Insulating Medium
Thin resin-rich layers provide the necessary isolation between conductive patterns in advanced circuit boards. The buildup dielectric allows for the addition of high density layers after the initial core lamination has occurred. Usage of these materials provides the foundation for microvias.
Traditional glass reinforced prepregs are often too rigid for such fine-line applications.
Sequential Addition
Multiple cycles of lamination and drilling define the fabrication flow for boards using these materials. Each buildup dielectric layer is typically applied as a film or a liquid before being cured and patterned. This process enables the creation of complex interconnects without increasing the total board thickness beyond functional limits.
Technical specifications often require these materials to support the routing of fine-pitch components like ball grid arrays where trace width and spacing are minimal. The material thickness stays uniform across the entire surface. This consistency ensures that subsequent plating and etching steps remain within tolerance.
Thermal Resistance
Materials must withstand multiple soldering cycles and environmental stresses while maintaining bond strength. A buildup dielectric often lacks the mechanical stability of woven glass. Management of the coefficient of thermal expansion is required to prevent delamination.
Failure usually occurs at the interface between the buildup material and the underlying copper if surface preparation is inadequate. Excessive heat causes the resin to expand at a different rate than the metal, leading to cracks in the microvia walls or separation of the pads.
