Spacing and Yield

The tightest spacing between neighboring 0201 components assembled was 8-mils.

Please refer to the response for the query entitled �Minimizing Tombstoning Defects� posted by martys, as the response provided there is also relevant to address this question.

Additional tests were done at 8-mil component spacing to determine the impact of the following variables on defects:

Printing and Placement Accuracy � Prints were intentionally misregistered either in �x� or �y�. Placement was also purposely misregistered, also in �x� or �y�. Printing and placement offsets were not combined in any trials as these variables were changed independently.

Amount Of 0201 Component Overlap On Solder Paste Deposits � Apertures were designed to be centered over the pads, and they also were designed at slightly further distances apart in order to have incrementally smaller amounts of solder overlapping the placed component terminations. In a perfect print registration and perfect placement position scenario, this results in both terminations of the component overlapping the paste by the same amount (i.e. a balanced overlap scenario). Given a balanced overlap scenario, the overlap values tested were 2 mils, 4 mils, and 6 mils. Keep in mind the magnitude of this overlap depends on the distance separating the apertures apart.

By combining misregistration with varying levels of component overlap on the solder paste deposits, the balanced overlap scenario no longer exists. This is the essence of the additional tests performed on the 8-mil spacing 0201s. Results indicated:

- Tombstoning Defects - Minimized: high printing / placement accuracy (for all overlaps) Maximized: low printing / placement accuracy and low overlap

- Bridging - Minimized: high printing / placement accuracy and low overlap Maximized: low printing / placement accuracy and high overlap

- Solder Balls - Minimized: low overlap (for all printing / placement accuracy levels) Maximized: high accuracy and high overlap

-Jeff

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