Documenting specialized pcb stackups
Application Note AP524 

Using the Speedstack HDI Navigator to document pcb stackup with coated and uncoated areas

Is it possible to model a pcb stackup where some areas are coated with resist and other areas deliberately left uncoated?
– Speedstack HDI customer

Very easily – with the Speedstack HDI Navigator or see AP552 if using Speedstack PCB.

Speedstack navigator
Speedstack Navigator

This note discusses how the Speedstack HDI Navigator can document a PCB stackup where the board includes areas that are coated with photoresist and surface traces that remain exposed.

First, consider each finished sub-stack in Speedstack HDI:

Uncoated stack
Uncoated stack

Coated stack
Coated stack

Start by creating the uncoated pcb stackup (the Master stack) in the Stack Editor, then press F4 to open the Speedstack HDI Navigator:

Uncoated stack
Uncoated stack area

This "Master" stack represents the uncoated area; right click the Navigator and use the Addstack command to add a copy of the Master and name it "Coated". Click the new stack and return to the Stack Editor to add the photoresist and ident layers – the Navigator should display both areas as separate stacks (below).

Navigator showing coated and uncoated areas
Uncoated and coated areas in Speedstack HDI Navigator

Including controlled impedance structures

This example creates controlled impedance structures in both coated and uncoated areas: the uncoated areas use Surface Microstrip structures and in the coated areas Coated Microstrip structures, shown in Speedstack HDI's controlled impedance tab pane below.

Surface microstrip
Coated microstrip

Using goal seek to calculate trace widths

Use Speedstack HDI's goal seeking facility to arrive at the trace widths for the two structures:

Uncoated layer section
Uncoated Layer 1 in Stack Editor

Coated layer section
Coated Layer 1 in Stack Editor

Speedstack HDI Navigator opens up not only the capability of documenting flex-rigid stacks but also allows you to document specialized pcb stackups. In the above example our customer needed to produce a board which had areas intentionally free from resist on the finished board. This application of Speedstack HDI would be equally applicable should a fabricator wish to predict the impedance of surface traces on a part finished board prior to the application of resist.

Contact Polar now and discover the benefits of documenting and designing your PCB stack up with Speedstack HDI.