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May 11, 2009

High Defect Rate on SOT 883

We are getting a high defect rate with a very small three lead SOT 883 component. The component lifts off one of the small pads during reflow.

Any advice on stencil design or reflow changes would be greatly appreciated.


Experts Comments

It's likely that the volume of solder being deposited on the largest of the three apertures is causing the part to tilt during reflow. It would be simple to address this issue with a change in the stencil.

If you are using lead free solder paste, the most effective way to reduce the solder volume without creating pad wetting issues is to reduce the stencil thickness. Reducing the stencil thickness could however create insufficient solder joints for larger components. With this in mind, your stencil supplier could make adjustments to the larger component apertures to compensate for the change in stencil thickness required for this smaller, leadless device.

If you are working with a leaded solder, reducing the size of the opening in the stencil will alleviate the excess solder issue and component shift. With the correct reduction in aperture size, pad wetting would not be a concern.

Michael Ray
Integrated Ideas & Technologies, Inc.
Mike Ray is founder and president of Integrated Ideas & Technologies, Inc., a manufacturer of SMT stencils. Mike Ray developed the first successful universal frame and holds patents on the AXIS laser system.
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