Bead Impact On ICT Nodal Access
DRI studied existing circuit boards for ICT contact coverage as a percent of total nets before and after adding beads. The boards were grouped into four categories: Consumer, Automotive, Aerospace and Communications.
Connecting reliably to traditional fixture probe targets is becoming more difficult. As via type pad sizes shrink below 25 mils (0.64 mm) on higher density boards, connectivity can begin to suffer to the point where false negative testing rates make probing the via undesirable, even if the added cost is not a factor. Some companies have already removed vias from the approved target list, eliminating a large source of contact opportunities and raising the question whether ICT is valid at all with the reduced access. Consequently, DRI studied the impact of using beads to enhance ICT access for the two cases where vias are allowed and vias are not allowed.
This evaluation looks at the percentage of probed nets before and after adding beads. The largest average increase in probed nets was 28% for consumer style boards, with increases of 10%, 3% and 9% respectively for Automotive, Aerospace and Communications boards.
The maximum percent increase for a single board in each category was 56%, 54%, 7% and 26% respectively.
This evaluation, summarized in Chart 2, looks at the percentage of probed nets before and after adding beads without allowing probing of any via targets. The largest increase in average coverage was 57% for consumer style boards, and 20%, 18%, and 25% respectively for automotive, aerospace and communications boards.
The maximum percent increase for a single board in each category was 79%, 43%, 36% and 41% respectively.
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