Engineering Analysis And Design
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Engineering Analysis And Design
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Electronic Packaging For Mark 50 Torpedo
The Mark 50 torpedo is one of three major torpedo designs in the U.S. Navy’s inventory. It is an advanced lightweight torpedo for use against the faster, deeper diving, and more sophisticated submarines. The Mark 50 can be launched from an anti-submarine warfare aircraft and from torpedo tubes aboard surface combatant ships. As with all defense related electronics, reliability under even the harshest environments is a critical requirement. When an inspection of the
initial production circuit cards for the Mark 50 torpedo indicated that the
thermal pads used und The thermal assessment began with a review of the original thermal analysis, its assumptions, and its conclusions to understand the basis for the current design. A new 3-D thermal model was developed of the Aft IFE circuit card to serve as an independent check of the original thermal modeling. The thermal model included an effective conductivity for the 12 layer PWB, together with its thru-holes and its three 2 oz. copper ground planes. Heat transfer from the PWB to the transducer array frame occurs via 19 standoffs fabricated of 7075-T6 aluminum. The presence of a foam and fiberglass insulating pad effectively prevents heat transfer into the array frame by any means other than direct conductance through the standoffs. The thermal resistance from the junctions within each of the twenty-six hybrid circuits to the case is set by the manufacturer of the hybrids, while the thermal resistance from the case to the PWB is based on parallel paths through the Kovar leads and through the case bottom and across th thermal pad.
This heat sink could consist of ambient air during operation onboard aircraft or surface ships, or the seawater during operations underwater. The 3-D thermal analysis established that the assemblies build to-date had an adequate thermal margin to ensure reliability and that a retrofit was not warranted. However, given the slight cost associated with the use of a thicker pad, it was recommended that all future assemblies be fabricated with the thicker pad to provide an even greater thermal margin. The temperature contour plot to the left represents the predicted temperature profile for the Aft IFE circuit card with a ‘hot start’ ambient temperature of 54.4°C.
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