Rigid Flex Architecture against Two Boards and a Connector
Rigid-flex architecture eliminates discrete connector failures and signal discontinuities while reducing assembly labor, justifying higher bare-board costs.
Coverlay Overlap
Sealing Zone Dimension
The minimum distance that a flexible dielectric film must extend over the copper traces of a rigid-flex boundary prevents exposure of the electrical conductors. Maintaining a correct coverlay overlap ensures that moisture and plating chemicals cannot penetrate the junction where the rigid and flexible sections meet. This parameter is specified during board layout and verified by automated optical inspection after laminate pressing.
Inadequate dimensions lead to copper corrosion and eventual circuit failure.
Lamination Squeezeout
Adhesive squeezeout during high-pressure thermal lamination can cover soldering pads if the design is too tight. Allowing sufficient coverlay overlap accommodates the flow of adhesive without compromising the solderability of adjacent surface mount pads. This requires careful alignment of the pre-drilled coverlay during the assembly setup.
Flexibility Maintenance
Dielectric films that are too thick or overlap excessively can stiffen the transition zone and cause trace cracking. Setting the coverlay overlap to the optimum dimension prevents stress concentrations that lead to copper fatigue during handling. Visual inspectors use magnification to verify that the overlap matches the design drawing and is within tolerance limits.
This balance of thickness and position ensures the board remains functional in tight spaces where the flex region must be bent during installation.