Putting Quality Products on the Shelves: Reliability DVT

Earlier in this series we discussed why design validation testing (DVT) is important and how environmental DVT is performed. Now we’ll take a look at Mechanical and Reliability DVT, and how electronic product designers ensure that their customers always receive the product in full working order.

The objective of mechanical DVT is to verify the integrity of the mechanical design and product assembly under various use cases. Mechanical DVT will usually contain drop tests, vibration, and shock impacts testing.

Drop Tests

A drop test verifies that the product will survive mishandling situations. A realistic scenario is where the product is dropped on to a hard surface such as hardwood floor, tile, or a concrete surface, and is best replicated using a free fall drop testing method. In the free fall drop test the product will be dropped from a recommended height based on its overall weight onto a hard surface (e.g. concrete) on all its faces and edges.

Vibration Tests

Random vibration testing, as the name suggests, simulates vibrations that are found in everyday life that are neither repetitive nor predictable. The goal of vibration testing is to uncover weaknesses in the mechanical design as a result of the environment it may encounter. This type of design validation testing will provide data points for improvement. During vibration testing a product is tested independently on each of its three orthogonal axes while operational. The vibration levels and frequency range is dependent on the target application for the product.

Shock Tests

Shock testing will verify the product’s response to a sudden acceleration or deceleration caused impact. Mechanical shock can potentially damage or weaken a product. Shock impacts for example may also cause a precision measuring instrument product to go out of calibration or shorten its reliability. In some cases it may appear that there is no damage by a single shock impulse however with repeated shock impacts the product may start to indicate minor failures and eventually become useable.

For this reason shock testing will consist of multiple shock pulses on each of orthogonal axis. The shape, duration and number of pulses are determined by the application for the product. Shock impacts and vibration testing are common for products that are used in transportation. Common testing standards for transportation include IEC 61373, RTCA DO-160 Section 8 and MIL-STD-810 514.6 for rail, air and military transportation.

Reliability DVT

Reliability testing falls into a category of design validation tests known as Stress/Life testing (STRIFE) or Highly Accelerated Life Testing (HALT). These tests are used to identify design weaknesses and manufacturing problems, and ensure that the prototype design will have sufficient margin and strength above that required to survive in normal operating environments. Accelerated life testing is used to reduce the time required to precipitate defects.

During HALT testing the product is exposed to an initial level of stress (typically a combination of temperature, humidity and vibration) for a predetermined period of time (typically between 30 and 60 minutes) and is then subjected to a higher level of stress. The incremental steps continue at successively higher levels of stress until a failure occurs, or until the period of time at the maximum stress level ends. When a failure is diagnosed it may be corrected and testing repeated until an acceptable level of margin is achieved. The acceptable level is the point where the design limit is reached, or the implementation of a fix is technically or economically unfeasible.

Transportation DVT

After reliability testing is completed there is still one final test to make sure a product gets to its final destination fully operational. Transportation testing verifies that the product and product packaging are able withstand transportation hazards. During transportation DVT the product is tested within its packaging, which maybe single or multi-pack, and once the tests have are complete the product is inspected and functionally tested for damage.

The International Safe Transit Association (ISTA) 2A series of tests listed in the table below is commonly used to validate the integrity of a product’s packaging under various distribution hazards. To satisfy the ISTA-2A standard the tests must be performed in the following sequence:

Packaging Environmental Tests

In summary, design validation testing encompasses the full spectrum of electronic product design. Each facet of DVT whether electronic, EMC, environmental, mechanical, reliability or transportation must be tailored to suit the product’s target application and use. A well-thought-out DVT program is necessary to ensure a product satisfies all design requirements and is reliable before going to production. Early planning is suggested to avoid cutting corners or minimizing DVT coverage in an attempt to rush a product to market. During the production phase DVT can be used to verify that the integrity of design has been maintained when there are component substitutions due to second sourcing or obsolesces.

Nuvation Engineering can provide design validation testing support through our New Product Introduction service. As part of this service we prepare test plans and test procedures tailored to customer requirements. We can also develop supporting test software to monitoring the behavior of the product under test during DVT. We work with local test houses to determine an overall DVT program tailored specifically for the products end application. Contact us to discuss your electronic product testing and prototype design requirements.