The article gives a brief overview of standard methods of quality control and defect diagnostics of plated-through holes (PTH) of printed circuit boards (PCB) and considers their main disadvantages. It scrutinizes the methods of thermal control, which are reduced to PTH heating and monitoring the temperature. The main disadvantage of common methods is that they require a contact during heating the PTH and temperature measurement, which leads to significant errors and low reliability of control. The article describes a non-contact method involving heating only one side of the PTH by a laser beam and non-contact temperature measurement of the PTH ends by an IR camera. The authors propose a thermal equivalent scheme of PTH to analyze the transient thermal processes in PTH, which takes into account the heat removal from the plating of PTH into the PCB material. It is shown that the quality of plating can be estimated by the temperature difference between the upper (heated) and lower ends of the PTH, and the quality of adhesion between PTH plating and the PCB material can be estimated by the ratio of temperature increments. The article describes peculiarities of this method and gives the results of its testing on a real sample.
Machine vision for automatic inspection of pin through hole components assembled on a PCB
