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ELECTRONIC DEVICE FAILURE ANALYSIS | VOLUME 18 NO. 2
After 10 to 30 s, the acid is rinsed with acetone for neu-
tralization. The process is repeated until the die and wire
bonds of the package are exposed.
While the rotary-tool method is the standard practice,
it does have some drawbacks:
• The drilling process introduces an outside source of
disruption to the device.
• The drilled well still allows the nitric acid to flow from
the surface of the encapsulant.
• It is difficult to direct where the acid is working on the
encapsulant.
THE SOLUTION
Faced with the shortcomings of the current process,
the company set out to find a better solution. They dis-
covered that Texas Instruments had successfully used
a 2078 Viton Caulk from Pelseal Technologies to assist
with decapsulation. This caulk exhibits strong chemical
properties and remains flexible in service. The company
decided to adopt this approach by using the caulk to build
up awell to contain the nitric acid, rather than drilling into
the component.[1]
To form the well, ACI built up approximately 2 to 4 g
of caulk above the die location (in place of carving out a
small well) and placed the component on the hot plate.
When the component reached the correct temperature,
the operator droppednitric acid into the fabricatedwell to
allow digestion of the packaging material. This was then
rinsed with acetone, and the process was repeated until
the die was exposed.
After using the caulk-constructed well method of
decapsulation, the company found:
• By not drilling directly into the surface of the die, no
additional mechanical damage was introduced.
• Electrostatic discharge/electrical overstress was
removed from the equation, thus increasing the con-
fidence in the results.
• The caulk adheres easily to awide range of component
materials.
• The caulk was easily removed after decapsulation by
simply tugging on it with a pair of tweezers. (The caulk
stood up to repeated acetone rinse steps.)
• The depositionof the caulk permits outlining of various
geometries, making it possible to use it with a wide
range of die sizes and shapes.
• Safety is increased by creating a well on the surface
of the die that stands above the original topography,
eliminating any splashing or accidental misuse of
concentrated acids.
• A larger quantity of acid could be used in the caulk-
constructed well, resulting in less time needed for the
decapsulation process.
After determining that the use of a caulk well made
the decapsulation process easier and more effective, the
engineering research company decided to continue using
the caulk, and they plan to integrate it into their standard
decapsulation procedures.
REFERENCE
1. K.D. Staller: “Safe Decapsulation Techniques Using Viton Caulk,”
Proc. 40th Int. Symp. Test. Fail. Anal. (ISTFA 2014), Nov. 9–13, 2014
(Houston, Texas).
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