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DuPont Braze System Simplifies Hermetic Packaging In Communications Satellite Power Control Module

Challenge: Reliability in an Extreme Environment

Space Systems/Loral of Palo Alto, Calif., is a manufacturer of high-power satellites for the telecommunications and direct broadcast industries. The satellites Space Systems/Loral builds must perform continuously for up to 15 years in extremely harsh thermal environments in space, where temperatures can oscillate rapidly between - 1 80°C and +150°C.

Recently, Space Systems/Loral developed a novel integrated hermetic hybrid package for a critical communications satellite power control module, which regulates power between the solar array panels and the spacecraft. The package is formed by integrating and electrically isolating the feed-throughs on the substrate, using a thick film seal ring and Au conductor compositions formulated for compatibility with low-temperature brazing.

Solution: Thick Film for Cost-Effective, Reliable Hermetic Packaging

To fabricate the two-layer thick film circuit for the hermetic package, Space Systems/Loral chose two DuPont thick film products, the 5062/5063 low-temperature gold braze system and 5704M multilayer dielectric. DuPont 5062/5063 was selected for the ring frame footprint because of its superior wetting characteristics when reflowing with a forming gas (5% H 2 , 95% N 2 ) atmosphere.

The ring frame footprint is electrically isolated from the feed-throughs and circuit using 5704M thick film dielectric . One advantage of the thick film material is that a uniform, concave solder fillet is formed between the ring frame and the thick film ring frame footprint, thus absorbing much of the thermal expansion mismatch stresses.

To make sure the new hermetic package design met requirements, Space Systems/ Loral conducted rigorous environmental tests on numerous sealed units, including thermal cycling for 100 cycles from -65°C to +150°C, followed by a mechanical shock of 1500 g, and fine and gross leak tests. The sealed units passed these tests. To further verify the robustness of the new design and soldering process, five units were subjected to additional thermal cycling at increasingly lower temperature extremes, down to -100°C. These five units experienced a 100 percent pass rate until they were cycled between -100°C and +150° C for 10 cycles, at which time only a single unit failed.

The new thick film design eliminates the need to place the substrate assembly in a separate and expensive hermetic package, avoids hermeticity problems associated with glass-sealed feed-throughs, and allows for a faster turnaround time in manufacturing. This new cost-effective approach to hermetic packaging is expected to find wide application in the growing market for commercial telecommunications and direct broadcast satellites, where reliability is a key requirement.

For more information, call DuPont at 1-800-284-3382, press 3.