MIL-STD 810, Method 501 High Temperature Testing is used to evaluate the effects of high temperature conditions on performance, materials, and integrity.  Method 501 is applicable for temperature testing products that are deployed in areas where temperatures (ambient or induced) are higher than standard ambient.  Note, the latest revision of this method is 501.7 from MIL-STD-810H.

Method 501 is limited to evaluating the effects of relatively short-term (months, as opposed to years), even distributions of heat throughout the test item. This method is not typically practical for evaluating materials where solar radiation produces thermal gradients or photochemical effects.  Method 505 is used to test the effects of solar radiation.  It is also not practical to evaluate degradation that occurs from continuous long-term exposure to high temperatures where synergetic effects may be involved.

The following are typical failures that could occur from products used in high temperature environments.

• Parts bind from the differential expansion of dissimilar materials.
• Lubricants become less viscous; joints lose lubrication by the outward flow of lubricants.
• Materials change in dimension.
• Packing, gaskets, seals, bearings, and shafts become distorted, bind, and fail causing mechanical failures.
• Gaskets display permanent sets.
• Closure and sealing strips deteriorate.
• Fixed-resistance resistors change in values.
• Electronic circuit stability varies with differences in temperature gradients and differential expansion of dissimilar materials.
• Transformers and electromechanical components overheat.
• Operating/release margins of relays and magnetic or thermally activated devices alter.
• Shortened operating lifetimes.
• High pressures are created within sealed cases (batteries, etc.).
• Discoloration, cracking, or crazing of organic materials.
• Out-gassing of composite materials or coatings.
• Failure of adhesives.

MIL-STD-810 Method 501 Tests: High Temperature Procedures

1. Procedure I – Storage.  Procedure I is for testing products that are stored at high temperatures.  After the high temperature storage test is completed, an operational test at ambient conditions is performed.  Procedure I can be either a cyclic temperature test or a constant temperature test. 
2. Procedure II – Operation.  Procedure II is used to investigate how high temperatures could affect the performance of items while they are operating.  Temperature Procedure II can be performed as either a cyclic temperature test or a constant temperature test. 
3. Procedure III – Tactical-Standby to Operational.  This temperature procedure evaluates the material’s performance at normal operating temperatures after being presoaked at high non-operational temperatures.  An example of Procedure III is a product that is stored in an enclosed environment that develops high internal temperatures before being removed and then operated in a relatively short period of time.

What is the procedure for MIL-STD-810 High Temperature Testing? 

First, identify the high temperature levels, test conditions, and applicable procedures. DES can help determine the appropriate temperature ramp rates and durations of the tests based on the equipment’s intended use and the operating environmental conditions.  Consider the following climatic temperatures from Table 501.7-I. (MIL-STD-810H):

Next, determine whether a constant temperature test or a cyclic temperature test is appropriate.  Constant temperature testing is used only for items situated near heat-producing equipment or when it is necessary to verify the operation of an item at a specified constant temperature.  The duration for constant temperature test temperature is at least two hours following test specimen stabilization.

For cyclic exposure, there are two 24-hour cyclic profiles contained in Tables 501.7-II and 501.7-III.  The number of cycles for the Procedure I storage test is a minimum of seven to coincide with the one percent frequency of occurrence of the hours of extreme temperatures during the most severe month in an average year at the most severe location.   The minimum number of cycles for the Procedure II operational testing is three. This number is normally sufficient for the test item to reach its maximum response temperature.

You can trust the DES MIL-STD-810 High Temperature Testing lab

Advantages with DES : 

• DES is A2LA accredited to MIL-STD-810, Method 501 High Temperature Testing
• DES has extensive experience running MIL-STD-810 Method 501.7 high temperature Tests
• DES has multiple temperature chambers capable of performing MIL-STD-810 high temperature compliance testing

Contact us today to to discuss testing your product in our MIL-STD-810 accredited Test Laboratory. 

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DES recently performed package testing per ASTM standard, ASTM D7386-12.  The test included shipping vibration testing which was conducted on DES’s Unholtz Dickie ED Shaker System.  ASTM D7386-12 requires packages to withstand random vibration levels of approximately ½ Grms over the frequency range 1 – 200 Hz.  This test is meant to simulate environments these packages could see in the field.  It is extremely important for manufacturers to test the effectiveness of their package designs prior to product shipment.  Shipping environments can put a lot of stress on products.

