proper stackup design in pcb assemblers

The layer stack of a printed circuit board (PCB) is crucial to the overall performance of the design. A poorly-planned stackup configuration can lead to issues such as signal degradation, unintended electromagnetic interference (EMI), and costly manufacturing delays. Proper planning and coordination between layout designers and their CMs can reduce the time it takes to turn PCB prototypes into high-volume production.

PCB layers are arranged to achieve specific electrical, mechanical, and thermal properties. Different layers serve different purposes, such as power distribution, signal integrity, and temperature management. Layer thicknesses are also important, and they can be influenced by the intended operating frequency and sensitivity to interference. For example, a high-speed design requires more space for controlled impedance routing and guarding against crosstalk. The layer stack must also provide adequate clearance between the traces and reference planes to minimize current flow.

In addition to layer configuration, the pcb assemblers metal plating and solder mask must be carefully planned. The conductive copper layer is the most critical component in a multi-layer PCB, and its characteristic impedance must be closely monitored to ensure proper performance. The copper’s characteristic impedance depends on its geometry, dielectric constant, and proximity to reference planes. Ideally, the characteristic impedance of copper traces should be as close as possible to zero for consistent transmission performance. This is achievable through careful selection of the trace width, thickness, and spacing, as well as the copper plane’s thickness and proximity to the reference plane. A specialized tool can help determine the optimal geometric properties for a given material and layer stack configuration.

How do you ensure proper stackup design in pcb assemblers?

A hybrid stackup construction allows for more flexible design options by combining different materials and technologies. It can be used to address unique design requirements, such as boosting signal transmission speed or increasing component density, while meeting manufacturing constraints like cost and thermal performance.

When creating a hybrid stackup, it is necessary to carefully plan the layer stack configuration. This includes determining the number of signal and power layers, defining their respective thicknesses, and assigning them to appropriate layer functions. The number of vias also needs to be considered, as well as their position in the design. For example, HDI-style vias need a larger diameter than standard through-holes to accommodate the large amount of copper used in the innermost layers. In addition, the layer stack should be arranged to allow for effective plasma etching and to prevent smear during the sequential lamination process.

Once the stackup is designed, a Gerber or ODB++ file can be downloaded and used to generate fabrication drawings. These files specify the layer order, materials, thicknesses, and copper weights. They can also include supplemental information like controlled impedance requirements, manufacturing tolerances, and testing reports. This allows CMs to accurately manufacture boards as designed. The layer stack must also be compatible with the fab house’s capabilities to expedite the transition from prototype to mass production. This is especially important because it will reduce the time to build the boards and lower the total manufacturing cost.