5.2.2 Boards

The circuit boards behind a front panel. A module has a parallel board, a right-angle board, or both.

Edge clearance

The one board requirement that affects fit is edge clearance. A board shall stay at least 9.25 mm clear of the top and bottom panel edges, and a rail shall cover no more than 9.25 mm of the panel face at each edge (PANEL-012). The opening between the rails' inner faces is then at least 110 mm at 3U, and a 110 mm board is the tallest that fits; at 1U the opening is at least 21.15 mm, and the usual board, two rack units shorter than the 3U board, is 21.10 mm.

Format Usual board height Clear of each panel edge
1U 21.10 mm 9.275 mm
3U 110.00 mm 9.25 mm

On a rail whose inner face is 5.075 mm from the hole center, such as Schroff 34560-184, the 3U opening is 112.35 mm and a 110 mm board has 1.175 mm to spare on each side. Annex A gives inner-face measurements of catalog rails.

The rest of this clause describes common construction and places no requirement. The numbers are in data/module.json.

Parallel boards

A parallel board faces the panel. Its front face is usually 10 mm behind the panel's back face, the height of a jack body. Its width is 0.6 mm under the nominal width of the panel, twice the panel clearance:

board width = N × 5.08 − 0.6 mm

An 8 HP parallel board is 40.04 mm wide and 110 mm tall at 3U, or 21.10 mm tall at 1U. 1.6 mm FR-4 is the usual material.

Right-angle boards

A right-angle board stands square to the back of the panel, with no gap. Its edge toward the panel is the left edge of the board, and the board faces right. Its height is the board height above; its depth back from the panel is a design choice, commonly 30, 35, 40, 45, or 50 mm. A 30 mm right-angle board already extends past a rail of the recommended section (5.4).

EIS · Parallel and right-angle boards, seen from above Parallel board front panel, 8 HP rail ends 25 to 28.5 mm behind parts 10 mm, a jack body 40.04 mm depth Right-angle board front panel, 8 HP rail ends 25 to 28.5 mm behind 30 35 40 45 50 common depths, mm parts face right A parallel board stands about 10 mm behind the panel, the height of a jack body, and is N × 5.08 − 0.6 mm wide. A right-angle board stands on the panel's back with its left edge to the panel. Either way the module publishes how far it reaches behind the panel (PANEL-003); EIS recommends at most 50 mm.

Module depth

EIS · Module cut at the top rail, seen along the rail edge clearance 9.25 mm: no board above this line panel 1.6 to 2 mm rail depth 25 to 28.5 mm rail height 7 to 10 mm 3 mm depth: EIS recommends at most 50 mm rail The rail is drawn at the most cover EIS allows: its inner face on the edge-clearance line, 9.25 mm below the panel's top edge. The mounting hole is 3 mm from the edge, drilled 3.2 mm; an M3 pan-head screw, head at most 7 mm, engages at least 3 threads in an insert that sits in a groove at least 5 × 2 mm. The board is 1.6 mm thick and stands on the panel's back below the clearance line, so the rail clears it. Depth is measured from the panel's back face to the module's deepest point.

EIS recommends that a module extend no more than 50 mm behind the panel's back face, measured to its deepest point. A deeper module still conforms; its published depth (PANEL-003) is checked against the row's (ENC-001). In the survey of Annex F, 94.8 % of 287 modules are within 50 mm and the median is 35 mm.