Improper package design can cause products to fail when the customer receives the product.  Environments such as high altitude, temperature, humidity, vibration and shock are common for most packages.  High return rates due to damage during shipment can cripple a company’s bottom line.  Prevent this from happening and send DES your packages to test!

Other package testing standards DES is capable of include (but not limited to):

• ISTA 1 Series
• ISTA 2 Series
• ISTA 3 Series
• ASTM D3580 Vibration (Vertical Linear Motion) Test of Products
• ASTM D4169 Performance Testing of Shipping Containers and Systems
• ASTM D4728 Random Vibration Testing of Shipping Containers
• ASTM D7386 Performance Testing of Packages for Single Parcel Delivery Systems
• ASTM D999 Vibration Testing of Shipping Containers

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Equipment with single or multiple chambers may be used to perform thermal shock testing. When using single chamber thermal shock equipment, the products or samples remain in one chamber and the chamber air temperature is rapidly cooled and heated. This usually results in a slower rate of change in the product response temperature as the entire chamber must be cooled down and heated up. However larger products can be tested in single compartment chambers. Some equipment uses separate hot and cold chambers with an elevator mechanism that transports the products between two or more chambers. This results in a more rapid rate of change in the air temperature. However, there is a limit to the size and weight than can be put in a chamber with an elevator mechanism.  DES has both types of chambers for thermal shock testing.

When performing thermal shock testing, the upper and lower temperatures must be carefully determined. Larger differences between the test chamber temperatures and the product normal use temperatures will result in higher acceleration factors as determined from the Coffin-Manson equation. However, the correct temperature limits must be chosen to not exceed the operating limits or material property limits of the product. For example, an upper temperature that exceeds the melting point of any material in the product would likely result in invalid test failures. It is therefore important that these temperatures be properly measured and monitored during the test through the careful placement of thermocouples on and around the products or samples.

Factors that can influence the test parameters include the thermal mass of the samples, the number of samples and the airflow around the samples that depends on the sample spacing in the chamber. The dwell time at each temperature should be included in the test specification along with the tolerances around the high and low temperatures. Test methods may also specify minimum rates of temperature change.

Products may be powered or unpowered during the thermal shock test. Products that are powered during the test need cables that are long enough to reach outside of the chamber and can fit inside the chamber feed through.

Delserro Engineering Solutions, Inc. (DES) has many years of experience performing thermal shock testing and can assist customers in setting up a test using the proper test conditions. So if you do not know what test conditions that you should use or what specification to choose, then we will help you because we are thermal shock testing experts!

Examples of some common thermal shock test specifications include:

• MIL-STD-202, Method 107, Thermal Shock
• MIL-STD-810, Method 503, Temperature Shock
• MIL-STD-883, Method 1010, Temperature Cycling
• JESD22-A104D, Temperature Cycling

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Specialized test chambers are needed to perform a HALT. Typical HALT chambers are shown in Figure 1. The specification for HALT chambers is typically the following:

Liquid nitrogen (LN2) is used to cool the air temperature in HALT chambers. This allows for very rapid temperature changes of 60°C per minute and a cold temperature extreme of -100°C.

HALT chamber heating is provided by high power resistive heating elements that can produce changes of 60°C per minute and a hot temperature limit of +200°C.

HALT chambers produce random vibration in 6 DOF simultaneously using pneumatic air hammers attached to the bottom of the chamber table. This means random vibration energy is applied simultaneous along three orthogonal translations and three rotations which is very unique to HALT chambers. Sometimes the vibration produced in HALT is called repetitive shock because pneumatic air hammers are used to produce vibration.

Random vibration accelerations up to 60 Grms and frequency content to 10,000 Hz are common. It is important to understand how the how HALT chambers compute Grms. DES’s HALT chambers calculate Grms using a 5 kHz bandwidth. Some chamber manufactures use a 10 kHz bandwidth which approximately doubles the computed Grms, but in reality the resultant vibrations are about the same! More information about random vibration can be found in our blog article Sinusoidal and Random Vibration Testing Primer

It is important that HALT chambers can be run in automatic or manual modes of operation. Temperature and vibration profiles are programmed to run automatically during parts of the HALT procedure. This allows the temperature rate of change to be accurately controlled during temperature transitions. The chamber can also be run in manual mode with the operator controlling the temperature and vibration set points. This is useful for other parts of the HALT procedure such as when operational or destruct limits are being determined.

