Lamination Defect
Unintended movement of internal copper-clad layers during the high-pressure lamination process compromises the electrical integrity of multi-layer circuit boards. Such physical displacement, widely known as core shift, occurs when the liquid resin flows under heat and pressure before curing, dragging the thin internal cores out of their aligned positions. This movement creates a mismatch between the drill holes and the internal pads, risking broken connections or shorts.
Mechanical Source
High lamination pressures combined with a rapid viscosity drop in the prepreg resin drive this physical displacement during the press cycle. As the temperature rises, the resin enters a highly fluid gel state, and any uneven distribution of pressure across the panel pushes the core to one side. This effect is particularly pronounced in thin-core constructions and high-density interconnect designs where the internal copper patterns are asymmetric.
Furthermore, the selection of the lamination pin configuration and the type of separator plates influence how easily a core can slide during the cycle.
Registration Impact
Precise registration of drills to the inner layer pads is severely degraded by such movement, leading to breakout where the drill misses the pad entirely. Test engineers detect this failure through automated optical inspection or post-drill X-ray verification. Corrective action relies on optimizing the lamination press profile and using heavy-duty pinning systems to lock the cores.
