SMT007 Magazine

SMT-July2016

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58 SMT Magazine • July 2016 of key importance for the reliable detection of the characteristic. The AOI systems of GÖPEL of electronic GmbH have been successfully used for this testing task for many years, due to their multi-spectral and multidirectional lighting. Measurement of Embedment Depth: a Particular Challenge There is, however, a sharp increase in re- quirements when the height of the pin tip has to be determined. This test task is known as em- bedment depth or press-in depth. As the name of the test task indicates, it is not possible to meet these requirements using the usual two- dimensional measurement and testing technol- ogy, as orthogonal inspection cannot provide information on height. This problem cannot even be resolved by using suitable cameras for testing, because the deformation of the pins and PCB is unknown prior to the test, and it is often difficult to detect the pin tip. The reverse conclusion is: An additional testing dimension is required! Attempts to solve this problem using fringe projection often failed because of uncoop- erative surfaces, which do not provide reliable measuring signals as they are strongly reflective. Neither is it possible to use a triangulation pro- cess to carry out measurements into connector housings, as the walls of the housing literally put the interior parts into the shade. This can be partly compensated for through the use of several projectors or cameras, but, if not before, it becomes apparent that it cannot be used for measurements into holes when determining the press-in depth of a pin into a PCB (e.g., pressfit technology) or into other objects (e.g., connec- tor housings). 3D Measurements Based on TMSA Technology One such technology that makes it possible to carry out 3D measurements even into deep holes with very small diameters (<0.5 mm) is telecentric multi spot array (TMSA). TMSA features a white light source coupled into a telecentric measuring lens developed spe- cially for this purpose. As a result, there is no angle between the light source and the sensors (in contrast to the triangulation process), which means that the lighting and signal beam path are identical. This configuration has the advan- tage that no shadows are created on high com- ponents, making it possible to carry out reliable measurements into deep gaps between compo- nents or into holes. With this arrangement, the lens now dif- ferentiates the individual light wavelengths, so that only a small wavelength range is focused and reflected back, depending on the distance between the measuring lens and the surface to be measured. The reflected light or measuring signal is associated with a height value based on the evaluation of the respective intensity. Since this lens projects individual measurement points onto the PCB, the spot array must be moved for a wide-area recording of measure- ment values. Depending on the increment, this makes it possible to implement different lateral PERFECT PLACEMENT OF CONNECTORS AND PINS Figure 1: Possible errors on a connector pin.

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