Mechanical Design Validation Test (MDVT) Fundamentals

Design validation tests are performed to validate a product’s design; as for design specifications, internal design or external standards, customer requirements, and product regulatory compliance testing. Test parameters and methodology are commonly derived from MIL, ASTM, ISO, ETSI, NEBS and IEC specifications are established by government agencies. However, it is common practice to adapt to a unique internal design validation specification to assure high quality of product design and high yield for production. While DVT parameters are chosen to get intended stress factors with well-defined mathematical formulas, the purpose of this article is to highlight importance of these parameters.

MDVT testing needs can be addressed by in-house test labs or through accredited outside test labs. MDVT is generally comprised of dynamic (mechanical) and environmental tests. These combination of operational and non-operational tests with varying test parameters and profiles should be carefully selected to validate specific product design areas. Some non-operating tests can be selected based on products storage and transportation conditions while some operating tests can be selected based on products actual deployment environments. Many products categories are defined by external standards based on it’s deployment (in-door v/s outdoor, mounting), physical attributes (size, and weight), and customer’s need (Datacenter, Service Provider, Railway, Marin, Wireless etc.). Also, one can rent or purchase test tools, there is always an option to innovate test solutions to minimize test cost and dependencies. 

Test cases and related stress parameters, which need careful considerations during MDVT, are listed below.

Temperature - dramatic change in temperature to test product’s real life exposer and to evaluate component reliability is often done operational and non-operational. Depending on various components of the system one has to carefully choose extreme temperatures, and depending upon required acceleration faction one has to choose duration of soak and ramp rate. The purpose is to uncover lots of issues related to product manufacturability (cold solder joints, softening or swelling of molded components, etc.), component package design, and latent defects as direct impact of thermal fatigue/aging. Also, This test can also surface weaknesses in electronics components e.g. junction temperature, transistor operates at faster and slower speed, resistance and inductance variations etc.

Humidity – Packed and un-packed products during it’s transportation, storage and operation are exposed to various levels of humidity. Purpose is to check packaging robustness and product reliability dictates selection of relative humidity levels in combination of temperature and soak time. Many standards define such profiles for various products with lots of details. Which one to use is always a tricky based on potential issues design team wanted to validate e.g. metal parts oxidation and corrosion, swelling or shrinking of gaskets, paint or conformal coating cosmetic appearance, brittleness or granulation etc. 

Altitude - Similar to humidity product experience reduced pressure at higher elevations can create harmful stress on sealed components or product packaging. It ensures product reliability by simulating the effects that altitude and pressure have on product.  Altitude chamber allows simultaneously testing altitude and temperature profiles. Air flows in a low air pressure environment slower and cause heat stress on product as well. 

Vibration – Bare operational product at end users environment and packed non-operating product in transportation both experience various types of vibrations. Vibration testing determines if product can survive intended use environment and do not fall apart during shipment. Vibration tests are widely used to screen out production defects, and to find reliability of product through stress testing. Generally vibration Electrohydraulic, or Electrodynamic shaker system is used to conduct various types of vibration such as Sinusoidal, Random, Sine on Random, Random on Random etc. Random vibration is used to simulate real environment with wide range of frequencies excited simultaneously at controlled energy levels. Sine sweep test is performed to find the resonance / natural frequency of a product. Dwelling on that that resonance points can thoroughly tests systems robustness. 

Shock – Similar to Vibration unpacked and bare product might experience various types of shock which can be simulated using Electrodynamic shaker, Free fall drop tower or Pneumatic shock machines by using half sine, haversine, sawtooth, and trapezoid impulses. Shock simulates real life impact product might experience such as drop during installation, impact during transportation, accidental hit by handling equipment etc and help determine failure such as fracture, shear, bend, cumulative damage, and fatigue to find robustness of the product.

Acoustic – To assure product meets end user’s noise requirements by taking sound pressure and sound power measurements using adequate microphone configuration in soundproof chamber. Various measurements at different fan speeds is generally taken to fine tune thermal and airflow of the system. Generally system fans, power supply fans, and obstacles creating wind resistance are common source for the acoustic noise.

Airflow and thermal testing and analysis could also be part of MDVT. While MDVT is used to validate design margin one can always perform Highly Accelerated Life Tests (HALT) where product is tested to increasing stress levels of temperature and vibration independently and then in combination along with rapid thermal transitions to determine functional operating and destructive limits. In production one can use Highly Accelerated Stress Screen (HASS) to identify process and latent defects by operating product near operating limits.