Abstract
Increased density of printed circuit board assembles (PCBAs) is diminishing physical contact test access of the in-circuit testing (ICT) solutions for defects detection. As a result, it is necessary to design contactless test solutions with high spatial resolution to overcome the current test limitations. In this paper, a compact contactless sensor is presented for monitoring the fabrication quality of PCBAs. The sensor consists of an inductor-capacitor-(LC)-based resonant circuit and it can detect defects on metallic traces of PCBAs in close proximity without a contact. The sensor is designed such that, strong electric field is confined around the sensor tip, which creates strong capacitive coupling between the sensor tip and devices under test (DUTs) within a small region for sensing, i.e. high resolution sensing. The sensitivity of the proposed sensor is verified by the simulated and experimental 2D surface mapping results with sample DUTs, and it shows that the sensor can detect the open or short defects with a size as small as 0.15 mm × 0.2 mm. Circuit models are proposed to predict the sensing behavior and for guiding the design. The proposed sensor shows great potential to be used in the real-time monitoring of defects along the manufacturing supply chain.
Highlights
Electronics manufacturers are continually challenged to ensure sufficient test coverage for their electronic products
It is composed of periodic parallel metallic traces with a width and a spacing both set to 0.15 mm, a thickness of 0.035 mm, and a length of 5 mm, which is of a similar scale of the soldering joints of small outline package (SOP) and quad flat package (QFP) with smallest pitch size [5]
When the sensor tip is placed near the devices under test (DUTs), additional capacitive coupling is induced between the sensor tip and the DUT, more detailed circuit models are proposed for different situations which are used to replace Ctip
Summary
Electronics manufacturers are continually challenged to ensure sufficient test coverage for their electronic products. To obtain a detailed and localized evaluation of a PCBA so that defects can be fixed, noncontact and non-destructive sensing without powering up the PCBAs become critical. For such an evaluation on PCBAs, a 1D spatial resolution of around 0.15 mm is needed to distinguish different pins of a package for example [5]. An alternative inspection technique for high density PCBAs is the thermography methods [8], [9]. It has the advantages such as easy operation and simple testing reconfiguration. The acoustic method [10], [11] has excellent long-range diagnostic capability and it is suitable to
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