Fixtures

DES’s has many stock channel fixtures that can be used for products with a flat top and bottom. Examples of DES’s stock channel fixtures are shown in Figure 2.

Custom-designed fixtures can be fabricated on a case by case basis. Figure 3 shows examples of custom-designed test fixtures. The fixtures must have a flat base with holes to enable them to be bolted to the chamber vibration table. Customers or DES can supply the fixtures used to attach the test units to the vibration table inside the chamber.

When performing HALT, it is desired to change the temperature of internal components as fast as possible. If products have existing vent holes or cooling fans, then air ducts can be placed to blow air through them as seen in Figure 2. Products with a sealed enclosure or case should be modified whenever possible to allow for internal airflow. This can be done by removing covers when practical or drilling holes in the enclosure. Air ducts can then be placed near these openings to direct air flow internally into the product.

Instrumentation and Monitoring

Monitoring can be accomplished with either digital recording instruments or by manually recording gauge readings or by visual observations. Monitoring sensors are usually thermocouples and vibration accelerometers. Reference thermocouples are placed at various locations on the product to measure the response temperatures on the product. Also, during the vibration step part of the HALT procedure, reference vibration accelerometers can be placed on the product to measure its vibration response. Therefore a digital temperature data recorder is needed and a vibration spectrum analyzer or Grms recorder is useful. HALT chambers will typically provide basic digital recording of the chamber temperature and table Grms. DES provides the equipment for recording all of the temperatures and vibrations. Many times the customer provides the equipment for monitoring the specific performance of their product. However, DES has the capability to provide all of the monitoring equipment and instrumentation if desired. DES has extensive experience in setting up custom monitoring to record many different parameters such as voltage, current, pressure, etc.

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The goal of this article was to teach product developers how to get the most bang for their testing buck; a goal that aligns perfectly with DES’s philosophy. No matter what your testing needs are, be they HALT, HASS, or other environmental or stress tests, DES is able to help you design and implement the most comprehensive and accurate test possible. As always, our client’s success is the source of our satisfaction.

Showing Our Advanced Testing Capabilities

The article highlighted DES’s advanced capabilities when it comes to designing complex testing equipment. In this instance, the devices being tested were a series of proposed new sensors for car engines. For this test series, the testing fixture was incredibly complicated and the testing included combined temperature, vibration, and electrical loads, a perfect fit for DES’s vibration shaker chamber.

When you need a HALT or HASS test, or any other testing services, DES has you covered. Our engineers have more than 60 years of combined successful engineering experience. We specialize in stress, reliability, durability, vibration, shock, highly accelerated life testing (HALT), highly accelerated stress screening (HASS), accelerated life testing, and environmental testing. When done correctly, these tests can help you save money, cut production time, and increase product reliability.

Helping Save on Production Costs

The article closed with a few tips from DES and other testing engineers on how they can form the best working relationship with a reliability testing facility. Appropriate communication was the top recommendation. However, there are a host of tips in the full article on getting the most out of your product test.

To read the full article, visit Desktop Engineering. If you’re interested in running a test, contact Delserro Engineering Solutions.

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The Equipment Capabilities Are:

• Combined shock or sinusoidal, random, mixed mode vibration and temperature
• Temperature range from -80°C to +180°C (-112°F to +356°F)
• Temperature rate of change up to 20°C/minute
• 9 cubic feet interior work space, cvo

To learn more about our combined temperature and vibration testing services, visit our website, and be sure to contact us if you would like to find out how our services can work for your products.

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• We completed a Pyroshock test on our Mechanical Impact Pyroshock Simulator (MIPS) on equipment that will fly into outer space.
• On the other end of the altitude spectrum, we completed environmental testing of components that will be used in submarines to MIL-E-917.  MIL-E-917 is a military specification for Naval shipboard electric power equipment.
• In the middle of the altitude range, we performed combined temperature and vibration testing on sensors that will be used in automobile engines to specification GMW 3172.  GMW 3172 is a General Motors Specification for electronic component durability.

