Beginners in HALT testing, come and see how experienced seniors usually conduct HALT tests! (Part 2)

Keywords: Reliability Testing,High Accelerated Life Testing, Environmental Stress Screening, Vibration Testing, HALT/HASS

In "HALT Testing Beginners, Come See How Experienced Seniors Conduct HALT Tests! (Part 1)", we mentioned that HALT testing should be done step by step, so today we will discuss in detail how to conduct HALT testing step by step!

Cooling Test

Testing at low temperatures is often the least destructive among all single environments. This makes it a good starting point for testing.

You can choose the magnitude of temperature fluctuations based on the actual situation of the product. For example, if you are very concerned about the impact of low temperatures on the product, you should reduce the step size; if you are looking for baseline data, it is best to start with larger steps and reduce them if you encounter premature failures. Generally, in cold environments, many engineers start with a change rate of 10°C per minute.

Once you have decided on your ramp rate, you need to determine your hold time. How long should your product stay at the temperature before warming up again? The general view is to keep the hold time at the shortest time required for the product to stabilize. For something like a PCB, this may only be five minutes. If you are testing components, it may require a longer time. Similarly, you need to use your expertise to decide.

Take a look at the chart below:

The above chart shows examples that can be used. Start from the laboratory environment and maintain stability, then quickly drop the temperature by 10°C and hold for 10 minutes. These steps continue until failure occurs.

Heating Test

This step is very similar to the cooling test, just in the opposite direction. It is based on the same principles as the cold step testing. First, settle in the laboratory environment, then start ramping up and holding. Heat is often more destructive than cold, so you might choose to increase the temperature by only 5°C per minute instead of faster.

I had the opportunity to work with a company whose products would ultimately be used in hospital environments. Their first major failure occurred at a temperature only 2°C higher than the laboratory environment. Initially, they were not worried, reasoning that hospitals have air conditioning, so they didn't have to worry about the surrounding air being too hot. I let them know I had an extended hold time, controlling the temperature based on the time of year, and that it would automatically start heating due to the date rather than necessity. The ward's temperature approached 30°C. The client reworked the circuit board, and their unit is now the top seller on the market.Moral:Ensure there is a gap between your expected usage environment and the environment your product can actually withstand. Set it in your mind as the worst-case scenario, then add a percentage. In other words, if it can go wrong — it will.

Vibration Testing Only

You have passed the simple tests of heat and cold. You have monitored and recorded data. You have made any changes you deemed necessary. Now you are ready for vibration.

Next, we start again from the laboratory environment temperature to ensure that temperature does not affect the test. This may not seem like a real-world situation, but we are now fully focused on vibration.

The standard method for measuring vibration testing is to assess it through g-levels. Where do we measure "g"?

If you start measuring from the bottom of the vibration table, what you are really seeing is what the vibration table is doing. This may have little to do with what your product is doing. The best position for the accelerometer is on or near your product. Some prefer to attach the accelerometer to a fixture that holds the product. This is perfectly acceptable. If there is no simple way to secure it to the product or fixture, it should be mounted on the desktop close to the fixture. This will at least provide an approximate value of what the product is experiencing.

In contrast to temperature, vibration needs to be handled in very small increments. It can be difficult to control very tightly, so we recommend starting at 2 g and moving up 2 g at a time. The hold time also depends on you and your understanding of the product. There should be enough stabilization time, so ten minutes is commonly used. You continue to increase until you see what you consider a failure, then continue monitoring and recording data.

After completing the above single tests, how do you feel? Did other members of the team ask you, "What are you doing to my design?What?" Be sure to patiently explain to them!

Now we are going to conduct a slightly more complex test —

Thermal Cycling Test

You have completed cold, heat, and vibration. The next logical test is thermal cycling, which combines heat testing with cold testing.

Set the chamber to start in the laboratory environment and let the product settle. Decide whether you want to heat it up first or cool it down. Adding nitrogen to the chamber air will help remove any potential moisture from the product, so this should be part of your consideration.

Determine the ramp amount, usually 5 or 10°C at a time, and decide your hold time. Then start.

As you can see in the chart, each step becomes wider. Assume you choose to increase in increments of 5°C, and your starting temperature is 25°C. You choose a 5-minute hold and think you want to warm up first. This is the basic scenario:

There is a valid reason to conduct temperature fluctuation tests. Differences in thermal coefficients can cause parts to pull apart from each other, sometimes leading to cracks. By applying these changes as quickly as possible, we exert pressure on the product that exceeds what it typically experiences. Some claim that in most cases you will never see a temperature change exceeding 30°C per minute, but consider the following:

I live in Michigan. We are not the coldest state in winter, but it is very typical to have a wind chill of -40°C at least once every winter. Suppose my car gets stuck in the snow about a mile from home. I decide to walk (we Michiganders are quite robust).

My phone just went from about 25°C to -40° because I held it to my ear while calling my husband to tell him about my bad luck. Since he was on the road, I had to pull out my trusty phone to get his number.

I got home, shivering, turned on the heat, and stood by the heater—still using my trusty phone. The phone and computer warmed up to 25°C under the warm air. At this point, not only the electronic devices were under stress, but I was too! I believe you can think of other severe situations we tend to put our electronics through.

That's all for today, and you can practice well! Next time, we will do more complex tests together in "HALT Testing Beginners, Come See How Experienced Seniors Usually Conduct HALT Tests! (Part 3)"HALT Testing, remember to follow our updates!