TWI Industrial Member Report Summary 975/2010
By Helen Goddin
Background
Reliability testing is an essential part of new product introduction within the microelectronics industry, particularly with the highly complex, three-dimensional nature of components today. Industrial reliability tests include thermal ageing and thermal cycling, where failure mechanisms are accelerated through temperature and fatigue. Typical failure mechanisms in printed circuit boards when subjected to thermal ageing include intermetallic growth at dissimilar metal interfaces and oxidation (for instance at copper/polymer interfaces). During thermal cycling between a high and low temperature, thermal expansion mismatch can occur between dissimilar material interfaces, resulting in weakening and cracking at the joint interface. On silicon chips, high current densities in metal tracks can cause a phenomenon known as 'electromigration', where metal displacement can cause opens and shorts in the electrical circuit.
Life times for the product can then be extrapolated, in some instances up to 50 years. At present, most electronic components are tested for failure by intermittently removing them from the chamber, and testing whether their value has exceeded a pass/fail criterion. The lengthy testing times this requires, can hold up new product introduction, and prevent market placement at the correct time. In this project, a new reliability regime, known as 'precision reliability', is investigated.
Precision reliability testing uses very accurate temperature control, alongside precision resistance and capacitance monitoring, to continuously monitor samples under testing. Using this process, deviations from optimum process conditions can be identified early, before failure has taken place. Components could therefore be removed before full qualification has taken place, providing as much as a 60% reduction time in a design cycle. The time saving can be fed back directly into early sales, a figure worth hundreds of millions of dollars to the semiconductor industry. In addition to this cost saving, failure mechanisms can be identified by interpreting the shape of the resistance/capacitance curves obtained from the test. These results can be directly fed back into processing conditions and design rules for the product.
Objective
Define the benefits of using the precision reliability test system to thermally age and cycle printed circuit boards, and to monitor electromigration on silicon chips.