What is Stress Screening Test (SST) ? Why Manufacturers MUST perform SST ?

 

                                           Battub Curve comparing Failure (Death) Rate against Time.  

The above picture is a typical 'bathtub curve'. The graph originates from the Life Insurance Industry which plots the life of people IN GENERAL. The curve curve can be dissected into 3 stages of life. 

1st stage : Birth (infant) to Toddler (5 years old).

2nd stage : 5 years to say 75 years of age. 

3rd stage : 75 years of age to end of life (for example) 90 years. 

1st stage,  irregardless of the country's developed status and wealth, infants and very young chidren DO NOT have the antibodies, and basic  health immunity built in them to withstand bacteria, viruses and the like. Hence, there is always a much  higher chance of them falling sick, contracting simple illnesses (since their body immunity takes several years to develop).Infants until about 2 years of age, have no cognitive awareness of themselves, and hence can't effectively communicate and receive communication - hence, they will do as they like and crawl on the floor, and through natural curiosity, pick up things on the floor, feel, smell and eat things. Hence, the incidence of hand foot and mouth disease is prevalent worldwide. 

As a result, the infant mortality rate is HIGH for the first 5 years.

2nd stage Roughly around 5 years of age, their cognitive awareness is developed, about themselves, their surroundings and taking care of their hygiene. Additionally, by nature, their bodies would have decent immunity and strength to ward off the basic virus and bacteria borne diseases. 

Of course having a strong health care support system in the country is very important too.

From 5 years of age till 75 years, it has been observed (through clinical studies tracking people from cradle to grave, there are countless reports out there) that the incidence of death, while it happens, is relatively small in comparison to the first stage. People would have developed body immunity as well as the support systems for them to seek urgent medical help if and when the health issues arise. The chances of death is relatively low compared to 1st stage. 

Incidents like road accidents, Tsumanis, COVID, and SARS are black swan events but the death rate barely hit 1 % of any population. 

3rd stage Approaching end of life (this is rather wide, from country to country, ranging from 76 in the US to 85 in Singapore and Japan), people are generally weaker and health issues will crop up more frequently and over several months and years before the end of life 

                                                                     Sports Watch 

Typical Notebook. 

So it is exactly the same curve which is applicable with consumer and industrial products. Sports watches, handphones, notebooks, IPads, cars and other stuff which practically everybody has and uses. Cars, buses, boats, planes and military equipment all exhibit the same behavior.

It is called the Product Life Cycle. It typcially falls into 3 segments as shown above too.  

So coming to the 6 million dollar question. I have been rather long winded but I need to explain the objective of this post.

1. What is a Stress Screening Test ?

2. Why Manufacturers MUST perform SST ? 

                                                 Typical Stress Screen 1 Cycle 

What is a Stress Screen Test ? 

A stress screen test is a test typically devised by QA engineers or managers of a manufacturer to ensure that the products made are robust. Typically this is done by utilizing environmental chambers and  controlling the following parameters below. The objective is to weed out infant mortalities from the products made in the assembly line. Hopefully, the infant mortalities only account for less than 5% of the total production run (hence yield or success rate is 95%). 

a) Temperature setpoints - high and low temperature settings

b) Dwell Times - ranging from a few minutes to a few hours.

b) Temperature Change Rates - from 1 to 5 deg C per minute are very common. 

c) Number of cycles - minimum of 4 days (96 hours) to 1000 hours (41.6 days). 

The Temperature Setpoints are devised by choosing temperatures which are higher and lower than what the product (for example the 2 shown above) would be subjected to, worldwide.

What Temperature Range would the 2 products be subjected to ?

Sportswatch :  - 20 C (cold winter runs) to say 50 C (desert run)

Notebook  :   10 C to 38 C (normally used indoors so the range is much smaller than sports watch).

What Temperature setpoint should I set for the 2 products to produce an effective Stress Screen ?

1 :  - 30 C to 60 C 

Notebook  :   0 to 45 C 

What Temperature Change Rates should I set ? 

1 to 5 C / minute is most ndustries standard though there are some military grade products requiring 15 C to 20 C / min. 

Dwell Time ?

30 minutes up to 4 hours each zone.  

Number of Cycles ?

For it to be effective, the more cycles the better. 

So 500 to 1000 hours is recommended

Why Manufacturers MUST perform SST tests ?

If the products are shipped out without the SST tests, if say even 5 % fail in the field, the brand name of the manufacturer is adversely affected. 

There have been incidents of complete recalls of car batches in EV and ICE cars in the past, This is due to major glitches in the products design and reliability hence the total recall which easily costs hundreds of millions of dollars in expenses.

Do you want to risk your company / product brand name ? 

The decision is a simple one.

Speak to the experts ; At QRA, we can assist you !

Website : www.qra.com.sg

Email    : mark@qra.com.sg

               qrasales@qra.com.sg