INA317: Thermal cycling

Hi Jagbir,

Questions:

What other parameters shall I pay special attention while evaluating the performance after thermal cycling.

Based on your thermal cycle test in INA317, it appears that this is non-operational thermal cycle test. The reasons that I am speculating is that no op amp components can handle temperature of 138C environment while it is in operating conditions (without some of kind of cooling, say cooling plate etc.)

When you are doing thermal cycle tests, there are two main different types of thermal cycling tests (dynamic or static thermal temperature cycling tests). Regardless which one you are doing, here is what you need to be aware: 

1. You have to perform the test in actual end product configuration. Potting the PCB with silicone compounds are not likely representative in your final product configuration. So you need to test the product as is, otherwise, your test result will not be valid. 

2. All thermal cycling has to follow a specific compliance in industry. Automotive has its defined thermal cycling test requirements. Aerospace is doing slightly differently. Thermal cycling test in medical industry is not the same either. So I need to know which industry compliance you are doing, and you need to follow that particular thermal test standard and test methods and procedures. 

3. The 138C for 38 mins seems to be high and long for high temperature operation, unless it is non-operational test. 

4. I have been involved in HALT & HASS tests over 6 years, and your thermal testing parameters do not look familiar to me. 

Here are a typical HALT & HASS test setup for thermal cycling test. 

1. The HALT & HASS test chamber is required to have very high temperature ramp rate for heating and cooling, something like 60-80C/min for hating and cooling. The chamber is cooled by liquid nitrogren. HALT &  HASS chamber also has random vibration profile, though you are not using per the test. The chamber is required to high very high flow rate, otherwise you may have hot temperature location somewhere in the chamber. The heating or cooling air duct is supposed  to be placed directly on top of EUT (INA317) for the duration of the test. 

2. Your monitored temperature sensors have to be placed on top of EUT. In this case, 1" above INA317 or directly on top of INA317 package. The INA317 package's temperature should be higher than air temperature of the chamber for INA317 operational test. 

3. The operating temperature of INA317 is rated from -55C to +125C. The IC's Junction temperature is rated at 150C. By the way, these are typical temperature figures. Although the part has some kind of  thermal designed margins in INA317, not every part will meet the same thermal requirements. 

4. If this is operational tests, you need to have a standard voltage rails, feed input signals to the input of the INA317, and monitor the output of the Op Amp over time and temperature. If INA317's power supply is part of the test, you need to record its voltage and current performances over time and temperature. The test need to reflect an actual thermal environment in a field. So keep all operating parameters as closely as possible for the test. 

5. It is a good ideas doing the thermal tests in stages. In other words, you need to establish a baseline. Say the chamber temperature is set at 125C, you complete the thermal cycle test, and all parts are passed. Then you increase the chamber temperature to 132C, and repeat the same test. It may pass or fail the test. Since your baseline is 125C, then you can increment accordingly to the next thermal point. If it passed 132C thermal cycle test, then you can move on to the next thermal setpoint. At some point, you will see that the INA317 starts to fail or not working properly. As long as you keep the thermal test within the absolute maximum ratings, this is not a destructive test (It may stop working at some point). 

6. If you have multiple INA317 samples, it is good ideas to perform these at the same time. 

7. Since INA317 has mass, there will be a thermal lag during test. When temperature of the chamber is reached a setpoint, it may take INA317 op amp longer time to reach the chamber temperature. It seems to me that you are doing thermal soaking tests at 138C. It is not clear to me that 38 mins at 138C is the total test time at 138C or temperature ramp time + soaking time. The conventional thermal chamber can only do 2-10C/min, so to reach 138C from room temperature may take a while. Since your thermal test is not described in detail, I am unable to comment on it. 

Anyway, I have written a lot here. If you have any additional questions. please continue to post on the thread. 

Best,

Raymond

Hi Jagbir,

the photo shows water bubbles under a layer of silicon caused by air humidity:

Kai