EMC Question of the Week: July 27, 2026

Cross section of a 24-layer circuit board showing decoupling capacitors at two locations. C1 is on the backside of the board sharing via connections with a BGA. C2 is on the top side 5 mm away.

The figure shows a cross-section of a 24-layer circuit board with GND planes on layers 2, 4, 7, 10, 12, 14, 17, 19, and 23. There are PWR planes on layers 5 and 15. Two decoupling capacitors are shown. C1 is on the backside of the board and shares via connections with a BGA. C2 is on the topside of the board and is 6.4 mm away from the BGA. Within the first 200 ps of a sudden demand for current to the BGA, where is most of the current coming from?

  1. C1
  2. C2
  3. C1 and C2 equally
  4. the plane capacitance

Reveal Question of the Week - Answer 260727