Application Note AN1023 Ruggedized ATR Military Chassis and ZIF III Board Retainers Ruggedized Military ATR Chassis ATR (Air Transport Rack) military enclosures protect critical systems across a wide range of military applications. They are installed in fighter and transport aircraft, nuclear submarines, advanced battle tanks, ships, simulators and ground test systems. The enclosures may be 1/2 ATR, 3/4 ATR, and Full ATR sizes uniquely configured for the applications, systems, and vehicles that demand reliability. These ruggedized military chassis are designed to protect internal VMEbus boards and the backplane while exposed to harsh environmental conditions in mission critical applications. Each application may require a different ATR chassis, but all must provide reliable performance. These military enclosures must meet EMI/EMC requirements, prevent noise interference, provide lightning protection and isolation from small particle contaminants. The rugged enclosures also create a harsh thermal environment with complex cooling demands. A sophisticated cooling solution is typically required to meet the high power consumption by the multiple circuit boards within the enclosure. Figure 1. Typical Ruggedized Full ATR Military Chassis Meeting Thermal Demands Military enclosure thermal management is a complex issue that is affected by several environmental factors and system constraints. Eliminating heat from these isolated enclosures is critical to the reliability of the VME boards and systems they contain. Thermal management within the isolated chassis requires maximizing conduction cooling, often with limited to no air flow. The ZIF III card retainer is the industry leader for maximizing thermal transfer between circuit boards and the chassis cold plate. The ZIF III retainer, Figure 2, benefits from zero insertion force, quarter-turn lock/unlock, and uniform clamping pressure along the full length of the chassis sidewall, maximizing the thermal path for the tight VMEbus board spacing (0.8” pitch). With a thermal resistance of 1.2°C-In/W, the ZIF III board retainer provides an extremely low thermal conduction path to the cold plate. CTS Electronic Components www.ctscorp.com Page 1 Ruggedized ATR Military Chassis and ZIF III Board Retainers February 07 AN1023 Figure 2. PCB with ZIF III retainer and chassis cold plate ZIF III Board Retainer Features The ZIF III board retainer is a three piece assembly: aluminum housing, stainless steel rod, and berylliumcopper spring. It is designed to mount along the full length of the PCB. The board and retainer assembly securely locks into an ATR chassis cold-wall with a simple cam-lock quarter-turn. The ZIF III does not require a torque wrench or special settings. The unique locking design of the ZIF III board mountable retainer produces a uniform pressure distribution along the PCB edge. Once locked into the ATR chassis cold plate, the retainer/PCB assembly provides a thermally conductive path to remove heat and a resistance to extreme shock and vibration. Screw mounting of the ZIF III to the VMEbus board provides uniform mounting pressure to the PCB with no board warping. The quarter-turn lock and unlock design allows quick loading and unloading of boards. The slot in the hex-head rod (Figure 3) is colored to provide visual indication of the lock-status of the retainer. Figure 3. ZIF III board retainer both mounted and un-mounted on PCB. Parameter Insertion and Extraction Cold Plate Clamping Pressure Locking/Unlocking Operation Repeatability Over-torque Sensitivity PC board operational damage Retainer Mounting Options Thermal Performance ZIF III Retainer Features Zero Card Thickness plus .300” Uniform pressure along the PCB edge 1/4 turn Always 1/4 turn lock/unlock Not susceptible to over-torque Constant and even edge pressure on boards Screw mounting 1.2°C-inch/Watt Benefits No PC board damage Standard for retainers Excellent heat transfer No torque gage required; Fast operation Consistent and easy to operate Does not damage PC boards No PC board damage Standard for retainer mounting Very good cooling efficiency Table 1. ZIF III Board Retainer Features CTS Electronic Components www.ctscorp.com Page 2 Ruggedized ATR Military Chassis and ZIF III Board Retainers February 07 AN1023 VMEbus Card Size 9U Size D 6U Size C 6U Size B ZIF III Retainer Size 12” (2 Required) 12” (2 Required) 6” (2 Required) CTS Standard Part Number Z3A12SBSBNL/R Z3A12SBSBNL/R Z3A60SBSBNL/R Table 2. ZIF III Board Retainer Common Sizes ZIF III Board Retainer Locking Torque & Thermal Characteristics Slot Width (IN) Insertion Depth *Locking Torque (IN – LBS) Top Bottom .150 17.5 .200 17.5 .250 17.5 .150 24.5 .487 .200 24.5 .250 24.5 .150 29.5 .480 .200 29.5 .250 29.5 * Torque value per 6” length of ZIF III retainer. .495 Thermal Resistance for ZIF III Retainer Per 1” of Length at Different Power Levels ( ºC/W/IN) 10 Watts 25 Watts 50 Watts 75 Watts 20.5 20.5 20.5 26.0 26.0 26.0 32.0 32.0 32.0 1.17 0.84 0.69 1.17 0.97 0.89 1.03 0.90 0.67 1.19 0.94 0.76 1.07 1.02 0.85 0.96 0.78 0.68 1.16 0.94 0.82 1.08 0.98 0.89 0.99 0.82 0.68 1.16 0.93 0.84 1.07 0.97 0.87 0.94 0.78 0.67 Table 3. ZIF III Thermal Resistance from Plate to Cold-wall (using Beryllium-Copper spring & Stainless Steel Rod) Environmental Qualification Tests Qualified to MIL-Std-810: • High Temperature: • Low Temperature: • • Salt Fog: Vibration: • Shock: Method 501, Procedure 1, Steps 1-7, 71°C, after 48 hours exposure to 150°C. Lock/Unlock Torque within 25% of initial value. Method 502, Procedure 2, Steps 1-3 & 6, -55°C, Lock/Unlock Torque within 25% of initial value. Method 509, Procedure 1, Lock/Unlock Torque within 25% of initial value. Method 514, Procedure 1, Part 1, Category B.1, Curve L, 5Hz to 2 KHz. Retainer shall not unlock. Method 516, Procedure 1, Figure 516 & 202. Retainers shall not unlock. Additional CTS/IERC ZIF III product information can be found at: http://www.ctscorp.com/components/heat_sinks.asp#Military Written by: Date: Damon Niswonger February 28, 2007 CTS Electronic Components www.ctscorp.com Page 3 Ruggedized ATR Military Chassis and ZIF III Board Retainers February 07 AN1023