Method and apparatus for inspection of solder joints by x-ray fluoroscopic imaging

An apparatus for inspecting solder joints on a substrate and areas between solder joints using X-ray fluoroscopic imaging, the apparatus comprising:

• irradiating means for irradiating an X-ray generated from an X-ray source;
• a specimen stage for locating an object to be inspected, the object having a lead of an electronic part soldered to a substrate;
• an X-ray detector for detecting an X-ray fluoroscopic image signal obtained by transmitting said X-ray through solder joints of the object located by said specimen stage;
• solder-joint position extracting means for extracting a position of each of the solder joints of said object to be inspected in accordance with said X-ray fluoroscopic image signal detected by said X-ray detector;
• inspection-area setting means for defining a plurality of inspection areas on each of i) a portion of a solder joint and ii) a peripheral portion of a solder joint, corresponding to each of the solder joints in accordance with the extracted position of each solder joint extracted by said solder joint position extracting means;
• preparing means for preparing a plurality of reference image signal shapes S.sub.j (j=1 . . . N) designated as typical good solder joints by measuring X-ray fluoroscopic image signal shapes for typical good solder joints in accordance with said X-ray fluoroscopic image signal detected by said X-ray detector;
• defect detection means for i) detecting a defect with respect to the solder joints in accordance with a degree of coincidence between an X-ray fluoroscopic image signal shape W obtained from said defined inspection area of said solder portion of the solder joint and a reference image signal shape S of a good solder joint by comparing said X-ray fluoroscopic image signal shape with said reference image signal shape of said good solder joint obtained by measuring the X-ray fluoroscopic image signal shape for said good solder joint for every said defined inspection area of said solder portion, and ii) detecting a defect between the solder joints in accordance with an X-ray fluoroscopic image signal obtained from said defined inspection area of said peripheral portion of the solder joint for every said defined inspection area of said peripheral portion;
• and,
• wherein, the defect detecting means includes second means for judging a defect of each of the solder joints by comparing the x-ray fluoroscopic image signal shape W of each of the inspection areas set, obtained from the X-ray fluoroscopic image signal detected by said X-ray detector, with the prepared reference image signal shape S of good solder joint, the second means including means for deciding between X-ray fluoroscopic image signal shapes and the prepared reference image signal shapes by a min .vertline.W-Sj.vertline. (j=1 . . . N) of an integrated value .vertline.W-Sj.vertline. of differential images.

An apparatus for inspecting a first solder joint and an area between a plurality of solder joints using X-ray fluoroscopic imaging, the apparatus comprising:

• irradiating means for irradiating an X-ray on an object to be inspected to obtain an X-ray fluoroscopic image signal of the object, the object being located by a specimen stage and formed by a lead of an electronic part soldered to a substrate at the first solder joint;
• extracting means for extracting a position of the first solder joint as the object to be inspected from said obtained X-ray fluoroscopic image signal;
• defining means for defining, from the X-ray fluoroscopic image signal, a plurality of inspection areas on a solder portion of said first solder joint and a peripheral portion of the first solder joint in accordance with the extracted position of said first solder joint;
• subtracting means for subtracting an X-ray fluoroscopic image signal shape I.sub.1 derived from said X-ray fluoroscopic image signal from an X-ray fluoroscopic image signal shape 12 comprising a state where no solder is present for each of said plurality of inspection areas in accordance with the extracted position to calculate a fillet shape;
• and,
• detecting means for i) detecting a defect with respect to the first solder joint in accordance with a minimum of an integrated value of differences between an X-ray fluoroscopic image signal shape obtained from said defined inspection area of said solder portion of the solder joint and a plurality of reference image signal shapes of a good solder joint by comparing said X-ray fluoroscopic image signal shape with said plurality of reference image signal shapes of said good solder joint obtained by measuring the X-ray fluoroscopic image signal shape for said good solder joint for each of said plurality of defined inspection areas of said solder portion of said first solder joint, and ii) detecting a defect between the plurality of solder joints in accordance with an X-ray fluoroscopic image signal obtained from said defined inspection area of said peripheral portion of the first solder joint for each of said plurality of defined inspection areas of said peripheral portion of said first solder joint.

A method of inspecting a solder joint in an x-ray fluoroscopic imaging apparatus, the method comprising the steps of:

• obtaining an x-ray fluoroscopic image signal by irradiating an x-ray on an object to be inspected, the object being located by a specimen stage of the apparatus and formed by soldering a lead of an electronic part to a substrate at said solder joint;
• extracting a position of the solder joint as the object to be inspected from said obtained x-ray fluoroscopic image signal;
• defining, from the x-ray fluoroscopic image signal, a plurality of inspection areas on a solder portion of the solder joint in accordance with the extracted position of said solder joint;
• and,
• detecting a defect with respect to the solder joint in accordance with a min .vertline.W-S.sub.j .vertline. (j=1 . . . N) of an integrated value .vertline.W-S.sub.j .vertline. of differential images between an x-ray fluoroscopic image signal shape W obtained from said defined inspection area of said solder portion of the solder joint and a plurality of reference image signal shapes S.sub.j (j=1 . . . N) designated as a typical good solder joint by comparing said x-ray fluoroscopic image signal shape W with said plurality of reference image signal shapes S.sub.j (j=1 . . . N) designated as the typical good solder joint obtained by measuring an x-ray fluoroscopic image signal shape for the typical good solder joint for every said defined inspection area of said solder portion.