PCB Stackup - Building a rigid-flex construction

Building a rigid-flex construction

Application Note AP543

Building a rigid-flex construction with Speedstack

This note describes the construction of the rigid-flex-rigid stackup in the graphic below.

Speedstack Navigator showing completed rigid-flex construction

Prior to construction ensure that the Units are set to Mils/Thou and that the Speedstack Flex/HDI License Option is checked.

The note assumes an existing stack to which will be added a series of sub-stacks. This stack is referenced by Speedstack as the master stack.

The master stack is effectively a "bill of materials" stack and contains all the materials used in all sub-stacks. The electrical layer numbers of sub-stacks are determined from the master stack, so this stack should be created first.

In the 12 layer master stack shown above the flexible core material is depicted in grey.

Adding sub-stacks

Use the Speedstack Navigator to create and modify sub-stacks. Press F4 to open the Navigator – the master stack is displayed.

To add a sub-stack:

Click on the master stack in the Navigator – the selected stack will be highlighted in red
Right-click the master stack and select Add Stack | Define by layers.

The Define New Stack dialog specifies which materials in the master stack are added to the new sub-stack.

Choose layer 6 as the Top Layer and layer 7 as the Bottom Layer to add just the flex core,
Position the new stack to the far right of the master stack
Name the new stack "Flex" as shown above

The new Flex stack (highlighted in red in the Speedstack Navigator) is added to the master

Click the new Flex stack in the Navigator to display the stack in the Speedstack Editor

Adding materials to the sub-stack

Use the Speedstack Editor to add materials to the new Flex sub-stack – for example, to add coverlays to the flex core.

Adding coverlays to the sub-stack

Select the flex core material, layers 6 / 7
Right-click the core and select Add | Coverlay

Choose coverlay material from the list.
Select Add Material Above

Select the flex core material again
Right-click the core and select Add | Coverlay
Choose the coverlay material from the list.
Select Add Material Below

The completed 2-layer flex sub-stack contains a flex core with coverlay material above and below the exposed copper surfaces.

Adding a second sub-stack

To complete the rigid-flex-rigid stack right-click the master stack, select Add Stack and choose Duplicate Master.

Assign the new stack the name "Rigid" to add the additional rigid sub-stack.

The rigid-flex-rigid construction is complete and is shown in the Technical Report below

The Technical Report includes full details of the stack construction with all material parameters – the master stack is shown below.

The Flex sub-stack is shown below.

Save the stackup as a project (.sci) file.

Project files contain all the stack constructions along with any controlled impedance structures. Impedance structures may be added to each sub-stack, with the structure types being determined by the materials in each sub-stack.