Buildup HDI Stackup Design and Layer Thickness Control
Stackup thickness control requires calculating pressed prepreg heights over local copper patterns to hold impedance and microvia drilling tolerances.
IPC-TM-650 Microsection
Internal Inspection
Vertical slices taken from a circuit board panel allow technicians to examine the internal layers and plated holes. The ipc-tm-650 microsection is a formal laboratory procedure that involves mounting a sample in resin and grinding it down to a mirror finish. This view reveals the quality of the connections between the different copper layers and the integrity of the drill holes.
Cross Section
Quality control procedures use this method to find defects that are invisible from the surface of the board. An ipc-tm-650 microsection allows for the measurement of the copper plating thickness on the walls of through-holes and microvias. It also shows the alignment of the internal pads with the drilled holes, which is a critical factor for the reliability of the finished assembly.
Technicians look for signs of resin recession, copper cracks, plating separation and layer voids. This destructive test is the final word on the internal workmanship of a production batch.
Vertical Measurement
Measuring the thickness of dielectric layers and foil becomes possible once the sample is polished and etched with chemicals. The ipc-tm-650 microsection provides the data needed to calibrate the lamination presses and ensure the board meets the impedance requirements of the design. Results are documented in a report that accompanies the shipment to prove that the manufacturing process stayed within the defined limits.