Despite differences in dielectrics, flex material performance is globally consistent.

Question: I would like to have the flex circuits for my current project manufactured in China in order to reduce costs. I had the qualification circuits manufactured in the US using US-manufactured materials, and they worked great. The factory in China has asked if they can use “local equivalent materials.” Is this common, and is there anything that I should be worried about if I approve this?

Answer: There are a lot of companies in Asia that manufacture flexible circuit materials, and Chinese circuit manufacturers prefer to use these alternatives whenever possible. There are both technical and logistical issues that come into play when weighing the decision to permit Asian-equivalent materials.

Logistical issues. Every flex circuit manufacturer, whether in the US or Asia, is going to stock a significant amount of raw material ranging from copper-clad base laminates used for circuitry to adhesive-clad dielectric films used for covers and bond plys. They typically stock raw materials from a very small number of material suppliers. The main reasons are procurement and acquisition costs, and also familiarity with processing a specific brand of material. Obviously, if a flex circuit manufacturer buys 10,000m² per month of material from one supplier, they are going to get preferential pricing on that material. They will also usually get preferential delivery any time a particular material is in short supply.

On the other hand, if the flex circuit manufacturer only buys from a raw material supplier occasionally and in small quantities, they will pay a premium for the material they buy. If that material ever goes into short supply, they will be way down the list as material becomes available. Many material manufacturers will also have minimum order quantities that can really drive up the cost of a small order. If a supplier has an MOQ (minimum order quantity) of 5m², and your project only needs 1m², the cost of the extra 4m² will most likely be added to your overall project cost and the extra material scrapped. The cost of cataloging and storing the extra material on the off-chance that another customer will specify it is not justified. Also, flex circuit materials have a shelf life which would need to be monitored and again would not be cost-effective for small amounts of overrun material.

Technical issues. As stated, many Asian companies manufacture raw materials for flexible circuits. The vast majority of these suppliers use various thicknesses of polyimide film as the dielectric material with an epoxy (most common in Asia) or acrylic (most common in the US) film adhesive. These are the same basic materials that would have been used on your US-built prototypes. So when the flex circuit manufacturer asks to use “local” or “Asian equivalent” materials, what you receive should be identical or nearly identical to what you had made in the US. The biggest difference would probably be the film adhesive. If you had prototypes made with US materials, chances are they were built with acrylic film adhesive. The Asian equivalent would most likely be epoxy-based, but should be the same thickness and will look and perform nearly identical to its acrylic counterpart. When weighing whether to permit replacement materials, an important thing to check is that the Asian materials are certified to the pertinent IPC specifications (IPC-4202, IPC-4203 and IPC-4204). Include a cross-sectional view of the circuit construction on the drawing that shows any critical material thicknesses (for flexibility or impedance performance) so that the Asian-made flex circuit performs as the US circuit did.

So to answer your question, Asian-equivalent materials should not pose issues provided they are equivalent in thickness to the materials used in US-made prototypes and are certified to the appropriate IPC specifications. To put your mind at ease, virtually all the commercial electronics that you use every day (mobile phones, tablets, cameras, etc.) are filled with flexible circuits built in Asia using Asian-manufactured materials. As a supplier, I can say that the number of flex circuits that fail due to defective materials borders on nonexistent.

Figure 1. The material origin will have no bearing on board reliability.

Mark Finstad is senior application engineer at Flexible Circuit Technologies (flexiblecircuit.com); This email address is being protected from spambots. You need JavaScript enabled to view it.. He and co-“Flexpert” Mark Verbrugge, sales applications engineer at Amphenol Sincere (amphenol-afc.net), welcome your suggestions.