Structured Light Projection Technique For BGA Void Inspection

Ball grid array (BGA) is an important kind of SMT (Surface Mount Technology) chips. It solves the conflict between the sharply increase of I/Os and smaller chips.BGA has advantages of pin structure, package size and density, reflux welding compared with other package technology. But the inspection of void defection is always a big difficulty. Recently methods such as X ray inspection cost too much. Based on this, a novel structural light auto inspection system was developed for ball grid array (BGA) void inspection.The primary research tasks are as follows:1) Special structured light was used. A light emitting diode (LED) ring light and a LED cross light were used to illuminate the BGA package with a charge-coupled device (CCD) to capture the image through the center hole of the ring light and the cross light. So it contains more information for one image.2) The mathematical statistics was applied to image feature analysis. 3) Symmetry Hough transforms was used to extract rectangle. Traditional method is to extract lines for position maintain. But the inspection of four lines of the rectangle cost too much time and space. So we take the rectangle as a whole. Symmetry Hough transform take use of the symmetry property, the method can shorten the computing time and reduce the space complexity.4) Proposed a new concept of symmetry firstly. When extracting features of an image, rotate the image for 180 degree and let subtract of the original image and the rotated image as symmetry measurement.5) By extracting the spectral energy distribution features as a function of radius from the center of the spectrum using artificial neural network (ANN), the voids of different size and position were inspected successfully.6) Applies to different illumination and focus. By training the new image under new environment, the result clearly indicate our method is applicable.