Systems and methods for detecting defects in printed solder paste

A method of detecting a defect in a substance deposited through a stencil and onto a substrate, comprising:

• capturing an image of the stencil;
• detecting variations in texture in the image to determine a location of the substance on the stencil;
• defining a region of interest in the image, the defined region of interest having a first axis, wherein a set of pixels in the image lie along the axis;
• computing, for each pixel along the axis, a sum of all the pixels in the region of interest that are in perpendicular alignment with the respective pixel along the axis;
• representing the sums of each pixel along the axis as a single dimensional array perpendicular to the axis;
• evaluating the single dimensional array to determine whether any defects exist in the region of interest;
• and
• actuating a stencil wipe procedure to clean the stencil when a defect exists in the region of interest.

A method of inspecting a stencil having apertures through which a substance is deposited onto an electronic substrate comprising:

• depositing the substance through the stencil and onto the substrate;
• capturing a first image of the stencil after the deposit of the substance and detecting variations in texture of the substance in the first image;
• capturing a second image of the electronic substrate having the substance on its surface and detecting variations in texture of the substance in the second image;
• defining a region of interest in the first image and in the second image to determine whether at least one feature exists in the region of interest;
• measuring a first span of the at least one feature in the region of interest in the first image and a second span of the at least one feature in the region of interest in the second image;
• correlating the first span of the at least one feature and the second span of the at least one feature to determine whether a threshold span of the at least one feature has been reached;
• and
• actuating a stencil wipe to clean a surface of the stencil when it is determined that the threshold span has been reached.

A method of dispensing material at predetermined locations through a stencil and onto an electronic substrate within a stencil printer, the method comprising:

• delivering a substrate to a stencil printer;
• positioning the substrate in a print position;
• positioning a stencil onto the substrate;
• dispensing the material through the stencil and onto the substrate;
• performing texture-based recognition of a predetermined location of the material on a bottom side of the stencil;
• determining whether there is at least one feature in the predetermined location on the bottom side of the stencil;
• comparing the at least one feature on the bottom side of the stencil with a position of the substance on the substrate to determine whether the at least one feature is a defect;
• and
• actuating a stencil wipe procedure to clean the bottom side of the stencil when the at least one feature is determined to be a defect.