Communication equipment
Compact HDI module: microvia stackup without over-building
HDI 1+N+1 · via-in-pad · controlled impedance
A module team specified a 2+N+2 HDI stackup for a fine-pitch BGA. Engineering review showed a simpler 1+N+1 with staggered microvias could route the escapes.
Challenge
- Initial fab notes assumed stacked microvias and an extra lamination cycle—raising cost and yield risk for a prototype-to-pilot volume.
- Via-in-pad was required in the BGA field but not fully called out in the fabrication notes.
- Impedance targets existed in a spreadsheet, not as a panel coupon plan.
Approach
- DFM compared escape routing against 1+N+1 staggered vias versus the requested 2+N+2; the simpler structure was validated with the layout owner.
- Via-in-pad fill/cap requirements were added to fab notes before quote lock so plating and planarization were priced correctly.
- Stackup and impedance coupons were panelized with the prototype lot so SI checks could happen on the same spin.
Outcome
- Prototype lot shipped on the agreed simpler HDI construction with documented via architecture.
- Cost and schedule risk from an unnecessary lamination cycle were avoided before production hardening.
- The same stackup notes carried into the pilot quote without reopening basic via questions.