DESIGN
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efficiency from the die to the package, with the thermal resistance reducing from ~16 C/W in column-grid array ceramic packages to ~0.8 C/W in plastic BGA packages. By allowing the system around the chip to run hot and stay reliable, you expend less size, weight, and cost in the system to dissipate heat by removing a fluid pump, additional heat-sink metal or other heat-removal systems. Design challenge No. 2: Size constraints The space industry calculates launch costs on size and weight, so a smaller, lighter solution is cheaper to launch into orbit. The total package size of flip-chip BGA packaging is smaller than the ceramic equivalent in all dimensions. Figure 1 shows a 15 x 15mm hermetic ceramic package, used for the QML-V ADC12DJ3200QML-SP, with a total height of >6mm. The plastic BGA shown on the right is the package used for both the new ADC12DJ5200-SP and ADC12QJ1600-SP, which fit in a 10 x 10mm package with a total height of <2mm. This significant size reduction means a smaller total solution, reducing the size and weight of the entire system or creating an ability to fit more analog-to-digital converters (ADCs) in the same area. Figure 2 illustrates the improvements in package size of the 10 x 10 x 1.9mm ADC12DJ5200-SP and ADC12QJ1600-SP (which share this package) to the prior generation 15 x 15 x 6.2 ceramic ADC12D- J3200QML-SP. Design challenge No. 3: Increasing bandwidth For high-frequency products in flip-chip packages, plastics provide superior electrical performance when compared to ceramic for these reasons: • The relative permittivity of the organic substrates in plastic packages is about 3.7; for ceramic, it is 9.8. As a result, capacitive
space missions. As listed in Table 1, the most important differences are higher single-event latch-up immunity, a higher total ionising dose, the production burn-in and the life test per wafer lot. It is possible to mitigate design challenges by using plastic packaging with the same pinout and basic package used in space- and industrial-grade versions. In addition to reducing development time and resources, space application designers should consider the thermal efficiency, size, and bandwidth benefits of plastic packages. Design challenge No. 1: Thermal efficiency Traditional hermetic ceramic package designs require placing the die in a cavity and welding a lid to the top of the cavity to provide a moisture-proof solution. This design leaves an airgap between the die and the metal lid that is difficult to bridge with a thermal epoxy. With flip-chip BGA SHP packaging, the metal lid connects to the back of the flip-chip die directly with thermal epoxy; there is no airgap to fill.
Figure 1. Comparing hermetic-ceramic packaging to plastic packaging
TI has seen an improvement in thermal
Figure 2. Comparing the packaging size across generations of space-grade ADCs
32 ELECTRONICSPECIFIER.COM
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