilkin, commented: "Since we took delivery of the Revolution in the spring of this year we have noticed that its inspection capability has assisted the soldering process and the advanced x-ray has helped us to improve our reflow process. The Revolution is a significant part of Aspect's expansion plans and allows us to target the latest technology work, considerably more than previously."
Established 13 years ago Aspect now operates out of an impressive facility. One operational assembly line comprises of a Samsung CP40CV placement system, a DEK 265 GSX printer and Ersa 2/14 reflow oven. Preferred solder pastes are Indium SMQ92 and Qualitek 856 for lead-free work. A fully automatic selective soldering machine along with a new SMD line are scheduled to be installed early next year.
Dean Wilkin proudly told EM&T that Aspect rarely advertised and that the majority of work was word of mouth recommendation from satisfied customers, "Everything we do is customer focussed, we have never lost a customer because we operate a total "can-do" culture."
Recent work has been in Telecoms, Vehicle tracking, industrial controls and refrigeration for the local pottery industry. The decision to purchase the Revolution was "Very straightforward, once we looked at the specification of various units in the market, based on the need for flexibility, advanced technology and low cost of ownership we were convinced the X-Tek system was what we needed," commented Wilkin. He went on to say that the Revolution is "trouble-free, responsive and offers a greater degree of inspection than any other system. We also like the compact footprint of the Revolution to allow us more space to help our expansion plans." The company is expanding and currently sourcing additional equipment and assembly staff.
The Revolution is claimed to offer a greater degree of inspection than any comparable system with a viewing angle of up to 75o, just 15o to the plane of the board. This combination allows for maximum magnification (up to 6000x) at all angles over the entire 16" x 16" (410mm x 410mm) manipulator scan area, for 100% BGA, æBGA, multilayer board and PCB solder joint inspection, with quick analysis of BGA ball wetting, attachment, cracks and delaminations. The NanoTechTM source offers improved defect detection due to feature recognition in the submicron range.
The InspectX software from X-Tek has recently been upgraded to feature an advanced triple-mode programming interface incorporating off-line, teach repeat and high level library function for program building. Aspect has also been very satisfied with the level of support from X-Tek, "choosing a UK manufacturer with direct local support is highly important" comments Wilkin.
Nanotechnology in x-ray
Significant developments have recently been made to open type x-ray sources and x-ray imaging detectors. Such developments may provide an end-user with the ability to image features in the Nanometer range.
The term Nanotechnology is no longer new to most of us, in most part thanks to the media. We have probably all heard of a new Nanotechnology mechanism or medicine that will improve our lives. There are some examples of real life Nanotechnology such as Nano tubes or fibres and some examples of marketing usage such as IPOD Nano(tm) used to promote an object that is small. Nanotechnology today is the Hi-Tech of the 80's and 90's.
A description published on the National Nanotechnology Initiative (NNI) website defines Nanotechnology as the following: "Nanotechnology is the understanding and control of matter at dimensions of roughly 1 to 100 nanometers, where unique phenomena enable novel applications. Encompassing nanoscale science, engineering and technology, nanotechnology involves imaging, measuring, modelling, and manipulating matter at this length scale".
There are no specific claims that commercially available x-ray systems actually provide a resolving capability as described by the NNI. So how can an x-ray system be assessed to prove its capability?
Understanding terminology:
Most of the leading x-ray companies have begun to market some of their products with a "Nano moniker", such as NanoTech(tm). It is therefore important to understand the terminology associated or used by different x-ray system suppliers.
X-ray tube or x-ray source resolution defines the best resolution that the x-ray tube can provide. This in effect is describing the smallest focal spot or emission point that the x-ray tube can maintain. Terms such as feature recognition or defect detectability are describing the smallest defect or feature that the system can image. This is often described as one half of the source resolution. Nano resolution or nano-focus is therefore a factor of two coarser in resolution than Nano feature recognition or Nano defect detectability. Therefore a manufacturer that specifies a focal spot of 1uM (1000nM) would in effect be specifying a feature recognition or defect detectability of 0.5uM (500nM). For example NanoTech(tm) is the commercial name for an x-ray source from X-Tek that has a focal spot of less than 1000nM. Systems that contain the NanoTech(tm) x-ray source can achieve a feature recognition of 500nM or better.
X-ray tubes
Resolution is determined by the tube which emits the x-rays. There are two main types of x-ray tube; sealed x-ray tubes and open x-ray tubes. A sealed x-ray tube can be described as a "sealed for life" tube that after a period of time will fail and need to be replaced to continue usage of the x-ray system. An open type tube is typically a machined metal tube which is continuously pumped down to a high vacuum using a self contained vacuum system.
It is generally accepted that open tube technology is the only commercially available technology that is capable of producing very high resolution of 1uM (1000nM) or below. Contrary to some beliefs there are few "real-life" limitations to the open tube resolution capability, although some have quoted 3uM resolution as the practical limit. Those who have stated this as fact have overlooked what is currently available from other x-ray source manufacturers and the resolving capability of the Scanning Electron Microscope (SEM) and the significant similarities of the two technologies. For example, some open tubes use off the shelf SEM filaments as their source of electrons and SEM's make use of electromagnetic lenses to achieve a focused point of electrons in the 1-10nm range.
There are standardised test devices** that can be obtained to prove a system's capabilities and substantiate what a manufacturer means by Nano. To achieve very high resolution a user will require a very stable high resolution x-ray tube and a sensitive high contrast low noise x-ray imaging system. Amorphous silicon detectors are a desirable option but are not essential to imaging small features if the right combination of image intensifier and digital camera are provided. Buying a high end x-ray system requires research, hands on demonstration and understanding of the technology and terminology
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