Automated Inspection Reveals Stencil Defects
by Holly Wise, Technical Accounts Manager with MicroScreen
With components shrinking and boards becoming more densely packed, it becomes mandatory to ensure that solder paste meets the criteria for each given component.
As components get smaller and boards become denser, there is a greater need to ensure that the deposition of solder paste meets the criteria for a given component.
Before we can determine the feasibility of such deposition, we must consider the stencil being used and factor in its manufacture, problems that may occur, and the ability to examine the stencil's accuracy.
Stencils are fabricated through laser cutting, electroforming or chemical etching. Today, the majority are laser cut.
The laser cutting process can, itself, unknowingly produce
defects in the stencil:
In the past, inspection typically consisted of visually inspecting the foils with a microscope and measuring a few apertures. Physically counting the apertures to ensure 100 percent presence wasn't, and isn't, realistic. Today's technology for the manufacture of stencils requires a sophisticated inspection system such as the ScanCheck unit.
Precision guides move the stencil on a granite base over a high-resolution scanner. The automatic functions of the ScanCheck allow the scanned data to precisely align to the Gerber data, reducing the need for operator interpretation. Other systems depend on contrast for aperture definition and require the operator to identify the aperture edge for measurement, which can be an uncertainty much of the time.
Image Analysis Is Critical
Image analysis of stencils is critical given the growing trend towards boards heavily populated with small and tightly spaced components.
Whether you are an electronics manufacturing service or an original equipment
manufacturer, you need assurance that your stencil has been properly manufactured and is 100 percent accurate.
Experience has shown that the only way to find even the slightest deviation from size and position is with an automated optical inspection system.
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