Low-CTE materials for printed wiring boards

This paper looks at the approaches of a printed wiring board producer to the challenges of stress-free bare-die assembly and increased reliability. The results of this investigation show that reducing the CTE of PWB base materials is a very effective way to increase the reliability of PWBs. Depending on the application, it may be enough to reduce the CTE in the plane of the board for better interconnection reliability between the PWB and surface-mounted devices. This can be done by using standard materials for the major part of the multilayer and materials with alternative reinforcements for the outer layers. Even better reliability can be attained by building the whole multilayer with materials with low CTE properties in all three dimensions. Current developments in telecommunication, automotive and other markets will raise demand for PWBs with higher component density and reliability. Therefore, low-CTE applications will gain in importance. The development of new materials and further development of new concepts for build-up PWBs is the answer to these challenges. This process has already been started and several products are available, but there is still much work to be done.