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

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 rails' inner faces are then at least 110 mm apart at 3U and 21.15 mm at 1U. A 110 mm board is the tallest that fits at 3U; the usual 1U board is 21.10 mm, two rack units shorter.

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. 5.3 gives the inner-face measurements of catalog rails.

The rest of this clause describes common construction and sets 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 panel's nominal width, 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 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 left edge meets the panel, and its parts face right. Its height is the board height above. Its depth is the maker's choice, and the module publishes how far it reaches (PANEL-003). Even a 30 mm deep right-angle board reaches 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 depth, 25 to 28.5 mm parts 10 mm, a jack body 40.04 mm depth Right-angle board front panel, 8 HP rail depth, 25 to 28.5 mm depth, the maker's choice 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 square to the panel, its front edge on the panel's back. Either way the module publishes how far it reaches behind the panel (PANEL-003); EIS recommends at most 50 mm.

Module depth

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 eis-reference survey, 94.8 % of 270 modules are within 50 mm and the median is 35 mm.

EIS · Module cut at the top rail, seen along the rail right-angle board, seen face on edge clearance 9.25 mm: no board above this line panel 1.6 to 2.0 mm rail depth 25 to 28.5 mm rail height 7 to 10 mm 3.0 mm module depth: EIS recommends at most 50 mm rail The rail is drawn at its tallest, 10 mm, centered on the hole as catalog rails are: its inner face is 8 mm below the panel's top edge, inside the 9.25 mm a board keeps clear (PANEL-012). The hole is 3.0 mm from the edge (PANEL-008), Ø3.2 mm (PANEL-010), for an M3 pan-head screw with a head at most 7.0 mm across (RAIL-010). A parallel board keeps the same clearance. Depth runs from the panel's back face to the module's deepest point (PANEL-003).