Metal frame
Stacking board form factors like PC/104 (see “Playing The Board Game: Stack’em, Pack’em, And Rack’em” at www.electronicdesign.com) are used in a range of military and avionic applications (see “Rugged Technologies Make Military Hardware Tougher” at www.electronicdesign.com). Typically, the board stacks are housed in conduction-cooled cases such as Adlink Technology’s MilSystem 800 (see “Rugged PC/104 System Targets Military Apps” at www.electronicdesign.com). This Pentium M-based system has STD-MIL-38999 connectors for external expansion and space for a pair of PC/104 cards.
Octagon Systems’ RMB-S Core takes a similar approach to Adlink (see “Expandable Mobile Server Plays It Cool” at www.electronicdesign.com). It has options for a MIL–810F version with military-grade connectors and gasket sealing. But typically, its case and connector complement are sufficient for industrial applications.
EuroTech’s Stack 104 takes a more flexible approach by enclosing each board in the stack with its own metal frame (see the figure). These mate with each other, providing a sealed environment as well as a heat dissipation system. Power is provided through the normally PC/104 stacking mechanism. Each board has its own I/O connections similar to Themis’ VITA-74 proposal. The Eurotech board is open on the ends and would require covers for a single-board solution.