Board-Stacking Fit for the DF40TC(4.0)-30DS-0.4V(51)
The Hirose DF40TC(4.0)-30DS-0.4V(51) is a 30-position receptacle from the DF40T series, built for mezzanine board stacking at a fixed 4 mm mated height.
What the 4 mm Stack Height Means for Your Layout
The 4 mm mated stacking height is a fixed parameter for this variant — the "(4.0)" in the order code locks it. That height sets the distance between the two PCBs when mated. At 0.40 mm pitch, the routing escape from the inner rows requires micro-vias or blind vias on most designs; a standard through-hole via at this pitch blocks too many channels. The 30 positions in two rows give you 15 signals per row, which is enough for a parallel camera interface or a low-pin-count mezzanine link. The receptacle's height above board is 3.90 mm, so the mating header must account for the remaining 0.10 mm in its own body height to hit the 4 mm total.
Mating Half and Series Positioning
The DF40T series is Hirose's high-speed mezzanine line, distinct from the earlier DF40C series primarily in contact design and signal integrity performance — the DF40T uses a wider contact beam for better impedance control and lower insertion loss at higher data rates. If you are replacing a DF40C on an existing layout, verify the footprint compatibility; the pitch and position count are the same, but the contact geometry and recommended pad layout differ between the two series.