Construction
The LVDC was approximately 30 inches wide, 12.5 inches high, and 10.5 inches deep and weighed 80 pounds. The chassis was made of magnesium-lithium alloy LA 141, chosen for its high stiffness, low weight, and good vibration damping characteristics. The chassis was divided into a 3 x 5 matrix of cells separated by walls through which coolant was circulated to remove the 138 Watts of power dissipated by the computer. Slots in the cell walls held “pages” of electronics.
A page consisted of two 2.5 x 3-inch boards back to back and a magnesium-lithium frame to conduct heat to the chassis. The 12-layer boards contained signal, power, and ground layers and connections between layers were made by plated-through holes.
Up to 35 alumina squares 0.3 x 0.3 x 0.070 inch could be reflow soldered to a board. These alumina squares had conductors silk screened to the top side and resistors silk-screened to the bottom side. Semiconductor chips 0.025 x 0.025 inch, each containing either one transistor or two diodes, were reflow soldered to the top side. The complete chip was called a unit logic device. Copper balls were used for contacts between the chips and the conductive patterns.
The hierarchy of the electronic structure is shown in the following table.
| LEVEL | COMPONENT | MATERIAL | IBM TERM |
|---|---|---|---|
| 1 | Transistor, diode | 0.025 x 0.025 inch silicon | - |
| 2 | Up to 14 transistors, diodes and resistors | 0.3 x 0.3 x 0.07 inch alumina | ULD (Unit Logic Device) |
| 3 | Up to 35 ULDs | 2.5 x 3 inch printed circuit board | MIB (Multilayer Interconnection Board) |
| 4 | Two MIBs | Magnesium-lithium frame | Page |
Read more about this topic: Saturn Launch Vehicle Digital Computer
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