Structural Nonuniformity
Physical property where substrate characteristics like thermal expansion or mechanical strength vary significantly depending on the axis of measurement. Circuit designers must account for laminate anisotropy because the resin and glass reinforcements expand at different rates in the longitudinal and vertical directions. This effect is most noticeable when comparing the horizontal movement within the copper plane to the vertical movement through the z-axis.
Precise orientation of layers reduces internal conflict.
Mechanical Performance
Differences in stiffness between the warp and fill directions of the woven glass often lead to board curvature during heat exposure. Due to laminate anisotropy, the board may twist in a predictable pattern that depends upon how the fabric was oriented during the pressing process. Stability at high temperatures requires balanced layouts that compensate for these directional variations.
Designers align copper patterns to match these structural traits.
Fabrication Consequence
Holes drilled through the board encounter different resistance and coefficient profiles depending on the material stackup. If laminate anisotropy is ignored during the design phase, via reliability may decrease due to uneven pressure in the barrel of the hole. Correct calculations ensure that multi-layer systems stay bonded through repeated thermal cycles.
Homogeneity is rarely achieved in standard laminates.
