What the 3.9 pF C0G rating means
The EMK042CG3R9CD-W: 3.9 pF in a C0G/NP0 dielectric is a precision RF and timing value — C0G is the only ceramic coefficient with effectively zero temperature drift across the full operating range, so the capacitance does not wander as the board heats or cools. For a crystal oscillator load or RF matching network, this means the tuned frequency holds without active compensation. The ±0.25 pF tolerance is the tightest available for this capacitance decade — tighter than the standard ±0.1 pF floor on some datasheets, meaning the 3.9 pF bin is selected, not just the tolerance grade.
01005 footprint and what it demands from layout
The 01005 body measures 0.40 mm × 0.20 mm with a 0.22 mm maximum thickness — this is the second-smallest SMT package in common use, requiring vacuum pickup tips and a fine-aperture stencil for reliable paste deposition. At this thickness the paste volume under the terminations is the primary driver of tombstoning risk; confirm the stencil thickness and pad design against the manufacturer land pattern before releasing the board.
Active Series M — sourcing posture
Taiyo Yuden lists EMK042CG3R9CD-W as Active under Series M, supplied on tape & reel.