The following is a sample of some additional testing projects we have completed recently:

• Reliability and HALT tests on a heart assist device

• Reliability testing on sports equipment used by professional athletes to MIL-STD-810G

• Vibration testing on a fire safety product to UL specifications

• Salt fog testing on security equipment to ASTM B117

• Threshold reliability testing on a medical cart

• Temperature, humidity, vibration and shock tests on industrial electronic equipment to IEC specifications

• Thermal cycle testing on commercial lighting equipment

• HALT testing on military equipment

• Vibration testing on heavy duty truck equipment to SAE J1455

• Built a custom life cycle test rig for a medical device used for heart surgery

• Vibration tests on credit card readers that plug into cell phones

• Temperature and vibration tests on thermometers used in aircraft

• High G level vibration tests on transmitters used in rockets

We can’t discuss too many details due to the sensitive nature of the products.

To learn more about our variety of different testing techniques including: vibration testing, stress screening and new product reliability, feel free to contact us.

The post Recent Testing Projects appeared first on Delserro Engineering Solutions.

Environmentally friendly is a term rapidly invading the electronics industry.

The electronic industry will be facing great challenges over the next few years as the solder used in electronic products is migrating toward lead-free.  This is being driven by mandates in Europe such as Waste Electrical and Electronic Equipment (WEEE) and Restrictions of Hazardous Substances (RoHS) and similar ones in Japan.  There also is a great deal of pressure in the US to do the same.

Many electronic component suppliers have or will be phasing out their parts used for tin-lead solder.  The new components made for lead-free solder will have different finishes on the leads than those used for tin-lead solder.  If that is not enough reason to change to lead-free solder, some of your competitors may be already producing electronic products with lead-free solder and are using this as a strong competitive marketing tool.  Furthermore there is and will be ever-increasing pressure to be environmentally friendly.

Changing over to lead-free solder is a very significant change over.  After all, solder is the glue that holds our electronics products together.  We have successfully used tin-lead solders for years and have good engineering knowledge about their reliability.  Now we must change this most fundamental and important building block.

We also must make certain that the lead-free product is just as reliable as the one that has been using tin-lead solder for years.  We must ensure that it is reliable for use in sometimes-critical applications with very demanding environments.  And, we must do this without having the benefit of long-term engineering or product experience with lead-free solder.

Reliability Issues of Lead-Free Solder

Broad lead-free vs. tin-lead solder reliability trends cannot be assumed.  The creep-fatigue models for lead-free solder are not fully developed at present.

Published test results comparing the reliability test life of lead-free vs. tin-lead solder are inconsistent.  Many different variables including solder alloy mixes, solder fluxes, board finishes, manufacturing process variables, component finishes, packaging, and test variables such as stress type, temperature range, and dwell time affect the testing.  The results are test and product specific.

Lead-free solders have a higher melting point than tin-lead solders.  Many lead-free solder alloys have a melting point above 215 °C compared to 179 °C to 188 °C for tin-lead solders.    

Figure 1.  Tin Whisker Growth on Capacitor Terminations after 200+ Temp Cycles from -40°C to +90°C Followed by Months of Ambient Storage.  Courtesy of the NASA Electronic Parts and Packaging (NEPP) Program (http://nepp.nasa.gov/whisker/)

Lead-free solders have poorer wetting characteristics than tin-lead solders which increases the risk of solder defects.  This means that much higher process temperatures must be used to melt lead-free solder for longer durations to overcome the poorer wetting characteristics.  These harsher process conditions may cause damage to the circuit board and the electronic components and reduce product reliability.

Lead-free solder is susceptible to failure modes such as tin whiskers, Kirkendall voids, and resistance to mechanical shock.  Tin whiskers can grow from tin-based finishes on components and connectors in a lead-free solder joint (Figure 1).  A whisker is a thin cylindrical growth or filament.  These whiskers are brittle and can break off or bridge cross solder joints to cause electrical shorts.

Tin-whisker growth is aggravated when there are compressive stresses in the tin plating.  Ironically, lead was added to the tin to mitigate whiskering in the past.

