Characterizing Dielectric Loss in Adhesiveless Polyimide Substrates
Adhesiveless polyimide substrates eliminate high-loss acrylic adhesives, dropping dielectric loss tangents to 0.002 at 10 GHz when paired with smooth rolled copper.
Flex Circuit Yield
Production Metric
Manufacturing efficiency metrics for flexible printed circuits quantify the ratio of functional units to the total number of units started in a production lot. Calculation of flex circuit yield measures the success rate of the fabrication process for polyimide based substrates. Because flexible materials are prone to dimensional instability, this value often tracks lower than the yield for rigid boards.
It accounts for defects such as trace fractures and coverlay misalignment. The measurement determines the final cost per unit for the customer.
Defect Control
Controlling the yield requires strict environmental regulation during the imaging and etching stages. Handling flexible panels introduces risks of creasing or contamination that ruin the copper traces. Automated optical inspection identifies shorts or opens before the board moves to the assembly stage.
Since a single fracture in a long flex tail makes the entire part useless, the sensitivity of the inspection must match the minimum feature size of the design. Proper tensioning of the material during roll to roll processing prevents stretching that would lead to registration errors.
Acceptance Standard
Acceptance criteria for these circuits follow industry guidelines regarding fold endurance and conductor spacing. A batch that falls below the target yield necessitates a root cause analysis of the lamination cycle. Consistent data helps the manufacturer adjust the scaling factors used during laser drilling.