Humidity Testing can be used to accelerate the aging of products that are affected by ambient humidity levels. Increasing the humidity above the normal use level humidity can cause defects or failures to occur in shorter times than what would be observed in the field. Humidity testing is most commonly performed along with testing at elevated temperature so that the resulting acceleration factor is affected by both humidity and temperature. The Acceleration Factor (AF) which is the ratio of the life at use conditions to the accelerated life at test conditions for temperature humidity testing is given by the following Arrhenius-Peck equation:
This is part two of a series of blog posts concerning the MIL-STD 810 Vibration Section. This blog was written with reference to MIL-STD-810G w/Change 1 dated 15 April 2014. DES has the experience and expertise to help you determine what profiles are appropriate for your product and to run your MIL-STD-810 vibration test. For more information, please check out Part 1 – MIL-STD-810 Vibration Testing Overview blog and our Vibration Testing services page.
Category 4 of Method 514.7 Vibration testing details the transportation random vibration environmental conditions from cargo interaction with vehicle suspension and structures with road and surface discontinuities. “This environment may be divided into two phases, truck transportation over US highways, and mission/field transportation. Mission/field transportation is further broken down into two-wheeled trailer and wheeled vehicles categories.”
Truck Transportation over US Highways Vibration Testing
This vibration test method is used when products or equipment will be transported by large trucks tractor-trailers commonly seen on US highways. The truck transportation over US highways random vibration profile is designed to simulate 1609 km (1000 miles) on interstate highways. The random vibration profile along each axis can be seen in the plot below in Figure 1. The length of this profile is 60 minutes per axis for each 1000 miles of transportation. For example to simulate 2000 highway miles, the vibration test duration would be 2 hours per axis x 3 axes = 6 hours total.
Altitude (Low Pressure) Testing makes use of a vacuum chamber to simulate the effects of high altitude conditions. The pressure inside the altitude chamber can be reduced to correspond to the air pressure at a specific altitude. Products can be placed inside the altitude chamber and tested to determine if they will still function after exposure to a given duration at a specified altitude.
Components sealed with internal fluid such as batteries or capacitors may fail or leak during altitude testing because an internal pressure results at rising altitudes as the external pressure is reduced. It is also possible to power a product during the test to verify that it remains operational during the altitude test. The lower pressure at higher altitudes can reduce the cooling of components which can lead to possible failures. For this type of testing, it is necessary to have power and signal wires that can be fed into the altitude chamber without causing vacuum leaks. DES can provide a generic feed through that can be used for most testing. A custom feed through can also be fabricated if the component to be tested has specialized power or signal cables. It will be necessary to seal these cables to maintain the low pressure. Continue Reading Altitude Testing: Low Pressure Vacuum Chamber
Thermal shock testing also called temperature shock testing or temperature cycling exposes products to alternating low and high air temperatures to accelerate failures caused by repeated temperature variations during normal use conditions. The transition between temperature extremes occurs very rapidly during thermal shock testing, greater than 15 °C per minute. Alternatively, temperature cycle testing uses slower rates of change between high and low temperatures. The failure acceleration rate for thermal shock testing is determined by the Coffin-Manson equation as previously discussed in DES’s blog article Temperature Cycling Testing: Coffin-Manson Equation.
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.
DES added another larger AGREE Chamber to perform Combined Temperature and Vibration Testing. This gives DES additional capability to perform combined environmental testing on larger products. DES has performed Combined Temperature and Vibration Testing on car engine sensors, helicopter sensors and outdoor heavy industrial products. Some of the test specifications include MIL-STD-810 and General Motors GMW 3172.
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
- 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:
This article discusses the reliability challenges of switching over to lead-free solder and the test methods used to demonstrate reliability, written by Gary Delserro and published in Evaluation Engineering Magazine. Click on the link to download the article in PDF, Lead Free Solder Reliability Issues & Test Methods.
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.