Documenting Your Flex Circuit Design


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As a flex circuit applications engineer, when I receive an RFQ, the first thing I do is look at the customer’s data and review their manufacturing notes. Quite often, I find notes that supersede IPC specifications in manufacturing documents, as customers often believe these added notes and associated specifications will make the circuit more robust. However, these non-standard IPC manufacturing specifications/notes can wreak havoc on the manufacturing process and can actually lead to a less robust circuit.

For example, a customer will sometimes specify additional copper plating, believing it will result in a more reliable circuit. In reality, that type of requirement can make the circuit less reliable, more difficult to manufacture, and more expensive. When manufacturing yields go down, the price goes up!

In taking a deeper dive into manufacturing notes and the potential issues that they can create, let’s use a three-layer multilayer flexible circuit as an example. The first note on a manufacturing print is usually “Manufacture to IPC6013, Class 2, Type 3.” This note should always be included; I cannot stress that enough!

Unfortunately, in the continued review of the documentation, I often find one or more additional conflicting notes further down in the manufacturing notes that overrule IPC6013 specifications.

Copper Plating
One example would be “Minimum copper plating shall be 0.0015”.” This note supersedes the IPC-6013 specification in Table 1.

plemel_table1.jpg
Table 1: IPC-6013 copper plating requirements.

PCB designers who are not well-versed in flex circuit manufacturing may not know that exceeding IPC-6013 of 984 µin (0.000984”) can cause the circuit to be less reliable and possibly cause problems later in the manufacturing process. Having a specified requirement this large (0.000516” thicker) will require the plating line at the factory to plate more than 0.0015” to ensure the minimum plating is 0.0015” thick.

To read this entire article, which appeared in the September 2020 issue of Design007 Magazine, click here.

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