Know what details to include – or not include – in the flexible circuit drawing.

Since our most recent column covered drawing notes for flexible circuits, this may be a good time to go over many of the other features a good flexible circuit drawing should include, and maybe a few things to avoid.

Along with the drawing notes, the rest of the drawing features help define the details of the part as well as some of the acceptability requirements.

For starters, drill tables are important to help describe via structures. The manufacturer needs to know which holes are which. If there are filled vias and/or via-in-pad-plated-over (VIPPO), for instance, they are identifiable with a flag note, or segregate filled from non-filled holes on the table.

Fabricators need to understand your via strategy. Is this a simple through-hole construction, or are buried, blind and/or microvias employed? Sometimes we see blind vias overlapping layers; for example, one blind via from layer 1 to 8 and another from layer 12 to 6. Sounds cool on paper (or in CAD), but we can't do that. The fabricator can help you align the via choices with cost and reliability.

Clarify key features, but don’t use 10 notes where one will do.

You have been tasked with documenting a flexible circuit you are preparing to send out for quotes. Should specific drawing notes be included?