Dimensional Stability
Dimensional changes occurring in circuit board substrates during the thermal and chemical processes of multi-layer fabrication must be carefully managed to ensure layer alignment. This phenomenon, known as multi-layer laminate drift, is the movement or distortion of the inner-layer laminate sheets relative to their original design coordinates. Such shifting can cause misregistration between drill holes and internal pads, jeopardizing the electrical continuity of the board.
Drift Mitigation
Fabricators analyze this movement by measuring the board’s dimensions before and after lamination, using these measurements to apply scale factors to the artwork of the inner layers. The amount of drift depends on the fiber direction, resin content, and copper density of each individual layer. During the high-temperature pressing phase of lamination, the resin melts and flows, releasing the stresses built up during laminate manufacturing and causing the material to shrink or expand.
By adjusting the layout design to balance copper distribution and using dimensionally stable materials, fabricators can minimize this dimensional movement.
Registration Control
Failure to compensate for these dimensional shifts results in breakout defects where drill holes miss the internal copper pads entirely. Controlling multi-layer laminate drift is essential for producing high-density interconnect boards with reliable multi-layer structures. This control avoids inner-layer shorts and open circuits in fine-pitch layouts.
