Temperature Cycling Testing: Coffin-Manson Equation

Temperature cycling testing is another method of accelerated life testing for products that are exposed to temperature variations during use in normal operation. The temperature variations can be a result of self heating for products that are repeatedly turned on and off, or can be the result of cyclic environmental changes — such as temperature variations from day to night — or other causes.

thermal cyclingThese repeated temperature changes can result in thermal fatigue and lead to eventual failure after many thermal cycles. Accelerated life testing can be performed by cycling the product to high and low temperatures that exceed its normal use temperatures.

It should be noted that temperature cycling may also be referred to as thermal cycling or thermal shock testing.  However, some test standards, such as MIL-STD-883, make the distinction between temperature cycling being performed as air to air testing and thermal shock being performed with the samples transferred between liquids. This article deals with testing performed using an air to air thermal cycle chamber.

Typical temperature cycling equipment consists of at least one hot chamber and one cold chamber. The test samples are automatically transferred between the two chambers by an elevator-type mechanism. It is also possible to perform temperature cycling in a single compartment chamber where the temperature is ramped between hot and cold. This generally produces a slower rate of temperature change compared to the two chamber method.

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DES Adds New Unholtz-Dickie Vibration Test System

Vibration Testing Bed

Our new Unholtz-Dickie vibration and shock testing platform.

To keep up with increasing vibration and shock testing demand, DES added a brand new Unholtz-Dickie Electro Dynamic (ED) Shaker Test System. The shaker is a model SAI30F-S452/ST system with slip table to perform vibration and shock testing along 3 axes. This gives DES additional vibration and shock testing capability and also will help us turn your projects around faster. Continue Reading DES Adds New Unholtz-Dickie Vibration Test System

Case Study: Combined Temperature & Vibration Testing of Automotive Mass Air Flow Sensors

Mass Air Flow Sensors (MAFS) are used to measure the mass flowrate of air entering engines in newer model cars. The mass air flow information is transmitted to the engine control unit (ECU) to balance and deliver the correct amount of fuel mass to the engine.  These sensors operate in a very harsh environment, a car engine compartment! Testing their reliability and proving their durability is a very difficult task.

Mass Air Flow Sensors (MAFS) Combined Temperature Vibration Testing
Mass Air Flow Sensors (MAFS) Combined Temperature Vibration Testing

DES was awarded multiple contracts to perform combined temperature and vibration reliability testing of Mass Air Flow Sensors from various automotive part manufacturers and from a major auto parts supplier. Continue Reading Case Study: Combined Temperature & Vibration Testing of Automotive Mass Air Flow Sensors

What is Pyroshock Testing?

First we should answer, what is a pyroshock or a pyrotechnic shock? Both pyroshocks and pyrotechnic shocks are the same thing. A pyroshock occurs when explosive events are used to separate the stages of rockets or missiles, or from a ballistic impact to a structure by a projectile. When a pyroshock occurs, a stress or shock wave propagates through the structure and into the electronic equipment contained within the structure.

Pyroshocks are unique shocks that have high G-level, high frequency content with very little velocity and displacement change during the shock. The frequency range of a pyroshock is usually 100 Hz to 10,000 Hz or greater. Pyroshocks have a very short duration of usually less than 20 milliseconds. The acceleration time history of a pyroshock approximates a combination of decaying sinusoids as shown in Figure 1. Continue Reading What is Pyroshock Testing?

Classical Shock Testing

Classical shock testing consists of the following shock impulses: half sine, haversine, sawtooth, and trapezoid.  Pyroshock and ballistic shock tests are specialized and are not considered classical shocks. Classical shocks can be performed on Electro Dynamic (ED) Shakers, Free Fall Drop Tower or Pneumatic Shock Machines. The parameters required to define a shock test are peak acceleration expressed in G’s or m/sec^2, shape of the impulse, and duration in milliseconds.  A classical shock impulse is created when the shock table changes direction abruptly.  This abrupt change in direction causes a rapid velocity change which creates the shock or acceleration impulse.

Figure 1.  Shock Test by DES

Figure 1. Shock Test by DES

Classical shocks are applied along one direction and one axis at a time.  Most specifications require the product to be shocked in both the positive and negative directions along each axis.  If shock tests are performed on an ED shaker, the shaker can reverse polarity and perform the shock along both directions of each axis without rotating the fixture and specimen.  When performing shock testing on a shock machine, the machine can only apply shock in one axis and one direction.  The fixture and specimen must be rotated to apply shocks along different directions and axes.

A typical shock test setup using a pneumatic shock machine is shown in Figure 1.  DES can also perform shock testing using an ED shaker and drop tower.

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Lead Free Solder Reliability Issues and Test Methods

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.

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