Harsh environments call for increased durability. Here MCE Newmarket reports on an interesting find in directly mounting a chip on a printed circuit board.
Tests prove reliability of ‘chip on board' technology
MCE Newmarket has undertaken an extensive programme of reliability tests to validate the performance of chip-on-board (COB) technology for harsh environment applications.
COB technology involves mounting bare semiconductor chips directly onto the printed circuit board. The chip and its wire bonded leads are then encapsulated in an appropriate medium such as an epoxy or silicone adhesive - so called ‘glob topping'.
One of the main concerns about the implementation of COB technology is the reliability f glob-topped components in harsh environments. MCE Newmarket has developed new criteria for the evaluation of COB assemblies based on the BS9450 scheme for the certification of electronic components.
A comprehensive test programme has been undertaken on test circuits fabricated on high temperature FR4 and flexi-rigid printed circuit boards and ceramic substrates using both Pb-free and Pb-based solders and selected glob-top encapsulants. The tests performed included high temperature storage, operation under rapid change of temperature and ‘damp heat' testing for representative industrial, telecoms and aerospace/defence environmental performance specifications.
The materials and assembly processes tested have passed all of the environmental tests for durations of at least 1000 hours.
This data provides the assurance that COB technology can be applied in demanding applications, with specific advantages in space restricted systems.
This programme is just one example of the ways that MCE Newmarket is responding to meet the needs of its end customers. Other programmes are in progress to transfer traditional hybrid technologies onto different substrate materials including low temperature co-fired ceramic (LTCC) and insulated metal substrates (IMS), extending the frequency, temperature and power handling characteristics of hybrid microcircuits.