FEATURE THERMAL IMAGING
DIMENSIONAL MEASUREMENT of microelectronic circuits
Chris Jones of Micro-Epsilon UK discusses the role of thermal imaging cameras and confocal displacement sensors in the inspection of electronic devices, circuit boards and MEMS
M
anufacturers of electronic components and printed circuit
boards (PCBs) are increasingly turning to non-contact temperature measurement systems to capture, analyse and optimise the thermal behaviour of electronic components and fully assembled PCBs. By using thermal imaging cameras in
R&D, product development and high volume production hot spots and defects can be detected quickly and reliably without influencing the target object. Detailed, real time analysis of the thermal behaviour of integrated circuits can be carried out using infrared thermal imaging cameras. These are able to capture and store thermal video and images with high optical resolution at high frame rates. Camera detectors provide excellent thermal sensitivities (typically 80mK-40mK) enabling the camera to detect extremely small temperature differences. Micro-Epsilon’s latest thermal imaging
camera, the thermoIMAGER TIM 640 is able to record radiometric video images at an optical resolution of 640x480 pixels and is the smallest VGA resolution infrared camera available today.
DETECTING SMALL TEMPERATURE DIFFERENCES With dimensions of 45x56x90mm and weighing just 320g compared to other similar-size cameras the TIM 640 is the only camera that enables the recording of radiometric video images at 32Hz and a VGA resolution of 640x480 pixels. With a thermal sensitivity of 75mK this
camera can detect very small temperature differences. At ambient temperatures of 0-50°C the camera can measure object temperatures ranging from -20°C to +900°C.
For easy process integration the camera
is supplied with the TIM Connect software as standard. This enables users to monitor and document measurements and to edit infrared video images. The software provides quick and easy set up together with a range of software tools that enable the cameras to be used in R&D tasks as well as process control. A USB 2.0 interface allows video recording at 32Hz. This is highly
16 NOVEMBER 2014 | FACTORY EQUIPMENT
beneficial for short term thermal measurement activities which need to be analysed in slow motion playback. Individual snapshots can be taken from these recordings. Measurement points are freely selectable and can be analysed via user-defined areas of interest. Alarms can be set up and displayed
along with maximum, minimum and average temperatures. The TIM 640 is supplied with an integral process interface for input and output of analogue and digital signals (alarms, temperature values). Open connectivity drivers are provided for software integration via DLL, ComPort and LabVIEW, simplifying connectivity to fieldbus networks and automation systems.
DIMENSIONAL MEASUREMENT OF MEMS MEMS (Micro Electro Mechanical or Micro Electronic Systems) is the technology of very small devices. This typically comprises components between 1 to 100 micrometres in size. Normally machined from silicon MEMS
usually consist of a central unit that processes data (the microprocessor) and several components that interact with the surroundings such as micro-gears and micro-sensors. Fabrication of MEMS evolved from the process technology
Detailed, real time analysis of the thermal behaviour of integrated circuits can be carried out using infrared thermal imaging cameras
used in semiconductor manufacturing. The basic techniques are deposition of material layers, patterning by photolithography and etching to produce the required shapes. The latest confocal chromatic sensors offer extremely high sensitivity and sub-micrometre resolution, providing significant advantages when it comes to inspecting the shape and size of MEMS structures during or post-production. These can be integrated to linear X-Y stages, machine tools or special purpose inspection systems. IFS 2405 sensors from Micro-Epsilon, for example, are designed for measurement tasks that require maximum precision – particularly electronics R&D and production and semiconductor manufacturing. In addition to distance measurements on reflective and transparent materials the sensors can be used for one-sided thickness measurement of clear film, PCBs or layers. The maximum resolution of these sensors is 0.01µm and maximum linearity is 0.3µm.
CONFOCAL MEASURING PRINCIPLE The confocal chromatic measuring principle works by focusing polychromatic white light onto the target
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