Selection of the Routing Class according to the component package

The conductor dimensions and spacings, and therefore the Routing Classes (RC) to be used, are closely linked to the layout and pitch of the package's lead pins.

The following tables show which RC should be used depending on the type of package chosen and the associated routing requirements. Other functional criteria may lead to a different routing class to the recommended RC.

Wherever possible, use the lowest RC and limit the use of higher classes for local component routing. When several RC are used for the same board, the highest RC (even used locally) defines the board's RC and therefore its price.

The boxes marked with a tick () represent the recommended RC for the components mentioned. A higher RC may be required in certain situations, such as the need to route two conductors between vias. In addition, a lower RC may also be used if routing requirements are lower.

Board structure and Routing Classes

The structure of the printed board and the types of vias required are associated with the often matrixlike nature of the component footprints. The use of complex board structures comprising stacked or non-stacked microvias may be necessary for some BGA components depending on the matrix size and pitch. For all routing classes, it is important to have symmetrical structures, i.e., type, position and thickness of the dielectric and conducting layers.

The following table identifies which RC should be used according to the types of vias/structure of the board. Boxes marked in brackets () show that via structures are possible, but with significant constraints on the parameters of the conductors on the external layer.

Mechanical parameters

Plated board outlines introduce additional constraints that are not covered in this document. The drilling parameters for mechanical holes are described in in tables VM1 VM2 and TM.

Conductor parameters

Higher routing classes correspond to increasingly narrow conductor widths/spacings, which allows for greater routing density. The thickness of the copper (plated or non-plated) is the main factor that affects the achievable routing class. It is important to ensure that the copper is evenly distributed (balanced) across the same layer, especially in case of a high routing class.

In case of a plated layer, only the finished thickness indicated in the tables below should be specified in the definition file (data package). By default, the choice of base copper and plating processes is the responsibility of the PCB manufacturer in order to achieve the selected routing class and meet the quality and performance requirements.

Plated-through mechanical vias and microvias will induce one or more copper platings on the conductive layer(s) concerned, with an impact on the achievable routing class.

For the same board, different Routing Classes can be associated with each conductive layer. In this case, the highest RC defines the board's RC and therefore its price.

Minimum drilling diameter depending on the thickness to be drilled

The thickness comprises the dielectric thickness plus the thickness of the copper to be drilled. This may be the thickness of the finished board, a sequence or a layer. The maximum thickness not to be exceeded for each routing class is specified in Chapter 4 (mechanical parameters).

Minimum via pad diameters depending on the drilled hole

The table does not take account of constraints associated with flexible layers, which by default require an increase in via pad size.

Minimum pad diameters for plated-through holes for component insertion (by soldering)

The presence of a second parameter in brackets indicates a limit value that should not be exceeded.

The pad diameter for plated-through holes for component insertion is defined in relation to the TM3 diameter of the finished hole (plated-through). The TM3 diameter is defined by the selected component.

Drilling parameters for laser-drilled microvias

Using a microvia requires the use of a routing class ≥ RC6 in line with the complexity in creating the microvias. However, lower routing classes can be used for other parameters, such as conductor parameters.

Solder mask parameters

The parameters shown in the tables represent the preferred values. The presence of a second parameter in brackets indicates a limit value that should not be exceeded.

Ink marking parameters

The values in this chapter only apply to a marking on the solder mask; the ink applied to the base material brings additional constraints that are not taken into account in this document.