Question:
Is it possible to model a stackup where some areas are coated with resist and other areas deliberately left uncoated?
- Speedflex HDI customer

Answer:
Very easily! - with Speedflex HDI's Navigator.

In this note you will see how Speedflex HDI's Navigator can document a stackup where the board includes areas that are coated with photoresist and surface traces that remain exposed.

First, consider each finished stack in Speedflex HDI's Stack Editor below:

Uncoated stack

Coated stack

Start by creating the uncoated stack in the Stack Editor, then press F4 to open the Speedflex HDI Navigator:

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).

Uncoated and coated areas in Speedflex 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 Speedflex HDI's controlled impedance tab pane below.

Controlled impedance structure for uncoated area	Controlled impedance structure for coated area

Using goal seek to calculate trace widths

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

Uncoated Layer 1 in Stack Editor

Coated Layer 1 in Stack Editor

Speedflex HDI Navigator opens up not only the capability of documenting flex-rigid stacks but also allows you to document specialized 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 Speedflex 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 stackups with Speedflex HDI.