Project Number: C96-25
Failure of Plastic Encapsulated Microelectronics at Low Temperature
Point of Contact: Dr. Pat McCluskey
Phone: (301) 405-5323
Fax: (301) 314-9269
Characterize the effects that limit the use of plastic encapsulated microelectronics
(PEMs) at low temperatures to -65° C, and identify potential failure
mechanisms. Characterize delamination and cracking of PEMs in low temperature
Recently attention has focused on the use of electronics at highly elevated
temperatures. This is a result of the potential benefits to be gained from
the development of distributed control systems, smart sensors, and remote
actuators, which can operate in high temperature environments. To address
this issue, a report was generated this past year describing the generic
materials-related limitations to the use of electronics at elevated temperatures
up to 200° C.
Current systems requiring operation at -40° C and lower, usually
use military grade, hermetically sealed ceramic packaged microelectronic
circuits. However, the limited availability of these devices has prompted
military and aerospace product developers to consider commercial or industrial
grade PEMs for these applications. Advantages to be gained from switching
to PEMs include small size, light weight, and low part cost. However, their
reliability at low temperature has not been well characterized. In particular,
delamination and cracking of the PEMs at low temperatures could lead to
wire breakage as well as corrosion during subsequent high temperature exposure.
A design of experiments study will be conducted to determine the effect
of cold temperature operation on delamination and cracking in representative
PEMs. Packages will be examined before and after low temperature exposure
with C-SAM. The effect of key operating parameters including but not limited
to moisture level, minimum temperature, temperature ramp rate, and package
geometry will be studied.
The materials-related limitations to the use of PEMs at temperatures
as low as -65° C will be determined. Potential failure mechanisms will
A Design of Experiments Plan has been developed to determine the susceptibility
of PEMs to delamination and cracking upon repeated exposure to low temperatures.
This study in its current form will expose 84 lead PQFPs and 14 PDIPs with
different moisture contents to different minimum temperatures at different
ramp rates. Half the samples of each package type will be encapsulated
with a 72% SiO2 filled epoxy novalac which has a low fracture
toughness, and half will be encapsulated with an 80% SiO2 filled
biphenyl compound with a high fracture toughness. Further information about
the proposed design of experiments is available in "Design of Experiments
for investigating delamination and cracking in plastic encapsulated microelectronics
exposed to low temperatures."
Packages encapsulated with an 80% SiO2 filled biphenyl compound
and having a geometry which is highly susceptible to cracking, were exposed
to low temperatures and examined for increased delamination and cracking
as a result of the exposure. Cooling rates of 2°C/min and air quench
(50°C/min) were used to lower the temperature to -55°C or -65°C.
The effect of moisture on cracking was examined by baking some samples
at 125°C for 24 hours prior to low temperature exposure and saturating
others at 85°C, 85%RH for 168 hours prior to low temperature exposure.
For results and details see "Delamination and Cracking in Plastic Encapsulated
Microelectronics Exposed to Low Temperatures."
A capability study has been conducted on a typical device of complex functionality,
a Motorola MC68332 microprocessor.
Ten devices were parametrically tested at -70°C, which is 15°C
below the coldest desired operating temperature, and nine were parametrically
tested at 150oC which is 25oC above the highest desired
75 devices were functionally tested at temperatures below -70°C to
as low as -150°C to determine the distribution of the lowest possible
operating temperatures. In this test the devices are turned on at -70°C
checked for functionality and turned off. The temperature is then decreased
10°C and the devices are again turned on, checked for functionality
and turned off. This is continued until the devices fail or reach -150°C.
Functionality is defined as the operation of the watchdog timer circuit
of the microprocessor. If the devices fail, they are warmed in 10°C
increments and rechecked for functionality to determine if the cession
of operation is a "hard" or "soft" failure. 25 devices are tested as received,
25 are tested after baking, and 25 are tested after moisture saturation.
The results to date are provided in the summary of electrical test results