The challenge
This defense board combines RF and digital circuitry on a 28-layer stackup with blind and buried vias, built by sequential lamination, and controlled impedance. It carries SMA connectors and RF shield cans, with about 3,000 components per board.
SMA launches and RF pads are sensitive to solder volume, placement accuracy and residues. Each of these can shift impedance and degrade RF performance. Shield cans need flat, consistent solder joints all the way around to form a continuous ground seal. Once a can is on, it blocks visual inspection of the parts underneath, so placement and inspection have to be right before it goes on.
The order was 100 boards, roughly 300,000 placements, needed in 3 weeks.
What BSU did
- Solder volume. Koh Young 3D SPI measured paste volume, area and height on every print, so the RF pads and launches got consistent solder.
- Inspection before shielding. Placement and the parts under each can were verified before the shield cans went on, because the cans block inspection afterward.
- Class 3 throughout. Every board was built and inspected to IPC Class 3.
- ITAR controls. The job was built under ITAR controls, with controlled data handled only by authorized U.S. persons.
Result
100 boards, roughly 300,000 placements, built and inspected to IPC Class 3 and delivered 3 weeks from full kit: high complexity, mixed signal, defense and a fast schedule on the same job.
