====== PCB Mechanical Specifications ======
This page presents the mechanical specifications for PCB's in the ICE Platform when being integrated by an OEM.
===== PCB Dimensions =====
All PCB's in the ICE Platform follow identical board dimensions and header/mounting hole locations. The PCB's themselves are 4 inches square and contain 4 mounting holes for 4-40 screws on each corner. The dimensions of the boards are shown in <imgref singlePCB>. All contain a power bus header on each side ([[http://cloud.samtec.com/catalog_english/ESQ_TH.PDF|Samtec PN: ESQ-106-13-T-D]]) and a digital communications bus header ([[http://cloud.samtec.com/catalog_english/ESQ_TH.PDF|Samtec PN: ESQ-104-13-T-D]]) in the middle of the PCB. These headers are 0.1 inch pitch board-to-board headers that allow interconnection between boards when stacked, as shown in the [[pcb_mechanics#PCB Stackup|next section]]. At the edge of the board there are copper tabs extending from four IC's (TO-220 package) for heatsinking. Details on proper heatsinking are described in a [[pcb_mechanics#Thermal Management|later section]]. 

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Not all circuit boards will utilize all four heatsinking positions and therefore may have copper tabs in only a few positions. The four possible tab positions shown in the drawings will are fixed for every board even though a copper tab may not be utilized there.
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<imgcaption singlePCB|PCB dimensions.>{{ :ice:single_pcb_dimensions.png?800 |}}</imgcaption>

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{{:ice:ice_board_high_detail_01.pdf|Technical Drawing}}
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===== PCB Stackup =====
The PCB's are designed to stack on one another with each of the board-to-board headers mating, thereby forming a power distribution and communications bus between boards. The PCB's can be stacked by using 0.5 inch length 4-40 standoffs ([[http://www.mcmaster.com/#93505a432/|McMaster-Carr PN: 93505A432]]) between boards in the four mounting holes at the corner as shown in <imgref stackedPCB>. The maximum stack height is 9 boards total.

<imgcaption stackedPCB|PCB stacking mechanics.>{{ :ice:stacked_pcb_dimensions.png |}}</imgcaption>

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{{:ice:ice_board_high_detail_01_-_stack_of_9_boards_01.pdf|Technical Drawing}}
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===== Thermal Management =====
Each PCB exposes up to 4 copper tabs to conduct heat out from power dissipating components to an external heat sink. The copper tabs are not electrically isolated, so electrical isolation is **required** at the interface between the heatsink and copper tab. Failure to isolate these tabs will result in malfunction of the ICE module. For electrical isolation with good thermal conductivity, [[http://www.bergquistcompany.com/thermal_materials/sil-pad.htm|Sil-Pad]] can be used. Sil-Pad requires a certain amount of pressure to ensure good thermal conductivity, so a clamp mechanism should be applied to the copper tabs. In the <imgref singlePCB> and <imgref stackup3>, the Sil-Pad is shown in pink. In the [[ice:enclosure|ICE Platform]] enclosure, a wedge-based clamping system is used. The mechanics and dimensions of this are detailed below
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The copper tabs **must** be electrically isolated from the heatsink. For electrical isolation with good thermal conductivity, [[http://www.bergquistcompany.com/thermal_materials/sil-pad.htm|Sil-Pad]] can be used.
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<imgcaption stackup1|Overall pcb heatsink stackup.>{{ :ice:oem_heat_sinking_wedge_spec_-_image_01.png |}}</imgcaption>

<imgcaption stackup2|Top view of the stackup.>{{ :ice:oem_heat_sinking_wedge_spec_-_image_03.png |}}</imgcaption>

<imgcaption stackup3|Detail view of wedge clamp. Pink material is Sil-Pad for electrical isolation.>{{ :ice:oem_heat_sinking_wedge_spec_-_image_07.png |}}</imgcaption>

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{{:ice:ice_heat_sinking_wedge_spec_-_drawing_01.pdf|Technical Drawing}}
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