15-30
AN0013
15
Copyright 1997-2002 RF Micro Devices, Inc.
Packaged Component Reliability
All NBB and NDA products complete a junction temperature measurement before design qualification is completed. The
test verifies device junction temperature in the package at the maximum recommended baseplate operating tempera-
ture.
From Figure 1, RFMD recommends that all NBB and NDA products be operated with a junction temperature below
150°C to ensure MTTF greater than 1 million hours.
The junction temperature is dependent upon several key factors:
1. Baseplate temperature
2. Package type
3. Device bias
4. Die to package attachment process
5. Package to board attachment process
6. Board via layout
Each of these key factors is addressed during thermal junction measurements. Details are given below.
RFMD recommends that these devices be used at a baseplate temperature no greater than 85°C, to ensure that the
device junction temperature limit outlined above is maintained. Therefore all device junction thermal measurements are
performed on components at 85°C baseplate temperature.
RFMD tests all die types in every package style offered. For the NBB series and NDA series the package styles currently
offered are the Micro-X 4-lead surface mount ceramic package and surface mount ceramic multi pin grid array (MPGA)
package.
The junction temperature measurement is carried out at three bias points:
Low current, Id set between half the recommended current and the recommended bias current.
Nominal current, Id set at nominal recommended current.
Limiting current, Id is set to the draw the maximum current while maintaining a device junction temperature of 150°C.
Die are mounted in packages using the standard manufacturing process. However the package lids are not fitted to allow
the die junctions to be viewed during testing.
The packages are then mounted to an evaluation board using a standard RF board material, with the recommended via
hole layout. This layout uses multiple ground via holes to ensure good thermal dissipation away from the package to the
baseplate.
In conclusion, the parts are mounted in a realistic application setting, and the test simulates actual device junction tem-
perature operation at the maximum recommended baseplate temperature for a variety of device biases.
Measurements are performed using a calibrated thermal imaging camera to accurately determine the temperature varia-
tion across the die when mounted in the package. Multiple components of each die type and package style are mea-
sured to allow an average junction temperature result to be generated.
An example of the thermal image generated is shown in Figure 2. This shows the temperature variation across an NBB-
300 (Micro-X style package) at 85°C baseplate temperature, with nominal 50mA device current. The temperature scale
is shown below the image. The image clearly shows the region of maximum temperature with a peak temperature of
139°C. This occurs at the transistor junction.
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