There are 4 Key Parameters which manufacturers must bear in mind when designing a robust product - this is based on decades of experience working with the best in class and industry for electronics, aerospace and defence and automotive.
1. Temperature Extremes.
2. Dwell Times at the Extreme Temperatures
3. Rates of Change in deg C / min from Hot Extreme to Cold Extreme
4. Duration of One Cycle and Number of Cycles Run in total.
Temperature Extremes.
Typically if a manufacturer wishes to do environmental simulation, they must simulate the condition which the product is being subjected to, plus add further extremes just to ensure that the product can perform wider than the expected range of usage.
Dwell Times at Extreme Temperatures.
How long the products are kept at the temperature extremes is dependent on the product itself. From experience, the dwell times at the extreme temperature zones do not go beyond 6 hours, before, moving up or down to the next extremes.
A simple analogy of a robust product you (as a person) can try for yourself. If you have strong immunity, and you are daily subjected to temperature cycling, from airconditioned room at 23 C to cold bath, to hot morning of 30 to 35 C, enter the car at 25 C and then down to 20 C (air cond takes effect), to the office and so on and so forth.
Your body is subjected to temperature cycling though not as extreme as some products, so if your immune system is strong, then nothing happens.
If you are weak, you will fall sick.
Its as simple as that.
Robust products will need to be subjected to temperature cycling to ensure their
a) useability and functionality
b) robustness
during the most strenuous of times, and temperature cycling does that.
Rates of Change in C / min.
Typically a gentle temperature cycles is from 1 C / min to 3 C / min.
More severe change rates can range from 5 C / min to 20 C / min.
The change rate of Temp / min is to stimulate FAILURES in the product (for QA), these failures are attributed to the different Coefficient of Thermal Expansions of the materials used for the product such as
- polyimide base (PCB)
- nickel/gold underfill solder bumps
- gold wire connections
- epoxy substrate for ICs.
Number of Cycles Run
500 to 1000 cycles run are common numbers for manufacturers who want to test run their products resilience and robustness.
QA Sampling (What Percentage ?)
5 to 10 % of the first batch should be sufficient to qualify the reliability - provided that the yield of 95% is attained.
So for a first batch of 1000 product run.
50 to 100 samples are chosen and tested under QA set conditions.
Of the (say) 100, 95% must PASS the QA test for the rest of the production run to continue and then ship out.
This is only a rule of thumb.
It is by no means reflective of any one industry which MAY be much more stringent or less stringent depending on which industry.
CARPE DIEM.
https://www.qra.com.sg/
Email : mark@qra.com.sg
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