Cost: Plastic packages cost pennies, ceramic packages 10's of cents, and power and hermetic packages cost dollars. Unpackaged die are usually priced in the same range as ceramic packaged devices due to the high handling costs associated with these devices.
Volume assembly requirements: Surface mount compatibility (SMT) and trimmed leads are usually required
Hi-Rel screening or hermeticity: ceramic packages are OK for lower levels of screening; gold hermetic packages are needed for full "Space level" qualification.
Electrical performance: Less expensive packages often have higher parasitic inductance and capacitance than higher quality packages. The effect of these higher parasitic levels is to reduce gain at higher frequencies (typically noticeable above 1 GHz) and, in some cases, to reduce stability. For some higher powered products, the poorer thermal conductivity of certain packages will require operation at lower bias levels, and hence reduce device performance.
depends on application
packages are denoted by a 2 number code, usually the last two numbers of the part number (see nomenclature). Package types include:
SMT (surface mount)
Surface mount packages have co-planer leads that allow for device mounting without the use of through holes. Surface mount capability is generally considered to be a requirement for automated assembly.
4 formed lead 145 mil power
SO-8: 8 lead industry standard (for power)
SOT-143: industry standard low parasitic
SOT-343: SC-70 4 lead miniature
SOT-363: SC-70 6 lead miniature
4 formed lead 85 mil low parasitic improved thermals
4 lead ceramic "micro-x"
4 lead ceramic "micro-x" with lead trim
4 lead ceramic with lead trim
8 lead 180 mil microstripline
4 lead 100 mil stripline for high performance for larger die
4 lead 70 mil stripline for high performance
4 trimmed lead 145 mil power
4 trimmed axial lead 85 mil low parasitic improved thermals
4 axial lead 85 mil low parasitic improved thermals