Leak Testing method is a highly sensitive technique used to measure fine and
gross leak rates in high reliability devices. It is the preferred method to
characterize small leak rates in critical military components.
The technique was developed in the 1950’s and is still in use today for
evaluating military hybrids, commercial sensors, medical implants, silicon
based MEMS packaging applications and many others.
The advantages of Krypton 85
over other methods include extremely fast test times, lower overall testing
cost, lower leak rate detection (<10-12 atm cc/sec Air limits),
minimal absorption to glasses, leak site(s) identification and the ability to
test in ambient conditions.
of Test Procedure:
The device is placed into a specialized test chamber and pressurized with a gas
mixture of air and small amounts of Krypton-85 gas. The mixture will then enter
the package cavity if a leak is present. The Krypton-85 leak rate equation
determines the pressure and duration of the test based on a reject leak rate
value. The client only needs to determine the reject leak rate (Qs)
value for the package under test.
Krypton-85 equation is defined as:
Qs = R
Qs = reject leak rate (atm cc/ sec Kr)
R = detector reject level (cpm)
S = specific activity (uCi/atm cc)
K = counting efficiency (cpm/uCi)
P = (Pe2 – Pi2)
Pe2 = external bomb
Pi2 = internal
pressure of part (atm)
T = bomb time (hours)
t = 3600 (sec/hr)
pressurization cycle, the packages are typically screened using an X-ray
scintillation crystal. The crystal is capable of detecting up to 15,000 cpm/uCi
of residual Krypton-85. This type of ultra-sensitive detection capability
allows for the measurement of extremely small quantities of Krypton-85 gas that
may have entered the package.
Various crystal geometries are available but two types are the most common. A
flat crystal and/or a well type crystal are commonly utilized depending on the
package size and quantity being tested.
The net X-ray count rate measured is proportional to the total Krypton-85
content within the package. The count rate measured is the actual detection of
the disintegration rate of Krypton-85 molecules. Each Krypton-85 molecule emits
a 0.51 MeV Gamma ray. The total number of molecules that entered the package
can also be calculated and hence the total leak rate of the package. In addition,
the detection process is performed at ambient conditions and thus the packages
are not exposed to vacuum. Testing at ambient conditions mitigates or
eliminates the problems encountered with helium based leak testing.
Gross leaks can
also be measured using a small directional counter (Geiger Müller tube) that
detects the 0.69 MeV Beta particles. This system can be used to pin point the
exit site of the gas from the package.
° Mil-Std 750 method 1071 condition G1, G2
° Mil-Std 883 method 1014 condition B1, B2
° Radioisotope: Krypton-85 gas
° Pressurization range. 30-120 psia
° Minimum detection limit: <1X10-12 atm cc/sec Air
° Accuracy: +/- 10% of value.
° Measurement method: Batch Testing or Read and Record
Oneida Research Services® (ORS)
offers specialized laboratory testing services to support the microelectronics,
tele-communications, aerospace, medical, and defense industries. Our services
focus on research, development
and quality control of our client's products exclusively for our client. ORS
strives to develop long term relationships with our clients through unwavering
professionalism, flexibility and attention to detail.
8282 Halsey Road
Whitesboro, NY 13492
Phone: (315) 736-5480
Fax: (315) 736-9321
For further information
please contact: Deborah
Phone :( 315) 736-5480 ext. 2202