AN1231 Motorola / Freescale Semiconductor, AN1231 Datasheet - Page 18

• Manufacturer Part Number: AN1231
• Description: Plastic Ball Grid Array (PBGA)
• Manufacturer: Motorola / Freescale Semiconductor

AN1231
18
currently susceptible to moisture induced delamination or
popcorning if it is heated to reflow temperatures with exces-
sive moisture content. The moisture weight percentage at
which damage can occur is typically 0.15%. The PBGA is
currently specified to meet Level 5 of the JEDEC classifica-
tions for moisture sensitivity in Test Method A112
(JESD22–A112). Level 5 in this test method, states that the
PBGA will not exhibit delamination after exposure to
30 C/60%RH for 30 hours. The accompanying user handling
requirements are a 24 hour out or drypack life. Any exposure
over this 24 hours will require baking at 125 C for 24 hours. It
is recommended, where possible, that this bake be per-
formed in an inert atmosphere such as nitrogen to minimize
potential solder ball oxidation.
age is delamination of the die attach from the die flag. This
delamination, caused by the vaporization of the trapped
moisture, is clearly visible in the form of a bubble in the BT
substrate immediately under the die location. If the moisture
content is high enough this delamination occurs violently
(i.e., popcorning) and the delamination will propagate along
the mold compound/BT interface until it is visible around the
perimeter of the package. When this occurs, it is likely that an
accompanying shorting of solder balls will occur in the area
under the die. For this reason, it is advised to bake and dry
pack even mechanical samples or daisy-chain devices prior
to process assembly experiments.
ability tests included in the packaging reliability program.
This program includes the PBGA.
SMT Preconditioning Stress
storage, and solder attach steps involved in mounting and
reworking a surface mount device. The preconditioning flow
begins with ten temperature cycles at –65 to 150 C,
dehydration bake at 125 C for 24 hours and is followed by a
moisture soak. The moisture soak may involve simulating a
worst case “no dry pack” condition in an 85 C/85% RH
environment, a worst case dry pack condition of 85 C/60%
RH, or a typical manufacturing environment condition of
30 C/60% RH. The duration of the moisture condition will
vary depending on the moisture level tested. Moisture
exposure is followed by two passes of infrared reflow
(230 C) for 20 seconds per pass. Infrared reflow equipment
is capable of heating the top side package body to 230 C
with a ramp rate of 2–10 C per second.
Temperature Cycle
match among the different components within a specific die
and packaging system. This test is typically performed to
minimum and maximum temperatures of –65 to 150 C for a
duration of 500 or 1000 cycles. During temperature cycle
testing, devices are inserted into a cycling system and held
at a cold dwell system for at least ten minutes. Following this
cold dwell, the devices are heated to the hot dwell where
As with all plastic surface mount packages, the PBGA is
The mode of moisture-induced failure in the PBGA pack-
The following summary briefly describes the various reli-
The purpose of this test is to simulate the shipping,
This test accelerates the effects of thermal expansion mis-
MOISTURE AND POPCORNING
RELIABILITY STRESS TESTS
they remain for another ten minutes. the system employs a
circulating air environment to assure rapid stabilization at the
specified temperature.
Thermal Shock
ture cycle testing: to emphasize differences in expansion co-
efficients for components of the packaging system. However,
thermal shock provides additional stress because the device
is exposed to a sudden change in temperature due to the
transfer time of ten seconds maximum as well as the in-
creased thermal conductivity of a liquid ambient. This test is
typically performed to a minimum and maximum tempera-
tures of –65 to 150 C for a duration 500 or 1000 cycles. De-
vices are placed in a fluorocarbon bath and cooled to
minimum specified temperature. After being held in the cold
chamber for five minutes, the devices are transferred to an
adjacent chamber filled with fluorocarbon at the maximum
specified temperature for an equivalent time. Two five minute
dwells plus two ten second transitions constitute one cycle.
Temperature Humidity Bias (THB)
of 85 C. The test is designed to measure the moisture resis-
tance of plastic encapsulated circuits. A nominal static bias is
applied to the device to create the electrolytic cells neces-
sary to accelerate corrosion of the metallization. Typical
stress duration is 1008 hours.
Autoclave
resistance to moisture penetration and the resultant effects
of galvanic corrosion. Conditions employed during the test
include 121 C, 100% relative humidity, and 15 psig. Corro-
sion of the die is the expected failure mechanism. Autoclave
is a highly accelerated and destructive test. Typical test dura-
tion is 96 hours.
cluded in Appendix D.
have appeared in trade journals and have been published in
conference proceedings that discuss issues related to
PBGA. All articles are listed alphabetically by principal au-
thor/editor last name. Articles for which there is no copyright
may be available informally through Motorola.
Electronic Engineering Times , March 1, 1993, p. 70.
neering Times , August 2, 1993, p. 16.
Assemblies Using Thermal Stress Simulations and a Coffin-
Manson Relation”, Proceedings of ECTC, 1991.
Based Solder Joints,” IEEE Trans on CHMT, Vol. 15, No. 6,
December 1992, pp. 1013 – 1024.
Mount Solder Joints,” Proceedings ISHM 25th International
Symposium on Microelectronics, Dallas, TX, 1993.
Free from Design Constraints”, Computer Design , June
1993, pp. 65 – 68.
RELATED TECHNICAL ARTICLES AND PAPERS
The objective of this test is the same as that for tempera-
This is an environmental test performed at a temperature
Autoclave is an environmental test that measures devices
Results from a qualification of an 86 pin PBGA are in-
This section provides only a partial listing of articles that
R. Boyd-Merritt, “Moto Fields New Package Technology”,
T. Costlow, “Moto Pact Big for BGAs?”, Electronic Engi-
R. Darveaux and K. Banjeri, “Fatigue Analysis of Flip Chip
R. Darveaux and K. Banjeri, “Constitutive Relations for Tin
R. Darveaux, “Crack Initiation and Growth in Surface
M. Donlin, “Packaging Innovations Help Engineers Break
MOTOROLA FAST SRAM