Flex Circuit Fids

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Has anyone ever used local fids on flex circuits that are ap... - Mar 10, 2008 by SWAG

We'd be unhappy with features that are not in copper that is... - Mar 10, 2008 by davef

SWAG

#53951

Flex Circuit Fids | 10 March, 2008

Has anyone ever used local fids on flex circuits that are applied by the board house as black ink dots? Good or bad experience?

We have a flex board that has two identical 60 pin, fine pitch connectors on it. From limited experience and reading some old threads, it seems shrink and stretch of flex circuits is very tough to deal with. I know I can place these parts well if the local fids are accurate but do you think that maintaining a good print job will be next to impossible if these come as panelized arrays?

From what I understand, applying a rigid to the back of an array will simply act as a carrier/stiffener, not really a means of correcting stretch or shrink of a flex. True statement? Thanks in advance!...

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davef

#53958

Flex Circuit Fids | 10 March, 2008

We'd be unhappy with features that are not in copper that is at the same level as the component pads, because of difficulties the fabricator would have in maintaining registration between the copper pads and the ink used for the features not in copper.

The issues with shrink and stretch in flexible circuits is best delt with by using fiducials on the panel, circuit, and at each critical component location. This approach is discussed further in IPC-2223A - Sectional Design Standard for Flexible Printed Boards.

Yes, applying a rigid backer to an array acts primarily as a carrier/stiffener to improve handling. It is not intended to compensate for stretch or shrink of a flex. The fabricator needs to do an excellent job of securing the entire panel to the backing to prevent variations in placement height accross the panel.

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