What is environmental testing?

Environmental testing is when we take any number of environmental conditions that can be found on or around our planet such as temperature, humidity, pressure and vibration and apply them to a product to see what happens to it.

Why should I carry out environmental testing?

• To ensure that your product will perform as specified under the conditions that it will be used in.
• To build robustness into the design well before the manufacturing process begins.
• To determine how long a product or device will last in the field.
• To have a good idea of its condition after a number of years.

What conditions can be applied to a product?

What is combined testing?

Applying more than one condition simultaneously to a product. Usually this means vibration and temperature cycling.

What products can be tested?

• Anything
• Cardboard packaging and food containers.
• Mobile phones
• Aircraft components

What sectors use testing?

What is accelerated ageing?

This is a process whereby a product is stimulated by cycles of temperature and humidity in order to determine its future condition. An effective accelerated ageing process can show in just a few hours or days what a product will be like after several years.

How do I go about environmentally testing my products?

Once you have determined the conditions that your product needs to go through, you will need to source equipment that will simulate these conditions.

Buying, renting or in house testing are some options available to you.

Will I have to buy expensive equipment?

You will have to assess the type of testing you need to carry out particularly with regard to how much and how often. If your requirement is only occasional then one of a number of excellent Test Houses will more than likely offer a cost-effective solution. Another alternative may be to hire the equipment for the time you need it.

What effect does temperature have on my products?

Depending on the material, high temperature will accelerate ageing. Heating and cooling of certain devices can lead to fatigue and eventual failure, rapid temperature cycling will accelerate failure in materials or components containing weaknesses.

What range of temperatures can I expect to achieve inside a chamber?

YMost test chambers will be heated by electrical elements and the upper range limited to about 180°C. Cooling can be by means of mechanical refrigeration or the expansion of a cryogenic liquid gas injected directly into the chamber. A single-stage refrigeration system would normally be able to achieve -40°C and a cascade system -70°C. Chambers using liquid nitrogen are able to achieve temperatures below -100°C

What is stress screening?

Stress screening is a process whereby latent faults in a product are converted to hard failures so that conventional testing or inspection can identify them. Failure mechanisms seen by a product in real life, such as vibration, mechanical shock and thermal cycling can all be reproduced in the laboratory. Stress screening can be divided into two disciplines, vibration stress screening and thermal stress screening. Depending on the material or device to be screened either one may be more effective and in some cases both vibration and thermal stress screens should be applied.

What is thermal stress screening?

Very rapid cycles of temperature are applied to products causing them to expand and contract. This movement causes mechanical stresses, which will concentrate at any weak point to bring about failure. The process is often applied at a design stage in order to build robustness into a product. It is also used at various stages in a manufacturing process to ensure that reliable product is shipped to the customer and so reducing the potential for field failures. An effective thermal stress screening process will call for approximately 6 or more very rapid cycles of high and low temperature. The upper and lower temperature extremes and the optimum number of cycles can be established by experimentation. They will vary from one product type to another and will depend on such factors as the product mass and material type.

How does thermal stress screening work?

Subjecting a product to rapid cycles of heating and cooling will cause it to expand and contract. If a device is made up of a number of different materials then their different thermal expansion coefficients will cause them to expand and contract at different rates and by different amounts. This leads to high levels of mechanical stress concentrating at any point of weakness. Robustly designed and well-manufactured products will be able to withstand these stress reversals, however weak product will fail be identified by conventional testing or inspection. This process is particularly effective at finding latent faults caused by poor design, component failure or manufacturing problems in electronic assemblies or devices.

What sort of chamber would I need in order to carry out thermal stress screening?

An effective thermal stress screen requires a specialist piece of equipment capable of very fast temperature transitions of up to 100°C per minute. This is quite beyond the scope of standard off-the-shelf equipment. Liquid nitrogen is used to provide the rapid cooling capability and open element heaters provide the fast response when heating. Powerful fans would be employed to provide high airflow velocity around the products with careful consideration given to even distribution of the conditioned air throughout the working volume of the chamber. This is important in order to achieve the same level of screening to all the products inside the chamber. There is also an optimal chamber volume of around 700 - 800 litres in order to keep the internal chamber mass to a minimum. It is unlikely that the desired temperature ramp rates will be achieved in a chamber of more than 1000 litres.

What is humidity?

It is a measure of how much water vapour is being held in the atmosphere. There is a relationship between temperature, atmospheric pressure and moisture. The warmer the air, the more water vapor it can hold. In the environmental test industry when we talk about humidity we are usually referring to relative humidity. This is the amount of humidity of the air expressed as a percentage of the total amount of water vapor that the air could hold at a given temperature. 100%RH (or saturation) means that the air cannot hold any more moisture at that temperature. Should the air temperature increase its capacity to hold more water vapor will increase and the relative humidity will fall.

What is dew point?

Dew point is the temperature at which moisture will condense out of the air.

What effect does humidity have on my products?

Some materials will absorb moisture in humid conditions. High humidity accelerates corrosion and can be the cause swelling and dendrite growth. Levels of high humidity will also support fungal growth. Low humidity or very dry conditions can cause cracking and shrinkage.

What range of humidity conditions can be generated inside a chamber?

A general-purpose humidity chamber will usually be able to generate humidity conditions from 10%RH to 98%RH at temperatures ranging from +20°C to +90°C (sometimes called the climatic range).

What is vibration stress screening?

The mechanical failure mechanisms a product is exposed to in its natural environment can be reproduced on a shaker system. High levels of mechanical stress will concentrate at any point of weakness.

How often should I have my chamber calibrated?

Once a year.

How often should maintenance be carried out?

This depends largely on the usage of the chamber.

Preventative maintenance contracts can usually be tailored to suit chamber availability and calibration can also be scheduled at the same time.

If you require any further information regarding any of these points please contact Trevor Leake.