Accelerated Aging - Part I

^{Long - Term Storage of Product with ESD Materials Requires Validation!}

Part I.  Accelerated Aging per MIL-PRF-81705E-2010

Mil-PRF-81705E w/AMENDMENT 1 (8 February 2010) requires Surface Resistivity (converted to Surface Volume Resistance), Shielding and Static Decay. Testing to ANSI/ESD STM11.11-2006 & STM11.12-2007 or ASTM D257-1999, ANSI/ESD STM11.31-2006 and Mil-STD-3010B-2008 to simulate long-term storage or use.

Testing Procedure

Specimens are oven conditioned for a period of 12 to 14 days at 160⁰F and placed immediately into an environment of 12%RH, +/-3%RH for approximately 48 to 72 hours:

4.6.8.2 Conditioning of test specimens. Test specimens shall be conditioned at 12 ± 3% relative humidity and 73 ± 5°F for at least 48 hours (Mil-PRF-81705E).

4.6.8.3 Test environment. Perform tests in an atmosphere maintained at 73 ± 5 °F and 12 +/- 3% RH (Mil-PRF-81705E).

The Chemistry of Dissipative Plastics (1989) established that antistats can become insulative in fourteen (14) days. This calculates to a life expectancy or shelf life of about 238 days. Other more severe test methods cut this figure down to only a 90-day life expectancy to maintain a surface resistance value below the upper cutoff limit of <1.0 x 10¹¹ ohms per ANSI/ESD S541 (preconditioned for 48 to 72 hours at 12% +/-3% RH, 73⁰F +/-5⁰F). Dr. John Kolyer (Boeing, ret.) in his book, “ESD from A to Z” discusses the problems that antistats pose by facilitating tribocharging at less than 10% RH. It should be noted that one day at 160⁰ F equals seventeen (17) days at room temperature[1]. 

Antistatic transfer of surfactants (amine agents/fatty acids) can cause stress cracking of the polycarbonate structure of a FR4 circuit board. Mirror fogging, reduced soldering capability and discoloration can take place over time.  http://www.cemag.us/digital_editions/2010/09/flash.html#/12/

Part II.  ANSI/EIA-564-1992 Validates Polycarbonate Compatibility

Test Procedure:

Five EIA-564 specified stress levels can be required while the specimens are subjected to oven conditioning using upwards to four temperatures levels. The polycarbonate specimens are first annealed and placed into strain jigs (Figure 2-left). The agent or material under consideration are applied or fabricated to make intimate contact with the polycarbonate specimens. The samples are place into the oven at a recommended maximum temperature of 185⁰F. Sometimes, specimens are conditioned at room temperature at 730F and evaluated before placement into the over for exposure to heat. After five days the sets are removed from the oven(s) and all specimens are visually inspected for crazing and cracking in comparison to an unstressed sample using microscopic mapping. Figure 2-right shows uncut polycarbonate being microscopically photographed to serve as a benchmark against stressed specimens.

5. Test Specimens (Ref: EIA-564)

5.1 Test specimens are transparent injection molded polycarbonate IZOD bars per ASTM D256. Clean handling techniques should be observed in the preparation and utilization of the polycarbonate specimens.

6.4 Temperature (Ref: EIA 564)

Maintain one set of exposed and strained polycarbonate bars at each temperature being evaluated, namely 73⁰F, 120⁰F, 158°F and 185°F +/-2°F for five days. Reapply agents that volatilize in order to maintain continued chemical exposure.

After five days remove the bars from the jigs, wipe clean and inspect visually for crazes and cracks. Some organizations require testing at the maximum 185°F temperature only for 5 days using the strain jigs 1000, 1700, 2000, 2500 and 3400 psi. This serves as a “worst case” scenario at the 185⁰F temperature level.

The test, polycarbonate bars, which have been bent at various stress levels and exposed to the  supplier’s antistatic type agent or static packaging materials are then subjected to various temperatures for 5 days. Later, said specimens are examined for cracks or imperfections.

                 Table 11                      Highest Compatible Stress Level

(1EOS/ESD Symposium in 1989 by Dr. Marv Havens of Cryovac2 )

According to Dr. Marv Marvin Havens, “A general rule for polycarbonate compatibility is that there be no serious crazing up to the 2000 psi stress level at 1580F.”The data in Table 1 gives the polycarbonate compatibility date for the three versions of Type II film from Marv Haven, Ph.D.   

                Table 2                           EIA 564Full Testing Series

                 Table 3                         Worst Case Request Option (5 days)

                 Passing at 185⁰F would make it unnecessary to test at low temperatures.

3.  Mil-STD-3010B, 31 March 2008, Superseding Mil-STD-3010A-18 August 2005

Test Method 3005 – Contact Corrosivity

Mil-STD-3010B states: 5.3.2.5.4 Exposure. In all cases, the specimen and test surface so arranged shall be exposed for ½ hour in air, maintained at a temperature of 150⁰ ± 5 °F, followed immediately by exposure in air at 120⁰ ± 2 °F and 65⁰ ± 3 percent relative humidity for 20 hours. At the end of the exposure period, the specimens shall be separated from the test surface that shall be immediately examined for evidence of corrosion. Note for each area – the one covered by the specimen, and the other not covered – whether or not corrosion occurred and a description including the severity and distribution of any corrosion.

Some organizations will modify this test by using the actual material that a specimen would make intimate contact with during use.

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