Some precautions can be taken to help avoid whisker growth such as: not using tin plating, stress relieving or annealing the components with tin plating and using conformal coatings.  At present, there is no absolute recipe to avoid tin whiskers — except to not use tin plating — because this phenomenon is not fully understood.  Test results have shown that tin whiskers can be grown as a result of temperature cycle tests and constant temperature/humidity tests.

Kirkendall voids are caused by intermetallic growth between two dissimilar metals, specifically tin and copper in a lead-free solder joint.  Intermetallic growth is caused by diffusion of one material into another.

The diffusion between copper and tin is unbalanced causing Kirkendall voids to occur.  These voids can accumulate and reduce the strength of the solder joints.  Kirkendall void growth can be aggravated by accelerated aging at high constant temperature.

Many lead-free solder alloys are stiffer or less ductile than tin-lead solders.  This is an area of concern for highly stressed vibration environments and mechanical shock conditions.

Also, many lead free solder alloys lose their ductility very abruptly at approximately -30 °C.  This transition temperature is affected by different alloy blends and becomes very important when used in outside applications such as automotive or aerospace.

In addition, the possibility exits for reliability issues prompted by lead contamination in lead-free solder joints, especially those containing bismuth.  This may occur when using a lead-free alloy to solder a component with tin-lead plated leads.  The lead may accumulate and form voids that will weaken the solder joint.  The mechanical fatigue strength could be reduced by as much as 50% with as little as 0.5% weight contamination.  Some thermal cycling test results also show significant life reductions.

Reliability Testing

A typical circuit board may contain hundreds of solder joints with many different types of components.  So how do you ensure that your lead-free product will remain reliable in its intended use?

A comprehensive reliability test program is a must.  Start with a Highly Accelerated Life Test (HALT) using a HALT chamber.  HALT chambers can apply rapid thermal ramps rates and random vibration in 6-degrees-of-freedom simultaneously.

Sometimes a one day Rapid HALT is beneficial just to get preliminary reliability information.  The HALT can be started at the circuit-board level with special fixtures as shown in Figure 2.  After the HALT has been completed successfully at the circuit-board level, a verification HALT can be performed on the assembled product.

Figure 2.  Special HALT Fixture

It also is important to perform the HALT on a sample of both lead-free and tin-lead boards.  This can be performed simultaneously if space permits or as two separate tests.

Perhaps the product with tin-lead solder has already been completed HALT so just the new lead-free product will have to undergo HALT.  Still, it is very important that a HALT be performed on both lead-free and tin-lead products to ensure the lead-free product is as reliable as the tin-lead product or until unrealistic temperatures are reached.

By starting with HALT, reliability results can be obtained within days instead of waiting weeks for accelerated reliability tests.  A HALT is a qualitative step stress test¹.  The stresses will be increased until operating and then destruct limits are found.

In addition, HALT uses combined temperature, vibration, and electrical stresses so your lead-free product will be exposed to multiple types of stresses during one test.  Why spend weeks of accelerated reliability testing if HALT shows immediately that your new lead-free product does not perform as well as your existing tin-lead product?

Since the lead-free solder-joint reliability issues are broad, it is risky just to perform HALT or just one type of accelerated environmental test.  The overall test plan is dependent on the product type and application.  A product that will be used outdoors will have a different test program and test levels than a product in an office environment.

Vibration tests are performed to test a product’s tolerance to vibration in automotive or aeronautical applications.  Random spectrums typically are used during vibration tests using an electrodynamic (ED) shaker.  Durations generally are one hour or more per axis.

Mechanical shock and drop tests are completed to determine the solder joint’s capability to withstand rough handling environments.  Shock is a high-intensity, short-duration impulse load.

Shock or drop simulations usually are performed on special shock tables, ED shakers or drop testing machines.  The number of pulses could range from a few to many depending on the product’s intended use.  Classical shock pulse types are haversine, half-sine, saw-tooth, square and trapezoid.

If the product is not exposed to much vibration in its lifetime, perhaps just drop and severe shipping vibration tests are appropriate.  Test specifications depend on product type and application.

Vibration and mechanical shock tests usually are performed at ambient temperatures.  For combined effects, a HALT or ED shaker with an Advisory Group on Reliability of Electronic Equipment (AGREE) type chamber is typically used.

