The reliability of printed circuit boards is influenced by many factors. In the automotive, aerospace and industrial sectors, the ambient temperatures of printed circuit boards can fluctuate between -40° and +180°Celcius. In order to determine how reliably electronic assemblies perform under these conditions, PCBs can be subjected to a temperature cycling test - also known as a temperature shock test.
On pcb-blog.com we answer five frequently asked questions about our test method and show you how the influence of temperature fluctuations can be reduced.
What is the temperature change test for?
Electronic devices used in the automotive, aerospace and industrial sectors sometimes have to withstand very large temperature fluctuations.
For the printed circuit boards installed in them, this means that they must retain their functional properties as a component carrier and electrical conductor system even under thermal stress. This can be simulated using a temperature cycling test, which is used to test the ageing behavior of PCBs at rapidly changing temperatures.
What characterizes a temperature change test?
The temperature cycling test is often performed as an end-of-life test, i.e. it is completed as soon as all tested parts have failed. Following this, the data obtained is usually subjected to a Weibull failure analysis and evaluated using the characteristic parameters of service life, form factor and failure-free time. If a specific failure criterion is to be checked for compliance, this is referred to as a "success run". This means that all tested parts may only fail after a time limit.
How does a temperature change test work?
In the temperature cycling tests carried out by the KSG Group, the test specimens are installed in a test basket, which is moved cyclically into a cold chamber and a hot chamber.
Typical implementation conditions are
- Cold chamber: -40°C
- Hot chamber: +125°C
- Tempering per chamber: 25 min
- Changeover time between chambers: < 30 s
- Number of cycles: 1,000
With real circuits, the tests can be evaluated visually or by means of a microsection test. The use of resistance testing is much more efficient. For this, it is necessary to establish suitable test layouts and define suitable failure criteria.
What types of faults are tested using the temperature change test?
The temperature cycling test focuses on the following types of faults:
- Cracking in the copper sleeve of through-holes and large blind holes
- Demolition of the inner layer connections of through holes and blind holes
- Failure of the inner layer connection of LASER vias on the target pad
- Cracking in solder masks
- Delamination of composite superstructures
What is the main cause of PCB failure in the temperature cycling test?
A printed circuit board usually consists of copper, epoxy resin and glass fiber mats - materials that differ in their properties such as strength and coefficient of thermal expansion. This means that an increase in temperature leads to different material expansions, resulting in inhomogeneous stress fields. These in turn can cause local stress increases and thus crack formation. If these cracks spread, this leads to electrical interruptions and thus to the failure of the printed circuit board.
How can high thermal shock resistance be achieved for printed circuit boards?
In order to achieve a high thermal shock resistance for circuit boards, the following main influences should be taken into account:
- Low pre-aging due to low impact during storage and loading,
- a small expansion of the layer composite in the z-direction,
- the use of base materials with the lowest possible thermal expansion coefficients, especially in the z-direction,
- a high layer thickness of the copper sleeves in drilled holes,
- the largest possible drilling diameter and an even distribution,
- high production quality of the printed circuit board assembly.
Do you have further questions? You can find more information on the temperature change test in our XPERTS online seminar "It's the layering that counts: Printed circuit boards in temperature cycling tests" with Dr. Swantje Frühauf and Holger Bönitz. You can register for the on-demand version, which is available at any time register here.
English 
German
One Response
You really did a fantastic job of explaining that ;)
LG
Theda