Detection of defects at BGA solder joints by using X-ray imaging

Continual increases in IC-chip complexity and performance are placing demands on the density and functionality of package I/Os. Therefore, various SMT interconnection techniques are being developed to satisfy this need, including ball-grid-array (BGA). BGA has been used in a production of PCB (printed circuit board), because of their excellent characters such as high density of the lead pin pitch that can achieve a density of 400 I/Os per square inch. This paper deals with the detection of defects at BGA solder joints in PC boards by using X-ray imaging. It is possible to detect defects of solder joints by visual inspection, but only techniques utilizing X-ray could possibly inspect all BGA joints within the area array because they are hidden under the IC package. In traditional production, the inspection of BGA depends on the function test of electric circuits or boundary lighted inspection. Now with the employment of X-ray in solder joints inspection, it becomes very important about the detecting algorithm based on X-ray imaging. This paper discusses the flow of detecting defects based on the X-ray imaging and describes an approach to automatic inspection of BGA solder joint defects by using seed filling and contour extracting. Experimental results reveal that the proposed method shows practical usefulness in BGA solder joints inspection.