First, DES developed a reliability test plan that defined how the tests would be performed, the number of samples required and how the test results would be quantified into a field life. After the plan was approved by the manufacturer, the reliability test had to be designed.

Although opening and closing a drawer seems like a simple push pull motion, the cyclic motion was much more complex in this case. The drawer can be opened in opposite directions from either side of the cart. It has detents in the center of its slides that hold the drawer closed. DES had to create a complex automated cyclic motion that started with the drawer held in its center detents. The drawer had to be pulled opened until it hit the end stops in the slides. Then it had to be pushed past the center detents overcoming their latch force. Finally the drawer had to return to its closed position and latch in its detents. All of this had to be performed with maximum design weight inside of the drawer. In addition to this motion, the velocity and accelerations had to be controlled.

This complex cycling motion was performed using special actuators. The actuator travel, velocity and acceleration were programmed into a controller. The number of cycles for each complex motion was automatically counted until failure or a maximum design goal was achieved. During the test, the force to open and close the drawer was measured at various intervals. One of the challenges faced in this project was how to hit the end stops consistently without applying too much force to the drawer. Custom fixtures were designed and made by DES to control the force when the drawer hit the end stops and also to attach the drawer to the actuator.

Multiple samples were tested to ensure the manufacturers reliability and confidence level goals were achieved. Finally, the test results were analyzed with reliability computer software to determine the product’s field life or Mean Time To Failure (MTTF). A final comprehensive test report was delivered to the manufacturer. This customer chose DES because we were able to help them through every phase of their reliability program!

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HALT and HASS can accelerate a product’s aging process from actual months into test minutes much faster than traditional testing!

What is HALT?

HALT – Highly Accelerated Life Testing

HALT is used to find product design weaknesses making the product more rugged.

• HALT is typically done during Design.  It is destructive!
• Stresses are applied in steps to find a product’s weaknesses, operational design margins, and destruct limits.
• Stresses are higher than normal to obtain time compression and accelerate aging.
• HALT is not a pass/fail test.  It is pro-active!  The stresses are increased until the product fails, rather than testing to predefined limits.
• All HALT failures represent an opportunity for improvement and may show up in the field.
• Many failures are easy and inexpensive to fix.
• HALT typically takes 3 to 5 days.

What is HASS?

HASS – Highly Accelerated Stress Screening

HASS is used to find defects and flaws in production to monitor the quality and consistency of your manufacturing processes.

• HASS is done during Manufacturing.
• HASS is a screening method used to expose manufacturing process problems that would cause a failure in normal field environments including shipping, storage and use.
• Stresses may be higher than normal operation to precipitate defects in a short amount of time.  HASS stresses are typically higher than traditional Environmental Stress Screening (ESS).
• Types of stresses used are similar to those used in HALT.
• HASS screens take typically from an hour to a few hours.
• HALT must be performed before HASS.
• Safety of Screen (SOS) is used to validate the screen proving that sufficient life is left for a normal use lifetime.

Reasons to Use HALT/HASS

• To produce a rugged, reliable product.
• Products have many electronic parts subjected to combined high/low temperature and vibration loads.  Many parts are not tested for these combined loads.
• With thousands of electronic components present, a failure of a single component could cause the entire system to fail.  This will lead to warranty and engineering redesign costs, and unhappy customers.
• To find and understand the operating limits of your products.
• To find and understand the destruct limits of your products.
• To compare different electronic components and suppliers (Evaluation of Competing Vendors).
• To regularly audit or screen your production components to check for and improve manufacturing quality.

Typical Stresses Used in HALT and HASS Testing

• Vibration applied over a broad frequency range (6 DOF, 60 Grms, Random vibration energy to 10,000 Hz)
• Temperatures (-100°C to +200°C)
• High temperature rate of change (60°C / minute)
• Electrical loads
• More stresses (fluid pressure and viscosity, pH, unbalance, geometry, etc.)
• Combination of all loads

Typical HALT Profile

Why Products Fail

Every product has a statistical strength distribution. Failures will occur where the Product Strength and Field Stress Curves overlap shown in red.  HALT/HASS will force the weaker components to fail in the chamber.  HALT and HASS will shift the Product Strength curve to the right.  The goal of HALT/HASS is to produce a large design margin or gap between the 2 curves, resulting in less field failures and a more reliable product!

Benefits of HALT

• Shorter design cycle = Quicker Time to Market.
• Reduced design cost.
• Usually less expensive, faster, and more effective than traditional pass/fail testing.
• Find and improve design margins.
• Produce a more rugged/reliable product with less field failures and warranty expenses.
• Reliable products lead to happy customers.
• Happy customers lead to increased profits/market share.
• ROI’s in the thousands or greater are being reported.

Benefits of HASS

• HASS screens are shorter than traditional methods (ESS).
• Reduced time and cost to screen production.
• Finds defects sooner and correct problems faster.
• Fewer defects reach the customers hands.
• Improved product quality and manufacturing process control.

DES reliability testing can help you in all phases of your project.

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