HDI Structures Using Thin Films and Low Temp Paste

Catherine Shearer, James Haley, Chris Hunrath
Ormet Circuits Inc. - Integral Technology
CA USA

Circuit complexity and density requirements continue to push PCB fabrication capability limits. Component pitch and routing requirements are continually becoming more aggressive and difficult to achieve in good yield with current fabrication strategies. The trend is to bring the PCB closer to the density requirements currently required for semiconductor packaging. The ability to place interconnecting vias in any location on any layer is crucial to PCB fabricators in meeting this high density interconnect (HDI) trend.

The two fundamental elements in any type of PCB, conductors and dielectrics, both have to be considered when building "any layer" HDI. These PCB's have specific challenges for processing while maintaining thermal and electrical performance. Careful consideration of the interplay of the fundamental elements is critical to fulfilling all of these requirements. New methods and materials designed specifically with these challenges in mind are becoming available for building HDI.

Using materials specifically designed for HDI PCBs can significantly reduce the challenges producing these boards. However, along with easing the challenges of fabrication, these materials must also demonstrate the right combination of properties to meet electrical and thermal requirements while also being reliable. Validation of these new technologies is currently underway.

Combing a TLPS paste with a film that is engineered without the constraints of flex can produce thermally reliable z-axis interconnects. The TLPS paste offers a plating like metallurgical bond to the copper innerlayers while the film allows proper sintering and controlled z-axis expansion. Together these materials give the PCB manufacturer ease of implementation of high reliability sintered-paste interconnects and more construction options for HDI structures.