Temperature testing involves cycling a product between high and low temperatures.  These tests usually are performed in single-compartment chambers at rates of 20 °C/minute or less.  The maximum and minimum temperatures and the total number of cycles depend on the product and its application.

Lead-free solder requires greater dwell times during thermal cycling to produce the same amount of fatigue damage that would occur to tin-lead solders.  For that reason, a different accelerated-temperature cycle test using longer dwell times must be performed for lead-free solder.

Figure 3.  Data is for CBGA components on FR-4 circuit boards cycled between 0 °C to 100 °C.  Reprinted with permission from EPSI, Inc. [2]

There are various opinions on the minimum dwell times required during temperature cycle tests for lead-free solder.  Figure 3 suggests an optimum dwell time of 10 minutes is most efficient for lead-free assemblies using Sn-Ag-Cu (SAC) alloys; however longer dwell times technically are valid.²  This data is specific for Ceramic Ball Grid Array (CBGA) components mounted on FR-4 circuit boards cycled between 0 °C to 100 °C.

These optimum dwell-time results should not be extrapolated broadly.  Also, the dwell times should be measured on the product and not the incoming chamber air.  This may require longer dwells in the chamber profiles to achieve the proper dwell times on the product.

Thermal shock tests are performed to determine a products resistance to extremely rapid temperature changes.  Thermal shock tests are typically conducted in single-compartment liquid nitrogen-cooled chambers, or multi-compartment chambers where the product is moved between hot and cold compartments.

As a rule, thermal shock tests are usually performed at a rate of 30 °C/minute or greater.  In thermal shock, higher stresses and less creep occur in the solder joints; in thermal cycle tests, lower stresses and more creep occur.

Different failure modes will probably occur in the solder joints during thermal shock versus thermal cycle tests.  This is true for both lead-free and tin-lead solder joints. Thermal shock tests may not be appropriate for every product.

Constant temperature or humidity tests are conducted to determine a product’s susceptibility to thermal aging, humid environments, and extended use at cold temperatures.  These tests are conducted in single-compartment chambers under ambient atmospheric pressure.

Sometimes, a Highly Accelerated Stress Test (HAST) can be performed to significantly shorten the time required for humidity testing.  HAST is performed in a special chamber that provides non-condensing humidity at temperatures higher than 100 °C and pressures greater than atmospheric.  It usually achieves the same failure modes as an 85 °C/ 85% RH test conducted under normal atmospheric pressure.

These tests are the most commonly performed tests to determine the durability of both lead-free and tin-lead solder joints.  Other specific tests are completed depending on applications.

During these reliability tests, the solder joints typically are monitored by event detectors that continuously check the electrical resistance of the solder joints or use comprehensive functional testing.  After reliability testing, the solder joints should be examined under magnification for tin whiskers, cracks and defects.

Conclusion

There are many challenges to ensure that your lead-free electronic product will be as reliable as its tin-lead solder predecessor.  Lead-free solder reliability is depends on many variables such as solder alloy composition, manufacturing process variables, circuit board packaging, assembly, and reliability test conditions.

A comprehensive program with a multiple tests is a must to reduce the risk of early reliability failures in lead-free products.  One reliability test is not enough.  Only time will tell whether your new lead-free product will be as reliable as the existing product using tin-lead solder!

References

1. Hobbs, G.  “Accelerated Reliability Engineering: HALT and HASS”, Wiley 2000
2. Clech, J.P.  “Acceleration Factors and Thermal Cycling Test Efficiency for Lead-Free Sn-Ag-Cu Assemblies”, paper presented at 2005 SMTA International.

About The Author

Gary Delserro P.E., is president of Delserro Engineering Solutions, Inc. (DES).  He has more than 20 years of experience working in the field of stress optimization and reliability working for the Naval Air Warfare Center as an aerospace reliability engineer, Cooper Industries as a new product/R&D manager, and Mack Trucks as a senior durability/reliability test engineer.  Mr. Delserro holds a B.S.M.E. degree from Villanova University and an M.S.M.E. degree from Lehigh University.  

Permission given by Evaluation Engineering, June 2006 Copyright © 2006 by Nelson Publishing Inc*http://www.evaluationengineering.com/

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