5
Figure 2.0-3: Typical Model 4431 shielded bag waveform
Six specimens of a given sample are required. Six measurements per specimen
is specified. Testing is to be performed at both 12% and 50% ±3% RH at a
temperature of 73 ±3°F after a conditioning period of 48 hours minimum. Bag
size for this test should be 8x10 inches (20x25 cm).
ANSI/ESD STM11.31 specifies that the test conditions, peak current, minimum,
maximum and average energy levels of all 36 measurements be reported for
bag qualification.
2.2 EIA 541-1988 Packaging Material Standards for ESD Sensitive
Items
EIA 541-1988 - APPENDIX E describes the voltage differential test method for
evaluating the relative performance of static shielding bags. Unlike ANSI/ESD
STM11.31, this standard does not define the discharge waveform, capacitive
sensor capacitance or bag size. The standard references a R/C network of 400
kOhms and 200pF, but standard industry practice is to use 1500 Ohms and
200pF.
This test measures the voltage differential between the upper and lower
electrodes of the capacitive sensor. When the 1000 Volt discharge pulse is
applied to the outside of a non-shielding bag, such as plain polyethylene, a pulse
is induced on the upper electrode and a much smaller pulse is induced on the
lower electrode. On the other hand, when the same pulse is applied to a known
good shielding bag, such as aluminum foil sandwiched between two poly bags, a
smaller voltage is induced on the upper electrode, travels around the bag and
induces an even smaller voltage on the lower electrode. These two reference
tests typically result in voltage differentials of approximately 600 and 5 Volts
respectively as shown in Figure 2.0-4.
