Layer Material Setup Options

The Material Stock > Layer Material node of the Process Options Editor provides the following setup options:

• Panel Raw Material Cost

• Core Insulator Thickness

• Prepreg Sheet Thickness Beneath Current Layer

• Number of Prepreg Sheets per Layer

Panel Raw Material Cost

Panel raw material cost is the associated with the panel for a specific copper layer, including the cost of the core insulator beneath it, if it is part of a 1-ply core or is the top layer of a 2-ply core. Default panel cost depends on the panel type; see Material Cost. With the setup option Panel Raw Material Cost (provided by the Layer Material node of the Process Options Editor), users can override the default on a per-layer basis.

Core Insulator Thickness

By default, if a copper layer is part of a 1-ply core or is the top ply of a 2-ply core, the thickness of the core’s insulator is looked up in the lookup table tblDielectricThickness. The lookup table reflects typical insulator thicknesses for cores with a given copper thickness used in a board with given total thickness, number of layers, and number of cores (see About tblDielectricThickness).

With the setup option Core Insulator Thickness (defined by the Material Stock > Layer Material node of the Process Options Editor), users can override the default on a per-core basis. The available choices are those listed in tblDielectricThickness for the number of layers in the current part.

Note: If you set Core Insulator Thickness, you must also ensure that Prepreg Sheet Thickness Beneath Current Layer and Number of Prepreg Sheets per Layer are set to the appropriate values. The calculation of default Prepreg Sheet Thickness Beneath Current Layer and Number of Prepreg Sheets per Layer assumes a default value for core insulator thickness. So, if you override the default core insulator thickness, you might need to override the default Prepreg Sheet Thickness Beneath Current Layer and Number of Prepreg Sheets per Layer as well.

Core insulator thickness drives material cost. It also drives Computed Board Thickness, which affects machine feasibility for several processes.

See also Assigning Materials.

About tblDielectricThickness

The lookup table tblDielectricThickness reflects typical insulator thicknesses for cores with a given copper thickness used in a board with given total thickness, number of layers, and number of cores. The data in the table is based on industry-recognised, material stack-up configurations.

A lookup in tblDielectricThickness selects the table row for which all the following hold:

• Value of the Total Board Thickness column does not exceed the Target Board Thickness. If there is no such row, a row with the smallest Total Board Thickness is used.

• Number of copper layers in the board equals the value of the Number Layers column.

• Number of cores in the board equals the value of the Num Cores column.

The dielectric material thickness is the value in the column of the selected row that matches the weight of the core’s top copper layer. The matching column’s name mentions the layer weight:

• 0_5oz for 0.5 ounces

• 1_0oz for 1 ounce

• 1_5oz for 1.5 ounces

• 2_0oz for 2 ounces

Prepreg Sheet Thickness Beneath Current Layer

By default, the thickness of each sheet of prepreg beneath a given copper layer is selected from the lookup table tblPrepregThickness. aPriori selects the Nominal Thickness from the table that results in the best fit of prepreg sheets into the space available (possibly occupying a slightly larger or smaller space--see Default Space Available for Prepreg).

Users can override the default prepreg thickness with the setup option Prepreg Sheet Thickness Beneath Current Layer (defined by the Material Stock > Layer Material node of the Process Options Editor). The available choices are those listed under Nominal Thickness in tblPrepregThickness.

Note: The setup option Prepreg Sheet Thickness Beneath Current Layer is the thickness of each sheet of prepreg. The setup option Number of Prepreg Sheets per Layer specifies the number of sheets in each prepreg-occupied space between copper layers. If you set Prepreg Sheet Thickness Beneath Current Layer, you must also ensure that Number of Prepreg Sheets per Layer is set to the appropriate value.

Note: In the table tblPrepregThickness, the columns Min Thickness and Max Thickness represent the range of available sizes (depending on resin content) for a given prepreg Type. Cost model calculations use the Nominal Thickness for all sizes of a given type. This is a weighted average of the Min Thickness and Max thickness, weighted towards Min Thickness.

Prepreg thickness drives Material Cost. It also drives Computed Board Thickness, which affects machine feasibility for several processes.

See also Assigning Materials.

Default Space Available for Prepreg

By default, aPriori assumes that the total space available for all the board’s prepreg is the difference between the following:

• Target Board Thickness

• Total thickness of all non-prepreg materials, which is the sum of the following:

  • Solder mask thickness (see Computed Board Thickness)

  • Silkscreen thickness (see Computed Board Thickness)

  • Total copper thickness, which is the sum of the thicknesses of each Layer GCD.

  • Total default core insulator thickness, which is is the sum of the default Core Insulator Thickness for each copper layer.

aPriori further assumes, by default, that all prepreg-occupied spaces between copper layers are the same thickness. So, the default thickness of each prepreg-occupied space between copper layers is the total space available for prepreg divided by the number of prepreg-occupied spaces.

aPriori uses the default thickness of each prepreg-occupied space to determine the default thickness of each prepreg sheet (see Prepreg Sheet Thickness Beneath Current Layer). For each Nominal Thickness in tblPrepregThickness, it finds the optimal number of sheets, that is, the number of sheets of that thickness that most closely fits the available space (possibly occupying a slightly larger or smaller space). It selects the Nominal Thickness whose optimal number of sheets most closely fits the available space.

Number of Prepreg Sheets per Layer

By default, the number of sheets in each prepreg-occupied space between copper layers is the number of default-thickness sheets (see Prepreg Sheet Thickness Beneath Current Layer) that best fits in the Default Space Available for Prepreg (possibly occupying a slightly larger or smaller space).

Users can override the default with the setup option Number of Prepreg Sheets per Layer (defined by the Material Stock > Layer Material node of the Process Options Editor).

Note: If you set Number of Prepreg Sheets per Layer, you must also ensure that Prepreg Sheet Thickness Beneath Current Layer is set to the appropriate value.

The number of sheets per prepreg layer drives prepreg Material Cost. It also drives Computed Board Thickness, which affects machine feasibility for several processes.

See also Assigning Materials.