TWI Industrial Member Report Summary 904/2008
By C Otter
The cost and time required for new product introduction for electronics manufacturers is of primary importance both for high volume consumer electronics manufacturers (eg mobile phones) and safety and performance critical products used in automotive and aerospace manufacturing.
Consumer electronics manufacturers need to get products through development and into market as quickly as possible to gain competitive advantage. The development cycle for mobile phones is of the order of four months which includes qualification of the reliability of the electronics assembly design and manufacture. In fact the rate of new product development is such that a concurrent product development process may be adopted, where second and third iterations of a design are under development before the first iteration has reached the market. Therefore industry constantly requires better modelling processes for a faster verified design and test cycle and reduced physical test durations.
A key aspect of any reliability strategy is to increase the accuracy and precision of reliability measurement and simulation methods in order to decrease test times, improve the detailed understanding of failure mechanisms and improve reliability prediction accuracy. Present generation reliability tests involve high temperature storage, humidity testing, thermal and power cycling together with a range of mechanical tests including vibration and shock and are often based upon industry defined standards and semi-empirical acceleration factors rather than upon a true understanding of the actual failure mechanisms. These tests may be compromised by poor control of the test parameter (eg temperature) that then leads to poor data accuracy and lifetime prediction.
The traditional approaches to reliability testing are being challenged by techniques such as precision reliability testing, in-situ monitoring and computer based modelling which claim to offer a faster, cheaper and more accurate prediction.
The precision approach to reliability testing as described by De Schepper et al (1993), has been put forward as a means to assess the effects of electromigration in integrated circuit reliability testing. The approach incorporates a number of ideas designed to improve the accuracy of the test and improve assembly life prediction whilst shortening test times, the main features being:
- Precision control of the test parameters, eg temperature control to ±0.01°C.
- Precision measurement of circuit attributes, eg electrical resistance measurement to 0.1µO.
- Constant in-situ monitoring of the test device circuit.
The linear relationship between electrical resistance and test time as a result of electromigration is claimed to allow very short test times to be used to asses the rate of change and predict the time to failure for the electromigration failure mode.
In order to assess the precision reliability approach for application to the mechanical failure in soldered joints a test PCB was designed, which incorporated industry standard electronic packages. These PCBs were tested under thermal cycling loading using a 'high precision' technique using specialist equipment and a more typical approach using standard equipment.
- To demonstrate and evaluate the use of precision reliability testing for soldered connections.
- To compare high-precision and standard temperature cycling tests.
- To use circuit board modelling software for a test vehicle design and reliability prediction under temperature cycling conditions.