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On an eight-layer board, a signal with a 400 ps rise time changes from L1, referenced to the L2 ground plane, to L8, referenced to the L7 ground plane. Both planes are continuous near the transition, but their nearest interconnection is 60 mm away. The signal via's local impedance has already been optimized. Which revision addresses the remaining return-path discontinuity?
Correct answer: D - Add a ground stitching via beside the signal via.
A fabrication reviewer objects to a laminate with Tg = 175°C because the assembly profile peaks at 242°C. The exact construction has passed qualification for every intended reflow and rework exposure, including plated-hole and delamination requirements. Its operating-temperature requirements are also met. How should the objection be resolved?
Correct answer: C - Retain the construction; Tg marks a stiffness transition, not a reflow-temperature ceiling.
An inner-layer via land must retain at least 0.075 mm of copper between its edge and the drilled-hole boundary. The minimum land diameter after etching is 0.64 mm; the maximum drilled-hole diameter is 0.34 mm. The maximum drill-to-land center offset is 0.05 mm. No other allowances apply. What does the worst-case geometry permit?
Correct answer: B - A remaining ring of 0.100 mm; retain the land diameter.
Intermittent opens appear beneath a BGA immediately after its first reflow. A microsection shows that the package ball and solder-paste deposit each wet their respective lands, but retain distinct contours where they touch, without a continuous metallurgical bond between them. The board land remains attached to intact laminate. The observed defect is:
Correct answer: A - Head-in-pillow.
Steady-state thermal measurements in a product enclosure provide the temperature at the package-top center, local ambient temperature and total IC power dissipation. The supplier confirms that its ΨJT characterization parameter applies to this board and airflow; the published θJA comes from a different test board. The package top has no attached heat sink. How should the measured data be used to estimate junction temperature?
Correct answer: D - Add total device power times ΨJT to the measured package-top temperature.
An FPGA rail must stay within 60 mV of nominal. Of this one-sided deviation budget, 20 mV is reserved for DC regulation and distribution error; the remainder is allocated to transients. The load rises from 1 A to 3 A. Across the specified 100 kHz-100 MHz band, measured PDN impedance magnitude has a maximum of 24 mΩ. Using the target-impedance criterion, which assessment is correct?
Correct answer: D - 20 mΩ target; the measured PDN fails the criterion.
A manufacturer reports a bare board electrically correct. Its acceptance netlist was extracted from the same copper files used to fabricate the board. A later review finds that two schematic pins intended to share a net are separated in those files. Which missing release check would have detected the error before fabrication?
Correct answer: C - Compare artwork-derived connectivity with an independently generated netlist from the approved schematic.
To reduce insertion force on a compliant press-fit connector, a designer proposes the larger clearance holes already qualified for a soldered connector with the same pin pitch. The press-fit supplier specifies a plated finished-hole range, a plating system and a board-thickness range. What should govern the revised footprint?
Correct answer: B - Use the qualified finished-hole range, plating system and board thickness for that press-fit contact.
An instrument PCB combines fine-pitch SMT devices with an edge connector that will be mated repeatedly during service. Assembly needs planar solderable lands; the connector needs a wear-resistant wiping surface. Contact-grade hard gold is excluded from the qualified SMT soldering process. Which finish strategy best serves these different interfaces?
Correct answer: B - ENIG for soldering, with specified electrolytic hard gold over nickel on the mating contacts.
An isolated power-control PCB requires at least 3.0 mm air clearance and 5.0 mm surface creepage between hazardous-voltage and touch-accessible conductors. After a slot is added, verified creepage is 5.6 mm, but the shortest air path is 2.4 mm. No coating-based spacing reduction is permitted. What must change before the insulation geometry is acceptable?
Correct answer: A - Increase conductor separation to satisfy the air-clearance requirement while preserving creepage.
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